Projected Hydro-Climate Extremes under 1.5°C and 2°C Warming over Indian River Basins (IRBs)

Abstract Global warming is intensifying hydroclimatic extremes across the Indian River Basins (IRBs) under the 1.5°C and 2.0°C global warming levels (GWLs) relative to preindustrial levels. Using multi-model CMIP6 projections under SSP2-4.5 and SSP5-8.5, we evaluate precipitation extremes across the IRBs. The Consecutive Dry Days (CDD) index shows a scenario-dependent response: under SSP2-4.5, dry-spell duration declines by 17–28% (approximately 11-28 fewer days) in the Barak, Indus, Brahmaputra, EFR (Pennar-Kanyakumari), Pennar, and Cauvery basins, while the Sabarmati and Inland Drainage basins increase by 9–11% (approximately 20-23 additional days) at 2.0°C GWL. However, the Consecutive Wet Days (CWD) index also shows a scenario-dependent response: under SSP2-4.5, wet-spell duration increases by up to 20.2% (approximately 5–8 additional days) in the Indus and EFR (Pennar–Kanyakumari) basins, whereas under SSP5-8.5, CWD decreases by 19–21% (approximately 10–12 fewer days) in the EFR (Mahanadi–Pennar) and Krishna basins. Projected maximum 5-day rainfall (Rx5day) shows mixed signals, with the largest increases in the West-Flowing River (Kutch–Saurashtra–Luni) basin (+16%) and the Ganga basin (+5%), and the largest decreases in the basin draining to Myanmar (−22%) and the Inland Drainage basin (−21%). Hotspots of increasing flood risk emerge in the Ganga and West-Flowing River basins, while the Inland Drainage basin shows the largest projected decrease in extreme rainfall. Overall, the additional 0.5°C of warming produces basin-specific and scenario-dependent shifts in drought and flood indices rather than a uniform amplification of both hazards, underscoring the need for basin-specific adaptation.