Hydroclimatic Changes in the Marsyangdi River Basin, Central Himalaya Under CMIP6 Scenarios: Implications for the Water–Energy–Food–Ecosystem Nexus

Climate change is fundamentally altering hydroclimatic regimes across the Himalayas, with cascading impacts on water, energy, food, and ecosystems (WEFE). We applied the SWAT+ hydrological model in the Marsyangdi River Basin (MRB) of central Nepal, using bias‐corrected CMIP6 projections under SSP2‐4.5 and SSP5‐8.5 scenarios to study hydroclimatic regimes. We employed an envelope approach spanning warm‐wet, warm‐dry, cold‐wet, and cold‐dry states to capture plausible futures for mid‐century (2041–2070) and end‐century (2071–2100). By end‐century, warming reaches +3.0°C (SSP2‐4.5) and +5.0°C (SSP5‐8.5), with precipitation increasing by 13% and 27%, respectively, driven by monsoon intensification. Annual discharge rises by > 30% and > 50%, yet snowfall declines by ~20% and ~35%, eroding the cryospheric buffer that sustains dry season flows. Pre‐monsoon discharge decreases under both scenarios, exacerbating early‐season water scarcity. Climate extremes intensify with extremely wet‐day contributions increasing up to 85% under SSP2‐4.5 and more than tripling under SSP5‐8.5, daily rainfall intensity strengthens by 45%–55%, and consecutive dry days lengthen by 30%–87%, signaling concurrent flood and drought risks. Sectoral consequences are compounding with dry‐season hydropower deficits reaching 44% under drier futures, while wheat irrigation demand nearly doubles by end‐century under SSP5‐8.5; paddy remains stable and maize rainfed. Simultaneously, declining dry‐season flows and intensified runoff increase environmental‐flow stress impacting aquatic connectivity, and elevate sediment‐related risks in Annapurna Conservation Area headwaters. Our findings reveal a pronounced seasonal mismatch between water availability and cross‐sectoral demand in the MRB, underscoring the urgent need for coordinated, climate‐state‐informed WEFE planning to enhance resilience under future conditions.