Evaluation of RegCM4 in simulating the interannual and interdecadal variations of Meiyu rainfall in China

In this paper, the performance of the regional climate model (RegCM4) in simulating the interannual and interdecadal variation of Meiyu rainfall over lower and middle reaches of Yangtze River (LMRYR) in China is evaluated. The results show that the bias of the simulated Meiyu rainfall exhibits some uncertainties and obvious interdecadal variation similar with that of Meiyu rainfall itself. The rainfall bias and its interdecadal variation have little impact on the simulation of the interannual variation of the Meiyu rainfall. Not only the amplitude but also the phase of the interannual variation of the Meiyu rainfall can be reproduced by the RegCM4. However, the interdecadal variation of the rainfall bias has large impacts on the model's performance in simulating the interdecadal component of the Meiyu rainfall, leading to lower skill of RegCM4 in simulating the interdecadal variation of the Meiyu rainfall than that in simulating the interannual variation. In addition, the interannual signals of the temperature, humidity, and vorticity in the lower troposphere in the large-scale NCEP lateral boundary force are stronger than the interdecadal signals, and the model can respond well to these interannual signals. Therefore, the RegCM4 has better performance in simulating the interannual variation of water vapor budget than the interdecadal variation, which further favors the simulation of the Meiyu rainfall at interannual time scale.