Numerical simulation of heavy rainfall in August 2014 over Japan under Pseudo Global Warming Conditions

Abstract

Climate change as a consequence of global warming may enhance severe precipitation events. This study investigated the impact of global warming on summertime heavy rainfall using the Weather Research and Forecasting model with the pseudo global warming (PGW) method. WRF simulations were conducted for August 2014 over a domain covering Japan, in which two big typhoons attacked Japan and rain fronts frequently passed over, in a baseline and two PGW (RCP4.5 and RCP8.5) conditions. The analysis showed that the future climate led to a larger amount of precipitation than the past climate during the study period in Japan. The mean increase rate of upward moisture supply from the surface of the entire modelling domain was 2.8% K−1 in RCP4.5 condition and 3.3% K−1 RCP8.5 condition. The mean increase rate of 2-m specific humidity was 6.7% K−1 in both RCP4.5 and RCP8.5 conditions, which is comparable to the Clausius-Clapeyron relationship. Therefore, the water supply from the lateral boundaries contributed to the increase in humidity largely and precipitation subsequently. The increases in precipitation related to typhoons were larger than rain fronts, in particular, the changes were remarkable over the paths of typhoons. These results show global warming will significantly increase the summertime heavy precipitation over Japan in the future.