Modelling the effect of soil moisture variability on summer precipitation variability over East Asia

The potential role of surface soil moisture (SSM) in improving the simulation of interannual East Asian summer precipitation is investigated using a coupled land-atmosphere climate model, the Community Atmosphere Model version 3 (CAM3). Forced by specified observational sea surface temperature (SST), two ensemble simulations for 22 boreal-summer seasons (1979-2000) are conducted, one with interannually varying SSM (SSMinter) forcing and another with climatological SSM (SSMclim) forcing. Results show that, relative to the SSMclim run, interannual variability of East Asian summer precipitation is better simulated in the SSMinter run over the mid- and high-latitudes of East Asia, especially in northwest China, where the correlation coefficient between precipitation simulated and observed from the Climate Prediction Center Merged Analysis of Precipitation (CMAP) is increased from 0.12 to 0.56 during 1979-2000. Meanwhile, positive relationships between anomalies of local soil evaporation and summer precipitation in northwest China can be better reproduced in the SSMinter run than in the SSMclim run. Possible mechanisms for the improved simulations of the interannual summer precipitation variability in northwest China are analysed; the improvement is resulted from the reasonable reproduction of anomalous atmospheric circulation in Siberia and Iranian plateau.