Assessing the Changes in Indian Summer Monsoon in Warm Climates: Mid‐Pliocene and Future Projection by the End of 21st Century

ABSTRACT In this study, changes in the Indian Summer Monsoon (ISM) mean state have been examined in the future period (2071–2100 using the SSP5‐8.5 scenario with respect to the historical 1985–2014) and past period (mid‐Pliocene with respect to the pre‐industrial), having a similar global surface air temperature increase. The ensemble of six models from the Coupled Model Intercomparison Project phase 6 (CMIP6) has been considered based on the common availability of variables from these models' outputs. In the annual cycle of precipitation over the Indian landmass, by the end of the 21st century, a shift has been projected in the peak rainfall month from July to August. It is also found that the monsoon precipitation rate increases over the Indian region in the future warm climate and past mid‐Pliocene with respect to their reference periods; however, the increase rate is slightly lower in the future climate in comparison with the past warm climate. These changes are elucidated through dynamic and thermodynamic aspects of the monsoons. Our results reveal that the simulated moisture amount over the Indian region is found to be higher in the future warm climate as compared to the mid‐Pliocene period. Subsequently, enhanced surface and tropospheric temperatures in the Indian region in a future warm climate relative to the past are also noticeable. From a dynamical perspective, the large‐scale low‐level wind circulation changes and convection over the Indian subcontinent are simulated to be stronger in the mid‐Pliocene compared to the future warm climate. Furthermore, moisture budget analysis reveals that during the past warm climate, both the thermodynamic and dynamic components have contributed to intensified ISM conditions. However, by the end of the 21st century, the projected ISM rainfall increase is dominated by thermodynamic components (based on the extent of warming).