Changes in Flood Risk under Global Warming Estimated Using MIROC5 and the Discharge Probability Index

We evaluated change in flood risk under global warming using the output from the latest version of the Model for Interdisciplinary Research on Climate (MIROC5), an atmosphere-ocean general circulation model. River discharge for the 21st century were simulated for the two Representative Concentration Pathway (RCP4.5 and RCP8.5) scenarios and converted to the Discharge Probability Index (DPI) to evaluate future flood risk. The occurrence of flood events corresponding to various DPI categories was calculated for each continental region. The results show a significant increase in the risk of massive flood incidents during the 21st century in Asia, Africa, Oceania, and South America, with relatively large differences between the two scenarios. In contrast, both scenarios showed only slight increases in massive flood risk in North America and almost no change in Europe. For the RCP8.5 scenario in particular, the risk of massive flood occurrence will increase approximately ten times in Africa, seven times in Asia, and five times in South America by the end of the current century. Further analyses indicated that these projected flood increases will occur mainly due to the increases in the number of rainy days and the annual maximum daily precipitation, and the decrease in snowmelt in high latitudinal regions will play an important role on the unchanged risk in Europe in spite of the projected increase in precipitation.