Increased Summer Monsoon Rainfall Over Northwest India Caused by Hadley Cell Expansion and Indian Ocean Warming

From 1979 to 2022, the summer monsoon precipitation has increased by a substantial 40% over Northwest India compared to the 1980s. This wetting trend aligns with the future projections of the Coupled Model Intercomparison Project 6 (CMIP6). The observationally constrained reanalysis data indicates that significant sea surface warming in the western equatorial Indian Ocean and the Arabian Sea is likely driving this increase in rainfall by enhancing the cross-equatorial monsoonal flow and associated evaporation. We demonstrate that the strengthening of the cross-equatorial monsoon winds is due to the rapid warming of the Indian Ocean and the enhanced Pacific Ocean trade winds, which result from the poleward shift and expansion of the Hadley cell. These strengthened winds boost the latent heat flux (evaporation), leading to increased moisture transport to Northwest India. From 1979 to 2022, the summer monsoon precipitation has increased by a substantial 40% over Northwest India compared to the 1980s. The analysis suggests that a noticeable warming of the sea surface in the western equatorial Indian Ocean and the Arabian Sea could be causing this increase in rainfall. This warming strengthens the winds crossing the equator in the Indian Ocean and increases evaporation. The study also shows that the monsoon winds are strengthened due to the rapid warming of the Indian Ocean and the enhanced Pacific Ocean trade winds. These stronger winds cause more evaporation, which means more moisture is carried from the ocean to the land, leading to increased monsoon rainfall. Large increase in summer monsoon precipitation over Northwest India The strengthening of the monsoon winds and the Indian Ocean warming drives increasing evaporation Poleward shift and expansion of high-pressure belts and the Indian Ocean warming are responsible for the strengthening of winds