Evaluation of Indian Summer Monsoon Precipitation using CMIP5 and CMIP6 models

The performance of climate models and their multi-model mean (MMM) in CMIP6 and CMIP5 precipitation simulations is compared using the India Meteorological Department (IMD) observations over the Indian summer monsoon (ISM) season (June-September) from 1975-2005. It is found that CMIP6 MMM better simulates the spatial distribution of seasonal mean precipitation than CMIP5 MMM and has shown improvements in biases over central India, northeast India, and also in capturing orography related precipitation over western Ghats and the northeast Himalayas. CMIP6 MMM performed better than CMIP5 MMM in capturing precipitation trends but failed to capture the overall declining trend. In consequence, in terms of precipitation simulation, the CMIP6 models (pattern correlation 0.4-0.8) outperformed the CMIP5 models (pattern correlation 0.2-0.7). MMMs well capture the observed phase of the annual cycle of the precipitation but underestimate the amplitude during summer monsoon months. In contrast, most of the CMIP6 models and their MMM have improved skill scores (SS) (SS 0.66) in reproducing the climatological summer precipitation compared to CMIP5 models and their MMM (SS 0.57). Furthermore, the results show that the Somali jet strength is well associated with ISM rainfall and has risen by about 2 m s^-1 in CMIP6 MMM compared to CMIP5 MMM. 

Key Word: Indian Summer Monson, MMM, CMIP6, CMIP5, Precipitation