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Assessment and Adaptation to Climate Change-Related Flood Risks  

Brenden Jongman, Hessel C. Winsemius, Stuart A. Fraser, Sanne Muis, and Philip J. Ward

The flooding of rivers and coastlines is the most frequent and damaging of all natural hazards. Between 1980 and 2016, total direct damages exceeded $1.6 trillion, and at least 225,000 people lost their lives. Recent events causing major economic losses include the 2011 river flooding in Thailand ($40 billion) and the 2013 coastal floods in the United States caused by Hurricane Sandy (over $50 billion). Flooding also triggers great humanitarian challenges. The 2015 Malawi floods were the worst in the country’s history and were followed by food shortage across large parts of the country. Flood losses are increasing rapidly in some world regions, driven by economic development in floodplains and increases in the frequency of extreme precipitation events and global sea level due to climate change. The largest 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 a large proportion of losses can be contained successfully 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 various scenarios of climate change based on specific changes in rainfall, temperature, and sea level. To assess the impact of the modeled hazard (e.g., cost of damage or lives lost), the potential exposure (including buildings, population, and infrastructure) must be mapped using land-use and population density data and 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 floods on people and different 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 (e.g., inundation depth and flow velocity). Potential adaptation measures such as land-use change or new flood defenses can be included in the model in order to understand how effective they may be in reducing flood risk. This way, risk assessments can demonstrate the possible approaches available to policymakers to build a less risky future.

Article

Collective Choices Affecting Natural Hazards Governance, Risk, and Vulnerability  

Thomas Thaler, David Shively, Jacob Petersen-Perlman, Lenka Slavikova, and Thomas Hartmann

The frequency and severity of extreme weather events are expected to increase due to climate change. These developments and challenges have focused the attention of policymakers on the question of how to manage natural hazards. The main political discourse revolves around the questions of how we can make our society more resilient for possible future events. A central challenge reflects collective choices, which affect natural hazards governance, risk, and individual and societal vulnerability. In particular, transboundary river basins present difficult and challenging decisions at local, regional, national, and international levels as they involve and engage large numbers of stakeholders. Each of these groups has different perspectives and interests in how to design and organize flood risk management, which often hinder transnational collaborations in terms of upstream–downstream or different riverbed cooperation. Numerous efforts to resolve these conflicts have historically been tried across the world, particularly in relation to institutional cooperation. Consequently, greater engagement of different countries in management of natural hazards risks could decrease international conflicts and increase capacity at regional and local levels to adapt to future hazard events. Better understanding of the issues, perspectives, choices, and potential for conflict, and clear sharing of responsibilities, is crucial for reducing impacts of future events at the transboundary level.