Climate change impact assessment on the river discharge of the upper Ganga Subbasin

The HKH region has many glaciers, providing fresh water to a large population downstream. The hydrological system is susceptible to climate change, especially temperature and precipitation. The present study aims to investigate the impact of climate change on the discharge and water balance of the snow-dominated upper Ganga Basin. The study utilized CMIP6 scenarios SSP2-4.5 and SSP5-8.5 with SPHY to simulate future hydrological changes in the basin. We calibrated and validated the model for simulation by using observed discharge data at Devprayag. The historical period (1985–2014) calibrated at Devprayag showed rainfall, snow, glacier, baseflow, and total discharge of 509.5 m3/s, 117.5 m³/s, 86.1 m³/s, 78.9 m³/s, and 792.0 m³/s, respectively. Contribution to total flow was 63.3% (rain), 10.8% (glaciermelt), 14.9% (snowmelt), and 10.0% (baseflow). Total runoff increased, with rainfall runoff, contributing the most, followed by glaciermelt runoff and baseflow, while snowmelt decreased. By the end of 21st century, temperature and precipitation is anticipated to rise under SSP5-8.5. The model estimates substantially impacted the basin hydrology and water balance, with a 50% increase in total flow in the Far Future (2076–2100). The snowmelt contribution is estimated to decrease by 57% by 2090, but the water supply is not expected to desrease. The analysis showed that snowmelt runoff will be reduced through time, and river discharge will be highly impacted by climate change. This work will improve understanding of water availability, snowmelt, and glacier melt dynamics, which, along with climate change, lead to sustainable water resource management.