Added value of CMIP6 models over CMIP5 models in simulating the climatological precipitation extremes in China

Performance of six models in the Coupled Model Intercomparison Project phase 5 (CMIP5) and their new versions in CMIP phase 6 (CMIP6) in representing the climatological (1976-2005) precipitation extremes over China were evaluated based on five precipitation indices. Improvements are found in CMIP6 models in simulating the climatology of all five indices, in which GFDL-CM4 and GFDL-ESM4 show significant improvement. Dry biases over South China (SC) are reduced in five CMIP6 models (BCC-CSM, CanESM, GFDL-CM, GFDL-ESM, and IPSL-CM), with the largest decreased root-mean-square error (RMSE) of 59.2% in GFDL-CM. The reduced dry biases in CMIP6 can be attributed to more moisture transported into SC from the southern boundary and dynamic processes of the atmosphere except in BCC-CSM, where the increased evaporation dominates. Additionally, increased heavy precipitation events (>20 mm center dot day(-1)) are produced over SC in CMIP6 models. Wet biases over West China (WC) are also reduced. with the largest reduced RMSE of 46.8% in GFDL-CM, which are related to the reduced precipitation frequency (more than 40%) and weakened precipitation intensity. In addition, the CMIP6 models show a higher skill in simulating the frequency distribution of daily precipitation intensity. More heavy precipitation over SC and Northeast China, and fewer weak precipitation (<20 mm center dot day(-1)) over WC can be reasonably reproduced. Although the CMIP6 models have obviously improved in simulating total precipitation on wet days, wet days (WD), simple daily intensity index (SDII), and extreme precipitation amount (R95T), the bias still exists in simulating consecutive dry days (CDD).

Automated summary

The CMIP6 models show improvements in simulating climatological precipitation extremes over China, reducing dry biases in South China and producing more heavy precipitation events. Additionally, wet biases over West China are also reduced, related to reduced precipitation frequency and weakened precipitation intensity. Overall, the CMIP6 models have improved in simulating total precipitation on wet days, but biases still exist in simulating consecutive dry days.