Brenden Jongman, Hessel C. Winsemius, Stuart A. Fraser, Sanne Muis, and Philip J. Ward
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Natural Hazard Science. Please check back later for the full article.
Flooding of rivers and coastlines is the most frequent and damaging of all natural hazards. Between 1980 and 2013, total direct damages exceeded $1 trillion, and at least 220,000 people lost their lives. Events with major economic losses include the 2011 flooding in Thailand ($40 billion) and the 2013 Central Europe floods ($16 billion). Flooding also triggers great humanitarian challenges. The 2015 Malawi floods were the worst in the country’s history and were followed by food shortages across large parts of the country.
Flood losses are increasing rapidly in some world regions, driven by economic development in floodplains and increases in extreme precipitation events and global sea level due to climate change. The biggest increase in flood losses is seen in low-income countries, where population growth is rapid and many cities are expanding quickly. At the same time, evidence shows that adaptation to flood risk is already happening, and that a large proportion of losses can be successfully contained by effective risk management strategies. Such risk management strategies may include floodplain zoning, construction and maintenance of flood defenses, reforestation of land draining into rivers, and use of early warning systems.
To reduce risk effectively, it is important to know the location and impact of potential floods, under current and future social and environmental conditions. In a risk assessment, models can be used to map the flow of water over land after an intense rainfall event or storm surge (the “hazard”). Modeled for many different potential events, this provides estimates of potential inundation depth in flood prone areas. Such maps can be constructed for different scenarios of climate change, based on changes in rainfall, temperature, and sea levels specified in climate change scenarios.
To assess the impact of the modeled hazard, that is, the cost of damage or lives lost, exposure (including buildings, population, and infrastructure) must be mapped using land-use and population density data, as well as construction information. Population growth and urban expansion can be simulated by increasing the density or extent of the urban area in the model. The effects of flood on people and on types of buildings and infrastructure are determined using a vulnerability function. This indicates the damage expected to occur to a structure (or group of people) as a function of flood intensity (i.e., inundation depth and flow velocity).
Potential adaptation measures such as land-use change or new flood defenses can be included in the model, to understand how effective they may be in reducing flood risk. This way, risk assessments can demonstrate the possible approaches available to policy makers to build a less risky future.
Evolution of Strategic Flood Risk Management in Support of Social Justice, Ecosystem Health, and Resilience
Throughout history, flood management practice has evolved in response to flood events. This heuristic approach has yielded some important incremental shifts in both policy and planning (from the need to plan at a catchment scale to the recognition that flooding arises from multiple sources and that defenses, no matter how reliable, fail). Progress, however, has been painfully slow and sporadic, but a new, more strategic, approach is now emerging.
A strategic approach does not, however, simply sustain an acceptable level of flood defence. Strategic Flood Risk Management (SFRM) is an approach that relies upon an adaptable portfolio of measures and policies to deliver outcomes that are socially just (when assessed against egalitarian, utilitarian, and Rawlsian principles), contribute positively to ecosystem services, and promote resilience. In doing so, SFRM offers a practical policy and planning framework to transform our understanding of risk and move toward a flood-resilient society. A strategic approach to flood management involves much more than simply reducing the chance of damage through the provision of “strong” structures and recognizes adaptive management as much more than simply “wait and see.” SFRM is inherently risk based and implemented through a continuous process of review and adaptation that seeks to actively manage future uncertainty, a characteristic that sets it apart from the linear flood defense planning paradigm based upon a more certain view of the future.
In doing so, SFRM accepts there is no silver bullet to flood issues and that people and economies cannot always be protected from flooding. It accepts flooding as an important ecosystem function and that a legitimate ecosystem service is its contribution to flood risk management. Perhaps most importantly, however, SFRM enables the inherent conflicts as well as opportunities that characterize flood management choices to be openly debated, priorities to be set, and difficult investment choices to be made.
David Proverbs and Jessica Lamond
Flood resilient construction has become an essential component of the integrated approach to flood risk management, now widely accepted through the concepts of making space for water and living with floods. Resilient construction has been in place for centuries, but only fairly recently has it been recognized as part of this wider strategy to manage flood risk. Buildings and the wider built environment are known to play a key role in flood risk management, and when buildings are constructed on or near to flood plains there is an obvious need to protect these. Engineered flood defense systems date back centuries, with early examples seen in China and Egypt. Levees were first built in the United States some 150 years ago, and were followed by the development of flood control acts and regulations. In 1945, Gilbert Fowler White, the so-called “father of floodplain management,” published his influential thesis which criticized the reliance on engineered flood defenses and began to change these approaches. In Europe, a shortage of farmable land led to the use of land reclamation schemes and the ensuing Land Drainage acts before massive flood events in the mid-20th century led to a shift in thinking towards the engineered defense schemes such as the Thames Barrier and Dutch dyke systems. The early 21st century witnessed the emergence of the “living with water” philosophy, which has resulted in the renewed understanding of flood resilience at a property level.
The scientific study of construction methods and building technologies that are robust to flooding is a fairly recent phenomenon. There are a number of underlying reasons for this, but the change in flood risk philosophy coupled with the experience of flood events and the long process of recovery is helping to drive research and investment in this area. This has led to a more sophisticated understanding of the approaches to avoiding damage at an individual property level, categorized under three strategies, namely avoidance technology, water exclusion technology, and water entry technology. As interest and policy has shifted to water entry approaches, alongside this has been the development of research into flood resilient materials and repair and reinstatement processes, the latter gaining much attention in the recognition that experience will prompt resilient responses and that the point of reinstatement provides a good opportunity to install resilient measures.
State-of-the-art practices now center on avoidance strategies incorporating planning legislation in many regions to prohibit or restrict new development in flood plains. Where development pressures mean that new buildings are permitted, there is now a body of knowledge around the impact of flooding on buildings and flood resilient construction and techniques. However, due to the variety and complexity of architecture and construction styles and varying flood risk exposure, there remain many gaps in our understanding, leading to the use of trial and error and other pragmatic approaches. Some examples of avoidance strategies include the use of earthworks, floating houses, and raised construction.
The concept of property level flood resilience is an emerging concept in the United Kingdom and recognizes that in some cases a hybrid approach might be favored in which the amount of water entering a property is limited, together with the likely damage that is caused. The technology and understanding is moving forward with a greater appreciation of the benefits from combining strategies and property level measures, incorporating water resistant and resilient materials. The process of resilient repair and considerate reinstatement is another emerging feature, recognizing that there will be a need to dry, clean, and repair flood-affected buildings. The importance of effective and timely drying of properties, including the need to use materials that dry rapidly and are easy to decontaminate, has become more apparent and is gaining attention.
Future developments are likely to concentrate on promoting the uptake of flood resilient materials and technologies both in the construction of new and in the retrofit and adaptation of existing properties. Further development of flood resilience technology that enhances the aesthetic appeal of adapted property would support the uptake of measures. Developments that reduce cost or that offer other aesthetic or functional advantages may also reduce the barriers to uptake. A greater understanding of performance standards for resilient materials will help provide confidence in such measures and support uptake, while further research around the breathability of materials and concerns around mold and the need to avoid creating moisture issues inside properties represent some of the key areas.
People not only want to be safe from natural hazards; they also want to feel they are safe. Sometimes these two desires pull in different directions, and when they do, this slows the journey to greater physical adaptation and resilience.
All people want to feel safe—especially in their own homes. In fact, although not always a place of actual safety, in many cultures “home” is nonetheless idealized as a place of security and repose. The feeling of having a safe home is one part of what is termed ontological security: freedom from existential doubts and the ability to believe that life will continue in much the same way as it always has, without threat to familiar assumptions about time, space, identity, and well-being. By threatening our homes, floods, earthquakes, and similar events disrupt ontological security: they destroy the possessions that support our sense of who we are; they fracture the social structures that provide us with everyday needs such as friendship, play, and affection; they disrupt the routines that give our lives a sense of predictability; and they challenge the myth of our immortality. Such events, therefore, not only cause physical injury and loss; by damaging ontological security, they also cause emotional distress and jeopardize long-term mental health.
However, ontological security is undermined not only by the occurrence of hazard events but also by their anticipation. This affects people’s willingness to take steps that would reduce hazard vulnerability. Those who are confident that they can eliminate their exposure to a hazard will usually do so. More commonly, however, the available options come with uncertainty and social/psychological risks: often, the available options only reduce vulnerability, and sometimes people doubt the effectiveness of these options or their ability to choose and implement appropriate measures. In these circumstances, the risk to ontological security that is implied by action can have greater influence than the potential benefits. For example, although installing a floodgate might reduce a business’s flood vulnerability, the business owner might feel that its presence would act as an everyday reminder that the business, and the income derived from it, are not secure. Similarly, bolting furniture to the walls of a home might reduce injuries in the next earthquake, but householders might also anticipate that it would remind them that there is a continual threat to their home. Both of these circumstances describe situations in which the anticipation of future feelings can tap into less conscious anxieties about ontological security.
The manner in which people anticipate impacts on ontological security has several implications for preparedness. For example, it suggests that hazard warnings will be counterproductive if they are not accompanied by suggestions of easy, reliable ways of eliminating risk. It also suggests that adaptation measures should be designed not to enhance awareness of the hazard.
Recent extreme hydrological events (e.g., in the United States in 2005 or 2012, Pakistan in 2010, and Thailand in 2011) revealed increasing flood risks due to climate and societal change. Consequently, the roles of multiple stakeholders in flood risk management have transformed significantly. A central aspect here is the question of sharing responsibilities among global, national, regional, and local stakeholders in organizing flood risk management of all kinds. This new policy agenda of sharing responsibilities strives to delegate responsibilities and costs from the central government to local authorities, and from public administration to private citizens. The main reasons for this decentralization are that local authorities can deal more efficiently with public administration tasks concerned with risks and emergency management. Resulting locally based strategies for risk reduction are expected to tighten the feedback loops between complex environmental dynamics and human decision-making processes. However, there are a series of consequences to this rescaling process in flood risk management, regarding the development of new governance structures and institutions, like resilience teams or flood action groups in the United Kingdom. Additionally, downscaling to local-level tasks without additional resources is particularly challenging. This development has tightened further with fiscal and administrative cuts around the world resulting from the global economic crisis of 2007–2008, which tightening eventually causes budget restrictions for flood risk management. Managing local risks easily exceeds the technical and budgetary capacities of municipal institutions, and individual citizens struggle to carry the full responsibility of flood protection. To manage community engagement in flood risk management, emphasis should be given to the development of multi-level governance structures, so that multiple stakeholders share fairly the power, resources, and responsibility in disaster planning. If we fail to do so, some consequences would be: (1), “hollowing out” the government, including the downscaling of the responsibility towards local stakeholders; and (2), inability of the government to deal with the new tasks due to lack of resources transferred to local authorities.