Yet, the lack of data on the spatial distribution and coincidence of flood risk and populations means that this approach does not allow a robust estimation of exposure headcounts 17, 18. By using global historical inventories of recorded flood events (e.g., from EM-DAT), studies have estimated exposure indicators at the country level 17. Previous global flood risk assessments suffer from multiple limitations. Overall, there is limited evidence on the global scale of flood exposure and how it relates to the incidence of poverty. While studies exist for developing countries, attention is focused on large economic centers like Jakarta, Dhaka, Dar es Salaam, Accra, and Ho Chi Minh City 11, 12, 13, 14, 15, 16 few systematic assessments exist for the least developed countries and subregions, where floods are likely to have the most devastating impacts on livelihoods. Yet, local studies have focused predominately on high-income countries like the European Union, United States, and Japan, not least due to data availability and the large economic values at risk 9, 10. Recognizing the severe impacts of disasters on socioeconomic development, many flood exposure assessments have been conducted at local and national scales, often leveraging the recent availability of high-resolution flood, asset, and population maps, enabling increasingly accurate risk assessments. Considering the compounded effect of these drivers in the world’s 136 largest coastal cities, one study has shown that population and asset growth, climate change, and subsidence are likely to contribute to a drastic increase in global average flood losses, from $6 billion per year in 2005 to over $60 billion in 2050 8. By one estimate, in the absence of risk-mitigating measures, socioeconomic growth could result in the absolute damages from flooding to increase by a factor 20 by 2100. Land subsidence, often caused by unsustainable ground water extraction and drainage, has been shown to increase coastal flood risks at a rate four times faster than sea level rise 7.įlood risks are also driven by socioeconomic change, as the number of people, assets, and value of economic activities increase over time 3. Even in an optimistic climate change scenario (RCP 2.6), sea levels are estimated to rise up to 0.55 m by 2100, putting especially large coastal cities at risk 6. For a high-concentration climate change scenario, estimates from 11 climate models converge to the conclusion that flood frequencies in Southeast Asia, East and Central Africa, and large parts of Latin America could increase substantially by 2100 5. While the threat is already substantial, several ongoing trends could result in significant increases in flood risks in coming years. Understanding the scale and distribution of risks is crucial for devising targeted mitigation measures and allocating adequate resources. Rare, major floods and smaller, frequent events alike can revert years of progress in development 4 and poverty reduction. Recent disastrous floods in countries as diverse as Nigeria, Bangladesh, Vietnam, the United States, and the United Kingdom illustrate that the threat is a global reality. Especially in lower-income countries-where infrastructure systems, including drainage and flood protection, tend to be less developed-floods often cause unmitigated damage and suffering 3. While each country faces its individual set of natural hazards, including cyclones, earthquakes, or wildfires, floods are among the leading threats to people’s livelihoods and affect development prospects worldwide 2. Globally, natural shocks are estimated to cause an average of over $300 billion in direct asset losses every year this estimate increases to $520 billion when considering well-being (or consumption) losses 1.
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