Evaluation of CMIP5 and CMIP6 climate projections portrayed in the water balance components of a tropical humid region

Climate change impacts on the hydrologic regime are going to be significant, leading to severe and intensive extremities. Hence, regional-scale hydrological impact assessments are essential. This study evaluates the changing future hydroclimate conditions of the Western Ghats (WG) region in India, a biological hotspot, under CMIP5 and CMIP6 projections using a kernel-regression-based statistical downscaling approach and VIC hydrological model. CMIP6 models demonstrate superior skill in capturing historical spatiotemporal patterns of rainfall and temperature, particularly monsoon dynamics influenced by the WG orography. Future climate projections show a progressive warming of upto 3°C (SSP 8.5) by 2100, driving a shift in Kö-ppen climate classes from tropical monsoon to savannah in several coastalgrids. Downscaled CMIP6 rainfall shows 6–8% increase in monsoon precipitation in the northern region of WG and intensification of extreme rainfall events, consistent with recent flood occurrences in Kerala. Water-balance analysis reveals marked increase in annual rainfall, surface runoff, and evapotranspiration, with northern basins showing runoff increases of up to 600–800 mm towards the far future. Orographic influences, particularly the Nilgiris ridge gap, continue to dominate regional heterogeneity and modulate future rainfall amplification. The proposed methodological framework can be used for climate change impact studies in similar regions.