Effective adaptation to rising flood risk

Floods are causing increasing havoc in our rapidly urbanizing world, with disproportionally high impacts on the poorest and most vulnerable. Effective adaptation strategies are needed, which combine flood protection infrastructure, nature-based solutions, and risk financing schemes to manage floods and buffer their economic impacts. Global weather-related disaster losses exceeded US$300 billion in 2017, which made this the most costly year on record and continues a long-term upward trend1. For the first time in history, over half the world’s population now live in cities, many of which are located at rivers, along coastlines, or both. A new study shows that the total urban area exposed to flooding in Europe has increased by 1000% over the past 150 years2. On a global scale, trends in flood zone urbanization have been similarly steep and continue to climb, especially in Africa and Asia3,4. Not only does this mean that ever more human assets are in the way of floods, but urbanization with an increase of non-permeable surfaces and lack of natural drainage creates additional flooding issues that did not previously exist. Socioeconomic changes are further compounded by climate change-induced increases in extreme rainfall which amplify the intensity and probability of floods. In Europe, all climate models consistently show an increase in flood impacts across most Western and Central countries, approximately doubling the expected damage by the end of the century5. In addition, changing patterns of spring snowmelt and winter storms have dramatically affected the timing of floods throughout the year6. Within these long-term trends, inter-annual fluctuations due to large scale atmospheric patterns such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA) cause strong year-to-year fluctuations in rainfall and resulting flood damages7. The impacts of flooding go far beyond direct damages to assets and infrastructure. Economic losses resulting from business disruption, welfare effects and supply chain shocks can often at times equal or exceed direct damages8. In extreme cases, such as the shut-down of Wall Street due to Hurricane Sandy, economic ripple effects may be felt across an entire sector around the globe. The welfare loss from flood events hits the poorest in society hardest. In many countries, the poorest population groups are relatively overexposed to flooding, as they are often forced to live and work in low-lying areas9. In addition, the poorest households are more vulnerable to the resulting impacts to their income, and can often be pushed across the poverty line by a single event10. As such, natural disasters may effectively increase global poverty11. Positive trends, however, are visible. Economic development, technological progress and targeted adaptation interventions help reduce flood impacts over time. In Europe, fatalities and normalized economic losses (losses as % of GDP) have decreased significantly over recent decades, despite an increase in flooded area and absolute losses2. Globally, too, such a decline in relative impact has been observed, as low-income countries are becoming less vulnerable as percapita income rises12. This demonstrates that effective adaptation to flooding is feasible, even when faced by growing exposure and a changing climate.