Flood risk in China: observed changes and variability, management, and projections

Flood risk and its reduction in China

Despite an increasing number of people exposed to flood risks in Europe, flood risk perception remains low and effective flood risk management policies are rarely implemented. It becomes increasingly important to understand how local governments can design effective flood risk management policies to address flood risks. In this article, we study whether high flood exposure and flood risk perception correlate with the demand for a specific design of flood risk management policies. We take the ideal case of Switzerland and analyze flood risk management portfolios in 18 flood-prone municipalities along the Aare River. We introduce a novel combination of risk analysis and public policy data: we analyze correlations between recorded flood exposure data and survey data on flood risk perception and policy preferences for selected flood risk management measures. Our results indicate that local governments with high flood risk perception tend to prefer non-structural measures, such as spatial planning and ecological river restoration, to infrastructure measures. In contrast, flood exposure is neither linked to flood risk perception nor to policy preferences. We conclude that flood risk perception is key: it can decisively affect local governments’ preferences to implement specific diversified policy portfolios including more preventive or integrated flood risk management measures. These findings imply that local governments in flood-prone areas should invest in raising their population’s awareness capacity of flood risks and keep it high during periods without flooding.

Flood resilience is increasingly discussed in academia and practice as a complement to existing flood risk management approaches (Fekete, Hartmann, & Jüpner 2020). It is seen as a promising concept to deal with increasingly severe consequences of climate change in general, and with increasing flood risk in particular. The debate on flood resilience is linked to the paradigm shift from flood protection to risk management, which started in Europe after the major river flood events in 1993 and 1995 along the river Rhine (Hartmann, 2012), and has developed over the past decades—pushed by further major fluvial and pluvial flood events (Begum, Stive, & Hall, 2007; Hartmann & Juepner, 2014; Klijn, Samuels, & van Os, 2008; Patt & Jüpner, 2020). However, in flood risk management, the academic debate on resilience is only in its infancy (Jüpner et al., 2018; Vis, Klijn, Bruijn, & Buuren, 2003). Many different definitions exist (Disse, Johnson, Leandro, & Hartmann, 2020). Especially when it comes to specific implementation of resilience, the vagueness of the concept—which is sometimes described as one of its strengths (Baggio, Brown, & Hellebrandt, 2015; Brand & Jax, 2007)—can present a problem. How to design a resilient hydraulic infrastructure? This question has not only technical but also concerned with financial and legal aspects. This becomes more complicated when individual protection measures are put in a context of a larger system, such as a city or a region. When and how is a system such as a city or a region resilient, and how does one measure resilience? These questions are important, not only for construction but also for legal (such as liabilities), financial (budgetary), and political reasons. In other words, resilience is not (yet) a ready-to-use concept in flood risk management. Resilience challenges presumptions of traditional flood risk management in many ways. Resilience implies that more and different stakeholders and actors will be involved in flood risk management than before, such as landowners or spatial planners. Hitherto, flood risk management has been and still is mainly the domain of water management (Hartmann & Driessen, 2017), although the prevalence of the traditional civil engineering approach has been questioned before (van den Brink, 2009). This change is not positive for all actors—affected homeowners, but also city planners or mayors now must deal with questions that were previously outside of their realm of competence and responsibility. From a flood risk management perspective, many questions arise, such as: How does resilience add to and change the existing flood risk management system? How can resilience contribute to a more effective and efficient flood risk management approach? What are the specific advantages of integrating resilience in flood risk management? How can resilience be measured and quantified? Which parameters are most relevant? This special collection brings together contributions from different disciplines that address the specific challenges of implementing resilience in flood risk management. The special collection takes the European debate as a starting point. The European Floods Directive from 2007 (2007/EC/60) pushed the debate on flood risk management and resilience in Europe. This Directive established a legal frame on how countries in the European Union have to deal with flood risk for the first time (Hartmann & Jüpner, 2014). At the same time, the shift toward a risk-based approach raised questions such as "what can happen?" "what must not happen?" and "which security level can be realized at which costs?" Ultimately, flood risk management replaces the paradigm of complete protection against floods with the idea of managing the risk (Grünewald, 2005). This makes approaches to resilience and the reduction of damage potential (vulnerabilities)—not only for river floods but also for pluvial rainfall—important. The first three papers in this collection highlight the necessity and consequences of defining the concept of resilience. In their opinion paper, Fekete, Hartmann, and Jüpner (2020) point out that resilience is indeed a trend that neither can nor should be ignored in flood risk management, rather than it should be embraced—with a caveat: the concept is still not exactly defined and cannot be understood as a panacea for all shortcomings and challenges of flood risk management. So, is resilience merely a new buzzword? Dewulf et al. (2019) discuss the power and impact of defining resilience and therewith unravel the political-normative notion of flood resilience as a concept. This illustrates that, with flood resilience, flood risk management turns much more strongly towards social and political science than ever before. Discussing resilience and its definition is thus a crucial step toward successfully implementing it in flood risk management. In her advanced review, Rodina (2019) reveals different notions of resilience in different disciplines when taking on a broader view of the concept (i.e., not solely focusing on flood risks). She concludes that participation and stakeholder involvement are important components of resilience—a theme that is picked up in the next section of this special collection as well. So, though this article had not been part of the original set-up of the special collection, the conclusions are highly relevant for implementing flood resilience in flood risk management. Resilience requires more action by homeowners and citizens. All papers in this section of this special collection leave no doubt about that. Snel, Witte, Hartmann, and Geertman (2020), however, start with a very critical point of departure, namely that many publications on homeowner and citizen involvement do not seem to question if this involvement is necessary. The paper unravels the arguments that are prevalent in the academic debate for more involvement of homeowners in flood resilience, which supposedly comes along with a shift towards flood governance. Four types of main arguments are identified and discussed in the paper. Kuhlicke and the multidisciplinary team of authors writing on the behavioral turn in flood risk management (Kuhlicke et al., 2020) discuss in detail three underlying assumptions of increased involvement of citizens in flood risk management: the motivations of citizens, the effectiveness of measures, and capacities of citizens. In this vein, Rufat et al. (2020) discuss in their opinion paper need for a more nuanced debate on the link between flood risk perception and risk-mitigating behavior. Attems, Thaler, Genovese, and Fuchs (2020) then provide an overview of the measures that homeowners can take to enhance resilience by using property-level flood risk adaptation (PLFRA) measures. The paper confirms that such measures can indeed be an appropriate addition or complement to flood risk management. The third group of papers in this special collection addresses the issue of measuring and communicating resilience. The need for this comes not only from hydraulic engineering but also from the need to communicate about flood risk with homeowners and citizens, as they have to become more involved (as the earlier papers in this special collection clearly show). Pohl (2020) views resilience from a hydrological as well as a hydraulic engineering perspective and outlines what it means to include the concept in flood risk management. In particular, the contribution points out the difficulties of embedding resilience as a design criterion in hydraulic structures. Pohl concludes that—though the fuzziness of resilience is appreciated by some social scientists as a "boundary concept" (Baggio et al., 2015)—hydraulic engineering and hydrology inevitably require some quantifiable measurement of resilience. Fekete (2019) elaborates in his paper how cascading effects and critical infrastructure matter for flood resilience. It thereby shows how flood resilience with this perspective extends existing flood risk management approaches. Cascading effects of critical infrastructure can substantially affect the measurement of flood resilience. Schmitt and Scheid (2020) discuss the need for better risk communication and discuss approaches by focusing on pluvial floods. In particular, they show how a rainstorm severity index may supersede the communicative capacity of statistical rainfall parameters in the communication with nonexperts especially. In conclusion, the contributions in this special collection show how the concept of resilience is advancing flood risk management but also point out some crucial changes and challenges that flood resilience as a concept brings to the practical implementation of flood risk management. It seems inevitable that homeowners especially will play a much more fundamental role in flood resilience, which raises needs for measuring and communication of flood resilience. Along with this shift in flood risk management, the papers illustrate that flood resilience puts flood risk management in a hitherto unknown domain for many water managers, as flood resilience means embracing social and political science. Embedding flood resilience into flood risk management becomes a balancing act—on the one hand, resilience is a political and normative concept, but on the other hand, it needs to be implemented with concrete steps designed via civil engineering and hydrology. This tension is still unsolved and remains a dilemma in implementing flood resilience.

Central-Eastern European (CEE) post-communist member states of the European Union have experienced several catastrophic floods during the last two decades, resulting in further discussions on implementation of the European Flood Directive (EC in Directive on the assessment and management of flood risks. European Community 2007). A particular issue being discussed is the level of public involvement in flood risk reduction because these countries are burdened by former highly centralized policy resulting in certain specifics in flood risk perception by the public, stakeholders and authorities. Through this paper, we try to fill the gap in current understanding of limits in flood risk reduction in CEE countries by analysing the current research on flood risk perception. We reviewed 19 studies published between 1990 and 2014 that were analysed regarding determinants of flood risk perception and the role of individual and public involvement in flood risk reduction. Although the research agenda itself seems to reflect the current trends in Western Europe, the results display significant differences. Based on our analysis, we argue that the path dependencies in flood risk perception in CEE countries results in a “thin” concept of flood risk reduction. This concept can be characterized by (a) considering risk reduction as a temporary event rather than a process, (b) a reductionist view on risk reduction measures with prevailing financial tools and (c) strong reliance upon the regional and national authorities in terms of both the risk communication and prevention measures. This gives an impetus for further research on tailor-made strategies to overcome these limits and facilitate the implementation of the European Flood Directive.

Italy is particularly vulnerable to water-related disasters (flooding, landslides, drought) and to other related phenomena, such as soil and coast erosion, which affect land and human activities. Traditional strategies to face water-related hazards were based on structural measures, aiming at land reclamation by drainage networks, at soil conservation by agricultural and forestry practices and at flooding defence by hydraulic works such as structures against overflow and inundation (river banks, diversions) or for flood routing. The land transformation due to the growth of urbanized areas and infrastructures and the likely effect of climate change have increased the flood risk, while the structural measures began to be considered insufficient and costly and to be criticized for environmental reasons. Thus, non-structural measures such as constraints on land use, early warning systems and better information to increase public awareness and behavioural responses to floods have been emphasized. In this chapter, basic concepts of flooding risk and measures for its reduction are discussed. The most severe flooding disasters which occurred after the unification of the country (1861) and the development of policy about the flood risk reduction are analyzed. Then, a synthesis of flood hazard and risk assessments in Italian regions is presented. Finally, an attempt is made to identify priorities and trends to improve flood disaster resilience.

After 29 years of the largest flood event in modern times (with the highest recorded rainfall rate at the Iberian Peninsula with 817 mm in 24 hours), the municipality of Oliva faces the challenge of mitigating flood risk through the development and implementation of a local action plan, in line with other existent and ongoing structural measures for flood risk reduction. Located 65 km from Valencia, on the South-Eastern coast of Spain, Oliva is affected by pluvial, river and coastal flooding and it is characterized by a complex and wide-ranging geography and high seasonal variation in population. A quantitative flood risk analysis has been performed to support the definition of flood risk management strategies. This paper shows how hazard, exposure and vulnerability analyses provide valuable information for the development of a local action plan against flooding, for example by identifying areas with highest societal and economic risk levels. It is concluded that flood risk management actions, such as flood warning and monitoring or evacuation, should not be applied homogenously at local scale, but instead actions should be adapted based on spatial clustering. Implications about the impact of education and training on flood risk reduction are also addressed and discusse

This chapter presents all-important discussions relating to flood risk analysis which arguably is a subject of overwhelming significance within the context of less developed societies, for example Nigeria. Whilst a possible means of eradicating flooding from human environment is inconceivable, debates for more effective flood risk reduction methodologies for critical infrastructure protection must continue. Increased population and urbanisation scenarios drive worsened flood risk which trigger increased efforts for corporate adaptability to flooding. To ensure that social systems can cope with floods, it is important to investigate why best practices in flood risk reduction are not fully applicable. This chapter explores these issues drawing from extant dialogues on flood risk management (FRM). Arguably, the current flood modelling techniques and assessment of vulnerability operations largely do not support a realistic analysis of flood risk. Funnelled through an interpretative research paradigm, the chapter conceives that these limitations fall under five cardinal issues – (1) data, (2) theories and concepts, (3) existing flood risk analyses methods, (4) legislation and policy, and (5) sustainable development. It argues that the realisation of a more effective flood risk reduction for the poorer and less developed societies will depend on effective tackling of these issues which creates opportunities for flood risk analyses through simplified approaches, and use of free and open geospatial data infrastructure.

Flood can be assessed through flood vulnerability, risk, and susceptibility analysis using remote sensing, geographic information system, and hydrological modelling. In this chapter, different stages, complexities, and processes of flood vulnerability, risk, and susceptibility assessment were discussed. The study reveals that flood vulnerability should be assessed based on four aspects: physical, social, economic, and environmental. Flood risk should be assessed by three stages: risk analysis, disaster relief, and preparedness, whereas flood susceptibility assessment involves three processes. Overall, it was found that the responsible factors vary as per the local conditions, which need to be carefully analyzed and selected. Furthermore, the role of remote sensing and geographic information system in flood risk management were found important especially in flood risk mapping and in the selection of responsible flooding factors.

Understanding urbanization and its impact on flooding and flood risk is crucial to better manage flood risk in the future. This study analyzed land use/land cover changes and how urbanization would impact flooding and flood risk in Kathmandu Valley of Nepal, and assessed flood risk by integrating flood hazards based on hydrologic–hydraulic modeling with the Analytic Hierarchy Process-based Multi-Criteria Decision Analysis (AHP-MCDA) approach. Land cover maps for past years were generated using Landsat satellite images, and land use/land cover maps for future years were projected based on machine learning techniques. Flood simulations were conducted using a rainfall runoff inundation model with land cover maps for different flood scales to analyze the impact of urbanization and land cover changes on flood runoff, flood inundation extent, and flood inundation volume. Then, we comprehensively assessed flood risk by integrating hazard conditions simulated under different land cover conditions using a hydrologic–hydraulic model and the AHP-MCDA approach. The results showed that the flood inundation extent and the peak inundation volume for a 200-year flood may increase in the future by 10.66% and 15.04%, respectively, as a result of urbanization. The results also highlighted that urbanization may lead to an expansion of high-risk and very-high-risk areas in the future by 3.2% and 9.4%, respectively, indicating an increase in the valley’s flood vulnerability and greater severity of flood hazards.

Water related natural hazards and climate change issues such as flood has become a serious threat to the lives, livelihoods and sustainable development of Bangladesh. Chilmari Upazila of Kurigram district which is one of the most seriously flood affected areas of Bangladesh has been taken as the study area. Bangladesh is already known as a role model for flood risk management around the world. But, the situation of flood management is not the same all around the country. The objectives of this study are to find out the main problems of the flood control and risk management system of Chilmari Upazila, and to develop a planning intervention guideline for its flood control and risk management. The interactive approach of the study involves participation of the stakeholders to develop local solutions to the flood problems. The empirical part of this study is conducted by household questionnaire survey and semi-structured in-depth interviews with questions regarding flood control and risk management. Main findings of the study state that the floods in Chilmari are managed in ad hoc manner. A coordinated and comprehensive management approach along with strong institutional framework is very important for sustainable flood control and risk management at Chilmari. Journal of Bangladesh Institute of Planners, Vol. 8, Dec 2015, pp. 111-121

This study applied the interaction of social vulnerability and hazard to assess flood risk in three urbanized areas within the Pasig‐Marikina‐Laguna‐Lake catchment: Manila, Marikina, and Parañaque in Metro Manila, Philippines. This study examined risk patterns across different flood return periods (5, 50, and 100 years) in these urban river environments and provided both city‐wide and localized risk assessments. The social vulnerability to flood index (SVFI) was calculated using socioeconomic indicators, while the hazard index was derived from flood depth categories. Results show that city‐level risk indices are low to moderate, with Marikina consistently having the highest risk, followed by Manila and Parañaque. However, localized assessments reveal high‐risk areas within cities, with Manila being the most vulnerable to frequent floods (5‐year return period) and Marikina to less frequent but extreme events (50‐ and 100‐year return periods). Parañaque maintains the lowest risk profile across all scenarios. This study highlights the importance of considering both citywide trends and localized high‐risk areas in flood risk management. It provides valuable insights for disaster management planners and policymakers, enabling the development of targeted strategies for sustainable urban river management and flood risk reduction in rapidly urbanizing river systems. The methodology presented applies to other urban areas that face similar flood risks.

The Northland river is characterised by having a short stream and large catchments. Heavy rains in the region trigger the rapid rise of the water levels and causes flooding, affecting the urban community in the flood plain with flash floods and river overflow as double threats. The government-initiated programs to protect urban communities such as ‘predict and mitigate’ but primarily focuses on physical infrastructure protection. While providing infrastructure is beneficial, developing a resilient community comprises more holistic strategies. There is a need for improving the local capacity to enhance resilience. A resilient, human-focused mitigation strategy which includes the affected communities, as well as the existing infrastructure, can reduce flood risks more efficiently. This paper explores the ways the Northland communities follow to mitigate existing flood risks, including their perceptions of the current flood protection strategies. This study investigates also the social and cultural elements that influence responses to flood risks. The main recommendation, of the study advocates a community-based risk management plan to complement the government’s strategy to efficiently mitigate flood risk in the urban Northland.

Local developer and local government actions have implications for Flood Re. • Local government investment in SUDS

In previous assessments of UK flood risk, flood hazard has often been poorly represented by low skill models. Meanwhile, assessments of future flood risk have lacked a detailed representation of future flood exposure. This study represents a significant step forward in both flood hazard and future exposure representation. Using a state-of-the-art climate-conditioned hydrodynamic model for fluvial, pluvial and coastal flooding paired with the latest UK shared socioeconomic projections of population (UK-SSP), we explore how climate-induced changes in flood hazard interact with increasing exposure due to population changes. Using a detailed exposure dataset, we are also able to explore discrepancies in current and future flood risk between residential property types.Our model values current yearly residential economic floods losses at £894 million, with fluvial flooding accounting for approximately 75% of these. This flood risk is not borne equally between the devolved British nations, however. In Scotland and Wales approximately 30% of local authorities have over £100 of annual flood losses per property, whereas only 4% of local authorities in England experience such levels. There are also significant discrepancies in flood risk by property type. Flats and terraced housing experience almost twice the rate of yearly inundations than detached and semi-detached housing. Under a high emissions climate scenario (RCP 8.5), by 2070 we estimate flood risk will increase by 29% whilst under a low emissions scenario (RCP 4.5) flood risk will increase by 10%. Similarly to current flood risk, these increases too are not borne equally across regions and property types.Whilst climate change is set to drive an increase in flood risk over the next 50 years, our study suggests that population dynamics may have potential for offsetting relative flood risk rises. In all SSP projections studied here (SSP1, SSP2 and SSP5), an increase in population drives an increase in the yearly rate of property inundations. As such, the highest increases in flood risk due to population change are seen in SSP5 (+50%). However, due to population growth predominantly occurring in low flood risk areas, relative flood risk decreases most in SSP5 (-10%). Similar changes, although smaller in magnitude, are seen under SSP1 and SSP2. Despite these decreases in relative flood risk due to population change, when paired to climate change, we still see significant increase in flood risk over the next 50 years. Consequently, low emissions scenarios, such as SSP1/RCP2.6, see the lowest increases in flood risk by 2070 (+5%). These results show a clear need for climate change mitigation actions in order to limit flood risk increases. However, this study presents a promising signal where population growth may limit the burden of increased flood risk, due to climate change.

Flood risk management is shaped by complex feedbacks between hydrological processes and social responses, yet many existing sociohydrological models treat society as a homogeneous entity. This study develops a hierarchical sociohydrological model that explicitly represents socioeconomic heterogeneity by incorporating multiple disaster-vulnerable social groups. The study area is divided into three groups based on topography and socioeconomic characteristics, and group-specific dynamics are modeled by accounting for population movements within and beyond the region, as well as differences in flood memory loss, preparedness levels, and mobility. Key model parameters are estimated using household survey data collected in San Mateo City, the Philippines. Using this empirically grounded model, we evaluate the impacts of alternative flood management strategies through numerical simulations, focusing on variations in levee height and the frequency of disaster preparedness education. The model is applied to contrasting policy scenarios with and without levee protection to assess their differential effects on flood losses across social groups. The results reveal that under a no-levee scenario, flood losses become increasingly uneven over time, with widening disparities among social groups, indicating the amplification of social inequality. In contrast, levee-based scenarios reduce inter-group disparities in cumulative flood losses; however, they also lead to substantially larger losses per event when extreme floods occur. These findings highlight a trade-off between reducing chronic inequality and increasing vulnerability to rare but catastrophic events. By explicitly integrating socioeconomic heterogeneity into sociohydrological modeling, this study demonstrates the importance of distributional analysis in flood risk assessment and adaptation planning. The proposed framework provides a quantitative basis for evaluating equity–efficiency trade-offs in flood management policies and supports the design of more just and effective flood adaptation strategies.