Summer Convective Afternoon Rainfall Simulation and Projection Using WRF Driven by Global Climate Model. Part II: Over South China and Luzon

Abstract

This study is the second of a two-part investigation into summer convective afternoon rainfall (CAR) simulation and projection over the East Asian continents. In Part I, we examined the CAR activity over Taiwan. In this study we focus on CAR activity over South China and Luzon using the WRF (Weather Research and Forecasting Model) driven by HiRAM (High Resolution Atmospheric Model) (i.e., WRF-HiRAM). These examinations focus on two time-sliced simulations assuming the climate conditions at present (1979 - 2003, historical run) and at the end of the 21^(st) century (2075 - 2099, RCP 8.5 scenario). The results show that WRF-HiRAM is capable of simulating the spatial-temporal variation in CAR activity over South China and Luzon close to the recorded observations. In the future projections, WRF-HiRAM predicts that CAR events over most of South China and eastern Luzon will become fewer but stronger. Conversely, CAR events over western Luzon will become more frequent and stronger. Analyses also indicate that the projected change in CAR amount over most of South China (except for the coastal regions) and Luzon will be dominated by the change in CAR rate, not the change in CAR frequency. As for the cause of change in CAR rate, WRF-HiRAM projects that atmospheric humidity over South China and Luzon will increase significantly in the future. This will lead to an increase in local CAR rate. In contrast, the projected change in CAR frequency over South China and Luzon is suggested to be greatly modulated by the change in daytime surface wind convergence and thermal instability. Examinations were also performed to document the characteristics and causes of the projected change in CAR activity extracted from HiRAM.