Assessment of CMIP6 GCMs’ Simulation of Southwest Monsoon Rainfall over Indian Monsoon Core Region

In this study, performances of forty-one Global Climate Models (GCMs) from the data archive of Coupled Model Intercomparison Project Phase 6 (CMIP6) were evaluated in simulating the Southwest Monsoon Rainfall (SWMR) for the historical run from 1955 to 2014 over the Indian Monsoon Core Region (MCR) using gridded rainfall data available at daily scale from the India Meteorological Department (IMD). An evaluation framework based on statistical metrics and skill scores were adopted for assessment, and a Comprehensive Rating Index (CRI) was estimated for ranking the models. The systematic analysis showed that 51% of models performed well in the MCR of India for the study period taken. Later, the future possible precipitation variability in terms of intensity and frequency for the top-ranked model, NorESM2-MM, was analysed using a Probability Density Function (PDF) method in three categories of monsoon years, namely strong, weak, and normal. The analysis was done under four Shared Socioeconomic Pathway (SSP) scenarios, with the radiative forcing of 2.6, 4.5, 7.0, and 8.5 (W/m²) during near (2021–2040), mid (2041–2060), and long (2081–2100) term future projection periods. On the seasonal scale, it is speculated that the intensity of monsoon precipitation distribution may increase progressively up to 20 mm/day for strong and normal SWMR years by the end of the twenty-first century. The projected precipitation mean change during strong and normal SWMR years were calculated to increase up to ~ 27% and ~ 21%, and for weak SWMR, it was ~ 49%, the highest among the other two categories. The projected results confirm and indicate the strong sensitivity of regional monsoon to the increasing greenhouse gas emissions and land use change.