Impacts of global warming on changes in the East Asian monsoon and the related river discharge in a global time-slice experiment

Changes in the East Asian monsoon and the related river discharge under global warming conditions are investigated using 2 time-slice simulations of the IS92a scenario with a T106 atmospheric general circulation model (ECHAM4) for 1971 to 1980 and 2041 to 2050. Daily runoff and drainage calculated by the land-surface scheme are used as input to a hydrological model to diagnose changes in the Yangtze River and Zhujiang River discharges. In the future climate, the simulated annual cycle of precipitation over the southeastern coastal area of China is systematically shifted about 1 mo ahead compared with the present-day climate, and the rainy season starts 1 mo earlier for the Yangtze River Valley and North China. In line with the surface-warming distribution change, the East Asian summer monsoon (EAM) flow strengthens. This causes increased precipitation in North China. In winter, the subtropical part of the EAM flow strengthens and leads to a large increase in rainfall over the EAM region. The discharges of the Zhujiang and Yangtze rivers in the future climate decrease in the late summer and autumn, to which both increased evaporation and an early retreat of the monsoon rainfall contribute. In the early and mid-summer, the Yangtze River discharge increases, mainly due to the large increase in precipitation in the preceding months, which has been stored in the catchment.