Indian Summer Monsoon rainfall changes beyond the 21st century

Future rainfall changes in India are of paramount importance for crop production and water management, but to date, longer-term changes beyond the year 2100 have not been evaluated. Here, we leverage a 10-member extension of the CESM2 Large Ensemble under relatively strong emissions (SSP3-7.0) to identify projected rainfall changes and the underlying physical mechanism out to 2500. Our main finding is that after 2100, substantial changes occur in large-scale atmospheric circulation patterns, which are more pronounced and distinct from the changes projected over the 21^st century. We test the hypothesis that under substantial thermal perturbations to the climate system after 2100, the increased atmospheric stability caused by the enhanced differential heating in the upper troposphere relative to land weakens the large-scale monsoonal circulation, while enhanced warming over the Tibetan Plateau causes a poleward shift in low-level monsoonal circulation and the climatological pressure belt. This projected shift promotes enhanced northward moisture transport, resulting in a strengthened anomalous ascending motion over northern India, ultimately leading to increased Indian summer monsoon rainfall post-2100. These changes reflect local expression of large-scale climate dynamical perturbations and provide a broader mechanistic framework for understanding long-term future climate change over India.