27 January 2017

Global flood risk could increase five-fold with a 4-degree C temperature rise

Posted by Nanci Bompey

By the European Commission Joint Research Centre

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 percent.
Credit: EU

A new report looks at flood risk and economic damages under different global warming scenarios with temperature increases of 1.5 degrees Celsius, 2 degrees Celsius and 4 degrees Celsius. It concludes that, if global temperatures rise by 4 degrees Celsius, the flood risk in countries representing more than 70 percent of the global population and global GDP will increase by more than 500 percent.

The new research, published in Earth’s Future, a journal of the American Geophysical Union, presents a global assessment of the economic costs and the population affected by river floods under different global warming scenarios. The research team analyzed 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-degree Celsius temperature increase globally, countries representing 73 percent of the global population would face a 580 percent increase in flood risk. In addition, 79 percent of the global economy would face a 500 percent increase in flood damages. In the case of a 2-degree Celsius temperature increase, both the affected population and the related flood damages would rise by 170 percent compared to present levels. Even under the most optimistic scenario of a 1.5-degree Celsius temperature increase, the authors estimate that the flood-affected population would still double, and flood damages would increase by 120 percent.

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.

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 percent.
Credit: EU

These results support the recommendations of the Paris Agreement reached at the COP21 last year to keep a global temperature rise this century below 2 degrees Celsius above pre-industrial levels, and to pursue efforts to limit the temperature increase even further, to 1.5 degrees Celsius. The study confirms the urgent need for all countries to take active mitigation measures to limit global warming and the consequent increase in flood risk, according to the study’s authors.

As even the most optimistic warming scenario of 1.5 degrees Celsius 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, according to the authors. 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, according to the authors.

— This post originally appeared on the EU Science Hub website.