Projected Increase in Probability of East Asian Heavy Rainy Summer in the 21st Century by CMIP5 Models

Abstract

In the summer of 1998, heavy rainfall persisted throughout the summer and resulted in a severe prolonged flood event. Will a similar rainy summer happen again? To date, many studies have investigated the projected changes in seasonality or daily extreme precipitation events over East Asia; however, few studies have focused on the changes in extreme summer-averaged East Asian rainfall. We referred to this type of summer as “heavy rainy summer (HRS)” and investigated future changes in its probability, by analyzing CMIP5 model outputs in historical simulation (HIST) and under RCP4.5 and RCP8.5. All models projected an increased probability of HRS by a factor of two to three. Both the projected East Asian summer rainfall (EASR), i.e. EASRRCPs−EASRHIST, in climatology and HRS would intensify significantly. The increased EASR could be attributed to significantly intensified water vapor transport (WVT) originating from the tropical Indian Ocean (TIO) and the eastern subtropical North Pacific (SNP), which result from thermodynamic component. The WVT from TIO would supply more moisture for EASR because its stronger intensity and faster rate of increase. Meanwhile, the EASR anomaly in HRS relative to climatology, i.e. EASRHRS−EASRCLM, would increase by approximately 11%–33%. In HIST, the associated WVT anomaly, caused by only dynamic component, converges moisture from adjacent land and ocean. However, under RCPs, the WVT anomaly from TIO, resulted from thermodynamic component, would appear and increase triple to be comparable to the one from the eastern SNP. The latter would result from dynamic component but increase by only half.