This research presents a global assessment of the economic costs and the population affected by river floods under different global warming scenarios. The research team analysed a selection of high-resolution climate projections and simulations, and assessed the frequency and magnitude of river floods and their expected impacts under future scenarios.
The study reveals that, with a 4°C temperature increase globally, countries representing 73% of the global population would face a 580% increase in flood risk. In addition, 79% of the global economy would face a 500% increase in flood damages. In the case of a 2°C temperature increase, both the affected population and the related flood damages would rise by 170% compared to present levels. Even under the most optimistic scenario of a 1.5°C temperature increase, the authors estimate that the flood-affected population would still double, and flood damages would increase by 120%.
Average change in population affected per country given 4˚C global warming. Hatching indicates countries where the confidence level of the average change is less than 90%.
Average change in flood damages per country given 4˚C global warming. Hatching indicates countries where the confidence level of the average change is less than 90%.
The projected changes are not evenly distributed across the globe. The increase in flood risk is highest for Asia, America and Europe, while it remains low for most countries in Africa and Oceania, independent of the temperature increase.
These results support the recommendations of the Paris Agreement reached at the COP21 last year (to keep a global temperature rise this century well below 2˚C above pre-industrial levels, and to pursue efforts to limit the temperature increase even further, to 1.5˚C), and confirm the urgent need for all countries to take active mitigation measures to limit global warming and the consequent increase in flood risk.
As even the most optimistic warming scenario of 1.5°C would lead to a doubling of global flood risk, effective adaptation plans must be implemented to keep the flood risk rates at or below current levels. In addition, socio-economic drivers are likely to make the impacts greater in developing countries and in the regions with significant population growth. The increase in flood risk may become unsustainable in regions where the combination of socio-economic and climatic drivers trigger large-scale climatic crises involving conflicts and mass migration.