Climate change and socio-economic development result in increasing flood risk which challenges flood risk management policy making and practice. Each situation, however, is different and calls for not only understanding the natural context, but also the socio-economic and cultural context. Only then Flood Risk Management strategies can be designed that are not only 1) fit for purpose but also 2) feasible for local implementation and 3) sustainable into the future. Flood consequences that are accepted in some cultures (fatalist), may not be acceptable in other cultures (controlist). This calls for considering the local normative context in order to understand current differences in policy and practice. More importantly, the design of strategic alternatives for Flood Risk Management into the future should consider this socio-economic and cultural context as well because not every society aims for the same goals in the same proportion, nor is equally willing or capable to implement and maintain sophisticated infrastructure and dedicated institutions. Based on literature on cultural theory and national cultures, we hypothesized that acknowledging socio-economic and cultural differences would allow to better appreciate the rationale of current flood risk management policies and practices in different parts of the world. By analysing cases related to Deltares projects abroad, we explored whether these factors explain the main differences observed. Based on this preliminary exploration, we propose a shortlist of factors to consider when designing future flood risk management strategies tailored to local socio-economic and cultural contexts.

The need for explicitly considering equity in climate change adaptation planning is increasingly being recognized. However, evaluations of adaptation often adopt an aggregated perspective, while disaggregation of results is important to learn about who benefits when and where. A typical example is adaptation of rice agriculture in the Vietnam Mekong Delta (VMD). Efforts focused on flood protection have mainly benefitted large-scale farmers while harming small-scale farmers. To investigate the distributional consequences of adaptation policies in the VMD, we assess both aggregate total output and equity indicators, as well as disaggregated impacts in terms of district-level farming profitability. Doing so requires an adequate representation of the multisectoral dynamics between the human and biophysical systems which influence farming profitability. We develop a spatially explicit integrated assessment model that couples inundation, sedimentation, soil fertility and nutrient dynamics, and behavioral land-use change and farming profitability calculation. We find that inter-district inequality responds in a non-linear way to climatic and socio-economic changes and choices of adaptation policies. The patterns of who wins and who loses could change substantially when a different policy is implemented or if a slightly different uncertain future materializes. We also find that there is no simple ranking of alternative adaptation policies, so one should make trade-offs based on agreed preferences. Accounting for equity implies exploring the distribution of outcomes over different groups over a range of uncertain futures. Only by accounting for multisectoral dynamics can planners anticipate the equity consequences of adaptation and prepare additional measures to aid the worse-off actors.

Flood risk management decisions in many countries are based on decision-support frameworks which rely on cost-benefit analyses. Such frameworks are seldom informative about the geographical distribution of risk, raising questions on the fairness of the proposed policies. In the present work, we propose a new decision criterion that accounts for the distribution of risk reduction and apply it to support flood risk management decisions on a transboundary stretch of the Rhine River. Three types of interventions are considered: embankment heightening, making Room for the River, and changing the discharge distribution of the river branches. The analysis involves solving a flood risk management problem according to four alternative formulations, based on different ethical principles. Formulations based on cost optimization lead to very poor performances in some areas for the sake of reducing the overall aggregated costs. Formulations that also include equity criteria have different results depending on how these are defined. When risk reduction is distributed equally, very poor economic performance is achieved. When risk is distributed equally, results are in line with formulations based on cost optimization, while a fairer risk distribution is achieved. Risk reduction measures also differ, with the cost optimization approach strongly favoring the leverage of changing the discharge distribution and the alternative formulations spending more on embankment heightening and Room for the River, to rebalance inequalities in risk levels. The proposed method advances risk-based decision-making by allowing to consider risk distribution aspects and their impacts on the choice of risk reduction measures.

Over decades the concept of integration has been promoted to enhance alignment between policy domains, and to manage trade-offs and maximize synergies across management practices. Integrated approaches have the potential to enable better outcomes for flood risk management (FRM) and society as a whole. However, achieving integration in practice is a recurring challenge, especially for FRM where multiple actors need to work together across fragmented policy domains. To disentangle this complexity of integration, a framework is proposed for assessing integration and identifying different degrees of integration. This framework is based on evidence from a literature review, 50 interviews with FRM-related professionals in England, and participant observation at 24 meetings relevant for FRM. The framework sets out the context of integration, assesses the governance capacity for integration through the strength of relationships between different types of actors (bridging, bonding, and linking) and the mechanisms (actor-, rule-and resource-based) that influence them, and the realization of integration in practice through knowledge, policies, and interventions. The framework is applied for FRM in England and used to identify degrees of integration: high, intermediate, low, and minimal. An important characteristic of the framework is the interconnectivity between the governance capacity and realization of integration. The framework provides further theoretical insights into the concept of integration, while offering an approach for researchers, policy makers, and practitioners to recognize current degrees of integration in FRM and identify the critical elements for improvement. It is recommended that further research and practice-based applications of the framework are completed in different geographical and institutional contexts. Specifically, such applications can create further understanding of the interactions and dependencies between elements of the governance capacity and realization of integration.

Rivers typically flow through multiple flood-protected areas which are clearly interconnected, as risk reduction measures taken at one area, e.g. heightening dikes or building flood storage areas, affect risk elsewhere. We call these interconnections 'hydraulic interactions'. The current approach to flood risk management, however, neglects hydraulic interactions for two reasons: They are uncertain and, furthermore, considering them would require the design of policies not only striving for risk reduction, but also accounting for risk transfers across flood-protected areas. In the present paper, we compare the performance of policies identified according to the current approach with those of two alternative formulations: One acknowledging hydraulic interactions and the other also including an additional decision criterion to account for equity in risk distribution across flood-protected areas. Optimal policies are first identified under deterministic hydraulic interactions, and, next, they are stress-tested under uncertainty. We found that the current approach leads to a false sense of equal risk distribution. It does, however, perform efficiently when a risk-averse approach towards uncertain hydraulic interactions is taken. Accounting for hydraulic interactions in the design of policies, instead, increases efficiency and both efficiency and equity when hydraulic interactions are considered deterministically and as uncertain, respectively.

Most alluvial plains in the world are protected by flood defences, for example, embankments, whose primary aim is to reduce the probability of flooding of the protected areas. At the same time, however, the presence of embankments at one area influences hydraulic conditions of downstream areas located on the same river. These hydraulic interactions are often neglected in current flood risk management. The aim of this study is to explicitly acknowledge hydraulic interactions and investigate their impact on establishing optimal embankment heights along a stretch of the IJssel River. We find that the current approach leads to a single solution, while taking into account hydraulic interactions substantially expands the number of promising solutions. Furthermore, under a reference scenario, the current approach is in fact suboptimal with respect to both downstream locations and the system as a whole. Under uncertainty, it performs adequately from a system viewpoint, but poorly for individual locations, mostly due to risk overestimation downstream. Overall, the current approach proves to be too short-sighted, because spatial trade-offs among locations are neglected and alternative solutions remain hidden. Acknowledging the effect of hydraulic interactions provides policy makers with a broader and more comprehensive spectrum of flood risk management strategies.

The concept of resilience is used by many in different ways: as a scientific concept, as a guiding principle, as inspirational ‘buzzword’, or as a means to become more sustainable. Next to the academic debate on meaning and notions of resilience, the concept has been widely adopted and interpreted in policy contexts, particularly related to climate change and extreme weather events. In addition to having a positive connotation, resilience may cover aspects that are missed in common disaster risk management approaches. Although the precise definition of resilience may remain subject of discussion, the views on what is important to consider in the management of extreme weather events do not differ significantly. Therefore, this paper identifies the key implications of resilience thinking for the management of extreme weather events and translates these into five practical principles for policy making.

Knowledge on the different components of flood risk has much improved over the last decades, but research which fully takes into account not only the interactions between those components but also between different areas in a catchment or delta is still rare. Integrated analyses based on a complete system's approach at sufficiently large scale will improve our understanding of how flood risk systems with flood protection infrastructure in place behave under extreme conditions, it may help to develop sensible long-term strategies, and allows us to better prepare for flood events of all magnitudes. To illustrate the relevance of a hydrodynamic system's approach for flood risk management we analyse the effect of defence breaches on flood risks elsewhere along the lower Rhine River and discuss the use of this knowledge for flood risk management.

Since 1996, the Netherlands has adopted a flood risk management policy based on making more room for the rivers. Currently, the focus in flood risk management is being adapted again, in view of increasing societal vulnerability and foreseeable effects of climate change. In this context, the choice between making more room for the river and/or strengthening embankments is again of major concern. This calls for further quantification of the effectiveness, costs and benefits of all possible measures. Making room for rivers was originally advocated by referring to a reduction of the probability of failure of the embankments and a reduction of the consequences in case of breaching. These arguments still apply, but the effect of making more room for rivers on flood risk has never been properly quantified yet. In this paper we identify three potential risk reducing effects, and quantify their effect for along the Rhine and Meuse Rivers in the Netherlands. We show that lowering the flood levels means smaller flood probabilities, that larger floodplain surface area significantly influences the relationship between discharge and flood level, and that lower flood levels in the river translate into smaller flooding depths and/or flood extent, and thus reduce the consequences of flooding.

The Netherlands is updating its flood protection, whilst fully taking into account climate change and socioeconomic development. This translates in 'anticipatory standards' which need to be met in 2050, and which apply for the then foreseen climate and economy. Whilst the government maintains to have adopted a policy of adaptive planning and management, the new standards are thus based on one future situation, which qualifies as a 'high end scenario' from a flood risk management perspective. The consequences of adopting these new standards are now becoming clear. It is expected that many hundreds of kilometres of primary flood defences need to be reinforced and/or raised, at an estimated investment of about 9-14 billion euros. The many uncertainties about actual future development, however, complicate the decision making about the implementation of individual reinforcement projects: should one aim at immediately meeting the new standard or gradually improve and grow towards it? In this paper we discuss the uncertain decision making context, show that lawfulness (working according to procedures, rules and regulations) and expediency (towards a purpose) may jeopardize the good intentions of adaptive management, and argue that optimization may not provide the most useful answer to this decision making problem.