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Kerala flood case study

Kerala flood case study.

Kerala is a state on the southwestern Malabar Coast of India. The state has the 13th largest population in India. Kerala, which lies in the tropical region, is mainly subject to the humid tropical wet climate experienced by most of Earth’s rainforests.

A map to show the location of Kerala

Eastern Kerala consists of land infringed upon by the Western Ghats (western mountain range); the region includes high mountains, gorges, and deep-cut valleys. The wildest lands are covered with dense forests, while other areas lie under tea and coffee plantations or other forms of cultivation.

The Indian state of Kerala receives some of India’s highest rainfall during the monsoon season. However, in 2018 the state experienced its highest level of monsoon rainfall in decades. According to the India Meteorological Department (IMD), there was 2346.3 mm of precipitation, instead of the average 1649.55 mm.

Kerala received over two and a half times more rainfall than August’s average. Between August 1 and 19, the state received 758.6 mm of precipitation, compared to the average of 287.6 mm, or 164% more. This was 42% more than during the entire monsoon season.

The unprecedented rainfall was caused by a spell of low pressure over the region. As a result, there was a perfect confluence of the south-west monsoon wind system and the two low-pressure systems formed over the Bay of Bengal and Odisha. The low-pressure regions pull in the moist south-west monsoon winds, increasing their speed, as they then hit the Western Ghats, travel skywards, and form rain-bearing clouds.

Further downpours on already saturated land led to more surface run-off causing landslides and widespread flooding.

Kerala has 41 rivers flowing into the Arabian Sea, and 80 of its dams were opened after being overwhelmed. As a result, water treatment plants were submerged, and motors were damaged.

In some areas, floodwater was between 3-4.5m deep. Floods in the southern Indian state of Kerala have killed more than 410 people since June 2018 in what local officials said was the worst flooding in 100 years. Many of those who died had been crushed under debris caused by landslides. More than 1 million people were left homeless in the 3,200 emergency relief camps set up in the area.

Parts of Kerala’s commercial capital, Cochin, were underwater, snarling up roads and leaving railways across the state impassable. In addition, the state’s airport, which domestic and overseas tourists use, was closed, causing significant disruption.

Local plantations were inundated by water, endangering the local rubber, tea, coffee and spice industries.

Schools in all 14 districts of Kerala were closed, and some districts have banned tourists because of safety concerns.

Maintaining sanitation and preventing disease in relief camps housing more than 800,000 people was a significant challenge. Authorities also had to restore regular clean drinking water and electricity supplies to the state’s 33 million residents.

Officials have estimated more than 83,000km of roads will need to be repaired and that the total recovery cost will be between £2.2bn and $2.7bn.

Indians from different parts of the country used social media to help people stranded in the flood-hit southern state of Kerala. Hundreds took to social media platforms to coordinate search, rescue and food distribution efforts and reach out to people who needed help. Social media was also used to support fundraising for those affected by the flooding. Several Bollywood stars supported this.

Some Indians have opened up their homes for people from Kerala who were stranded in other cities because of the floods.

Thousands of troops were deployed to rescue those caught up in the flooding. Army, navy and air force personnel were deployed to help those stranded in remote and hilly areas. Dozens of helicopters dropped tonnes of food, medicine and water over areas cut off by damaged roads and bridges. Helicopters were also involved in airlifting people marooned by the flooding to safety.

More than 300 boats were involved in rescue attempts. The state government said each boat would get 3,000 rupees (£34) for each day of their work and that authorities would pay for any damage to the vessels.

As the monsoon rains began to ease, efforts increased to get relief supplies to isolated areas along with clean up operations where water levels were falling.

Millions of dollars in donations have poured into Kerala from the rest of India and abroad in recent days. Other state governments have promised more than $50m, while ministers and company chiefs have publicly vowed to give a month’s salary.

Even supreme court judges have donated $360 each, while the British-based Sikh group Khalsa Aid International has set up its own relief camp in Kochi, Kerala’s main city, to provide meals for 3,000 people a day.

International Response

In the wake of the disaster, the UAE, Qatar and the Maldives came forward with offers of financial aid amounting to nearly £82m. The United Arab Emirates promised $100m (£77m) of this aid. This is because of the close relationship between Kerala and the UAE. There are a large number of migrants from Kerala working in the UAE. The amount was more than the $97m promised by India’s central government. However, as it has done since 2004, India declined to accept aid donations. The main reason for this is to protect its image as a newly industrialised country; it does not need to rely on other countries for financial help.

Google provided a donation platform to allow donors to make donations securely. Google partners with the Center for Disaster Philanthropy (CDP), an intermediary organisation that specialises in distributing your donations to local nonprofits that work in the affected region to ensure funds reach those who need them the most.

Google Kerala Donate

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• Open access
• Published: 03 August 2022

The challenge of unprecedented floods and droughts in risk management

• Heidi Kreibich   ORCID: orcid.org/0000-0001-6274-3625 1 ,
• Anne F. Van Loon   ORCID: orcid.org/0000-0003-2308-0392 2 ,
• Kai Schröter   ORCID: orcid.org/0000-0002-3173-7019 1 , 3 ,
• Philip J. Ward   ORCID: orcid.org/0000-0001-7702-7859 2 ,
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• Hafzullah Aksoy   ORCID: orcid.org/0000-0001-5807-5660 7 ,
• Camila Alvarez-Garreton   ORCID: orcid.org/0000-0002-5381-4863 8 , 9 ,
• Blanca Aznar   ORCID: orcid.org/0000-0001-6952-0790 10 ,
• Laila Balkhi   ORCID: orcid.org/0000-0001-8224-3556 11 ,
• Marlies H. Barendrecht   ORCID: orcid.org/0000-0002-3825-0123 2 ,
• Sylvain Biancamaria   ORCID: orcid.org/0000-0002-6162-0436 12 ,
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• Chris Bradley   ORCID: orcid.org/0000-0003-4042-867X 14 ,
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• Wouter Buytaert   ORCID: orcid.org/0000-0001-6994-4454 16 ,
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• Hayley Carlson 11 ,
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• Gemma Coxon   ORCID: orcid.org/0000-0002-8837-460X 20 , 21 ,
• Ioannis Daliakopoulos   ORCID: orcid.org/0000-0001-9333-4963 22 ,
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• Claire Delus   ORCID: orcid.org/0000-0002-6690-5326 23 ,
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• Giuseppe Esposito   ORCID: orcid.org/0000-0001-5638-657X 24 ,
• Didier François 23 ,
• Frédéric Frappart   ORCID: orcid.org/0000-0002-4661-8274 25 ,
• Jim Freer 20 , 21 , 26 ,
• Natalia Frolova   ORCID: orcid.org/0000-0003-3576-285X 5 ,
• Animesh K. Gain   ORCID: orcid.org/0000-0003-3814-693X 27 , 28 ,
• Manolis Grillakis   ORCID: orcid.org/0000-0002-4228-1803 29 ,
• Jordi Oriol Grima 10 ,
• Diego A. Guzmán 30 ,
• Laurie S. Huning   ORCID: orcid.org/0000-0002-0296-4255 6 , 31 ,
• Monica Ionita   ORCID: orcid.org/0000-0001-8240-4380 32 , 33 , 34 ,
• Maxim Kharlamov   ORCID: orcid.org/0000-0002-4439-5193 5 , 35 ,
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• Aristeidis Koutroulis   ORCID: orcid.org/0000-0002-2999-7575 38 ,
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• Johanna Mård   ORCID: orcid.org/0000-0002-8789-7628 43 , 44 ,
• Hannah Mathew-Richards 37 ,
• Andrew McKenzie   ORCID: orcid.org/0000-0001-8723-4325 42 ,
• Alfonso Mejia   ORCID: orcid.org/0000-0003-3891-1822 45 ,
• Eduardo Mario Mendiondo   ORCID: orcid.org/0000-0003-2319-2773 46 ,
• Marjolein Mens 47 ,
• Shifteh Mobini   ORCID: orcid.org/0000-0002-3365-7346 48 , 49 ,
• Guilherme Samprogna Mohor   ORCID: orcid.org/0000-0003-2348-6181 50 ,
• Viorica Nagavciuc   ORCID: orcid.org/0000-0003-1111-9616 32 , 34 ,
• Thanh Ngo-Duc   ORCID: orcid.org/0000-0003-1444-7498 51 ,
• Thi Thao Nguyen Huynh   ORCID: orcid.org/0000-0001-9071-1225 52 ,
• Pham Thi Thao Nhi   ORCID: orcid.org/0000-0003-4118-8479 36 ,
• Olga Petrucci   ORCID: orcid.org/0000-0001-6918-1135 24 ,
• Hong Quan Nguyen 52 , 53 ,
• Pere Quintana-Seguí   ORCID: orcid.org/0000-0002-7107-9671 54 ,
• Saman Razavi   ORCID: orcid.org/0000-0003-1870-5810 11 , 55 , 56 ,
• Elena Ridolfi   ORCID: orcid.org/0000-0002-4714-2511 57 ,
• Jannik Riegel 58 ,
• Md Shibly Sadik   ORCID: orcid.org/0000-0001-9205-4791 59 ,
• Elisa Savelli   ORCID: orcid.org/0000-0002-8948-0316 43 , 44 ,
• Alexey Sazonov 5 , 35 ,
• Sanjib Sharma   ORCID: orcid.org/0000-0003-2735-1241 60 ,
• Johanna Sörensen   ORCID: orcid.org/0000-0002-2312-4917 49 ,
• Felipe Augusto Arguello Souza   ORCID: orcid.org/0000-0002-2753-9896 46 ,
• Kerstin Stahl   ORCID: orcid.org/0000-0002-2159-9441 19 ,
• Max Steinhausen   ORCID: orcid.org/0000-0002-8692-8824 1 ,
• Michael Stoelzle   ORCID: orcid.org/0000-0003-0021-4351 19 ,
• Wiwiana Szalińska   ORCID: orcid.org/0000-0001-6828-6963 61 ,
• Qiuhong Tang 62 ,
• Fuqiang Tian   ORCID: orcid.org/0000-0001-9414-7019 63 ,
• Tamara Tokarczyk   ORCID: orcid.org/0000-0001-5862-6338 61 ,
• Carolina Tovar   ORCID: orcid.org/0000-0002-8256-9174 64 ,
• Thi Van Thu Tran   ORCID: orcid.org/0000-0003-1187-3520 52 ,
• Marjolein H. J. Van Huijgevoort   ORCID: orcid.org/0000-0002-9781-6852 65 ,
• Michelle T. H. van Vliet   ORCID: orcid.org/0000-0002-2597-8422 66 ,
• Sergiy Vorogushyn   ORCID: orcid.org/0000-0003-4639-7982 1 ,
• Thorsten Wagener   ORCID: orcid.org/0000-0003-3881-5849 21 , 50 , 67 ,
• Yueling Wang 62 ,
• Doris E. Wendt   ORCID: orcid.org/0000-0003-2315-7871 67 ,
• Elliot Wickham 68 ,
• Long Yang   ORCID: orcid.org/0000-0002-1872-0175 69 ,
• Mauricio Zambrano-Bigiarini   ORCID: orcid.org/0000-0002-9536-643X 8 , 9 ,
• Günter Blöschl   ORCID: orcid.org/0000-0003-2227-8225 70 &
• Giuliano Di Baldassarre   ORCID: orcid.org/0000-0002-8180-4996 43 , 44 , 71  

Nature volume  608 ,  pages 80–86 ( 2022 ) Cite this article

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• Natural hazards

Risk management has reduced vulnerability to floods and droughts globally 1 , 2 , yet their impacts are still increasing 3 . An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data 4 , 5 . On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change 3 .

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Observed decreasing trends in the vulnerability to floods and droughts, owing to effective risk management, are encouraging 1 . Globally, human and economic vulnerability dropped by approximately 6.5- and 5-fold, respectively, between the periods 1980–1989 and 2007–2016 (ref.  2 ). However, the impacts of floods and droughts are still severe and increasing in many parts of the world 6 . Climate change will probably lead to a further increase in their impacts owing to projected increases in the frequency and severity of floods and droughts 3 . The economic damage of floods is projected to double globally 7 and that of droughts to triple in Europe 8 , for a mean temperature increase of 2 °C.

The purpose of risk management is to reduce the impact of events through modification of the hazard, exposure and/or vulnerability: according to United Nations (UN) terminology 9 , disaster risk management is the application of disaster risk reduction policies and strategies to prevent new disaster risk, reduce existing disaster risk and manage residual risk, contributing to the strengthening of resilience against, and reduction of, disaster losses. Hazard is a process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation; exposure is the situation of people, infrastructure, housing, production capacities and other tangible human assets located in hazard-prone areas; and vulnerability is the conditions determined by physical, social, economic and environmental factors or processes 10 , 11 , 12 , 13 that increase the susceptibility of an individual, a community, assets or systems to the impacts of hazards. To be effective, risk management needs to be based on a sound understanding of these controlling risk drivers 14 , 15 . Past studies have identified increasing exposure as a primary driver of increasing impacts 3 , 4 , and vulnerability reduction has been identified as key for reduction of impacts 16 , 17 . However, ascertaining the combined effect of the drivers and the overall effectiveness of risk management has been hampered by a lack of empirical data 4 , 5 .

Here we analyse a new dataset of 45 pairs of flood or drought events that occurred in the same area on average 16 years apart (hereinafter referred to as paired events). The data comprise 26 flood and 19 drought paired events across different socioeconomic and hydroclimatic contexts from all continents (Fig. 1a ). We analyse floods and droughts together, because of the similarity of some of the management methods (for example, warning systems, water reservoir infrastructure), the potential for trade-offs in risk reduction between floods and droughts and therefore value for the management communities to learn from each other 18 . The impact, quantified by direct (fatalities, monetary damage), indirect (for example, disruption of traffic or tourism) and intangible impacts (for example, impact on human health or cultural heritage), is considered to be controlled by three drivers: hazard, exposure and vulnerability 3 . These drivers are quantified using a large range of different indices—for example, the standardized precipitation index, the number of houses in the affected area and risk awareness, respectively (Supplementary Table 1 ). These three drivers are considered to be exacerbated by management shortcomings. Hazard may be exacerbated by problems with water management infrastructure such as levees or reservoirs 19 . Exposure and vulnerability may be worsened by suboptimal implementation of non-structural measures such as risk-aware regional planning 20 or early warning 21 , respectively. We analyse management shortcomings and their effect on the three drivers explicitly, as this is the point at which improvements can start—for example, by the introduction of better strategies and policies. Data availability understandably varies among the paired events, and this can introduce inconsistency and subjectivity. The analyses are therefore based on indicators of change, to account for differences between paired events in respect of measured variables, data quality and uncertainty. These indicators of change represent the differences between the first event (baseline) and the second, categorized as large decreases/increases (−2/+2), small decreases/increases (−1/+1) and no change (0) (Supplementary Table 2 ). To minimize the subjectivity and uncertainty of indicator assignment, a quality assurance protocol is implemented and indicators of change with sub-indicators are used.

a , Location of flood and drought paired events ( n = 45). Numbers are paired-event IDs. b , Indicators of change, sorted by impact change. Impact is considered to be controlled by hazard, exposure and vulnerability, which are exacerbated by risk management shortcomings. Maps of the paired events coloured according to drivers and management shortcomings are shown in Extended Data Fig. 1 .

Source data

The majority of paired events show decreases in management shortcomings (71% of paired events; Fig. 1b ), which reflects that societies tend to learn from extreme events 22 . Most cases also show a decrease in vulnerability (80% of paired events) as societies typically reduce their vulnerability after the first event of a pair 21 . The five paired events with a large decrease in impact (dark blue, top left in Fig. 1b ) are associated with decreases or no change of all three drivers.

Drivers of changes in impact

Changes in flood impacts are significantly and positively correlated with changes in hazard ( r  = 0.64, P  ≤ 0.01), exposure ( r  = 0.55, P  ≤ 0.01) and vulnerability ( r  = 0.60, P  ≤ 0.01) (Fig. 2a ), which is in line with risk theory 3 . Although a previous analysis of eight case studies 21 identified vulnerability as a key to reduction of flood impacts, this new, more comprehensive, dataset suggests that changes in hazard, exposure and vulnerability are equally important, given that they correlate equally strongly with changes in flood impact. Changes in drought impacts are significantly correlated with changes in hazard and exposure, but not with changes in vulnerability (Fig. 2c ). This suggests that changes in vulnerability have been less successful in reducing drought impact than flood impact, which is also consistent with those event pairs for which only vulnerability changed (Extended Data Table 1 ). However, quantification of the contribution of individual drivers is difficult with this empirical approach because there are only a limited number of cases in which only one driver changed. There are three cases in which only vulnerability changed between events, two cases in which only hazard changed and no case in which only exposure changed (Extended Data Table 1 ). Additionally, paired events without a change in hazard (0) are analysed in more detail to better understand the role of exposure and vulnerability (Extended Data Fig. 2 ). In all these paired events, a reduction in impact was associated with a reduction in vulnerability, highlighting the importance of vulnerability. In five of these eight cases with a decrease in impact there was also a decrease in exposure, whereas in one case (floods in Jakarta, Indonesia in 2002 and 2007 (ID 18)) there was a large increase in exposure. In the paired event of droughts in California, United States (1987–1992 and 2011–2016, ID 36) an increase in exposure and a reduction in vulnerability increased impact, which points to the more important role of exposure in comparison with vulnerability in this drought case (Extended Data Fig. 2 ).

a , c , Correlation matrix of indicators of change for flood ( a ) and drought ( c ) paired events. Colours of squares indicate Spearman’s rank correlation coefficients and their size, the P  value. b , d ,Histograms of indicators of change of flood ( b ) and drought ( d ) stratified by decrease ( n  = 15 and n  = 5 paired events for flood and drought, respectively) and increase ( n  = 5 and n  = 8 paired events, respectively) in impact. The asterisk denotes the success stories of Box 1 ; double asterisks denote pairs for which the second event was much more hazardous than the first (that is, 'unprecedented'). Mgmt shortc, management shortcomings.

Generally the changes in drivers are not significantly correlated with each other, with the exception of hazard and exposure in the case of floods ( r  = 0.55, P  ≤ 0.01) (Fig. 2a ). This finding may be explained by the influence of hazard on the size of the inundation area, and thus on the numbers of people and assets affected, which represent exposure.

The sensitivity analysis suggests that the correlation pattern is robust, as visualized by the colours in Extended Data Fig. 3 . The pattern of P  values is also robust for flood cases, although these become less significant for drought because of the smaller sample size (Extended Data Fig. 3 ).

We split the paired events into groups of decreasing and increasing impact to evaluate their drivers separately (Fig. 2b,d ). Overall, the pattern is similar for floods and droughts. Most flood and drought pairs with decreasing impact show either a decrease in hazard (ten pairs, 50%) or no change (eight pairs, 40%). Exceptions are two flood pairs that are success stories of decreased impact despite an increase in hazard, as detailed in Box 1 . The change in exposure of the pairs with decreased impacts (Fig. 2b,d ) ranges from a large decrease to a large increase, whereas vulnerability always decreased. All cases with a large decrease in vulnerability (−2) are associated with a decrease in impacts. Overall, the pattern suggests that a decrease in impacts is mainly caused by a combination of lower hazard and vulnerability, despite an increase in exposure in 25% of cases.

The role of hazard and vulnerability in impact reduction can be exemplified by the pair of riverine floods in Jakarta, Indonesia (ID 4 in Fig. 1 ). The 2007 event had a flood return period of 50 years, whereas it was 30 years for the 2013 event 23 (that is, the hazard of the second event was smaller). Vulnerability had also decreased as a result of improved preparedness resulting from a flood risk mapping initiative and capacity building programmes implemented after the first flood, to improve citizens' emergency response, as well as by an improvement in official emergency management by establishment of the National Disaster Management Agency in 2008. Additionally, exposure was substantially reduced. Whilst the first flood caused 79 fatalities and direct damage of €1.3 billion, the second event caused 38 fatalities and €0.76 billion of direct damage.

Another example is a pair of Central European droughts (ID 9). During the 2003 event, the minimum 3-month Standardized Precipitation Evapotranspiration Index was −1.62 whereas in 2015 it was −1.18—that is, the hazard of the second event was smaller 24 . The vulnerability was also lower in the second event, because the first event had raised public awareness and triggered an improvement in institutional planning. For instance, the European Commission technical guidance on drought management plans 25 was implemented. Many reservoirs were kept filled until the beginning of summer 2015, which alleviated water shortages for various sectors and, in some cities (for example, Bratislava and Bucharest), water was supplied from tanks 26 . Additionally, water use and abstraction restrictions were implemented for non-priority uses including irrigation 26 . The impact was reduced from €17.1 billion to €2.2 billion, despite an increase in exposure because of the larger drought extent affecting almost all of Europe in 2013.

Most flood and drought pairs with an increase in impact also show a larger hazard (11 cases, 85%; Fig. 2b,d ). For six of these paired events (46%), the second event was much more hazardous than the first (hazard indicator-of-change +2), whereas this was never the case for the pairs with decreasing impact. Of those pairs with an increase in impact, 12 (92%) show an increase in exposure and nine (69%) show a small decrease in vulnerability (vulnerability indicator-of-change −1). Overall, the pattern suggests that the increase in impact is mainly caused by a combination of higher hazard and exposure, which is not compensated by a small decrease in vulnerability.

The role of hazard and exposure in increasing impact is illustrated by a pair of pluvial floods in Corigliano-Rossano City, Calabria, Italy (ID 40). This 2015 event was much more hazardous (+2) than that in 2000, with precipitation return periods of more than 100 and 10–20 years, respectively 27 . Also, the 2000 event occurred during the off-season for tourism in September whereas the exposure was much larger in 2015, because the event occurred in August when many tourists were present. Interruption of the peak holiday season caused severe indirect economic damage. Another example is a pair of droughts (ID 33) affecting North Carolina, United States. Between 2007 and 2009, about 65% of the state was affected by what was classified as an exceptional drought, with a composite drought indicator of the US Drought Monitor of 27 months 28 , whereas between 2000 and 2003 only about 30% of the state was affected by an exceptional drought of 24 months 28 . The crop losses in 2007–2009 were about €535 million, whereas they were €497 million in 2000–2003, even though vulnerability had been reduced due to drought early warning and management by the North Carolina Drought Management Council, established in 2003.

Box 1
 Success stories of decreased impact despite increased hazard

The dataset includes two cases in which a lower impact was achieved despite a larger hazard of the second event, making these interesting success stories (Fig. 3 ). Both cases are flood paired events, but of different types (that is, pluvial and riverine floods (Table 1 )). These cases have in common that institutional changes and improved flood risk management governance were introduced and high investments in integrated management were undertaken, which led to an effective implementation of structural and non-structural measures, such as improved early warning and emergency response to complement structural measures such as levees (Table 1 ).

Effects of changes in management on drivers

The correlations shown in Fig. 2a,c also shed light on how management affects hazard, exposure and vulnerability and thus, indirectly, impact. For flood paired events, changes in management shortcomings are significantly positively correlated with changes in vulnerability ( r  = 0.56, P  ≤ 0.01), and both are significantly positively correlated with changes in impact (Fig. 2a ). For drought, however, these correlations are not significant (Fig. 2c ). Thus, achieving decreases in vulnerability, and consequently in impact, by improving risk management (that is, reducing management shortcomings) seems to be more difficult for droughts than for floods. This difficulty may be related to spillover effects—that is, drought measures designed to reduce impacts in one sector can increase impacts in another. For example, irrigation to alleviate drought in agriculture may increase drought impacts on drinking water supply and ecology 29 .

The paired floods in the Piura region, Peru (ID 13) illustrate how effective management can reduce vulnerability, and consequently impact. At the Piura river, maximum flows of 3,367 and 2,755 m 3  s −1 were recorded during the 1998 and 2017 events, respectively (that is, hazard showed a small decrease (−1)). Around 2000, the national hydrometeorological service started to issue medium-range weather forecasts that allowed preparations months before the 2017 event. In 2011, the National Institute of Civil Defence and the National Centre for the Estimation, Prevention, and Reduction of Disaster Risk were founded which, together with newly established short-range river flow forecasts, allowed more efficient emergency management of the more recent event. Additionally, non-governmental organizations such as Practical Action had implemented disaster risk-reduction activities, including evacuation exercises and awareness campaigns 30 . All of these improvements in management decreased vulnerability. The impact of the second event was smaller, with 366 fatalities in 1998 compared with 159 in 2017, despite an increase in exposure due to urbanization and population increase.

When the hazard of the second event was larger than that of the first (+1, +2), in 11 out of 18 cases (61%) the impact of the second event was also larger, irrespective of small decreases in vulnerability in eight of these cases (light blue dots/triangles in Fig. 3 ). There are only two paired events in our dataset for which a decrease in impact was achieved despite the second event being more hazardous (highlighted by the green circle in Fig. 3 ). These cases are considered success stories and are further discussed in Box 1 . For the two paired events (ID 21 and 30) for which the only driver that changed was hazard (+1), the impacts did not change (0) (Extended Data Table 1 ). Water retention capacity of 189,881,000 m³ and good irrigation infrastructure with sprinkling machines were apparently sufficient to counteract the slight increase in hazard for the drought paired event in Poland in 2006 and 2015 (ID 21). The improved flood alleviation scheme implemented between the paired flood events (2016 and 2018), protected properties in Birmingham, United Kingdom (ID 30). There are, however, seven cases for which the second event was much more hazardous (+2) than the first (highlighted by the purple ellipse in Fig. 3 )—that is, events of a magnitude that locals had probably not previously experienced. We term these events, subjectively, as unprecedented; almost all had an increased impact despite improvements in management.

Categories are: lower hazard and lower impact, ten cases; higher hazard and higher impact, 11 cases; lower hazard and higher impact, one case; higher hazard and lower impact, two cases. Circles and triangles indicate drought and flood paired events, respectively; their colours indicate change in vulnerability. Green circle highlights success stories ( n  = 2) of reduced impact (−1) despite a small increase in hazard (+1). Purple ellipse indicates paired events ( n  = 7) with large increase in hazard (+2)—that is, events that were subjectively unprecedented and probably not previously experienced by local residents.

One unprecedented pluvial flood is the 2014 event in the city of Malmö, Sweden (ID 45). This event was much more hazardous than that experienced a few years before, with precipitation return periods on average of 135 and 24 years, respectively, for 6 h duration 31 . The largest 6 h precipitation measured at one of nine stations during the 2014 event corresponded to a return period of 300 years. The combined sewage system present in the more densely populated areas of the city was overwhelmed, leading to extensive basement flooding in 2014 (ref.  31 ). The direct monetary damage was about €66 million as opposed to €6 million in the first event. An unprecedented drought occurred in the Cape Town metropolitan area of South Africa, in 2015–2018 (ID 44). The drought was much longer (4 years) than that experienced previously in 2003–2004 (2 years). Although the Berg River Dam had been added to the city’s water supply system in 2009, and local authorities had developed various strategies for managing water demands (for example, water restrictions, tariff increases, communication campaign), the second event caused a much higher direct impact of about €180 million 32 because the water reserves were reduced to virtually zero.

Even though it is known that vulnerability reduction plays a key role in reducing risk, our paired-event cases reveal that when the hazard of the second event was higher than the first, a reduction in vulnerability alone was often not sufficient to reduce the impact of the second event to less than that of the first. Our analysis of drivers of impact change reveals the importance of reducing hazard, exposure and vulnerability to achieve an effective impact reduction (Fig. 2 ). Although previous studies have attributed a high priority to vulnerability reduction 17 , 21 , the importance of considering all three drivers identified here may reflect the sometimes limited efficiency of management decisions, resulting in unintended consequences. For example, levee construction aiming at reducing hazards may increase exposure through encouraging settlements in floodplains 33 , 34 . Similarly, construction of reservoirs to abate droughts may enhance exposure through encouraging agricultural development and thus increase water demand 35 , 36 .

Events that are much more hazardous than preceding events (termed unprecedented here) seem to be difficult to manage; in almost all the cases considered they led to increased impact (Fig. 3 ). This finding may be related to two factors. First, large infrastructure such as levees and water reservoirs play an important role in risk management. These structures usually have an upper design limit up to which they are effective but, once a threshold is exceeded, they become ineffective. For example, the unprecedented pluvial flood in 2014 in Malmö, Sweden (ID 45) exceeded the capacity of the sewer system 31 and the unprecedented drought in Cape Town (ID 44) exceeded the storage water capacity 37 . This means that infrastructure is effective in preventing damage during events of a previously experienced magnitude, but often fails for unprecedented events. Non-structural measures, such as risk-aware land-use planning, precautionary measures and early warning, can help mitigate the consequences of water infrastructure failure in such situations 21 , but a residual risk will always remain. Second, risk management is usually implemented after large floods and droughts, whereas proactive strategies are rare. Part of the reason for this behaviour is a cognitive bias associated with the rarity and uniqueness of extremes, and the nature of human risk perception, which makes people attach a large subjective probability to those events they have personally experienced 38 .

On the other hand, two case studies were identified in which impact was reduced despite an increase in hazard (Box 1 ). An analysis of these case studies identifies three success factors: (1) effective governance of risk and emergency management, including transnational collaboration such as in the Danube case; (2) high investments in structural and non-structural measures; and (3) improved early warning and real-time control systems such as in the Barcelona case. We believe there is potential for more universal application of these success factors to counteract the current trend of increasing impacts associated with climate change 3 . These factors may also be effective in the management of unprecedented events, provided they are implemented proactively.

The concept of paired events aims at comparing two events of the same hazard type that occurred in the same area 21 to learn from the differences and similarities. This concept is analogous to paired catchment studies, which compare two neighbouring catchments with different vegetation in terms of their water yield 39 . Our study follows the theoretical risk framework that considers impact as a result of three risk components or drivers 3 : hazard, exposure and vulnerability (Extended Data Fig. 4 ). Hazard reflects the intensity of an event, such as a flooded area or drought deficit—for example, measured by the standardized precipitation index. Exposure reflects the number of people and assets in the area affected by the event. Consequently, the change in exposure between events is influenced by changes in the population density and the assets in the affected area (socioeconomic developments), as well as by changes in the size of the affected area (change of hazard). Vulnerability is a complex concept, with an extensive literature from different disciplines on how to define, measure and quantify it 13 , 40 , 41 , 42 . For instance, Weichselgartner 43 lists more than 20 definitions of vulnerability, and frameworks differ quite substantially—for example, in terms of integration of exposure into vulnerability 11 or separating them 3 . Reviews and attempts to converge on the various vulnerability concepts stress that vulnerability is dynamic and that assessments should be conducted for defined human–environment systems at particular places 12 , 44 , 45 . Every vulnerability analysis requires an approach adapted to its specific objectives and scales 46 . The paired event approach allows detailed context and place-based vulnerability assessments that are presented in the paired event reports, as well as comparisons across paired events based on the indicators-of-change. The selection of sub-indicators for the characterization of vulnerability is undertaken with a particular focus on temporal changes at the same place. All three drivers—hazard, exposure and vulnerability—can be reduced by risk-management measures. Hazard can be reduced by structural measures such as levees or reservoirs 19 , exposure by risk-aware regional planning 20 and vulnerability by non-structural measures, such as early warning 21 .

Our comparative analysis is based on a novel dataset of 45 paired events from around the world, of which 26 event pairs are floods and 19 are droughts. The events occurred between 1947 and 2019, and the average period between the two events of a pair is 16 years. The number of paired events is sufficiently large to cover a broad range of hydroclimatic and socioeconomic settings around the world and allows differentiated, context-specific assessments on the basis of detailed in situ observations. Flood events include riverine, pluvial, groundwater and coastal floods 47 , 48 , 49 , 50 . Drought events include meteorological, soil moisture and hydrological (streamflow, groundwater) droughts 51 . The rationale for analysing floods and droughts together is based on their position at the two extremes of the same hydrological cycle, the similarity of some management strategies (for example, warning systems, water reservoir infrastructure), potential trade-offs in the operation of the same infrastructure 52 and more general interactions between these two risks (for example, water supply to illegal settlements that may spur development and therefore flood risk). There may therefore be value in management communities learning from each other 18 .

The dataset comprises: (1) detailed review-style reports about the events and key processes between the events, such as changes in risk management (open access data; Data Availability statement); (2) a key data table that contains the data (qualitative and quantitative) characterizing the indicators for the paired events, extracted from individual reports (open access data); and (3) an overview table providing indicators-of-change between the first and second events (Supplementary Table 3 ). To minimize the elements of subjectivity and uncertainty in the analysis, we (1) used indicators-of-change as opposed to indicators of absolute values, (2) calculated indicators from a set of sub-indicators (Supplementary Table 1 ) and (3) implemented a quality assurance protocol. Commonly, more than one variable was assessed per sub-indicator (for example, flood discharges at more than one stream gauge, or extreme rainfall at several meteorological stations). A combination or selection of the variables was used based on hydrological reasoning on the most relevant piece of information. Special attention was paid to this step during the quality assurance process, drawing on the in-depth expertise on events of one or more of our co-authors. The assignment of values for the indicators-of-change, including quality assurance, was inspired by the Delphi Method 53 that is built on structured discussion and consensus building among experts. The process was driven by a core group (H.K., A.F.V.L., K. Schröter, P.J.W. and G.D.B.) and was undertaken in the following steps: (1) on the basis of the detailed report, a core group member suggested values for all indicators-of-change for a paired event; (2) a second member of the core group reviewed these suggestions; in case of doubt, both core group members rechecked the paired event report and provided a joint suggestion; (3) all suggestions for the indicators-of-change for all paired events were discussed in the core group to improve consistency across paired events; (4) the suggested values of the indicators-of-change were reviewed by the authors of the paired-event report; and finally (5), the complete table of indicators-of-change (Supplementary Table 3 ) was reviewed by all authors to ensure consistency between paired events. Compound events were given special consideration, and the best possible attempt was made to isolate the direct effects of floods and droughts from those of concurrent phenomena on hazard, exposure and impact, based on expert knowledge of the events of one or more of the co-authors. For instance, in the course of this iterative process it became clear that fatalities during drought events were not caused by a lack of water, but by the concurrent heatwave. It was thus decided to omit the sub-indicator ‘fatalities’ in drought impact characterization. The potential biases introduced by compound events were further reduced by the use of the relative indicators-of-change between similar event types with similar importance of concurrent phenomena.

The indicator-of-change of impact is composed of the following sub-indicators: number of fatalities (for floods only), direct economic impact, indirect impact and intangible impact (Supplementary Table 1 ). Flood hazard is composed of the sub-indicators precipitation/weather severity, severity of flood, antecedent conditions (for pluvial and riverine floods only), as well as the following for coastal floods only: tidal level and storm surge. Drought hazard is composed of the duration and severity of drought. Exposure is composed of the two sub-indicators people/area/assets exposed and exposure hotspots. Vulnerability is composed of the four sub-indicators lack of awareness and precaution, lack of preparedness, imperfect official emergency/crisis management and imperfect coping capacity. Indicators-of-change, including sub-indicators, were designed such that consistently positive correlations with impact changes are expected (Supplementary Table 1 ). For instance, a decrease in 'lack of awareness' leads to a decrease in vulnerability and is thus expected to be positively correlated with a decrease in impacts. Management shortcomings are characterized by problems with water management infrastructure and non-structural risk management shortcomings, which means that non-structural measures were not optimally implemented. These sub-indicators were aggregated into indicators-of-change for impact, hazard, exposure, vulnerability and management shortcomings, to enable a consistent comparison between flood and drought paired events. This set of indicators is intended to be as complementary as possible, but overlaps are hard to avoid because of interactions between physical and socioeconomic processes that control flood and drought risk. Although the management shortcoming indicator is primarily related to the planned functioning of risk management measures, and hazard, exposure and vulnerability primarily reflect the concrete effects of measures during specific events, there is some overlap between the management shortcoming indicator and all three drivers. Supplementary Table 1 provides definitions and examples of description or measurement of sub-indicators for flood and drought paired events.

The changes are indicated by −2/2 for large decrease or increase, −1/1 for small decrease or increase and 0 for no change. In the case of quantitative comparisons (for example, precipitation intensities and monetary damage), a change of less than around 50% is usually treated as a small change and above approximately 50% as a large change, but always considering the specific measure and paired events. Supplementary Table 2 provides representative examples from flood and drought paired events showing how differences in quantitative variables and qualitative information between the two events of a pair correspond to the values of the sub-indicators, ranging from large decrease (−2) to large increase (+2). We assume that an event is unprecedented in a subjective way—that is, it has probably not been experienced before—if the second event of a pair is much more hazardous than the first (hazard indicator-of-change +2).

Spearman’s rank correlation coefficients are calculated for impact, drivers and management shortcomings, separated for flood and drought paired events. Despite the measures taken to minimize the subjectivity and uncertainty of indicator assignment, there will always be an element of subjectivity. To address this, we carried out a Monte Carlo analysis (1,000 iterations) to test the sensitivity of the results when randomly selecting 80% of flood and drought paired events. For each subsample correlation, coefficients and P  values were calculated to obtain a total of 1,000 correlation and 1,000  P  value matrices. The 25th and 75th quantiles of the correlation coefficients and P  values were calculated separately (Extended Data Fig. 3 ).

Data availability

The dataset containing the individual paired event reports, the key data table and Supplementary Tables 1 – 3 are openly available via GFZ Data Services ( https://doi.org/10.5880/GFZ.4.4.2022.002 ).  Source data are provided with this paper.

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Acknowledgements

The presented work was developed by the Panta Rhei Working Groups 'Changes in flood risk' and 'Drought in the Anthropocene' within the framework of the Panta Rhei Research Initiative of the International Association of Hydrological Sciences. We thank the Barcelona Cicle de l’Aigua S.A., Barcelona City Council, Environment Agency (United Kingdom), Länsförsäkringar Skåne, Steering Centre for Urban Flood Control Programme in HCMC (Vietnam), VA SYD and the West Berkshire Council (United Kingdom) for data. The work was partly undertaken under the framework of the following projects: Alexander von Humboldt Foundation Professorship endowed by the German Federal Ministry of Education and Research (BMBF); British Geological Survey’s Groundwater Resources Topic (core science funding); C3-RiskMed (no. PID2020-113638RB-C22), financed by the Ministry of Science and Innovation of Spain; Centre for Climate and Resilience Research (no. ANID/FONDAP/15110009); CNES, through the TOSCA GRANT SWHYM; DECIDER (BMBF, no. 01LZ1703G); Deltares research programme on water resources; Dutch Research Council VIDI grant (no. 016.161.324); FLOOD (no. BMBF 01LP1903E), as part of the ClimXtreme Research Network. Funding was provided by the Dutch Ministry of Economic Affairs and Climate; Global Water Futures programme of University of Saskatchewan; GlobalHydroPressure (Water JPI); HUMID project (no. CGL2017-85687-R, AEI/FEDER, UE); HydroSocialExtremes (ERC Consolidator Grant no. 771678); MYRIAD-EU (European Union’s Horizon 2020 research and innovation programme under grant agreement no. 101003276); PerfectSTORM (no. ERC-2020-StG 948601); Project EFA210/16 PIRAGUA, co-founded by ERDF through the POCTEFA 2014–2020 programme of the European Union; Research project nos. ANID/FSEQ210001 and ANID/NSFC190018, funded by the National Research and Development Agency of Chile; SECurITY (Marie Skłodowska-Curie grant agreement no. 787419); SPATE (FWF project I 4776-N, DFG research group FOR 2416); the UK Natural Environment Research Council-funded project Land Management in Lowland Catchments for Integrated Flood Risk Reduction (LANDWISE, grant no. NE/R004668/1); UK NERC grant no. NE/S013210/1 (RAHU) (W.B.); Vietnam National Foundation for Science and Technology Development under grant no. 105.06-2019.20.; and Vietnam National University–HCMC under grant no. C2018-48-01. D.M. and A. McKenzie publish with the permission of the Director, British Geological Survey. The views expressed in this paper are those of the authors and not the organizations for which they work.

Open access funding provided by Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ.

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Heidi Kreibich, Kai Schröter, Nivedita Sairam, Max Steinhausen & Sergiy Vorogushyn

Institute for Environmental Studies, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands

Anne F. Van Loon, Philip J. Ward, Maurizio Mazzoleni, Marlies H. Barendrecht, Anaïs Couasnon & Marleen C. de Ruiter

Leichtweiss Institute for Hydraulic Engineering and Water Resources, Division of Hydrology and River basin management, Technische Universität Braunschweig, Braunschweig, Germany

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Department of Civil and Environmental Engineering, University of Houston, Houston, TX, USA

Guta Wakbulcho Abeshu & Hong-Yi Li

Lomonosov Moscow State University, Moscow, Russia

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Center for Climate and Resilience Research, Santiago, Chile

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Global Institute for Water Security, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

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LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France

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Department of Groundwater Management, Deltares, Delft, the Netherlands

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School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK

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Agency for the Assessment and Application of Technology, Jakarta, Indonesia

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Department of Civil and Environmental Engineering, Imperial College London, London, UK

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Department of Civil Engineering, Beykent University, Istanbul, Turkey

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Graduate School, Istanbul Technical University, Istanbul, Turkey

Faculty of Environment and Natural Resources, University of Freiburg, Freiburg, Germany

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Geographical Sciences, University of Bristol, Bristol, UK

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Cabot Institute, University of Bristol, Bristol, UK

Gemma Coxon, Jim Freer & Thorsten Wagener

Department of Agriculture, Hellenic Mediterranean University, Iraklio, Greece

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Université de Lorraine, LOTERR, Metz, France

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University of Saskatchewan, Centre for Hydrology, Canmore, Alberta, Canada

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Department of Economics, Ca’ Foscari University of Venice, Venice, Italy

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Pontificia Bolivariana University, Faculty of Civil Engineering, Bucaramanga, Colombia

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California State University, Long Beach, CA, USA

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Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Palaeoclimate Dynamics Group, Bremerhaven, Germany

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Emil Racovita Institute of Speleology, Romanian Academy, Cluj-Napoca, Romania

Monica Ionita

Forest Biometrics Laboratory, Faculty of Forestry, Ștefan cel Mare University, Suceava, Romania

Water Problem Institute Russian Academy of Science, Moscow, Russia

Maxim Kharlamov & Alexey Sazonov

Faculty of Environment, University of Science, Ho Chi Minh City, Vietnam

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School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece

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Servicio Nacional de Meteorología e Hidrología del Perú, Lima, Peru

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Department of Applied Physics, University of Barcelona, Barcelona, Spain

María Carmen LLasat

Water Research Institute, University of Barcelona, Barcelona, Spain

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H.K. initiated the study and led the work. H.K., A.F.V.L., K. Schröter, P.J.W. and G.D.B. coordinated data collection, designed the study and undertook analyses. All co-authors contributed data and provided conclusions and a synthesis of their case study (the authors of each paired event report were responsible for their case study). M. Mazzoleni additionally designed the figures, and he and N.S. contributed to the analyses. H.K., G.D.B., P.J.W., A.F.V.L., K. Schröter and G.D.B. wrote the manuscript with valuable contributions from all co-authors.

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Extended data figures and tables

Extended data fig. 1 location of flood and drought paired events coloured according to their indicators-of-change..

a , Change in hazard; b , change in exposure; c , change in vulnerability and d , change in management shortcomings.

Extended Data Fig. 2 Parallel plot of paired events with the same hazard of both events.

The hazard change is zero for all shown paired events. The lines show how the different combinations of indicators-of-change result in varying changes in impacts. Small offsets within the grey bars of the indicator-of-change values enable the visualization of all lines.

Extended Data Fig. 3 Results of the sensitivity analyses.

a–d Correlation matrix of indicators-of-change for 25th and 75th quantiles of correlation coefficients and p-values, respectively ( a , c ) and 75th and 25th quantiles of correlation coefficients and p-values, respectively ( b , d ) separate for flood and drought paired events. Quantiles of correlation coefficients and p-values were calculated separately; colours of squares indicate Spearman’s rank correlation coefficients; sizes of squares indicates p-values. Fig. 2a, c is added to the right to ease comparison.

Extended Data Fig. 4 Theoretical framework used in this study (adapted from IPCC 3 ).

This theoretical risk framework considers impact as a result of three risk components or drivers: hazard, exposure and vulnerability, which in turn are modified by management.

Supplementary information

Supplementary tables.

Supplementary Tables 1–3.

Source Data Fig. 1.

Source data fig. 2., source data fig. 3., source data extended data fig. 1., source data extended data fig. 2., source data extended data fig. 3., rights and permissions.

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Kreibich, H., Van Loon, A.F., Schröter, K. et al. The challenge of unprecedented floods and droughts in risk management. Nature 608 , 80–86 (2022). https://doi.org/10.1038/s41586-022-04917-5

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Nature-based solutions to enhance urban flood resiliency: case study of a Thailand Smart District

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A Research through Designing approach was used to explore nature-based solutions (NbS) for flood management at the fluvial (regional) and pluvial (local) scales as part of a Smart District visioning study in a peri-urban area north of Bangkok, Thailand. The NbS visions were informed by community surveys (total n  = 770) as well as in-depth, semi-structured interviews with community leaders and key stakeholders representing private sector business. Both fluvial and pluvial flooding commonly occur in the study area and the cost of damage incurred by individuals generally exceeds aid remuneration. The surveys revealed that flood insurance was not widely used as a form of resiliency to flood conditions. Furthermore, survey participants generally considered common space and green space unsatisfactory and inadequate to meet community needs. In light of these survey responses, example NbS visions were developed to address community concerns and promote well-being, while concurrently providing resiliency and improved ecosystem services through connectivity of blue and greenscapes. This case study provides a novel linkage between the concepts of NbS, Research through Designing, and Smart City/District, in exploring sustainable and resilient approaches to flood management in the context of tropical, Global South development and also provides a first step towards developing an NbS typology.

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Introduction

Approximately 57% of the world’s population currently live in urban areas ( https://data.worldbank.org/indicator/SP.URB.TOTL.IN.ZS accessed 23 Dec 2022) and this proportion is expected reach 68% by 2050 ( https://www.un.org/development/desa/en/news/population/2018-revision-of-world-urbanization-prospects.html accessed 23 Dec 2022). This increasingly urbanized population will experience liveability stresses, including greater risk of flooding due to more frequent, high intensity storm events (Miller and Hutchins 2017 ) and health impacts from increased urban temperatures (Vicedo-Cabrera et al. 2021 ). Nature-based solutions (NbS) is a newly emerged design and visioning approach that has the potential to mitigate these increased environmental stresses and move urban development along a better path towards sustainability and resiliency (Lafortezza et al. 2018 ; Hanson et al. 2020 ; Moosavi et al. 2021 ; Irvine et al. 2022a ; Sowińska-Świerkosz and García 2022 ). Ruangpan et al. ( 2020 ) define NbS as …participatory, holistic, integrated approaches, using nature to enhance adaptive capacity, reduce hydro-meteorological risk, increase resilience, improve water quality, increase the opportunities for recreation, improve human well-being and health, enhance vegetation growth, and connect habitat and biodiversity. While the more traditional design ideas of Low Impact Development (LID), Water Sensitive Urban Design (WSUD), or Sustainable Urban Drainage Systems (SUDS) share some common water management elements with NbS (Fletcher et al. 2015 ; Lim and Lu 2016 ; Ahammed 2017 ; Irvine et al. 2014 , 2021a ; Hamel and Tan 2022 ), in general, NbS employs a broader, more encompassing approach that embraces and integrates community and ecosystem well-being. NbS inherently involves urban greenspace (Brokking et al 2021 ; Irvine et al. 2021b ; Zwierzchowska et al. 2021 ) and greenspace often is included as an indicator of Smart City development (Lombardi et al. 2012 ; Shen et al. 2018 ; Irvine et al. 2022b ). To date, the NbS literature has focused on socio-economic and policy issues, as well as ecosystem service provisioning, including water quality treatment and flood management (Keesstra et al. 2018 ; Collier and Bourke 2020 ; Tozer et al. 2020 ; Tiwary et al. 2020 ; Almenar et al. 2021 ; Li et al. 2021 ; Jessup et al. 2021 ; Dutta et al. 2021 ; Kumar et al. 2021 ; Dorst et al. 2022 ). However, while Frantzeskaki ( 2019 ) concluded that successful NbS must be aesthetically appealing to citizens, creating a new green urban commons through social innovation and collaborative governance, there are relatively few case examples in the literature of “guided seeing” to NbS for urban water management. In other words, “how would NbS be visioned in the design phase and what would these visions look like”? The objective of this paper is to address these questions of guided seeing, specifically by applying a Research through Designing approach within a Smart City/Smart District framework in a case study of a peri-urban area, about 55 km north of Bangkok, Thailand. Given the importance of green space within the Smart City concept the objective of this paper is to illustrate how NbS can be included in urban design to enhance community well-being while concomitantly supporting improved sustainability and resiliency of urban water management. The need for community familiarity, as well as considerations of scale and connectivity in guiding design principles to enhance community well-being and resiliency, also is emphasized.

Connectivity is an important Smart City theme. Connectivity can occur between components of the Smart City, including transportation and energy systems, but also includes connectivity of NbS spaces. Gardiner and Hardy ( 2005 ) concluded that WSUD often is considered an individual design solution rather than being integrated holistically into the community design and, therefore, fails to gain traction. This challenge to effective WSUD implementation also might be considered a problem of familiarity, which includes a lack of meaningful engagement with the community, or what Morison and Brown ( 2011 ) call “policy without publics”. Weinstein et al. ( 2019 ) have argued flood resiliency literature generally reflects the idea that by “simply advocating more sustainable development and utilization of green building technologies” cities can achieve both economic development and reduce flood risk with minimal conflict or compromise, which ignores the issues of urban governance, power relations, and uneven vulnerabilities. This argument suggests there is a lack of connectivity and familiarity in the planning and design of green infrastructure to improve urban flood resiliency and in this paper we seek to reconcile these issues. The Smart City framework was particularly helpful in guiding an integrated, connected community design at multiple scales that should provide a successful roadmap for future development within the Smart District.

Our paper represents new contributions to the literature in several specific areas. First, it develops a novel linkage between the concepts of NbS, Research through Designing, and Smart City to explore sustainable and resilient approaches to flood management (including both mitigation and adaptation approaches) at the fluvial and pluvial scale. Second, it provides examples of NbS designs and the guided seeing process to illustrate “what NbS might look like” for this peri-urban Bangkok study area. Yereseme et al. ( 2022 ) recently provided an excellent review of sustainable integrated urban flood management strategies for planning of smart cities that noted the importance of including LID, but they focused more on the technical aspects of real time monitoring and modeling. Our paper complements the work of Yereseme et al. ( 2022 ) by providing examples of the LID (or NbS) visioning process. In some way, then, we take a first step towards establishing an NbS typology for Smart Cities. Crewe and Forsyth ( 2003 ) consider typology for landscape architecture as classifications that have both functional and symbolic dimensions. In our work, the NbS typology function would be sustainable urban water management, while the symbolic dimensions would include scale, connectivity, and familiarity. Third, we focus on NbS for a Global South community in a tropical climate. Much of the NbS literature represents conditions in the Global North but communities in the tropical Global South are particularly vulnerable to flooding and such disruptions may be exacerbated by a changing climate (Fuchs et al. 2011 ; Winsemius et al. 2015 ; Arnell and Gosling 2016 ). Although Irvine ( 2013 ) worried WSUD features in tropical climates based on earlier designs from temperate climates may be less effective, with appropriate modification, experience has now allayed these concerns (Yau et al. 2017 ; Wang et al. 2018 ).

We begin the paper by establishing the study’s theoretical framework, including a discussion on characteristics of Smart Cities and Research through Designing. Subsequently, we focus on community familiarity methods and results, including passive observation and community surveys, that were used to inform the NbS designs. Finally, the paper presents NbS designs at different scales, including a discussion on how community consultation informed the designs. These example designs can help stakeholders better vision possible community directions and engage the planning, design, landscape architecture, and engineering communities in deeper discussions and understanding of NbS typologies.

Theoretical framework

The “Smart City” philosophy increasingly has become a guiding approach to urban planning and design (Neirotti et al. 2014 ; Albino et al. 2015 ; Kummitha and Crutzen 2017 ; Yigitcanlar et al. 2019 ; Caird and Hallett 2019 ; Irvine et al. 2022b ; Yereseme et al. 2022 ), although the characteristics of a Smart City are still debated. The project reported herein was conducted to investigate and develop visions of alternative futures for the Thammasat-Nava Nakorn (TUNN) Smart District, Thailand. In undertaking this project, the Thai Smart Cities initiative was used to inform and frame the local context ( https://www.depa.or.th/th/smart-city-plan accessed 13 Apr 2022). The Thai Smart Cities initiative, established by the Thai Digital Economy Promotion Agency (DEPA), defines a Smart City as:

A city that takes advantage of modern technology and innovation to increase the efficiency of the city service and management, reduce the cost and resource usage of the target city and citizens. It focuses on good design and participation of business and public sectors in urban development, under the concept of modern and livable city development, for people in the city to have a good quality of life and sustainable happiness.

This Smart City characterization strikes a balance between community and technology and is structured around 7 “smart pillars”: (i) Smart Environment; (ii) Smart Economy; (iii) Smart Energy; (iv) Smart Mobility; (v) Smart People; (vi) Smart Living; and (vii) Smart Governance. Irvine et al. ( 2022b ) provide more detail on how each pillar is defined and discuss the Smart City concept within the context of the Smart District project, emphasizing the differences between a technology-focused approach and a community well-being-focused approach. The technology-focused approach tends to be a top-down planning philosophy, while the community well-being-focused approach uses technology as a support tool and is more of a bottom-up planning philosophy. Our study decidedly emphasized community well-being over technology-led design, but also integrated bottom-up and top-down considerations.

Lenzholzer et al. ( 2013 ) suggest four traditional epistemologies characterize Research through Designing approaches that may be used to generate new knowledge about landscape transformation: (post)positivist, constructivist, advocacy/participatory and pragmatic. Although Lenzholzer et al. ( 2013 ) explicitly discussed Research through Designing in the context of the Landscape Architecture discipline, each of these epistemologies necessarily is transdisciplinary in nature, integrating methods and knowledge from sciences, social sciences, and engineering within the design context. The (post)positivist epistemology addresses the performance of the project, with typical questions being: “How does a design have to function to fit natural processes (e.g., climate, hydrology, ecology)? How does a large scale design intervention work within a landscape system?” (Lenzholzer et al. 2013 ). The constructivist epistemology explores the type of landscape that the designer can create, addressing questions, such as “Can the design bring about a shift in people’s sensing, thinking or behavior?” (Lenzholzer et al. 2013 ). The advocacy/participatory epistemology directly involves the research team and the community in a deeper collaboration through problem identification and data collection but also strives for community capacity to self-advocate for a better environment. The pragmatic approach, which was applied in this study (see also Irvine et al. 2022b ), integrates elements of all three previously noted epistemologies to examine the potential community transitioning towards a Smart District.

Figure  1 shows the location of the Smart District study area which includes the Nava Nakorn industrial estate, Thammasat University, Asian Institute of Technology (AIT), and Valaya Alongkorn Rajabhat University (VRU) campuses, Thailand Science Park, and rural areas of both Pathum Thani and Phra Nakhon Si Ayutthaya provinces. Approximately 55 km northeast of downtown Bangkok, the study area is located in the Central Plain of Thailand, which is dominated by the Chao Phraya River. The climate is Tropical Savanna (Aw), with hot and humid summers, wet rainy periods, and a relatively dry “cold” season. Mean annual temperature (1999–2019, https://en.climate-data.org/asia/thailand/pathum-thani-province/rangsit-715034/#climate-table accessed 13 Apr 2022) for the Pathum Thani Rangsit area is 27.7 °C and annual precipitation is 1301 mm.

Historically, Pathum Thani was a rural, agriculturally based province that grew in importance with the construction of the Prem Prachakorn Canal in 1869. This canal provided a transportation connection between Ayutthaya and Bangkok and subsequently, the Tung Rangsit project (1890–1900) added 43 canals. One of the main east–west canals of the Tung Rangsit project was the Rangsit Canal (Suwanarit 2010 ) and in addition to the east–west canals, 17 north–south oriented canals, 20–30 km long, were constructed at intervals of approximately 2.5 km, together with a number of tertiary canals. The Rangsit Canal and large north–south canals were used for transportation, irrigation, and drainage, while the tertiary canals were used solely for irrigation and drainage (Suwanarit 2010 ).

As part of the Bangkok Metropolitan Region (BMR), Pathum Thani has experienced a dramatic increase in population and industrial activity over the past 50 years, as well as a shift in agricultural production from mono-culture rice to a mix that includes orchard and vegetable farms (Jongkroy 2009 ). The Bangkok Metropolitan Administration (BMA) is the historical capital city core area (population 5.7 million) which drives economic growth, having a dominant position financially, politically, socially, and educationally within Thailand (Fry 1983 ). Industrial estates more recently became part of the fabric of Pathum Thani and Phra Nakhon Si Ayutthaya provinces as access to deep water ports, airports, and highways facilitated movement of goods to large local (Bangkok) and international markets.

Nava Nakorn Pathum Thani became the first industrial estate developed by Nava Nakorn Public Co. Ltd. in 1971 and currently covers an area of 6485 rai (1038 ha), with approximately 203 rai (32.5 ha) as yet unsold. Because much of the available land has been sold, Nava Nakorn Public Co. Ltd. now obtains its revenue primarily by managing the Pathum Thani site and providing or overseeing traditional municipal services including water, wastewater treatment, electricity, telecommunication services (e.g., fibre optics), security, solid waste management, and urban infrastructure. Nava Nakorn also acts as a community development and well-being leader (Irvine et al. 2022b ), organizing bi-monthly town hall meetings to address community issues and proactively developed an app that enables the community to seamlessly report any faults (e.g., water leak, road disrepair, lighting and electrical problems). Nava Nakorn Pathum Thani is an atypical industrial estate in Thailand, because industrial, commercial, and residential areas are integrated within the property. The population of Nava Nakorn peaked prior to the historic 2011 flood in Thailand at over 200,000. However, as the estate was flooded for more than 6 weeks in 2011, resulting in extensive property damage and the temporary (and in some cases permanent) closing of industry, population did not fully recover and currently is estimated at 150,000.

The Thammasat University Rangsit campus, occupies an area of 1757 rai (281 ha) and currently enrols approximately 25,000 undergraduate students. The Asian Institute of Technology (AIT) is a regional postgraduate institution that focuses on engineering, environment, and management studies and enrols approximately 1600 graduate students.

This Superblock area was selected for study because it is undergoing rapid urban transformation and guidance on sustainable planning and design is timely. The Superblock benefits from having a deep knowledge-base that includes universities and the Thailand Science Park, with the private sector stakeholders from this study interested in stronger links to address the Thailand 4.0 economic development policy focusing on higher valued production (Irvine et al. 2022b ). Since Nava Nakorn Public Co. Ltd. functions essentially as a private sector municipality, it makes direct decisions on development within the property and as such there is a higher chance of project implementation compared to areas overseen by local government in Thailand (Irvine et al. 2022b ).

Study approach and the central notion of community familiarity

The study took an innovative approach to address the objective of visioning possible futures for the Smart District by including the project as a main theme for authentic learning experiences across 5 Thammasat Design School (TDS) classes. The classes spanned year 2, 3, and 4 levels and represented 5 different programs: Architecture, Landscape Architecture, Urban Design, Urban Planning, and Design, Business, and Technology Management; three of the classes (Architecture, Landscape Architecture; Urban Design) were studio classes. While the overarching framework for the project was the Thai DEPA 7 smart pillars, each class was given latitude to explore the pillars using different techniques and with different focus. The learning objectives of two courses, LN316, Landscape Architectural Design 4 , and UD327 , Urban Design and Development Studio, Greenfield Development , in particular, linked directly to the NbS design and community familiarity focus. The learning objectives for LN316 were: (i) identify a wide range of interconnecting issues that affect a landscape, including risks and vulnerabilities; (ii) apply relevant theories, concepts, strategies, and skills in dealing with landscape planning and design; and (iii) propose a sustainable, visionary solution to the problem at hand. The students in UD327 were required to investigate a study area at the macro-, meso-, and micro-scale, and develop their own vision for an innovative urban design response. Both courses emphasized nature and ecology in urban and peri-urban development, with consideration of connectivity, vulnerability/resiliency, and sustainability that by necessity require community interaction and familiarity. Greater detail about the general study approach, course structures, and student design assessment is provided by Irvine et al. ( 2022b ).

Later in life, Dr. Dhrubajyoti Ghosh, a UN Global 500 laureate, reflected on his efforts to conserve the natural wetlands of East Kolkata, India, that treat urban wastewater and provide a host of other ecosystem services (Ghosh 2016 ). In particular, he discussed the shortcomings of academically trained ecologists and environmental managers to adequately manage ecosystems, because they did not appreciate community expertise nor understand the community’s lived experience, thereby underscoring the importance of community familiarity (Ghosh 2016 ). This idea of community familiarity also is a missing component of the waterscape management in Thailand, but the Thammasat courses sought to address this shortcoming.

Approaches to community familiarity: primary data collection

Three community surveys were conducted to provide an understanding of resident and industry concerns, local experiences, and visions for their community. The first survey was administered face-to-face by the UD327 students to 241 Nava Nakorn community members. This survey provided general demographic data, information on housing stock, public space, mobility and public transportation, and natural disaster resiliency. Questionnaire structure included both closed and open-ended questions. The second survey, conducted online by the Design, Business, and Technology Management class, included 506 participants from Nava Nakorn and Thammasat University. The questionnaire covered general demographic data and specific issues regarding DEPA’s 7 Smart City pillars, with particular focus on green space, air quality and other environmental issues, leisure time practice, mobility, and neighbourhood society. Participants were recruited through Line community groups, a popular social media platform in Thailand. The third survey was an online survey of Nava Nakorn industries conducted by the UD327 class with assistance from Nava Nakorn Public Co. Ltd. A total of 23 industries responded, a 13% response rate. All surveys were anonymous, participation was entirely voluntary, and the methods followed university ethics practices for undergraduate research projects. The methods were reviewed at the faculty level to ensure compliance. The questions associated with each survey can be obtained from the corresponding author. The surveys represent the bottom-up component of the study.

Nava Nakorn Public Co. Ltd. conducts bi-monthly community meetings and student representatives attended one meeting on 8 March 2020. After the formal meeting, the students were provided the opportunity to interview community representatives and senior administrators from Nava Nakorn and this effort could be considered a top-down/bottom-up approach. Extensive photodocumentation of the physical and social landscapes within the study area also was conducted by all classes.

Finally, the study management team from Thammasat University met with the private sector partners on a monthly basis. Progress on the project was summarized at the meetings and the private sector partners provided comments, including shifting visions and priorities, based on each summary report. This iterative consultation process is summarized more fully by Irvine et al. ( 2022b ), but in general, the monthly meetings were valuable in shaping the final plans and designs and represent the top-down component of the study.

Results and discussion

Survey results.

TDS ( 2020 ) summarized the general findings of the surveys as they pertained to Smart City characteristics and here the focus is specifically on aspects and experiences related to flooding, green space, and NbS. The face-to-face survey included questions that distinguished between pluvial and fluvial flooding, with specific attention on the 2011 flood. We focused on the 2011 flood because it remains in recent memory and was the most damaging flood in Thai history (Nabangchang et al. 2015 ). For the face-to-face survey, 80% of respondents reported observing pluvial flooding within Nava Nakorn, with most people (42%) indicating the duration of such flooding being between 4 and 6 h. Most respondents (61.3%) reported that pluvial flooding occurred in alleyways, followed by the main road (19.7%); residential areas (13.9%); and commercial areas (5.1%).

When asked about fluvial flooding, 50.6% of the respondents in the face-to-face survey indicated that they had experienced such flooding, with 33.6% of those who have experienced fluvial flooding saying that it occurred on average 1 time per year and 42.6% saying it occurred every 2–3 years. The majority of those responding had been impacted by the 2011 flood. The impact from the 2011 flood included workplace closure (15.9% of reported impacts), no transportation (15.9% of reported impacts), food and water shortage (11.3% of reported impacts), housing relocation (27.2% of reported impacts), and damage to property (22.7% of reported impacts). Of the 161 responses related to assistance, 39.1% said they had not received any type of aid in association with the 2011 flood, while 60.9% indicated that they had received aid, with the aid coming from various sources, including the employer, local authorities, and NGOs. The type of aid received is summarized in Fig.  2 a and the estimated property damage associated with the 2011 flood is shown in Fig.  2 b. These estimates are consistent with those reported by Nabangchang et al. ( 2015 ), who conducted a detailed damage survey of the 2011 flood with 469 households in three suburban Bangkok areas. Figure  2 c indicates the level of financial aid provided in association with the 2011 flood. Figure  2 b shows that 61.8% of the respondents who incurred property damage experienced a damage level of 10,000 THB ($320.91 USD) or greater, while only 27% of the respondents received damage compensation of 10,000 THB ($320.91 USD) or more (Fig.  2 c); 16% of those reporting damage incurred impacts of 100,000 THB ($3209.17 USD) or greater, but only 6% received compensation at this level. It appears that the survey participants generally absorbed a large proportion of the flood damage. Only 31% of 171 respondents have considered some form of flood mitigation measure (Fig.  2 d), with raising the ground level using concrete being the most common.

a Type of aid received in association with the 2011 flood; b estimated property damage (THB) associated with the 2011 flood (1 USD ~ 32.09 THB); c estimated financial aid (THB) received by those impacted by the 2011 flood (1 USD ~ 32.09 THB); d identified flood mitigation options (based on 66 responses from 53 respondents who indicated that they had implemented some flood mitigation measure; 118 respondents indicated they had not implemented flood mitigation)

Of the 23 companies that responded to the industrial survey, 3 were not affected by the 2011 flood, because they opened in Nava Nakorn after 2011. The majority of the companies affected by the 2011 flood (15 of 20, or 75%) indicated that they closed temporarily during the 2011 flood, while the other 25% had greater resiliency, temporarily moving production elsewhere but returning to Nava Nakorn after the flood.

These survey results establish that the Nava Nakorn community is vulnerable to both fluvial and pluvial flooding and that there is a varying level of resiliency to flooding. Some industries temporarily shifted production during the 2011 flood, while Nava Nakorn Public Co. Ltd. strengthened and heightened the flood wall surrounding the industrial estate and increased pumping capacity to move water from the internal drainage canals to outside receiving canals. These latter hard engineering measures are consistent with the general trend in Thai flood management, discussed in more detail, below. Interestingly, only 31% of respondents had considered some form of flood mitigation measure, and again, these generally were hard engineering measures. Most of the economic impact from flooding was absorbed somehow by the community.

The larger online community survey found that 70% of respondents had used public areas either in Thammasat University or Nava Nakorn, but only 20% of the respondents were entirely satisfied with these areas. Furthermore, almost half of the respondents (44.7%) defined green areas as green fields or lawns, while 30% and 17% defined them as public parks and agricultural land, respectively. Respondents suggested that a good public park should consist of the following elements: (1) big trees (77.5%), (2) benches (69.8%), and (3) lawn area (67.8%). The majority of respondents (61.5%) go to a park for general leisure activities, while 41.8% go to a park for sport activities. A lack of recreational space was the second most commonly cited community problem in the face-to-face surveys.

The survey results were important in underpinning community familiarity and informing subsequent flood resiliency and NbS/green space/public space designs. There has been a reliance on traditional hard engineering approaches to improving community resiliency to flooding. The community had certain visions regarding green space and were dissatisfied with current spaces. However, community response did not consider green space/NbS functionality as a water management approach, and that is where the integrated landscape architecture visioning became important, for both pluvial and fluvial flooding scales. These issues are examined in the next section, with example designs provided as possibilities for future nature-based development and flood management.

Nature-based solution visioning

In exploring planning strategies for Elements at Risk (EaRs) associated with coastal community resiliency, Graff et al. ( 2019 ) identified four operationally defined spatial scales: (i) small-scale (1:100,000–1:250,000), used for regional, strategic planning; (ii) medium-scale (1:25,000–1:50,000), used for identification of critical facilities; (iii) large-scale (1:10,000–1:25,000), used for characterization of infrastructures; and (iv) local-scale analysis (1:2000–1:10,000), which provides more detailed information about the structural components of infrastructure. For design of individual WSUD features within the NbS framework, we would add an additional scale, on the order of 1:100–1:500. The purpose and level of detail will vary by scale, as may the pertinent structural and non-structural options, in the case of flood management. In this paper, we consider fluvial flood management plans at the small-to-medium scale and pluvial flood management at the local-to-design scale, although the scales may be linked as a continuum by the drainage network and water flow path.

Fluvial flood management

The 2011 flood covered an area of 97,000 km 2 in the Chao Phraya Basin and the peak discharge flowing through Bangkok was 4700 m 3 /s, nearly double the maximum channel capacity of 2500 m 3 /s. A variety of factors appear to have contributed to the flood, including extreme rainfall (especially remnants of four tropical storms that reached northern Thailand in close succession); poor upstream reservoir management decisions; in-filling of wetlands and paving of surfaces for development and urbanisation; encroachment of informal housing on drainage canals; poor maintenance of drainage systems; land subsidence in the Bangkok area due to groundwater withdrawals; and high tide levels that restricted outflow to the ocean (Chaosakul et al. 2013 ; Loc et al. 2020 ). The AIT campus experienced flood conditions of approximately 2 m for several weeks, while the Nava Nakorn estate also experienced extensive flood damage. Chanthamas et al. ( 2017 ) employed Potential Surface Analysis, Analytical Hierarchy Process analysis, and Sieve Analysis of GIS overlays to assess flood risk at the provincial scale of Pathum Thani. The Smart District study area was categorized as a High Flood Risk area in this analysis, consistent with the findings of our study.

The concept of Retreat, Adapt, and Defend was explored at a regional scale to begin addressing fluvial flood issues (Fig.  3 ). This conceptual plan identified areas in which green space and green infrastructure would accommodate flood waters (Retreat), while other areas would have structural (building) adaptation to floods (Adapt), or enhanced green and hard engineering flood protection (Defend). The Retreat concept includes temporary storage of water on agricultural land (primarily rice fields) as well as enhanced naturalization and pond storage areas. The temporary storage concept to manage floods has been used in Europe and explored in Thailand via groundwater recharge or diversion into wetlands, green space, or lowland agricultural fields (Morris et al. 2004 ; Pavelic et al. 2012 ; Kositgittiwong et al. 2017 ; Trakuldit and Faysse 2019 ). However, Trakuldit and Faysse ( 2019 ) note that the negotiation of payment for ecosystem services must involve effective stakeholder consultation and to date, such negotiations have proved challenging in Thailand.

Regional plan to manage fluvial floods following the Retreat, Adapt, and Defend concept. Design credits to Mananchaya Nomnumsub, Supisara Khumruangrit, Rinrada Pijitha, and Nafha Promkuntong, UD327 class

Examples of specific design visions for fluvial flood management that incorporate the Retreat, Adapt, and Defend concepts are presented in Figs.  4 and 5 . Figure  4 demonstrates how the fluvial flood management and habitat areas may be linked through the existing, complex canal system within the district and also shows the general location of a proposed “Eco-corridor” development that aligns adjacent to and parallel with a larger canal and rail line (Fig.  5 ). The Eco-corridor would provide additional, connected channel and wetland storage to increase flood resiliency, as well as biodiversity, recreation, and life-long learning opportunities to enhance community liveability and well-being, consistent with the community surveys. This design also is consistent with the current Thai flood planning practice of “monkey cheeks”. The concept was introduced in 1995 by King Rama IX and refers to low-lying lands in the vicinity of major rivers (generally rice paddy, with some natural wetlands) that are used to temporarily store flood water, much as a monkey stores food in its cheeks to later be released and digested (Trakuldit and Faysse 2019 ; Irvine et al. 2022c ).

Connectivity of canals, waterbodies and the Chao Phraya River associated with the TUNN Smart District. The red, dashed line indicates the location of the proposed Eco-corridor, while the blue circle indicates the location of the wetland treatment park shown in Fig.  5

Segment of the Eco-corridor design, southwest of Nava Nakorn. The upper photo shows the segment as it currently exists, with a mix of wetland and secondary growth forest. The middle image shows the masterplan view of the proposed wetland treatment park, while the lower image provides detail of the design cross section along A – A ʹ. The wetland treatment park would provide enhanced flood resiliency through storage; water cleansing through settling basins, natural vegetation, and maximization of hydraulic residence time; enhanced natural habitat and biodiversity; and recreational and educational opportunities through the signed boardwalk and observation tower. Traversing the entire longitudinal profile, the Eco-corridor design provides bluescape and greenscape connectivity between the canals and an intentionally varied patch habitat. Design credit to Peerada Chuaybudda, LN316 class

Figure  6 represents a developing area immediately north of Nava Nakorn. There is an existing 7.5 ha pond feature, partially contained by a bund, and the general area is undergoing land clearing for development (Fig.  6 a). The pond would connect to the canal system via a watergate and provide both flood storage for resiliency, as well as habitat/biodiversity and water recreation opportunities to enhance liveability. Residential and commercial areas are integrated within this design through the Eco-village vision (Fig.  6 b). The Eco-village embraces the “Adapt” philosophy and includes amphibious flood-resilient housing, a strategy increasingly proposed (Nilubon et al. 2016 ; Nekooie et al. 2018 ) and piloted ( https://www.reuters.com/article/us-disaster-risk-architecture/thailand-tests-floating-homes-in-region-grappling-with-floods-idUSKBN0M100N20150305 , accessed 13 Apr 2022).

a Eco-village—the upper photo shows the area as it currently exists, with cleared, vacant, and eroding land bordering the large pond. The middle image shows the masterplan view of the proposed Eco-village development, with the blue circle indicating the location from which the upper photograph was taken. The lower image shows design plans for the Eco-village that incorporate natural, recreational opportunities and planned greenspace. The detail design proposes opportunity to use the water resources for urban farming activities as well as floating residential or commercial structures. Design credit to Sulukkana Nuttipan, LN316 class. b Eco-village—in this example, resilient, amphibious housing and commercial opportunities are incorporated into the design. Amphibious structures also could be designated as emergency healthcare and logistics centres during extreme floods. Design credit to Mananchaya Nomnumsub, Supisara Khumruangrit, Rinrada Pijitha, and Nafha Promkuntong, UD327 class

Pluvial flood management

The face-to-face surveys identified areas of most frequent pluvial flooding within Nava Nakorn as being alleyways, the main road, residential areas, and commercial areas (e.g., Fig.  7 ). Pluvial flooding is exacerbated by improper solid waste disposal, particularly with plastics that clog drains and canals, and oil and grease discharge from roadside food stalls and restaurants that clog smaller street drains. These issues are addressed by Nava Nakorn Public Company Ltd. in their public meetings, but more outreach is needed to encourage community best-management practices.

Minor pluvial flooding in a Nava Nakorn alley due to a rainfall of 43 mm in 3 h on 1 September 2020 (photo by authors)

A planning level calculation done in GIS using a spatially weighted Rational Method indicated that an increase of green space and WSUD by 31 ha (or 3% of the total area of Nava Nakorn) would reduce the runoff coefficient, such that there would be a 12.9% decrease in peak flow (and potential flooding) from the entire Nava Nakorn area. The WSUD measures could include grassed swales and raingardens in the medians of main thoroughfares (e.g., Fig.  8 ), constructed wetlands, bioretention cells, and pervious pavement in parking lots (e.g., Fig.  9 ). Enhanced connectivity and expanded wetland and canal space would be allocated to store and gradually release water to the perimeter pumps (e.g., Fig.  10 ), while green space is enhanced through local parks and community event space (e.g., Fig.  11 ). The local parks and community space would provide both general leisure opportunities as well as sports fields, in response to the community surveys. The individual WSUD features connected through natural waterways/wetlands and constructed canals collectively form NbS visions for the study area that not only would reduce flooding, but concurrently would improve water runoff quality through adsorption and natural, biological processes (e.g., Irvine et al. 2022a ). Storage and a reduction in flooding could be explored in more detail and optimised using a dynamic, process-oriented conceptual deterministic modelling approach (e.g., Irvine et al. 2021b , 2022c ; Yereseme et al. 2022 ). Examining multiple spatial scales using conceptual deterministic models is important for optimization of both individual feature performance and the collective performance of the entire system (e.g., Teang et al. 2021 ). To date, system-wide performance modeling is not routinely done in Southeast Asia (Hamel and Tan 2022 ).

Example of a main arterial road design in the central area of Nava Nakorn to enhance greenery, smart mobility (walkability and bicycle lanes), and including raingardens with underdrains connecting to nearby canals. Current conditions are shown inset. Design credit to Tanavara Chawanid, Paveena Kusaranukun, Manita Intarachaisri, and Yuto Motani, UD327 class

Green space and WSUD redevelopment in central Nava Nakorn. a The upper photo shows the area as it currently exists. The second from top image shows the masterplan view of the area; the third from top image shows the perspective vision of the area; and the bottom image shows the cross section along transect A. While retaining and re-developing some of the buildings for new office spaces, a Learning Center for Nava Nakorn Sustainability also is included, with the objective of promoting green technology for the urban development. The shoreline is softened by greenspace that includes raingardens, while floating wetlands are included as a pond feature to improve water quality; b the upper photo shows one of the current informal parking areas to the right. The middle image includes a plan view and perspective of a re-visioned parking lot with bioswales, pervious pavement and shoreline having a vegetated buffer zone (see also cross section of the design in the bottom image, transect D in a ). Design credit to Tarin Ponin LN316 class

Enhanced, connected green space and WSUD features (including constructed wetlands), central area of Nava Nakorn. Design credit to Manus Janthik, Wipawee Khantikittikul, Panyawat Terdkeat, and Kanokwan Srisamer, UD327 class

Perspective for Community Center and Park (sites 8 and 9 in Fig.  10 ) to improve community space by enhancing connectivity, liveability, and well-being. Design credit to Manus Janthik, Wipawee Khantikittikul, Panyawat Terdkeat, and Kanokwan Srisamer, UD327 class

The visions presented in Figs.  10 and 11 are examples of the scenarios developed by the classes within the study framework. Figure  12 presents an alternative masterplan for the same area as shown in Fig.  10 . Both designs (Figs.  10 and 12 ) incorporate the Digital Village idea, a development feature of interest to Nava Nakorn Public Co. Ltd. (Irvine et al. 2022b ), but the housing configuration and drainage details differ. Both designs retain the large, existing, central pond and wetland (see also Fig.  9 ), with community space and a transportation hub to link the regional rail with local bus service, following the principles of Transit-Oriented Development (Ibraeva et al. 2020 ; Irvine et al. 2022b ). Both designs also include a park area to the south, but the WSUD and green space features differ (e.g., Fig.  11 vs Fig.  13 ).

Alternative vision to Fig.  10 for the masterplan of central Nava Nakorn. The park area for Fig.  13 is denoted with the number 1. Design credit to Chaowat Chamnangit, Natthatida Suwanyothin, Chadchaya Wongsiri, and Soichiro Sugimoto, UD327 class

Park area (number 1 in Fig.  12 ) example details for a community organic farm, or Agrihood (top) and a retention pond with observation boardwalk (bottom). Design credit to Chaowat Chamnangit, Natthatida Suwanyothin, Chadchaya Wongsiri, and Soichiro Sugimoto, UD327 class

Figure  13 includes space for community gardening/urban agriculture (i.e., the “Agrihood” design, Irvine et al. 2023 ). Community gardening in urban environments is practiced globally and the associated ecosystem services potentially are diverse, including food provisioning and food security, particularly for at-risk communities, enhanced biodiversity, carbon sequestration, urban heat island and noise mitigation. Cultural services can include community well-being through place-based connection, enhanced physical and mental health through activity and feelings of joy and fulfilment, and environmental education/literacy (Corrigan 2011 ; Lovell et al. 2014 ; Clucas et al. 2018 ; Sonti and Svendsen 2018 ; Caneva et al. 2020 ; Zasada et al. 2020 ; Irvine et al. 2023 ). Despite these benefits, Lawson ( 2004 ) noted that, at least in the United States, where community garden programs have existed since the 1890s, an ambivalence exists within the planning profession, because community gardens often are viewed as local, temporary interventions and are not placed in the long-range planning vision. Community gardens may be contested space for a variety of reasons. In major cities, for example, many community gardens have evolved through reclamation of vacant lots, which results in a tension between public goods, private use, and, ultimately, new development (Lawson 2004 ; Milbourne 2021 ). The Agrihood vision shown in Fig.  13 presents a different scenario, since it is included as part of community development from first design that would be marketed to those looking for an urban/nature balance, rather than being a retrofitted or organically established space (see Irvine et al. 2023 ). Figure  13 presents example crop type, representing the potential biodiversity, but it would be important to consider this plant community assemblage in more detail to ensure optimum ecosystem service performance (Clucas et al. 2018 ; Caneva et al. 2020 ; Irvine et al. 2023 ).

Flooding, resiliency, and ways forward

The NbS designs as presented in Figs.  3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , and 13 reflect the pragmatic epistemology of Research through Designing, integrating aspects of the (post)positivist, constructivist, and advocacy/participatory epistemologies to ultimately answer the bigger questions of “how would NbS be visioned in the design phase and what would these visions look like”? These designs also may be considered a first step in developing an NbS typology focusing on the function of sustainable urban water management with symbolic dimensions of scale, connectivity, and familiarity. The design process took a hybrid bottom-up/top-down approach, including consultation with community and private sector partners. The various design visions were presented at a final meeting with the private sector partners for the Smart City project. This was an important step, since Nava Nakorn Co. Ltd., which oversees the estate, has the ability to implement such visions. The project also was presented publicly at Central World Mall in downtown Bangkok, an event that was covered by Thai news outlets (Irvine et al. 2022b ). The next step of this visioning effort should be re-engagement with the local community to review and receive feedback on the alternative design visions. Unfortunately, due to COVID-19 restrictions, this has not yet been possible. Ultimately, these designs could serve as a basis for the study partners to apply for DEPA’s Smart City designation, which would provide tax incentives and funding to help implement the vision.

Performance of the designs should be assessed using both a dynamic, conceptual mathematical modeling approach and ecosystem services evaluations, for example, following the iterative and interactive interdisciplinary Framework for Theory design approach outlined by Steinitz ( 2020 ; see also Irvine et al. 2022c ). While NbS has the potential to deliver multiple ecosystem services, in choosing between different NbS designs, it would be helpful to better define a theoretical framework for assessment (Caneva et al. 2020 ; Castellar et al. 2021 ; Almenar et al. 2021 ). A starting point for such evaluations, at least at the large scale, could be Stanford’s InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) suite of models ( https://naturalcapitalproject.stanford.edu/software/invest , accessed 14 Apr 2022) (e.g., Guerrero et al. 2022 ), while at a neighborhood scale Irvine et al. ( 2023 ) included dynamic, hydrologic modeling to quantify water quantity and quality ecosystem services, as well as considering carbon sequestering, food provisioning, temperature mitigation, biodiversity, and aesthetics. This ecosystem service approach to evaluating NbS design performance is promising.

In Thailand, flood planning and management has tended to involve hard engineering and reactive emergency management approaches directed from the top-down (Nair et al. 2014 ; Singkran 2017 ). Flood planning and management challenges are complicated by inter-agency fragmentation (as well as overlap), political polarization, a lack of local (i.e., provincial and tambon (sub-district)) administrative capacity, public communication and community mistrust (Lebel et al. 2011 ; Kittipongvises and Mino 2015 ; Maier-Knapp 2015 ; Marks and Lebel 2016 ). Singkran ( 2017 ) provided a review of flood insurance availability in Thailand through the National Catastrophe Insurance Fund, but as noted in the residential community of Nava Nakorn flood insurance was not widely used as a form of resiliency (17% of respondents, Fig.  2 d). Similar to the findings in our study, Marks and Thomalla ( 2017 ) reported a low flood insurance participation rate (12%) for SMEs in the Bang Bua District of Nonthaburi Province, while in northeastern Thailand, Paopid et al. ( 2020 ) found only 1 of 401 survey respondents had residential flood insurance. Nair et al. ( 2014 ) recommended that insurance be explored more aggressively as a possible non-structural flood management measure. While the flood insurance approach that integrates land use planning has successfully increased community resiliency in North America and Europe (King 2012 ; Paleari 2019 ) market penetration in Thailand may be challenging.

Participatory collaboration between all stakeholders has been recommended as a step towards improving flood planning in Thailand (Lebel et al. 2011 ; Nair et al. 2014 ; Singkran 2017 ). Certainly, community involvement in flood planning is well-established in some countries, but even then, questions of legitimacy and meaningful participation remain (Irvine et al. 1996 ; Highfield and Brody 2017 ; Pettersson et al. 2017 ; Sadiq et al. 2019 ). Hino and Nance ( 2021 ) identified barriers to effective flood management planning at the community level in general and these included the need to address mechanisms that perpetuate socio-economic inequality and broadening community involvement in flood management research. Based on a survey of projects from Kenya, Ananga et al. ( 2020 ) found that community participation in water management planning and practice enhanced beneficiary satisfaction. The Thailand Disaster Management Plan 2015 notes one of its goals is: “To promote and encourage every part of society at every level to develop code of practice for disaster risk reduction.”, so in principle the groundwork for community consultation has been laid. Despite the calls for greater community participation as part of flood management planning in Thailand, Kittipongvises and Mino ( 2015 ) reported that in a survey of 437 people from the Bangkok area, 49% felt flood planning and management was primarily the responsibility of government, including federal agencies, local authorities, and community leaders. Less than 10% of the respondents saw a role for the private sector, academia, and media. Certainly, these issues present a challenge to the advocacy/participatory epistemology of Research through Designing.

Challenges remain with respect to enhancing community resiliency to flooding in Thailand. We would argue that there should be no single approach to addressing the issue, but rather, a holistic approach that includes traditional hard engineering, stronger flood zone and land use planning, improved reservoir and flooding prediction, structural and non-structural adaptation, flood insurance (particularly for businesses), and implementation of NbS, should be pursued. With respect to NbS, the implementation of such urban green space is consistent with Smart City/Smart Environment philosophy, but NbS typology should be further refined. Hydrologic and water quality design guidelines have been established for WSUD features and are starting to be adapted for NbS (Brauman et al. 2022 ; Irvine et al. 2022a ; Orta-Ortiz and Geneletti 2022 ), but community awareness on NbS functions and benefits needs to be enhanced and more data on system maintenance procedures and costs are needed. Despite the challenges, there is an encouraging trend of NbS implementation in Thailand, including the recent construction of the 42 ha Benjakitti Forest Park, the 2 ha Metro Forest, the 1.1 ha Forest Pavillion, the 30 ha Nong Fab LNG Receiving Terminal, the 4.9 ha Chulalongkorn University Centenary Park, and Puey Centenary Hall, Thammasat University, which includes a 0.7 ha green roof urban farm, the largest of its kind in Asia.

A Research through Designing framework was integrated with Smart City concepts in developing a holistic approach to NbS planning and design and a preliminary consideration of NbS typology using a peri-urban area of Bangkok as a case study. The NbS typology function would be sustainable urban water management, while the symbolic dimensions would include scale, connectivity, and familiarity. Importantly, the designs were informed through community consultation or what we call “community familiarity”. The NbS planning and designs would provide a number of ecosystem services, including reduced flood damage, improved runoff quality, enhanced recreational and community space, greater biodiversity, education and life-long learning opportunities, food provisioning (Agrihood), and increased diversity and resiliency in housing. Quantification of ecosystem services provided by NbS designs is a promising approach to assessing the success of the design and standardization of such assessments should be explored in more detail. Connectivity is a central theme of Smart City development and NbS planning and design is no exception. The WSUD and NbS features were collectively linked to enhance both storage and flow of water, thereby improving community liveability, well-being, and resiliency.

At the broader, regional scale, if agricultural land is to be used for flood storage, community consultation must be the cornerstone of payment for ecosystem services. The designs presented in this paper are but examples of a number of possible green space designs that could be implemented under DEPA’s Smart City designation. Certainly, elements of the designs (e.g., vegetation, emphasis on wetlands and monkey cheeks, amphibious houses) reflect a tropical climate and these design aspects should be further characterized. Rather than simply encouraging community consultation, a design-thinking process that presents the community with examples of possible visions should become a standard component of such consultation.

Data availability

All data are available from the corresponding author upon reasonable request.

Code availability

Not applicable.

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Irvine, K.N., Suwanarit, A., Likitswat, F. et al. Nature-based solutions to enhance urban flood resiliency: case study of a Thailand Smart District. Sustain. Water Resour. Manag. 9 , 43 (2023). https://doi.org/10.1007/s40899-023-00821-6

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Flood Management in China: The Huaihe River Basin as a Case Study

Submitted: 16 November 2016 Reviewed: 07 April 2017 Published: 30 August 2017

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The Huaihe River Basin (HRB) is a transitional river located in the transitional climate zone in China, and it has been frequently hit by big floods and suffered from flood disasters. Flood control and management of the areas are of vital importance of the Huaihe River Basin in its social and economic development. In this chapter, pioneer works of summarizing the flood management have been done for the Huaihe River in China. It first introduces flood and flood disasters of the River basin. In addition, this chapter summarizes achievements in flood control and management. Furthermore, it discusses experiences and enlightenment in flood control and management and draws conclusions for the research.

• flood management
• flood control
• the Huaihe River
• transitional river

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Qian mingkai.

• Hydrologic Bureau of Huaihe River Commission, Bengbu, China

*Address all correspondence to: [email protected]

1. Introduction

China is located in eastern Asia. It is impacted by monsoonal climate and the temporal, and therefore, spatial distribution of precipitation is uneven. The terrain in China is high in the west and low in the east with mountains, plateaus, and humps, which account 67% of China’s areas and basins and 33% plains. Special geographical and climatic conditions result in very serious flood and drought disasters in China. Since 1949, great efforts have been made for flood control in China. A series of policies and regulations has been formulated for flood control and management. Furthermore, numerous structural measures such as construction of reservoirs, flood detention areas and lakes, building of dykes, water gates and hydro junctions have been constructed. In addition, non-structural measures of hydrological monitoring system and flood forecasting system have been made for flood control in China.

The Huaihe River Basin (HRB) is located in the transitional climate zone in China ( Figure 1 ), which is known as the transitional river of China [ 1 ]. It has been frequently hit by big floods and suffered from flood disasters, and the frequency of disaster is one time in 10 years on average [ 2 – 5 ]. The critical issue is that about two-third of the middle and downstream of the major rivers are prone to floods, where is inhabited 13% of people of China, 12% of cultivated land area of China, one-sixth of food product of China, and one-fourth of the food as commodity of China. Flood control and management of the areas are of vital importance for the Huaihe River Basin in its social and economic development. Strenuous efforts have been made in fighting against floods; however, there is still a long way to go.

Figure 1.

Location map of the study area.

This chapter is organized as follows: Section 1 introduces general situation of flood management in China and the Huaihe River Basin, Sections 2 and 3 summarize the study area of the Huaihe River Basin. Section 4 presents floods and flood disasters of the River basin and concerns achievements in flood control. Section 5 discusses experiences and enlightenment in flood control and management. Section 6 draws conclusions for the research.

2. Geographical features

The Huaihe River Basin is located in the east China, with the Yellow River in the north and the Yangtze River in the south, and its catchment area is 270,000 km 2 . Starting in the Tongbai Mountains of Henan province, it flows from west to east. The upper reaches of the river are located in Henan and Hubei Provinces, the middle of the river is located in Anhui Province, and the downstream of the river is located in the Jiangsu Province. The length of the trunk stream is about 1000 km. The upper reaches of Huai river flow from the river head to the mouth of Honghe River between Henan and Anhui provinces, and the total length of the upper reaches is 360 km; the middle reaches, from Honghe River to Hongze Lake, are 490 km in length; and the lower reaches have a total length of 150 km. In the lower part of the Huaihe River Basin, there are four major outlets for floods, i.e., the Floodway to the Yangtze River, the Floodway to the Yellow Sea, the Northern Jiangsu Irrigation Canal to the Yellow Sea, and diversion waterway from the Huaihe River to new Yi River, then to the Yellow Sea.

The average annual precipitation of basin is about 875 mm, of which 50–80% precipitation is concentrated in the rainy season (June–September). Located in the north-south climate transition zone, with uneven spatial-temporal distribution of precipitation and the capture of the headwaters of Yellow river into the Huaihe River, Huaihe River flood disasters occurred very frequently. The basin-wide floods hit the Huaihe River in 2003 and 2007 of this century.

Due to the frequent flood disasters in the Huaihe River Basin, the State attaches great importance to harness of the Huaihe River. For nearly half a century, many flood control buildings have been built, including 38 large reservoirs, 21 flood storage areas, 1716 km embankment of grade I, diversion rivers such as Huaihongxinhe canal, Ruhaishuidao canal (floodway to the sea), as well as large lakes such as Hongze Lake. In addition, non-structural measures such as communication systems, hydrological forecasting system, the remote monitoring system of flood control works, remote consultation system, and flood control system have also been built. All these measures have played a positive role in the defence of floods.

3. Outstanding characteristics of the HRB

Compared with other rivers all over the world, the Huaihe River has its own outstanding characteristics:

HRB is located in the transitional zone from southern to northern climate of China, the weather system changes dramatically, and precipitation varies greatly in both space and time. Therefore, it is prone to flood and drought disaster. The average annual precipitation of HRB is 875 mm, the average annual precipitation in the northern area is 600–700 mm, and in the southern area reaches to 1400–1600 mm. The precipitation is concentrated in flood season (from June to September) and accounts for 70% of the annual amount.

The Huaihe River Basin is short of water resources, and water pollution problems have not been effectively solved yet. The total amount of average annual water resources in the Huaihe River Basin is 79.4 billion m 3 , and the average amount of water resources per capita and per mu only accounts for one-fourth and one-fifth of that of China (1 mu =1/15 ha). Water is unevenly distributed in time and space, unmatched with the production and population pattern. River regulation capacity is weak, and development and utilization of water resources are difficult.

The Huaihe River Basin is with flat terrain, where mountainous area is less with poor flood incept and storage condition. It has a broad plain area accounting for two-third of the total area, which has flat terrain and small gradient ratio in the middle-low stream. The total fall-head of the Huaihe River is 200 m (gradient ratio is 0.2‰). In the upstream, the gradient ratio is greater, with a fall-head of 178 m (gradient ratio is 0.5‰), and flood concentrates rapidly. In the middle reach, the gradient ratio and the fall-head of the midstream are 0.03‰ and 16 m, respectively. The river channel is curved and flat, and several parts of the river even have inverse slopes. The floods cannot flow smoothly and freely, which can easily cause flood disaster. In the middle reach, the gradient ratio and the fall-head of the midstream are 0.04‰ and 6 m, respectively.

Historically, with the diversion (capture) of the headwaters of Yellow river into the Huaihe River dramatically changes the natural water system, aggravates flood burden on the one hand, and increases the difficulties in harnessing the Huaihe River on the other hand. Originally, the Huaihe River is a separate river flowing into the East Sea; however, from the end of twelfth century to the middle of nineteenth century, in the 700 years of the Yellow river capture into the Huaihe River, a large number of sediments silted up the middle-low channel of the Huaihe River and made the Huaihe River lose its outlet to the Sea. It changes the natural water system to a great extent and has profound influences. It aggravated flood burden on the one hand and increased the difficulties in harnessing the Huaihe River on the other hand.

The Huaihe River Basin is densely populated, contradictions between human and water are sharp, and coordinated development is difficult. The Huaihe River Basin has a population of 0.178 billion, which accounts for 13% of that of China. Moreover, the Huaihe River Basin is also a main grain production area in China, with a cultivated land area of 0.19 billion mu accounting for 10.5% of the total amount of China; grain yield of the Huaihe River Basin takes up 17% of the total amount of China, and commodity grain of the Huaihe River Basin constitutes 25% of that of China. There are so many trans-boundary rivers that numerous conflicts of interests between different regions occur in terms of drainage and water resources utilization and protection. As a result, water affairs and conflicts are complex, and therefore, it increases the difficulties in river harness and management.

4. Floods and flood disasters

4.1. floods characteristics.

The Huaihe River Basin is located in the transitional zone from southern to northern climate of China, the weather system changes dramatically, and precipitation varies greatly in both space and time. Therefore, it is prone to flood and drought disasters. The average annual precipitation of HRB is 875 mm, the average annual precipitation in the northern area is 600–700 mm, and in the southern area reaches to 1400–1600 mm. The precipitation is concentrated in flood season (from June to September) and accounts for 70% of the annual amount. The maximum records of point rainfall of different durations in the Huaihe River Basin are close to or higher than the corresponding maximum records of China and the world. Extremely large flood peaks caused by such high intensity and extensive coverage rainstorms result in serious flood disasters ( Figure 2 )

Figure 2.

The relationship between catchment area and peak discharge in the Huaihe River Basin, China, and the world.

The magnitude of the maximum floods varies greatly from one area to another over the whole basin, and the important events are given in Table 1 .

Table 1.

The maximum flood discharge for major rivers in HRB (Unit m 3 /s).

4.2. Flood disasters

According to statistics, during the 2256 years from 246 B.C. to 2010, totally 1946 flood and drought disasters had occurred in the Huaihe River Basin, among which, number of flood disaster is 1008, while number of drought disaster is 938, which means disaster almost happens every year. Number of basin-wide flood and drought disasters is 340 (number of flood disaster is 268 and number of drought disaster is 72), and frequency is approximately once every 6.6 years on average. From the diversion (capture) of the Yellow river into the Huaihe River in 1194, flood disasters became more frequently. From the thirteenth century to the nineteenth century, there were 165 flood and drought disasters occurred in the HRB, one time in every 4.2 years on average.

Due to the unique natural features of the HRB, in recent years, large-area flood and drought disasters happen frequently, and local flood and drought disasters happen annually. According to statistics, from 1949 to 2008, average annual flood disaster area of the HRB is 25.29 million mu ( Figure 3 ), among which, number of annual flood disaster area above 30 million mu reaches to 15 accounting for 25% of the number of statistical years; number of annual flood disaster area higher than 40 million mu reaches to 11 accounting for 18.3% of the number of statistical years; and number of annual flood disaster area above 50 million mu reaches to 8 accounting for 13.3% of the number of statistical years. Table 2 shows statistics of flood disasters for three basin-wide floods in the HRB.

Figure 3.

Disaster area in different years in the Huaihe River Basin.

Table 2.

Statistics of flood disasters in 1991, 2003, and 2007 in HRB.

5. Achievements in flood control

Since the foundation of the new China, for the purpose of effectively reacting to flood and drought disasters and reducing losses, under the guidance of “jointly considering storage and discharge of floodwater” principle for harnessing the Huaihe River, with 60-year continuous river harness, tremendous achievements have been made in engineering construction of the Huaihe River harness. Laws and regulations, i.e., “Flood Control Law of The People’s Republic of China,” “Flood Control Regulation of The People’s Republic of China,” “Drought relief regulation of The People’s Republic of China,” and “Administrative regulation for flood storage and detention areas,” have been established, and basin flood prevention and dispatching programs have been improved, and all these play a vital role in reducing flood and drought disasters.

5.1. Structural measures

Overall arrangement: In the upper reaches, carrying out water-soil conservation and constructing reservoirs are important to intercept and store floods. In the middle reaches, taking structural measures to dredge & broaden river course, construct dykes and flood diversion & storage areas to increase channel flood discharge capacity. In the lower reaches, taking structural measures to excavate river channels for enlarging flood discharge capacity. The overall layout of structural measures is shown in Figure 4 .

Figure 4.

Simplification of major water conservancy projects of the Huaihe River.

Water and soil loss have accumulatively been harnessed with an area of 40,000 km 2 .

About 6300 reservoirs have been constructed, with a total storage capacity of 30 billion m 3 , and 40 of them are large reservoirs, with a total storage capacity of 20 billion m 3 and a flood control capacity of 6.2 billion m 3 . Seventeen flood detention areas and large lakes for controlling flood have been constructed, with a total storage capacity of 3.59 billion m 3 and a flood storage capacity of 2.63 billion m 3 . Figure 3 illustrates the major structures in the Huaihe River Basin.

Artificial channels have been constructed with a length of 2100 km. Different types of dikes have been constructed with a length of 50,000 km, and the length of key dike is 11,000 km. River channel discharge capacity has been significantly promoted, channel discharge capacity of the upper mainstream has been enhanced from 2000 to 7000 m 3 /s, channel discharge capacity of the middle mainstream has been enhanced from 5000 to 7000 m 3 /s to 7000 to 13,000 m 3 /s, and channel discharge capacity of the lower mainstream has been enhanced from 8000 to 18,270 m 3 /s. In addition, 1200 sluices have been constructed.

At present, flood control standard of the mainstream in the upstream is once-10-years, and flood control standards of the key flood protection areas and important cities in the middle and lower reaches were promoted to once-100-years. Flood control standards of the important tributaries can reach to once-20-years to once-50-years. Specifically, in the upper mainstream, channel discharge capacity has been enhanced from 2000 to 7000 m 3 /s. In the middle mainstream, channel discharge capacity has been enhanced from 5000–7000 to 7000–13,000 m 3 /s. In the lower mainstream, channel discharge capacity has been enhanced from 8000 to 18,270 m 3 /s.

5.2. Non-structural measures

So far, non-structural measures of flood prevention regulation command system jointly form system mechanism for flood prevention and disaster reduction.

5.2.1. Legal and institutional system for flood control

China has already promulgated laws and regulations concerning water, e.g., water law, flood control law, regulation on river channel, regulation on flood control, etc.

(1) Flood control law

The Law of Flood Control was adopted at the 27th Meeting of the Standing Committee of the Eighth National People’s Congress on August 29, 1997, and promulgated by Order No. 88 of the President of the People’s Republic of China on August 29, 1997. It is the first law on the prevention and control of natural disasters in China. It is also a very important law following the Water Law and the Law of Soil and Water Conservation in water domain in China.

Numerous administrative regulations were promulgated to clarify the responsibilities of responsible parties concerned in the flood control, such as flood Control Regulation of the People’s Republic of China (2005 Revision), Regulation of the People’s Republic of China on the Administration of River Courses, Guidelines for safety and construction of flood detention areas and flood control operation plan, etc., which have played an vital role in flood control and management in China. However, with the rapid socio-economic development, population growth, and acceleration of urbanization, numerous problems and new challenges have risen in terms of flood control, which can be summarized as follows: (a) Lack of legal consciousness on the importance of flood planning and at the same time the approved flood plan was not fully observed or strictly enforced; (b) Flood protection standard was relatively low; (c) There was no effective means for river channels management, e.g., sand excavation; (d) No effective management of flood plains area; and (e) Lack of funds in flood control and infrastructure construction. Therefore, there is an urgent call for specific law on flood control to ensure that necessary measures could be implemented legally.

(2) Institutional Arrangement

(a) Ministry of Water Resources (MWR)

Ministry of Water Resources (MWR), the Chinese Government Department responsible for water administration, was founded in October 1949. In order to clarify the responsibilities among different ministries/departments under the State Council, Ministry of Water Resources was reorganized on July 22, 1988. In accordance with the stipulations of the State Council of the People’s Republic of China, the function and responsibility of the department were summarized as follows:

ensure rational development and utilization of water resources in China,

formulate water resources development strategies, plans, and policies in China,

provide draft legislations,

promulgate water administrative rules and regulations,

undertake integrated water resources management and supervision,

take charge of water resource protection and water conservation,

organize, coordinate, and supervise the work of flood control and drought relief, and be responsible for control of soil and water losses.

(b) Flood control and drought relief commanding headquarters (FCDRH)

The flood control and drought relief commanding system has been constructed at national, river basin, and local levels ( Figure 5 ). On a national level, the General Commander is a vice premier of the State Council. Its members are from administrative leaders of governmental departments and the military, who are responsible for organizing and guiding efforts in flood control and drought relief throughout the whole country [ 6 – 9 ]. In the six major river basins, namely, the Yangtze River, Yellow River, Huai River, Hai River, Songhua River, and Pearl River, Flood Control and Drought Relief Headquarters are constructed, and they take the same responsibility of flood control and drought relief on a river basin level. In local governments that undertake flood and drought tasks, flood control and drought relief commanding headquarters are constructed as part of the local governments.

Figure 5.

Institutional framework of Flood Control and Drought Relief Commanding Headquarters.

(c) The Huaihe River Basin Commission

The Huaihe River Commission is a river basin authority dispatched by the Ministry of Water Resources of China to exercise water administrative functions in the Huaihe River Basin and Shandong Peninsula, which is responsible for basin design and planning, flood control and drought relief, integrated water resources management, etc.

In accordance with the stipulations of the Ministry of Water Resources(MWR), the Commission is given the following major mandates in Huaihe River Basin (HRB):

It is in charge of making the integrated planning and related professional planning for HRB, such as water resources developing planning, annual water projects construction implementing planning, and so on.

It is in charge of HRB’s water resources management and supervising.

It is in charge of checking the water body acceptance capacity for pollutant, and monitoring the water quality for the water functional areas located in the boundary of provinces.

It is in charge of dealing with routine work of the Huaihe River Flood Control and Drought Relief Headquarters. This includes the organization, coordination, supervision, and direction of flood control for HRB, and execution of operations of flood control and drought prevention for major river basins and key water projects.

It is in charge of building, managing, and operating for important water projects.

It is in charge of enforcing the laws and regulations relative to water administration.

It is in charge of organizing water and soil conservation in HRB, including development of engineering measures for water and soil conservation, and organization of the monitoring and overall prevention and control of soil and water losses.

(d) The local water resources management agency

The local water resources management comprises four levels, i.e., the provincial, prefecture, country, and the village (town). Overall, it has the most of main functions and responsibilities as that of the central government. Specifically, there are also direct legal duties of flood control and drought relief.

5.2.2. The flood forecasting and warning system

(1) The flood monitoring system

Hydrological information and flood forecasting provide basic information for flood control. By 2014, totally 329 hydrological stations (hydrologic information including information of precipitation, water level, and discharge), 220 stage gauging stations, and 2488 rain gauges had been constructed. For those stationary gauging stations, they collect rainfall information using rainfall recorder, water level information using telemetering stage recorder, and discharge information using acoustic doppler current profilers (ADCP) or current meter. In addition, 1489 water quality monitoring stations, 324 moisture stations, and 3024 ground water monitoring stations had been constructed; all of these constitute the hydrological network and also the flooding monitoring system over the Huaihe River Basin. During flood period, with the aid of water information transmission system, 1250 stations (including important hydrological stations, stage gauging stations, and rain gauges) are mandated to collect, transmit, and share hydrological information from single state level to provincial, river basin, and the national levels. It runs at a regular time interval ranging from 6 minutes to 6 hours as stipulated on the basis of the requirement of flood forecasting for the river system [ 2 ].

(2) Information transmission

The hydrological information is transmitted through the national telecommunication system. Most of the hydrological information collected are transmitted using client software of the transmission system. For those river reaches and water projects of special importance, short wave radio stations were established to ensure more effective information transmission. Furthermore, data collection and management have been computerized in the real-time flood forecasts on the state level, the river basin level, the province level, and the municipal level.

(3) Flood forecasting and warning

Flood forecasting and warning were made by hydrological bureau or flood control office, which is the member of the Flood Control and Drought Relief Headquarters (FCDRH) at various levels ranging from municipal level to the country level. Faced with emergence, the FCDRH will issue warning via government at different levels. Before the flood season in every year, annual meeting of FCDRH at different levels is held to ensure preparatory work is well organized. In addition, on a national level, there are about 1000 hydrological stations that conduct river flood forecast as requested, and there are 66 hydrological stations conducting river flood forecast in the Huaihe River Basin. Numerous models, e.g., the Antecedent precipitation index (API) model, the Xinanjiang model, and tank model, have been employed for flood forecasting ( Table 3 ) [ 9 – 13 ]. Most of the hydrological bureau above municipal – level established flood forecasting system in the flood forecasting [ 14 ] ( Figure 6 ). In addition, a new real-time flood forecasting platform FEWS_HUAIHE has also been established for probability forecasting ( Figure 7 ).

Table 3.

Flood forecasting models applied in the Huaihe River Basin.

Figure 6.

Real-time flood monitoring, forecasting, and warning system for the Huaihe River Basin.

Figure 7.

Probability flood forecasting system for the Huaihe River Basin.

(4) Decision support system for flood control

The major flood control measures can be summarized as “upper-stream storage, middle-stream passage, and lower-stream discharge” in accordance with the principle of flood prevention and regulation. Decision support system for flood control was designed for real-time control of structures in the Huaihe River Basin in case that big floods hit the basin ( Figure 8 ). It has the following functions: reservoir regulation ( Figure 9 ), flood bypass regulation ( Figure 10 ), sluice regulation, hydrojunction regulation as well as joint dispatching of hydraulic structures, etc.

Figure 8.

Topological diagram of hydraulic structures for the Huaihe River Basin.

Figure 9.

Interface of flood bypass regulation.

Figure 10.

Interface of reservoir regulation.

(5) Flood disaster assessment system

Flood disaster assessment system is designed for evaluating losses of flood disasters during the whole process in several key flood-prone areas in the Huaihe River Basin. It has the major function of pre-disaster evaluation, real-time evaluation, and post disaster assessment ( Figure 11 ).

Figure 11.

Flood disaster assessment decision support system.

(6) Flood risk mapping

Flood risk mapping identifies flood hazards, assesses flood risks, and partners with provinces and communities to provide accurate flood hazard and risk data to guide them to mitigation actions. Flood risk mapping is an important part of flood regulations and flood insurance requirements. It maintains and updates data through Flood Insurance Rate Maps (FIRMs) and risk assessments. FIRMs include statistical information such as data for river flow, storm tides, hydrologic/hydraulic analyses, and rainfall and topographic surveys ( Figure 12 ).

Figure 12.

Flood risk mapping for a key area in the Huaihe River Basin.

In summary, an integrated system of flood monitoring, forecasting, and warning system, including weather prediction, flood monitoring and forecasting, flood dispatching, and flood control discussion, has been preliminarily established in the Huaibe River Basin ( Figure 13 ), which plays a vital role in basin flood control. However, system for flood risk management, e.g., probability flood forecasting system, flood risk dispatching models for reservoirs and hydro-junction, still stays at a starting stage.

Figure 13.

Integrated system of flood monitoring, forecasting, and warning system.

6. Case study

6.1. flood management for the huaihe basin-wide flood in 2007, 6.1.1. floods in 2007 in the huaihe river basin.

In 2007, a long-time, wide-range, and high-intensity rainfall occurred in the Huaihe basin, in which area average rainfall reached to 465 mm. Influenced by the rainfall, a multi-peak flood appeared in the mainstream of the Huaihe River. Among them, four flood peaks have been found in the upstream of Wangjiaba of Huaihe River, three peaks in the Wangjiaba-Linhuaigang section, two peaks in the Linhuaigang-Huainan section, and one peak in downstream of Huainan.

The water level of the Wangjiaba-Runheji section rose over the guaranteed stage, and the water level of the Runheji-Wangji section rose to a historically high value. According to a preliminary analysis, the return period of the Mid-Huaihe River is about once-in-15-years to once-in-20-years, while that of the downstream is about once-in-25-years.

The fierce flood lasted for a long time, affected 2.5 million hectares crops, and caused a direct economic loss of 15.5 billion Yuan. However, compared with floods in 1991 and 2003, the loss was reduced by 54.3 and 45.7%, respectively. Why did the same magnitude floods make such differences? It is primarily resulted from scientific regulation of the Huaihe River flood.

6.1.2. Flood management

Flood regulation is an important part of the Huaihe River flood Management work. In 2007, all levels and branches of government facing a serious flood situation took many measures comprising of “intercept, discharge, store, divert” in accordance with “the programs for the defenses of the Huaihe River floods.”

(1) Intercept flood with the reservoirs on upstream

In the general flood defense process, the first step is to discharge flood with river channels, and the second step is to intercept water with reservoirs and then to store flood by detention basins. In 2007, the 18 large reservoirs in the Huaihe River upstream, such as Suyahu, Nianyushan, Meishan, and Xianghongdian, totally stored flood with an amount of nearly 2.1 billion cubic meters, which greatly released the flood defense pressure.

Although the reservoir played a significant role in the Huaihe River flood in 2007, in actual operation, it also faced many difficulties. At first, the Suyahu Reservoir and Meishan Reservoir, which are closely related to the flood control and prevention, are facing different levels of safety problems. Reservoir regulations are subject to the safety of reservoir projects, if a reservoir has safety problems, which means that the project itself is prone to the flood, and it cannot intercept flood according to design standards. The second is the difficulty of forecasting. At present, it is difficult to accurately and timely forecast sudden heavy rain in Huaihe Basin for our technology. Third, the provincial conflicts need to be coordinated. Most of the reservoirs in the upstream of the Huaihe River are located in Henan Province. How to weigh the pros and cons has always been a difficult issue.

Suyahu Reservoir regulation is a typical example. The reservoir is located in Henan Province. On July 15, the reservoir water level reached to 54.76 m, over the flood control water level l 2.26 m, and a lot of land was flooded and therefore reservoir operation was facing great pressure. At the same time, as the downstream part of the river exceeded the guaranteed stage, flood situation was very tense. The Flood Control and Drought Relief Headquarter (FCDRH) of Huaihe River, Henan Province, and Anhui Province launched flood consultations repeatedly and regulated Suyahe Reservoir carefully, and finally intercept 500 million cubic meters for downstream on the premise of guaranteeing projects safety, and thus the masses in this reservoir area have paid a heavy price.

(2) Pre-discharge capacity of rivers and lakes

Under normal circumstances, it takes 2 days for the formation of flood peak in mainstream of the Huaihe River from the beginning of rainfall to a flood peak appears. Short-term weather forecasts can basically predict the location and quantity of rainfall. It provides an opportunity to use the project ahead of time. The Bengbu Gate is the important control hydro-junction in the middle reaches of Huaihe River. When rainfall started in upstream and a large flood forecast was reported, the Bengbu Gate opened all 40-hole gates to pre-discharge the water. As a result, when the flood arrived, the water level can be reduced from 17.85 to 16.03 m. The reduction of 1.82 m of water level provided an opportunity to receive the upstream runoff and drainage.

Hongze Lake is the largest lake in the Huaihe Basin, and Sanhe Gate is the largest controlling gate of the lake. On July 4, before the floods arrived at Hongze Lake, the FCDRH of Huaihe River coordinated with the FCDRH of Jiangsu Province and opened Sanhe Gate and began to discharge water. When flood discharge and water level reach to a warning value in the upstream, open Sanhe Gate of Hongze Lake in the lower stream in advance to decrease water level for discharging flood freely. Through analysis and calculation, Sanhe Gate discharged a cumulative capacity of 16.8 billion cubic meters for flood prevention from July 4 to July 31 for totally 28 days and reduced the water level of the lake by 0.2 m, all of which win an advantageous opportunity in flood prevention.

(3) Make full use of detention basins for flood storage

The detention basins are important parts of the Huaihe River flood control system. When large floods occur, the use of the floodplain detention can reduce the flood volume, decrease flood peak, and lower the water level of rivers, which is a major feature of the flood prevention of the Huaihe River. The Mengwa Detention Basin is the first one in the Huaihe Basin. Due to the important location that involves the two provinces, it is scheduled by State Flood Control and Drought Relief Headquarters (FCDRH).

On July 8, the water level raised rapidly due to a heavy rain. The water level of Wangjiaba hydrological station, which is known as the Huaihe River Flood Control barometer and flood weathervane, reached quickly to 29.3 m, the guaranteed stage. At this point, the 18 large reservoirs in Huaihe River upstream were in full load operation, and the flood control capacity was exerted to the most, many rivers exceeded the guaranteed water level, and the dangers of embankment appeared ceaselessly.

Facing the severe situation, the FCDRH promoted the flood emergency response level to grade II on July 9 and to the highest level I on July 10. This is the first time to start the highest level of flood emergency response. In accordance with request of the grade I response, the Mengwa Detention Basin was operated timely when the water level of Wangjiaba of the Huaihe River reached 29.3 m.

However, there are several real problems in storing floodwater, namely the migrant relocation and resettlement, inundated farmland, heavy loss of property, and waste of human and material resources. To operate, or not to operate? That’s the question. At that time, the SFCDRH made an analysis and found that there would be three negative results when not using detention basin or using not properly. At first, inundated farmland in the upstream would be increased to 2530 hectares, with an increased area of 1340 hectares more than the use of the Mengwa Detention Basin. The second is the raising of the Huaihe River water level, which would increase the difficulty of flood prevention and threaten safety of the mainstream embankment. Lastly, probability of the use of the detention basins in downstream would be increased. However, the use of the Mengwa Detention Basin means that more than 3000 people have to be transferred, 12,000 hectares farmland would be flooded, and the part of the infrastructure in the region to be destroyed. After the five consultations by the relevant authorities, it was determined finally that the Mongwa Detention Basin would be opened. According to analysis, the basin had diverted water for 46 hours, stored flood with a volume of 250 million cubic meters, lowered the Wangjiaba water level by 0.2 m, reduced the water level of the downstream of the Zhengyangguan pass by 0.1 m, and has played a significant role in clipping flood peak. Subsequently, the Huaihe River Basin started using nine more detention basins diverted floodwater with a total capacity of 1.5 billion cubic meters. The use of these detention basins shorten the duration of Wangjiaba stage at high level nearly 20 hours.

(4) Divert water with the channels timely

It can relieve the pressure of flood prevention in the main stream by regulating diversion rivers to discharge a part of the flood water. Both Huaihongxinhe canal and Ruhaishuidao canal (canal to the sea) played the role of accelerating flood discharge in the Huaihe River flood prevention in 2007.

Huaihongxinhe canal is an artificial diversion river that passes through Jiangsu and Anhui provinces. In late July, the Huaihe River water level was still high. After soaking in high level water, much more dangerous situation of the embankments appeared. On the one hand, the rescue personnel were tired due to the long struggle; on the other hand, the high temperatures of 38°C caused inconvenience for the rescue team and relocated people. In order to reduce the water level of Huaihe River and relieve the defensive pressure of the downstream from Bengbu city as soon as possible, the FCDRH of the Huaihe River actively coordinated Jiangsu and Anhui provinces for reasonable operation of Huaihongxinhe canal, thereby reducing the dike defense and emergency pressure, and 110,000 metastatic masses returned home 2–4 days ahead of time and returned to a normal production and living order.

6.2. Room for river project in the Huaihe River Basin

6.2.1. development of “room for river” idea in the huaihe river basin.

From 1950 to 1969, there were 10 flood storage areas (total area is 3788 km 2 and flood storage capacity is 10.18 billion m 3 ) and 21 flood bypasses (total area is 1301 km 2 and flood discharge capacity is 1000~3500 m 3 /s when fully open).

The HRB has constructed five flood storage areas (total area is 3300 km 2 , and flood storage capacity is 9.3 billion m 2 ) and totally 21 flood bypasses. These flood diversion and storage areas constitute as part of the flood control engineering system and played important roles in preventing basin-wide floods in the past.

However, there are also outstanding problems, e.g., too many flood bypasses occupy river’s room, evacuation of 1.8 million people is a hard work, etc.

Since mid-1980s to the twentieth century, problems of flood diversion and storage areas have received a great deal of attention, new ideas about the Huaihe harness have progressively formed, i.e., properly reducing number and area of flood diversion and storage areas, enhancing river channel discharge capacity, reducing the probability of using flood bypasses, and reinforcing security construction of people’s safety.

By 2010, number of flood bypasses along the Huaihe mainstream reduced from 21 to 17, of which four flood bypasses were abandoned and returned room to river with an area of 24.3 km 2 , other flood diversion and storage areas returned room to river with an area of 96.4 km 2 by partial dike retreat, and totally returned 120.7 km 2 area to river.

By the plan completion in 2020, only six of the 17 flood bypasses will be preserved, among which two of the them will be abandoned, three of them will be changed to flood storage areas, and five of them will be adjusted to flood protection areas ( Figure 14 ).

Figure 14.

Adjustment of flood detention areas and flood bypass in 2020.

Totally, 230 km 2 will be returned to river, width of river channels will be increased 100~2500 m, and flood discharge capacity will be increased from 800 to 1200 m 3 /s. The operation standard of the preserved flood bypasses will be promoted to once in 10–20 years ( Figure 15 ).

Figure 15.

Achievements after completion of adjustment of flood detention areas and flood bypass.

From the start time of the flood diversion and storage areas construction to now, flood diversion and storage areas have experienced from “conflicts between human & water”, to “co-existence of human & water” and finally to “harmony between human & water”, which also reflects development of idea about “Room for river” in the HRB.

What follows take Jingshanhu flood bypass as a case study.

6.2.2. Room for river: Jingshanhu flood bypass as a case study

Jingshanhu flood bypass is about 4 km long from east to west, and 17 km wide in south-north direction, with an area of 72.0 km 2 . It plays a vital role in raising the flood-diversion capacity and decreasing water levels of Bengbu and Huainan cities.

The major problems before the harness were as follows: (1) The river channel is narrow, river channel for flood discharge is only 500 m wide, and maximum discharge capacity is only 5700 m 3 /s. (2) There are 10,000 people in the Jingshanhu flood bypass and most of them live in the plain area, which involves a large amount of works when carrying out immigration. (3) The flood bypass operates so frequently that it causes serious property losses. (4) The controlling gates of the flood bypass are so inconvenient that it cannot be timely and effectively operated. (5)Reconstruction after disaster involves hard works.

By retreating, reinforcing, and newly constructing dykes with a length of 42 km, constructing one withdrawal sluice and one intake sluice, and security construction, e.g., retreat road construction, reinforcement of Zhuangtai (small villages on raised ground with higher elevation), communication and warning facilities, etc., the chance of flood diversion was promoted from once-in-7-years to once-in-15-years, and it has significant effects.

After the control measures were implemented, the following achievements have been made:

The problems of local people’s security have been solved. There are only 855 people living in the flood-protected villages.

The flood dispatching measures have been strengthened. In 2007, the Huaihe River Basin was hit by a basin-wide large flood event again and the newly-built intake and withdrawal sluices firstly came into use and showed good effects.

The flood passage of the mainstream has been enlarged. After the implementation of dike reconstruction and reinforcement, the width of the dike inside reached to 600 m, and the release discharge of the reaches lower than Zhengyangguan pass in the mainstream can reach to 8000 m 3 /s without using the flood bypass.

Probability of using the flood bypasses has been promoted from once-in-7-years to once-in-15-years.

If inundated, economic losses of peasants have been compensated by our country and it is conductive to resume production.

Table 4 summarizes control measures and achievements of Jingshanhu flood bypass.

Table 4.

Control measures and achievements of Jingshanhu flood bypass.

7. Experiences and enlightenment

China is a flood-prone country, and flood disasters occur frequently. The Chinese Government attaches great importance to flood management and drought relief, and great efforts and achievements have been made with aid of the structural and non-structural measures. However, flooding is still a big issue in China. The ability to control floods needs further improvement of the non-structural measures, including the relevant laws, monitoring networks, warning and forecasting, and social management [ 14 ].

Both the structural and non-structural measures are very important for flood control and management. However, for the over-standard flood cases, the non-structural measures, such as the hydrological monitoring and flood forecasting, become much more important.

Flooding is still a big issue in China. The ability to control floods needs further improvement of the non-structural measures, including the relevant laws, monitoring networks, warning and forecasting, and social management.

7.1. Experiences in flood management

Flood disaster, which occurred suddenly and inevitably, is different from the general emergency disasters. It is determined by the natural conditions of the Huaihe Basin. By review of the Huaihe River flood regulation, it is found that the keys of success are still dependent on the following factors:

The complete flood control structural system is the foundation of flood regulation and management. The standard and quality of the flood control works are directly related to flood management and projects operation. Although the standard of the flood control system in Huaihe Basin is not high enough, it is compounded by a wide range of works with high correlation. Their operation is very flexible, especially the flood regulation of detention basins and diversion channels like Huaihongxinhe canal and Ruhaishuidao canal (floodway to the sea), and plays a vital role in flood control. In future, we should strengthen the construction of structural system for flood prevention and increase the flood control standard appropriately.

Accurate hydrologic forecasting is the prerequisite of the flood regulation. The forecast accuracy and the lead time will directly affect the correctness and timeliness of the flood regulation decision. In recent years, the extreme weather events have increased significantly from global perspective. The sudden strong rainfall is unforeseeable, and it becomes a new issue for flood prevention work. In the future, we should continue to strengthen early warning system, to optimize flood forecasting model, and to improve forecast accuracy and quality. Particularly, there is an urgent call for constructing an ensemble flood forecasting system integrating with numerical weather models, distributed hydrologic models, hydraulic models, and real-time control models.

Scientific analysis and judgment of the flood are the key to flood regulation. Flood regulation should consider all factors as an integrated system, including upstream and the downstream, both sides of river, global and local, flood control and drought relief, as well as economy and society. To balance different interests is a hard nut to crack in decision-making. In future, we need to continue to strengthen the flood management and risk management and to resolve the problems in laws and regulation, mechanism, technology, and other issues.

Advanced technology and perfect plan are the effective support for flood regulation. Huaihe River floods in 2003 and 2007 are not only a test of the flood structural system, but also a full inspection of the Huaihe River non-structural system. All of advanced technology and comprehensive plan of flood monitoring and forecasting, flood control scheduling, emergency management mechanism, and the joint regulation of the flood engineering system play an important role in joint operation of flood control structural system. In future, we should learn from domestic and international flood management experience, promote the application of high technology, constantly improve the flood control, and strive to reduce disaster losses.

7.2. Outlook on flood management in the Huaihe River Basin

In the future, we have to change from flood control to flood management and finally achieve the goal of flood risk management.

Room for River. In terms of river planning and training, it is necessary to make more room for flood and formulate relevant schemes and measures by comprehensive analysis of flood. Based on the structural system comprising of reservoirs, dykes, and flood detention areas, we have to enlarge passageway for small and middle magnitude floods in river harness for the purpose of releasing such kind of floods. To construct flood detention areas to receive extra floods that exceed the river channel capacity aims to solve the big flood issues.

Live with floods. In order to realize harmony between human and nature, first and foremost, an integrated flood control and management system should be well established on an operational level. In addition, in order to achieve a shift from flood control, flood management to flood risk management, there is urgent call for raising awareness of flood risk management both for the leader and the public.

Flood risk management. We do not have to control all floods of different magnitude, and we cannot bear enormous flood disaster risk. We have to avoid risks actively, take preventive measures as high priority, live far from flood disasters, and control flood disaster risk to a certain extend. We have to determine reasonable flood protection standards, and the standards should not be too high or too low. We have to classify function of flood structures in a reasonable way, because flood disaster risks could propagate if function of flood structures is not classified correctly or properly. We have to share risks. Construction of flood structures can absolutely cause risk propagation; therefore, we have to treat risk propagation in a right way and different regions have to share flood risk and construct flood risk compensation mechanism and flood insurance system.

Acknowledgments

The study was financially supported by Non-profit Industry Financial Program of MWR of China (201301066 and 201501007) and National key research and development program of China (2016YFC0402700).

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© 2017 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Enhanced communication for mt-2 submittals as part of the fema letters of map revision review partners program.

The Colorado Water Conservation Board and Mile High Flood Control District hold pre-submittal meetings. These meetings are a chance to answer questions about the Letter of Map Revision process. This joint effort has made for more complete submittals. It has also improved coordination among local agencies and mapping partners.

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Future Strategies

State Case Studies

Federal Review

Management Goals

• Holistic Approach to Coastal FRM

CONTENTS ≡

CONTENTS ✕

Coastal Management Program

Shoreline regulations, floodplain management, wetland management, building codes, community planning, stormwater and runoff management, erosion management, climate adaptation initiatives, state management capacity, alternatives to structural mitigation, long-term planning, balance of mitigation and disaster recovery, holistic management approach, new york coastal flood risk management case study.

Policies and Programs

The New York Coastal Management Program , established in 1982, is housed within the New York Department of State’s Office of Planning, Development, and Community Infrastructure . Much of the program’s legislative authority is drawn from the state Waterfront Revitalization of Coastal Areas and Inland Waterways law as well as the Coastal Erosion Hazard Areas law . The program pursues goals related to coastal resources protection and development, local waterfront revitalization, coordination of major activities affecting coastal resources, public awareness of coastal issues, and federal consistency with state coastal management policies. Within New York, the Department of State administers the program and coordinates its implementation in cooperation with the state Department of Environmental Conservation as well as other state agencies.

Coastal program boundaries extend along the coast of Long Island, New York City, Hudson River estuary, both Great Lakes that border New York, and the Niagara River. Specific landward boundaries of the coastal program vary by region and locality due to initial delineation proposals from local government agencies. All barrier and coastal islands on Long Island are included within program boundaries along with areas 1,000 feet landward of the shoreline, extending further in some cases. The New York City program boundary generally extends 500 to 1,000 feet inland from the shoreline, with select areas along major tributaries also extending further. Within the Hudson River Valley the landward boundary is generally 1,000 feet but may extend up to 10,000 feet in areas that possess high aesthetic, agricultural, or recreational value. In the Great Lakes region the boundary is also generally 1,000 feet, though urbanized areas or transportation infrastructure parallel to shore limit the boundary to 500 feet or less in some cases.

Coastal management program consistency reviews require federal actions in the state coastal zone to be consistent with the enforceable policies of the state program or the policies of an approved local waterfront revitalization program. The program also contains provisions to ensure consistency of state actions in coastal areas. Of the 44 coastal management program enforceable policies in New York, seven specifically address flooding and erosion hazards. These policies touch on a number of aspects of coastal flood risk management including the siting of buildings in coastal areas to minimize risk to property and human lives, protection of natural features that mitigate coastal flood risk, construction of erosion control structures to to meet long-term needs, prevention of flood level increases due to coastal activities or development, prevention of coastal mining or dredging from interfering with natural coastal processes, use of public funds for erosion protection structures, and use of non-structural mitigation measures when possible. Additional enforceable policies address coastal development, fish and wildlife resources, public access, recreation, historic and scenic resources, agricultural lands, energy and ice management, water and air resources, and wetlands management.

At the state level, aspects of New York’s Environmental Conservation Law , Local Waterfront Revitalization Program , and State Environmental Quality Review permitting program influence coastal zoning and development decisions. Article 34 of the Environmental Conservation Law requires the identification of coastal erosion hazard areas and rates of recession of coastal lands. Shoreline setbacks must then be implemented at a distance that is sufficient to minimize damage from erosion. Article 36 of the Environmental Conservation Law , the state Flood Plain Management Act, also addresses coastal hazards, requiring walled and roofed buildings to be sited landward of mean high tide and prohibiting mobile homes within coastal high hazard areas, among other restrictions. Article 15, Water Resources Law , regulates the placement of coastal structures such as docks or piers and also addresses the placement of fill in coastal areas. Together these elements of the Environmental Conservation Law provide much of the legal basis for zoning decisions that can affect coastal flood risk at the municipal and local level.

Participation in the Local Waterfront Revitalization Program can also influence a local government’s coastal zoning decisions. In the process of preparing and adopting a revitalization program, local governments provide a more specific implementation of the state Coastal Management Program, taking advantage of local regulatory powers such as zoning ordinances and site plan review. Upon approval of a Local Waterfront Revitalization Program, state actions must then be consistent with the local program. In this way the enforceable policies of the Coastal Management Program, including those that relate to coastal flooding and erosion, are incorporated into local zoning decisions. Elements of enforceable policies are also incorporated into environmental permitting through the State Environmental Quality Review Program, which requires state agencies and local governments to prepare an environmental impact statement for any action that may have a significant impact on the environment. If an action in a coastal area requires the preparation of an impact statement, it must also be determined that the action is consistent with any relevant coastal enforceable policies. Consistency reviews must also be applied to NYS SEQRA type 1 actions as well as unlisted actions.

Floodplain management activities within New York are primarily conducted through the National Flood Insurance Program . Any regulations developed by the state must be at a minimum as strict as those prescribed by FEMA. Beyond the state level communities may adopt more restrictive floodplain management regulations. Within the state, local communities largely regulate development within federally designated Special Flood Hazard Areas, with state assistance provided by the New York State Department of Environmental Conservation. Local development permits govern private development within floodplains as well as development by a county, city, town, village, school district, or public improvement district, as specified in the state Environmental Conservation Law.

State standards for floodplain development permits in all designated special flood hazard areas require adequate anchorage and use of flood resistant material for all new construction and substantial improvement to existing structures. Utilities must also be designed in a manner that minimizes or eliminates risk of damage or failure during flood events. In areas where base flood elevation data exists, new construction or substantially improved residential structures must have the lowest floor at two feet above the BFE, including basements and cellars. Nonresidential structures may employ floodproofing to provide protection. Any enclosed areas below the base flood elevation must be designed to allow for the equalization of hydrostatic forces on exterior walls during a flood event. If no base flood elevation has been determined, new construction or substantially improved residential structures must be elevated above grade to the depth specified on the corresponding flood insurance rate map or two feet if no number is specified, with nonresidential structures again able to employ floodproofing measures. All state agency activities, whether directly undertaken, funded, or approved by an agency, must also be evaluated in terms of significant environmental impacts under the State Environmental Quality Review program, which includes a substantial increase in flooding as a criteria of significance. An environmental impact statement must be prepared if it is determined that an action may have a potential significant adverse impact.

All structures must be located landward of mean high tide levels within coastal high hazard areas, and all new construction or substantially improved structures must be elevated on pilings or columns so that the bottom of the lowest horizontal structural member of the lowest flood is elevated to or above the BFE. Pilings or column foundations must be adequately anchored, and fill is prohibited for use as a structural support for any new structure or substantial improvement. Space below the lowest floor may not contain obstructions to flood flows or otherwise be enclosed with non-breakaway walls. Any such space below the lowest structural floor may not be used for human habitation. New development or substantial improvement to structures must also not affect sand dunes in any way that increases potential flood damages.

The New York State Department of Environmental Conservation is also responsible for wetland management within the state. Statutory authority for wetland regulations stems from the Tidal Wetlands Act and Freshwater Wetlands Act , part of the larger state Environmental Conservation Law . Wetlands and wetland regulations are divided into either tidal or freshwater, and wetlands are further classified within each category. State wetland inventories containing information on delineated areas and classifications are made available for public use as part of the state wetland mapping program. Activities within wetland areas are regulated through a permit system.

Tidal wetlands regulations are designed to allow uses of wetlands that are compatible with the preservation, protection, and enhancement of ecological values including flood protection and storm control. Development restrictions require that all buildings and structures in excess of 100 square feet be located a minimum of 75 feet landward from tidal wetland edges, with less stringent setbacks in place for buildings located within New York City. Similar setback requirements exist for impervious surfaces exceeding 500 square feet. On-site sewage systems must have a setback of at least 100 feet, and a minimum of two feet of soil must be between the bottom of a system and the seasonal high groundwater level.

Permit standards for activities within tidal wetlands require that any proposed activity be compatible with the overall state policy of preserving and protecting tidal wetlands, and as such any activity may not cause any undue adverse impact on the ecological value of an affected wetland area or any adjoining areas. Standards also require that any activity within tidal wetlands be compatible with public health and welfare, be reasonable and necessary, and take into account both alternative actions and the necessity of water access or dependence for the proposed action. The state also publishes compatible use guidelines for activities within wetlands based on wetland type. If any activity is presumed to be incompatible with state tidal wetland use guidelines, an applicant must overcome the presumption of incompatible use and demonstrate that the activity is compatible with the preservation, protection, and enhancement of wetland values. If a use is specifically listed as incompatible within guidelines the use is then prohibited. Permitted activities in areas adjacent to tidal wetlands must also be compatible with public health and welfare, have no undue adverse impact on wetland ecological values, and comply with use guidelines.

State flood-resistant construction requirements are listed in the International Residential Code as adopted by New York State . Regulations apply to new residential buildings and structures located fully or partially within flood hazard areas as well as any substantially improved or restored structures within flood hazard areas. Construction requirements are based on the design flood elevation, which at a minimum must be the higher of either the peak elevation of a 1% annual chance flood event or the elevation of the design flood event as adopted on community flood hazard maps. Structures within flood hazard areas must generally be designed and anchored to resist the flood forces associated with the design flood elevation, and methods and practices to minimize flood damage must also be employed.

For the purposes of determining appropriate structural elevations, the lowest floor of a structure is defined as the lowest floor of any enclosed area, including basements. Within flood hazard areas not subject to high-velocity wave action, structures must have the lowest floor elevated to two feet above the base flood elevation or design flood elevation, whichever is higher. Utility systems must also be elevated to this standard. If no depth number is specified structures must be elevated not less than three feet above the highest adjacent grade. Any enclosed area below the design flood elevation must be used only for building access, parking, or storage and must contain flood openings sufficient to equalize hydrostatic forces on exterior walls.

For buildings and structures located in coastal high-hazard areas, including both V zones and Coastal A zones, the lowest floor must be elevated so that the lowest horizontal structural members are elevated to either the base flood elevation plus two feet or the design flood elevation, whichever is higher. Any walls below the design flood elevation must be designed to break away without causing damage to the elevated portion of the building, and again may be used only for parking, building access, or storage. Structures must be elevated using adequately anchored pilings or columns, with select exceptions in Coastal A zones. The use of fill for structural support and any construction of basement floors below grade are prohibited. New buildings and any substantially improved structures in coastal high-hazard areas must be located landward of the mean high tide, and any alteration of sand dunes must not result in any increased potential for flood damage in surrounding areas.

Planning at the state level is guided by the State Smart Growth Public Infrastructure Policy Act , an article within the larger Environmental Conservation Law. The act outlines criteria for public infrastructure projects that are either approved, directly undertaken, or financed by state infrastructure agencies. Among these criteria is a requirement that future public infrastructure projects mitigate future climate risk due to sea level rise, storm surge, or flood events based on available data or predictions of future extreme weather conditions. This and other criteria must be met to a practicable extent, and if deemed impracticable an agency must provide a detailed statement of justification.

The Office of Planning, Development, and Community Infrastructure within the Department of State administers several programs involved in community planning. The New York Rising Community Reconstruction Program provides recovery and resiliency planning assistance to communities affected by severe storm events, including hurricanes Sandy and Irene. The program is operated through the Governor’s Office of Storm Recovery and involves collaborations between state teams and community members to develop reconstruction plans and strategies to increase physical, economic, and social resilience, often including elements related to mitigating future flood risk. State Waterfront Revitalization Programs are also involved in community redevelopment planning. These programs establish land and water use policies and identify revitalization projects at a local level to allow for sustainable use of coastal resources, including planning for coastal flood risk resilience. Local Waterfront Revitalization Programs can also be a conduit for technical assistance and grant funding to facilitate climate change adaptation through the New York State Environmental Protection Fund grant program , a permanent fund addressing a broad range of environmental and community development needs.

The majority of stormwater regulations in New York focus on water quality issues as part of the State Pollutant Discharge Elimination System , a state program that has been approved by the EPA as part of the National Pollutant Discharge Elimination System . The program regulates point source discharges to both groundwater and surface waters and also conducts permitting for stormwater runoff from industrial activities, municipal sewer systems in urbanized areas, and construction activities. The program is administered by the state Department of Environmental Conservation.

While water quality is the focus of stormwater programs within the state, the state stormwater design manual lists best practices that include measures to reduce overbank flooding in order to maintain pre-development peak discharge rates for two and ten-year frequency storm events following development. The design manual also addresses risks due to potential floodplain expansion following development as well as green infrastructure strategies. These green infrastructure strategies are presented as a means to meet runoff reduction standards, which require that post-development conditions replicate pre-development hydrology. Stormwater projects, like all activities undertaken, funded, or approved by state agencies, are also under the purview of the State Environmental Quality Review Act , which requires preparation of an environmental impact statement if a project is likely to cause a significant increase in flood risk.

Coastal erosion in New York is managed within designated coastal erosion hazard areas. Areas are designated as per requirements of the state Coastal Erosion Hazard Areas Act , part of the larger state Environmental Conservation Law. Regulatory programs within identified hazard areas are administered by the state Department of Environmental Conservation. Programs may also be established at a local level if minimum state standards and criteria are met. The objectives of the program, as outlined in the state administrative code, are to ensure that activities in coastal areas subject to flooding minimize or prevent damage to property and natural features, that structures are placed at a safe distance from hazard areas to prevent premature damage to both structures and natural features, that public investment likely to encourage development within erosion hazard areas is restricted, and that publicly financed structures are only used when necessary and effective. Sections of the state administrative code also describe the erosion protection functions of natural protective features in order to guide the review of permit applications.

Coastal erosion management permits are required for any regulated activity conducted within a designated coastal erosion hazard area. Coastal erosion management permit standards require that any proposed activity be reasonable and necessary, with consideration of proposed alternatives, and that an activity will not likely lead to a measurable increase in erosion at the proposed site or other locations. Standards also require activities to prevent or minimize adverse effects to natural protective features, existing erosion protection structures, or natural resources such as fish and wildlife habitat.

Regulations within structural hazard areas allow for placement of movable structures, with construction restrictions, if a permit has been granted. Construction or placement of nonmovable structures is prohibited. Any public utility systems within structural hazard areas also require a coastal erosion management permit. Additional restrictions on regulated activities are present within natural protective feature areas, including nearshore areas, beaches, bluffs, primary dunes, and secondary dunes. Construction of erosion protection structures is allowed within such areas provided the structure meets permitting requirements and is designed to prevent or minimize damage to property and natural features in a cost-effective manner. Structures must be designed to control erosion on site for a minimum of 30 years.

New York has put forth several climate adaptation measures at the state level, led primarily by the state Department of Environmental Conservation. Sea-level rise projections for threatened coastal areas are currently published within the state administrative code, a recommendation from the previously convened NYS Sea Level Rise Task Force . The projections formally establish sea-level rise levels throughout Long Island, New York City, and the Hudson River, providing information based on five risk scenarios and extending out to 2100. The Department of Environmental Conservation has also formally acknowledged its role in climate change adaptation through Commissioner’s Policy 49: Climate Change and DEC Action . The policy outlines methods by which climate change considerations may be integrated into current DEC activities and programs, including making greenhouse gas reductions a primary goal, creating specific mitigation objectives for existing and future programs, incorporating adaptation strategies into programs and activities, considering climate change implications in daily department activities, and identifying specific actions to further climate change goals and objectives as part of annual planning processes. The policy goes on to establish mitigation and adaptation objectives as well as departmental responsibilities and implementation procedures.

The 2014 Community Risk and Resiliency Act (CRRA) forms the basis for a number of climate adaptation initiatives within New York from a legislative standpoint. The previously mentioned sea-level rise projections were a product of the CRRA, as the act amended the state Environmental Conservation Law to include a requirement that the DEC adopt science-based projections. The CRRA also amended additional sections of the Environmental Conservation Law to require applicants for identified funding and permitting programs to demonstrate that risk due to sea-level rise, storm surge, and flooding have been considered in project design and requires the DEC to incorporate similar considerations into facility-siting regulations. The sea-level rise, storm surge, and flood risk mitigation components of the Smart Growth Public Infrastructure Policy Act are also tied to the CRRA. The CRRA also directs the Department of State and Department of Conservation to develop model local laws that consider data-based future risk due to sea-level rise, storm surge, and flooding as well as guidance on the use of natural resources and natural processes to enhance community resilience to such hazards.

Elements of Policy Goals/Management Principles

• State management capacity is bolstered by the New York Coastal Management Program’s federal consistency review process, which requires that federal activities within the state coastal zone be consistent with the program’s enforceable policies. The New York program has 44 enforceable policies in total, with 7 specifically addressing flood and erosion hazards.
• Local governments can implement the state Coastal Management Program at a smaller scale through the Local Waterfront Revitalization Program, extending the influence of state program goals and enforceable policies.
• The enforceable policies of the state coastal management program address the protection of natural features that mitigate coastal flood risk and the use of non-structural mitigation measures where feasible.
• Shoreline setbacks must be established within identified coastal erosion hazard areas, and setbacks must be at a distance sufficient to minimize damage from erosion considering the rate of recession of coastal lands.
• Floodplain management regulations require that any new development or substantial improvement to structures in coastal areas not affect sand dunes in any way that might increase potential flood damages.
• Wetland management regulations require that structures be located a minimum of 75 feet landward from the edges of tidal wetlands, preserving natural flood risk mitigation functions.
• Sections of the state administrative code related to erosion management include descriptions of the erosion protection functions of natural features to guide permit applications, and permit standards require that erosion management activities prevent or minimize adverse impacts on natural protective features.
• The state stormwater management design manual includes information on green infrastructure strategies, which are presented as a means to meet runoff reduction standards and maintain pre-development hydrology for project areas.
• The state building code requires structures not subject to wave action to have the lowest floor elevated a minimum of one foot above the base flood elevation. This rule applies to the lowest horizontal structural members of structures that are subject to wave action.
• State regulations require that erosion protection structures in coastal areas be designed to control erosion on site for a minimum of 30 years.
• Public infrastructure projects approved, undertaken, or financed by state agencies must account for and mitigate risk due to future climate risk factors such as sea-level rise, storm surge, and flood events. Mitigation efforts must be based on available data as well as projections of future conditions.
• The state has published sea-level rise projections for threatened coastal areas within the state administrative code, formally establishing risk based on five scenarios and extending to 2100.
• Commissioner’s Policy 49: Climate Change and DEC Action identifies ways that climate change considerations could be incorporated into current state programs and activities and defines departmental responsibilities and procedures for implementing the climate adaptation goals of the policy.
• The state Community Risk and Resiliency Act formally establishes a number of climate adaptation initiatives within the state, including the requirement that the state Department of Environmental Conservation adopt science-based sea-level rise projections and that applicants to funding and permitting programs demonstrate that climate risk has been incorporated into the siting of facilities.
• The enforceable policies of the state coastal management program address the siting of buildings in coastal areas to reduce risk and well as restrictions on the use of public funds for erosion protection structures.
• One of the objectives of the state erosion management program as described in the state administrative code is to restrict public investment that could encourage development within coastal erosion hazard areas. An additional objective is to use publicly financed erosion control structures only when necessary and effective.
• The New York Rising Community Reconstruction program works to develop reconstruction plans and strategies to increase coastal community resilience following severe storm events, often involving the mitigation of future flood risk.
• The New York Coastal Management Program lists coordination of major activities affecting coastal resources as one of the program goals, and multiple state agencies are involved in implementing the program’s broad suite of enforceable policies.
• If an action requires preparation of an environmental impact statement as part of the State Environmental Quality Review Program it must also be consistent with the enforceable policies of the state coastal program, including policies related to coastal hazards.
• State wetland regulations are based on the preservation, protection, and enhancement of ecological values as opposed to acreage, with flood control and storm protection listed among the functions provided.
• The State Environmental Quality Review Program includes the potential for a substantial increase in flooding as a criteria of significance, which then triggers the preparation on an environmental impact statement for state agency activities.
• State Waterfront Revitalization Programs establish land and water use policies that incorporate coastal resilience into revitalization projects and community redevelopment planning.

View the other State Coastal Flood Risk Management Case Studies: