The Regional Climate Model version 4 (RegCM4) has been used to dynamically downscale outputs from four different general circulation models (GCM) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) to the horizontal resolution of 25 km × 25km, in order to study 2050-to-2099 changes in the Southern China hydrological cycle according to Representative Concentration Pathway (RCP) 8.5, relative to the period of 1979 to 2003. The mean summertime precipitation is projected to increase by 0.5 – 1.5 mm/day over coastal Southern China, and with significantly enhanced interannual variability. In boreal spring, similar increase in both the seasonal mean and its year-to-year variation north of 25°N is also found. A novel moisture budget analysis shows that changes in mean background humidity (anomalous wind convergence) dominates the increase in the interannual precipitation variability in spring (summer). Extreme daily precipitation (based on the 95 th percentile) is projected to become more intense, roughly following the Clausius–Clapeyron relation for the aforementioned seasons.
On the other hand, autumn mean rainfall rate will be reduced over a broad area in Southern China (although this might be subjected to models’ ability in capturing tropical cyclone activities). The annual number of maximum consecutive dry days (CDD) is found to increase by about 3 to 5 days over locations south of 32°N. Analyses of GCM raw outputs indicate that strengthened northerlies over coastal East Asia , which is likely associated with the so-called tropical expansion, are responsible for the drier autumn.