Impact-Based Decision Making in Flood Risk Management: A Review of Behavioral and Technical Approaches

Managing flood risks in a changing climate

The construction of flooding and flood risk management are complex and there is potential for dissonance between individual and institutional understanding and experience of both. In this article, we start by investigating how flooding is managed and the change in paradigm from flood defence to more adaptive approaches, which embed resilience into flood risk management. Using analysis of semi‐structured interviews with members of the flood authorities in England, we explore how flood management authorities construct ‘flooding’ and establish that it is often defined by in‐the‐moment impacts. Whilst these in‐the‐moment impacts are understood to be devastating, there is less appreciation of long‐term human impacts of living at risk of flooding. We uncover how the construction of ‘flood risk management’ by the flood authorities is complicated by factors, such as the construction of resilience, availability of funding, technical expertise and responsibility fragmentation that the Floods and Water Management Act (2010) has created. We conclude that the differing constructions of flooding and flood risk management between flood management authorities in England hinder how flooding is managed. Therefore, we propose that a more nuanced understanding of flooding and flood risk management is essential for effective partnership working between flood risk management authorities and communities.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU

Floods cause distress and damage wherever and whenever they happen. Flooding from rivers, estuaries and the sea threatens many millions of people worldwide and economic and insurance losses from flooding have increased significantly since 1990. Across the European Union, flood management policy is changing in response to the EU Directive on the assessment and management of flood risks, which requires a move from flood protection and defence to comprehensive flood risk management. Flood Risk Management: Research and Practice includes about 200 contributions from the international conference FLOODrisk 2008 (Oxford, UK, 30 September – 2 October 2008). FLOODrisk 2008 was an initiative of the FLOODsite research project on Integrated Flood Risk Analysis and Management Methodologies. FLOODsite was a major “Integrated Project” in the European Commission Sixth Framework Programme; contract number GOCE-CT-2004-505420. The conference provided a forum for leading researchers, flood risk managers, policy makers and practitioners from government, commercial and research organisations to gain an overview of advances in this important subject. Flood risk management practice crosses several professions and disciplines and these are represented in the breadth of the scope of the conference and these proceedings. The conference covered all aspects of flood risk: the causes of floods, their impacts on people, property and the environment, and portfolios of risk management measuresm, while the principal themes included: climate change, estimation of extremes, flash floods, flood forecasting and warning, inundation modelling, systems analysis, uncertainty, international programmes, flood defence infrastructure and assets, environmental impacts, human and social impacts, vulnerability and resilience, risk sharing, equity and social justice, and, civil contingency planning and emergency management. Flood Risk Management: Research and Practice will be of interest to an international readership, ranging from authorities, consultants and engineers involved in flood management; researchers, post graduate lecturers and students, to policy makers, particularly at national level.

This study reviewed some of the challenges faced by local authorities in disaster management, especially flood disasters that occurred in Malaysia. Flood disasters are the most frequent disasters in Malaysia, especially during the monsoon seasons. The hard structure developed by Malaysia’s National Security Council (MKN) under ‘Directive 20’ is used to manage disasters in the country. Although Malaysia has become more skillful in managing flood disasters, the frequent climate changes along with weakness in implementing flood risk management plans resulted in much losses and damages throughout the country. Therefore, this study explored the gaps and weaknesses in flood risk management (FRM) in Malaysia by reviewing the available literature to recommend better flood management. This study revealed four main issues which are weaknesses in terms of (i) coordination and communication, (ii) manpower and assets, (iii) public awareness, and (iv) power and authority among local authorities to implement flood management plans. The capacity of local authorities and individuals in charge of disaster management is inadequate, especially for flood risk preparedness and management. Hence, responsible individuals are also in a vulnerable situation to implement management plans or rescue operations when flood disasters occur since they are also flood victims. Thus, the National Disaster Management Agency (NADMA) which acts as the main coordinator of disaster management in Malaysia should re-examine the flood management plan to ensure that it can be implemented efficiently and effectively, especially at the local level as they are the first respondents on the scene when the disaster occurs. The combination of both structural and non-structural measures might require in many cases the management of flood disasters; however, the disaster risk preparedness and management of individuals via customized training is a must to prevent flood disasters as well as minimize their impact. The flood management plan should also incorporate natural-based approaches at the whole-river-basin level for the long-term solution and sustainable development, not only focusing to manage the localized flood problem at the specific area.

On 27 June 2006 the Council of the European Union reached political agreement on a draft directive on the assessment and management of flood risks. This directive prescribes approaches and procedures which should be met by the member states. The website of the EU on this directive links to another EU‐initiative, the Integrated Project FLOODsite, which aims at providing methodologies for flood risk analysis and management. Obviously, the directive and the IP emerged in a common but much larger context of public and scientific debate on a more integrated and coordinated approach to dealing with flood risks. In this paper we briefly discuss this context and examine a few national cases in order to find out whether flood risk management is already common practice or is still in its infancy, or whether it involves merely good intentions. We base this examination primarily on our experiences within FLOODsite and on presentations held within the special session on River Flood Risk Management which was organised by The Netherlands Centre for River Studies (NCR) during the ISDF3 conference in May 2005. This paper goes into the similarities and differences between some national approaches and tries to place them in a cultural context. It appears that the seemingly most sophisticated management policies do not automatically imply the most comprehensive flood risk management approach. But the intention to evolve from flood management into flood risk management is evident and promising.

Flood risk management has become more significant in the face of rapid urban development and the climate change. Many governments and the decision makers have recognized the requirement of resilient flood management policies and strategies for sustainable urban development. During the recent decades, various conceptual framework of flood risk assessment and management emerged and they in turn questioned the characterization of resilience in flood risk management. More recently, research on flood risk management and spatial planning have demonstrated a common discussion platform appreciating the concept of flood resilience in policy and strategy making. However, assessment and operationalization of flood resilience is often questionable due to its conceptual vagueness. The present work is a review of the plurality views of flood resilience. Resilience thinking has moved the focus of flood risk assessment towards vulnerability. Flood resilience embeds the incorporation of spatially distributed land use policies and regulations which are a must for the management of flood vulnerability. Spatial planning reflecting flood resilience becomes vital when managing the uncertainty incorporated with flood risk management. However, the operationalization and legitimacy of the importance of the combined role of spatial planning and flood risk management with stakeholder acceptance still remains implicit and weak.

As the number of COVID19 cases is increasing again in Europe and other areas, the interest in flood risk management is declining. The public and politicians are occupied by more urgent issues, such as health, income, and employment. Especially in countries where the last flood occurred long ago, like the Netherlands, the issue of flood risk management may be moved down on the list of priorities. However, it remains important to continue improving the knowledge on assessing flood risks and developing and evaluating flood risk management strategies. If not, risks may increase, and opportunities for measures may be lost. Climate change will increase flood risks if no counteractions are taken (Haasnoot et al., 2020). Ice sheets are melting faster than anticipated, increasing coastal flood hazards; extreme weather events, and river floods may occur more frequently and become more severe. This may require drastic changes in our flood risk management strategies in the long term. Such changes need time and require debate among scientists, especially policymakers and society. They may also become increasingly difficult by today's decisions, which lock-in our current strategy. Much money is spent on flood risk management, not only after flood events on repair and recovery but also for flood protection. To make sure this money is spent wisely and to prevent regret from having made the wrong decisions, improved flood risk analyses and new approaches to flood risk management are needed. The COVID19 crisis may teach us things about crisis management that may also be useful for flood risk management. Although floods are very different from pandemics, important lessons can be learned, for example, on what is vital and must continue functioning (e.g., schools, health care), on how experts and politicians should or could best work together (sharing responsibilities), on the need of involving all relevant stakeholders when taking decisions, and on communication. The crisis reveals societies' abilities to join forces and take care of each other, as well as their innovative capacities, which results in workable alternatives for shortages in supplies, increased hospital capacity, and adapted procedures that allow opening of buildings and participating in activities in a safer way. These contribute to society's resilience to cope with the pandemic and will also contribute to its recovery in the future. Societal resilience is also crucial in flood risk management. Resilience has been applied to flood risk management for about two decades already (Vis et al., 2003; De Bruijn, 2004). Recently, its popularity has become overwhelming, especially because it has been adopted by three important global post-2015 agendas: The Sustainable Development Goals (SDGs), The Sendai Framework for Disaster Risk Reduction, and the Paris Agreement under the United Nations Framework Convention on Climate Change (IPCC, 2012). Furthermore, resilience is promoted by scientific communities (especially The Resilience Society, but also by the International Conference on Flood Management [ICFM7], who made it the leading concept in 2017) and picked up by many regional and national authorities (e.g., the ADB and EU (ADB, 2014; EU, 2013), the 100 Resilience City programme of the Rockefeller foundation (ARUP, 2014), and the Netherlands' Delta Program (MOIE, 2015). There is thus a broadly shared vision that enhancing resilience is needed. However, there is no common understanding on what precisely implies enhancing resilience. Resilience has been defined in different ways, varying from very narrow as “the ability to recover from a response to disturbance such as a flooding” to very broad as: “the ability to cope with disturbances and changes by avoiding or minimizing impacts and having the ability to learn and adapt in order to remain resilient into the future”. Lately, it appears to have become an umbrella concept, covering almost everything that was previously covered by “sustainability” and including adaptation (adaptive management) and transformation (DHS, 2008). Although the resilience concept has been used in many ways, this does not mean it is only a buzzword. As the popularity of the word already shows it covers something that was felt to be missing before. In flood risk management, decisions are often based on risk analysis. These risk analyses could, in theory, include potential impacts that are relevant to society. However, they are often simplified and focused on direct impacts corresponding with maximum flood depths with a certain probability of exceedance. Sometimes, business interruption of flooded companies and fatality risk are also included, but all other indirect and non-monetary impacts are generally excluded. As the analyses focus on maximum water depths only and not on the whole chain of events leading to those water depths, measures which do not directly affect that water depth cannot be easily considered. Specifically, measures aiming to increase warning time, improve effective emergency response, enhance recovery, or build differently or, elsewhere, reduce future risk increase are often not considered. Such a limited application of risk analysis may lead to suboptimal choices of measures. Moreover, science favours presenting integrated risk numbers, whereas laypeople do not perceive risk from small-probability catastrophes as similar to risk linked to frequent small-impact events. The very extreme events may seem irrelevant for the total risk, but they may be considered relevant by decision-makers if their potential effects would be shown to them. Although the insurance industry considers the entire flood loss curve, most flood risk analyses give only a single risk number. This number does not reveal deep uncertainties and potential surprises that may occur and their effects (Merz et al., 2015). Finally, flood risk management is still often the responsibility of water authorities, while a more comprehensive and tailored approach towards society would require the engagement of citizens, industries, critical infrastructure operators, and local governments. They are the ones that should benefit from improved flood risk management and, therefore, should be engaged, and they could contribute, although they may not have the full picture. As learned from the COVID19 crisis, to cope with a hazard, engagement of all actors is needed. Adopting resilience means being willing to address more aspects than usually addressed in flood risk analyses and developing comprehensive strategies that enable societies to cope with hazards of all magnitudes. Resilience analysis involves analysing the response of systems to extreme events (e.g., of cities, countries or societies, also including flood management infrastructure such as embankments or barriers), a response that cannot be expressed “only” by euros per year but should reveal the response to both frequent and very rare events, the effect on economy, well-being, and all that matters to society during the event, not only in its aftermath and during recovery but also in the long term. Furthermore, adopting resilience as a guiding principle for the design of future strategies may lead to a different starting point: The hazardous events are not considered central but the society and its most important characteristics and developments. What putting resilience into the practice of flood risk management means is still to be decisively established. Research on this is intensifying but still struggles making things practical. The adoption of a number of guiding principles may be of help in this regard (De Bruijn et al., 2017). Principles such as “applying a systems approach” (vs. local optimization) (Vorogushyn et al., 2018), “also consider beyond-design events and how to cope with such events”, “assess what must remain functioning” instead of only what damage is expected, “assess the recovery capacity” of a society, and identify trends and developments that may affect or offer opportunities to strengthen “future resilience” are mentioned. To really put these into practice, better indicators, examples, tools methods, and evaluation criteria are needed. Equity (in space, between groups, and between generations) may, next to cost–benefit ratios and effects on nature, be included more often, as covered by the term inclusive green growth. A focus on resilience thus changes our mindset from quantification of risk to understanding system behaviour and societal needs under a full range of possible events and prolonged time scales. This requires elaborating existing approaches and developing new approaches aimed at enabling societies to cope with flood hazards now and in the future.

A comparative analysis on flood risk assessment and management performances between Beijing and Munich

This paper develops the concept of flood problem framing to understand decision-makers’ priorities in flood risk management in the Los Angeles Metropolitan Region in California (LA Metro). Problem frames shape an individual’s preferences for particular management strategies and their future behaviors. While flooding is a complex, multifaceted problem, with multiple causes and multiple impacts, a decision-maker is most likely to manage only those dimensions of flooding about which they are aware or concerned. To evaluate flood decision-makers’ primary concerns related to flood exposure, vulnerability, and management in the LA Metro, we draw on focus groups with flood control districts, city planners, nonprofit organizations, and other flood-related decision-makers. We identify numerous concerns, including concerns about specific types of floods (e.g., fluvial vs pluvial) and impacts to diverse infrastructure and communities. Our analyses demonstrate that flood concerns aggregate into three problem frames: one concerned with large fluvial floods exacerbated by climate change and their housing, economic, and infrastructure impacts; one concerned with pluvial nuisance flooding, pollution, and historic underinvestment in communities; and one concerned with coastal and fluvial flooding’s ecosystem impacts. While each individual typically articulated concerns that overlapped with only one problem frame, each problem frame was discussed by numerous organization types, suggesting low barriers to cross-organizational coordination in flood planning and response. This paper also advances our understanding of flood risk perception in a region that does not face frequent large floods. Significance Statement This paper investigates the primary concerns that planners, flood managers, and other decision-makers have about flooding in Southern California. This is important because the way that decision-makers understand flooding shapes the way that they will plan for and respond to flood events. We find that some decision-makers are primarily concerned with large floods affecting large swaths of infrastructure and housing; others are concerned with frequent, small floods that mobilize pollution in low-income areas; and others are concerned with protecting coastal ecosystems during sea level rise. Our results also highlight key priorities for research and practice, including the need for flexible and accessible flood data and education about how to evacuate.

Confronting complexity

River flooding is a serious hazard in the UK with interest driven by recent widespread events. This paper reviews different approaches to flood risk management and the borders (physical, conceptual and organisational) that are involved. The paper showcases a multi-method approach to negotiating flood risk management interventions. We address three fundamental issues around flood risk management: differences and similarities between a variety of approaches; how different approaches work across borders between professionals, lay people, organisations and between different planning regimes; and, whether the science evidence base is adequate to support different types of flood risk management. We explore these issues through a case study on the River Tweed using Q methodology, community mapping and focus groups, participatory GIS, and interviews, which enabled co-production of knowledge around possible interventions to manage flooding. Our research demonstrated that excellent networks of practice exist to make decisions about flood risk management in the Scottish–English borders. Physical and organisational borders were continually traversed in practice. There was an overwhelming desire from professional flood managers and local communities for an alternative to simply structural methods of flood management. People were keen to make use of the ability of catchments to store water, even if land needed to be sacrificed to do so. There was no difference in the desire to embrace natural flood management approaches between people with different roles in flood management, expertise, training or based in different locations. Thus conceptual borders were also crossed effectively in practice.

Abstract. Flood estimation and flood management have traditionally been the domain of hydrologists, water resources engineers and statisticians, and disciplinary approaches abound. Dominant views have been shaped; one example is the catchment perspective: floods are formed and influenced by the interaction of local, catchment-specific characteristics, such as meteorology, topography and geology. These traditional views have been beneficial, but they have a narrow framing. In this paper we contrast traditional views with broader perspectives that are emerging from an improved understanding of the climatic context of floods. We come to the following conclusions: (1) extending the traditional system boundaries (local catchment, recent decades, hydrological/hydraulic processes) opens up exciting possibilities for better understanding and improved tools for flood risk assessment and management. (2) Statistical approaches in flood estimation need to be complemented by the search for the causal mechanisms and dominant processes in the atmosphere, catchment and river system that leave their fingerprints on flood characteristics. (3) Natural climate variability leads to time-varying flood characteristics, and this variation may be partially quantifiable and predictable, with the perspective of dynamic, climate-informed flood risk management. (4) Efforts are needed to fully account for factors that contribute to changes in all three risk components (hazard, exposure, vulnerability) and to better understand the interactions between society and floods. (5) Given the global scale and societal importance, we call for the organization of an international multidisciplinary collaboration and data-sharing initiative to further understand the links between climate and flooding and to advance flood research.

Climate change, urbanization, and inadequate infrastructure exacerbate urban flood risks, yet one critical factor remains largely overlooked: hazardous debris such as cars, construction materials, wood, plastic containers among others. In the Valencia 2024 flood alone, the Spanish Insurance Compensation Consortium reported about 144,000 vehicles damaged or destroyed, many of them mobilized by the flow, which demonstrates the scale of large‐debris impacts during floods. Debris alters and intensifies flooding impacts by clogging drainage systems and streets, decreasing flow conveyance, and causing direct damage to infrastructure, lives, and ecosystems. Nevertheless, debris dynamics are largely absent from flood risk assessments and management strategies. This Commentary highlights the urgent need to integrate debris considerations into urban flood planning and emergency response. Using case studies from recent catastrophic floods, we illustrate how debris amplifies hazard. We explore emerging scientific insights into the influence of debris in different flood types (flash, fluvial, coastal, tsunamis), and discuss why current management strategies fail to incorporate this factor. A solution‐oriented roadmap is possible and we propose an actionable strategy toward the integration of debris into flood risk management, contributing to adapting cities toward higher levels of safety and resilience.

This research explores the application of Geographic Information Systems (GIS) as a sustainable urban planning tool for flood management in the Gampaha District of Sri Lanka. It addresses the challenges posed by rapid urbanisation and increased flood vulnerability, where traditional approaches have proven inadequate in the face of complex urban development patterns and climate change impacts. While previous research has established GIS's potential in flood risk assessment and management, its application for sustainable urban planning and flood management in Gampaha District remains underexplored. This study aims to fill this gap by demonstrating GIS's effectiveness in enhancing flood management practices in the area. The research employs a mixed methods approach within a case study strategy, combining qualitative and quantitative approaches. Data collection relies on secondary sources. Analysis methods include thematic, content, and GIS-based spatial analysis using ArcGIS Pro software. Key findings reveal a strong correlation between urbanisation patterns and increased flood events in Gampaha District. The study identifies specific flood management challenges, including inadequate drainage infrastructure, encroachment on flood plains, and geographical and environmental vulnerabilities. GIS analysis provides detailed flood risk mapping with a model and identifies optimal locations for sustainable infrastructure development using the multi-criteria decision analysis (MCDA) method. The research contributes to the existing body of knowledge by offering a model that integrates GIS tools for mapping, risk assessment, and strategic planning to mitigate flood risks in rapidly urbanising areas. It provides evidence-based recommendations for enhancing flood resilience through sustainable urban planning practices such as wetland restoration, permeable pavements, rain gardens, urban forests, and floodwater pumping stations. Future work involves longitudinal studies and real-time data integration for more dynamic flood management strategies with system thinking approaches.Key Words: Urbanisation, Flood Management, GIS, Urban Planning, and Sustainability