Accelerated hydrological response of the Western Himalayan glaciers to warming

Western Himalayan (WH) glaciers provide critical water resources but are rapidly retreating under climate change. The WH has warmed at 0.31 °C decade−1 over 1979–2019, twice the rate of the broader Indian landmass (0.16 °C decade−1) and higher than the Himalayan mean (0.24 °C decade−1). Projections indicate further warming of ∼3.5 °C–6 °C by 2100 under SSP3–7.0. We assess the response of WH glaciers to global warming levels of +1.5, +2.0, +3.0, and +4.0 °C using the open global glacier model forced with bias-corrected multi-model coupled model intercomparison project phase projections. Glacier meltwater is projected to peak near +2 °C before declining, with the total WH meltwater flux falling by 65.4 ± 10.7% at +4 °C. The response is strongly size-dependent, with small glaciers (<2 km−2) already declining in melt at +1.5 °C, medium glaciers (2–10 km−2) peaking near +2 °C, and large glaciers (>10 km−2) sustaining melt increases through +3 °C before declining by 20.3 ± 21.3% at +4 °C. The hydrological cycle broadens, and the rain fraction rises from 0.34 to 0.52 across the warming range, with implications for water management. The results presented here are for the WH glacierized region and are susceptible to uncertainties arising from inter-model variability and unrepresented cryosphere processes. Nevertheless, they consistently emphasize the importance of limiting warming to below 2 °C to sustain glacier-fed water resources.