Modeling snowmelt-driven streamflow dynamics in a Himalayan Basin under climate warming scenarios

The snow and glacier-fed Swat River Basin (SRB), located in the Hindukush region of Pakistan, plays a vital role in supporting ecosystems and downstream communities. However, the basin is highly vulnerable to climate change, as evidenced by frequent historical floods. This study simulated historical and future snowmelt runoff using the Snowmelt Runoff Model (SRM), integrated with an enhanced MODIS snow and glacier product (MOYDGL06*), along with Digital Elevation Model (DEM) and hydro-meteorological data. The model was calibrated and validated over 2005–2009 and 2011–2015, respectively, using basin-wide and zone-wise simulation approach. The key findings of the study indicated: 1) SRM coupled with the improved snow product effectively simulated daily river discharge, achieving mean Nash–Sutcliffe Efficiency (NSE) values of 0.90–0.91 and Volume Differences (D v ) of 0.51% to –1.31% during calibration, and NSE of 0.84–0.87 with D v of –0.83% to –2.27% during validation. The basin-wide approach performed more consistently due to integrated hydrological representation and lower parameter uncertainty. 2) Future projections under three RCP scenarios indicate increases of ~8–18% (2046–2065) and ~7–34% (2081–2100) in mean annual flow and increases of ~7–16% and ~7–30% in mean summer flow, respectively. An increase of 1 °C in temperature is projected to enhance both seasonal and annual flows by about 6–7%. These projected increases are primarily attributed to enhanced snow and glacier melt due to rising temperatures. The findings emphasize the need for adaptive strategies in water resources management and flood risk mitigation in the study area, especially under changing climatic conditions.