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Global flood risk under climate change


A warmer climate would increase the risk of floods1. So far, only a few studies2,3 have projected changes in floods on a global scale. None of these studies relied on multiple climate models. A few global studies4,5 have started to estimate the exposure to flooding (population in potential inundation areas) as a proxy of risk, but none of them has estimated it in a warmer future climate. Here we present global flood risk for the end of this century based on the outputs of 11 climate models. A state-of-the-art global river routing model with an inundation scheme6 was employed to compute river discharge and inundation area. An ensemble of projections under a new high-concentration scenario7 demonstrates a large increase in flood frequency in Southeast Asia, Peninsular India, eastern Africa and the northern half of the Andes, with small uncertainty in the direction of change. In certain areas of the world, however, flood frequency is projected to decrease. Another larger ensemble of projections under four new concentration scenarios7 reveals that the global exposure to floods would increase depending on the degree of warming, but interannual variability of the exposure may imply the necessity of adaptation before significant warming.

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Figure 1: Projected change in flood frequency.
Figure 2: Projected return period of the 20C 100-year flood in 21C at the outlets of 29 selected river basins.
Figure 3: Global flood exposure for the 20C 100-year flood, or above, in millions.

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This paper was financially supported by the Funding Program for Next-Generation World-Leading Researchers, Japan Society for the Promotion of Science, CREST of Japan Science and Technology Agency, and the Environmental Research and Technology Development Fund (S-10, ICA-RUS) of the Ministry of the Environment, Japan. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. For CMIP the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.

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R.M., S. Koirala, D.Y. and H.K. carried out the simulation and analysis. L.K. and S. Koirala carried out the exposure estimation. S.W. contributed to the data archive. Y.H. and S. Kanae designed the research. Y.H., S. Koirala and S. Kanae co-wrote the paper.

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Correspondence to Yukiko Hirabayashi or Shinjiro Kanae.

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The authors declare no competing financial interests.

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Hirabayashi, Y., Mahendran, R., Koirala, S. et al. Global flood risk under climate change. Nature Clim Change 3, 816–821 (2013).

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