Mean states and future projections of precipitation over the monsoon transitional zone in China in CMIP5 and CMIP6 models

The mean states and future projections of precipitation over the monsoon transitional zone (MTZ) in China are examined based on the historical and climate change projection simulations from phase 5 and phase 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). Ensemble means of CMIP6 models exhibit a clear improvement in capturing the annual mean and seasonal cycle of the precipitation over the MTZ, both in its spatial pattern and magnitude, compared to the counterparts of CMIP5 models. In addition, both CMIP5&6 models project a remarkable increase in the annual total precipitation amount and annual precipitation range, but with slightly stronger changes in CMIP6. For the climatological mean precipitation amount, the two versions’ model ensembles show high consistency in the substantial role played by local evaporation in the supply of moisture in both the present-day and future-projection scenarios, with little contribution from the horizontal and vertical advection of moisture. The precipitation amount is projected to increase in all seasons, but with the strongest signals in summer. An analysis of the moisture budget indicates that the increase in summer precipitation is mainly due to evaporation and vertical moisture advection changes in both CMIP5&6 models. However, the change in vertical moisture advection in CMIP5 is primarily attributable to the thermodynamic effects associated with the humidity changes. By contrast, the dynamic effects induced by the atmospheric circulation changes play a dominant role for CMIP6, which is likely related to the stronger warming gradient between the mid–high latitudes and the tropics.