Shifting streamflow patterns in the Upper Jhelum Basin, Western Himalaya: implications for water availability under changing climate

We applied an integrated modelling framework combining SWAT for hydrological simulations, Coupled Model Intercomparison Project Phase 6 (CMIP6) climate projections under SSP1-2.6, SSP2-4.5, SSP5-8.5, and MODFLOW to assess surface-groundwater interactions. Results show that curve number, baseflow recession, groundwater delay, and snowmelt-driven runoff strongly regulate streamflow variability. Snowmelt contributes ~52 % of June discharge, as simulated using the temperature- index snowmelt routine in SWAT, while baseflow dominates at Asham and Baramulla. Historical patterns reveal declining spring flows, amplified summer runoff, and extremes such as the 2014 flood (1600 m3 s⁻1). Future scenarios project earlier snowmelt peaks (late April-early June under SSP5-8.5), resulting in ~30 % reduced April flows and ~15 % higher June flows. Baseflow is expected to rise by 10-18 % in dry months, whereas extreme floods may exceed historical magnitudes by up to 20 %. These shifts jeopardize water security, highlighting the need for adaptive, resilient management.