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The Regional Climate Model system 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 × 25 km, in order to study changes in the Southern China hydrological cycle according to the Representative Concentration Pathway (RCP) 8.5 between 2050‐to‐2099 and 1979‐to‐2003. Accompanying wetter boreal spring and summer, the interannual rainfall variability for these seasons is also enhanced. A novel moisture budget analysis shows that changes in mean background humidity (anomalous wind convergence) dominate the increase in the interannual variability in spring (summer). Extreme daily precipitation in these seasons (based on the 95th percentile) is projected to become more intense, roughly following the Clausius–Clapeyron (CC) relation for the aforementioned seasons. On the other hand, 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, where autumn mean rainfall rate is projected to reduce (although this might be subjected to models' ability in capturing tropical cyclone activities). Analyses of the 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. [ABSTRACT FROM AUTHOR]