Observation, Simulation and Projection Approach to Rainfall Extremes over Indo-Gangetic Plains, INDIA

The Indo-Gangetic Plains (IGP) are one of India’s most densely populated and agriculturally vital regions, making them highly sensitive to changes in monsoon rainfall. Projections under high-emission scenarios indicate that seasonal mean rainfall may decline across much of the IGP, while very heavy and extreme short-duration rainfall events are expected to become more frequent and intense. High-resolution regional climate simulations under the CORDEX-CORE framework provide a detailed assessment of these changes. Multiple ensemble members of RegCM4, driven by MPI-ESM-MR, MIROC5, and NorESM, were evaluated against observations, showing that the model reproduces the spatial distribution and intensity of rainfall patterns over the IGP reasonably well, though it tends to slightly overestimate wet-day frequency. Analysis of climate indices indicates that seasonal mean rainfall and wet-day counts are projected to decline across much of the region by the late 21st century, while very heavy and extremely heavy rainfall events are expected to increase, particularly over the northern belt and Himalayan foothills. The upper tail of daily rainfall is projected to rise by 1.9–4.9%, reflecting an intensification of extreme events under warming conditions. Spatial patterns suggest a reduction in moderate rainfall events over the lowlands, with the northern IGP increasingly prone to intense rainfall episodes. To explore the mechanisms behind these extremes, different dynamical configurations of RegCM4—including hydrostatic, non-hydrostatic, and convection-permitting modes—were employed. Composite analyses of wind, temperature, geopotential height, horizontal moisture flux convergence, and moist static energy indicate that enhanced low-level convergence, intensified monsoon trough dynamics, stronger temperature gradients, increased atmospheric moisture, and higher convective available potential energy drive extreme rainfall events. Lead-lag diagnostics show that these conditions develop several days in advance, highlighting the combined influence of large-scale circulation, orographic forcing, and localized convection. Multi-model simulations, including REMO2015, COSMO, and their ensemble mean, confirm that these thermodynamical and dynamical patterns are robust across models. The study emphasizes the significance of high-resolution, multi-model, and multi-mode regional climate simulations in capturing both broad monsoon dynamics and localized extremes, offering crucial insights for adaptation, disaster management, and water and agricultural planning in one of the world’s most climate-sensitive and socioeconomically vital regions.