Climate change impact assessment on the hydrological regime of the upper Ganga Basin

The Hindu Kush region of the Himalayas is a valuable source of fresh water and is facing significant challenges due to its sensitivity to temperature and precipitation. Our study emphasizes Devprayag a snow-dominated area in the upper Ganga Basin. The study uses SPHY and CMIP6 Shared Socioeconomic Pathways (SSP2 4.5 and SSP5 8.5) data to project future changes in the hydrological variables. Historical observations from 1985 to 2014 already indicate a notable increase in total runoff. The most significant increase is seen in rain runoff, followed by glacier melt and base flow. Interestingly, snowmelt has exhibited a decreasing trend over the last three decades. The hydrological system undergoes more intense changes, likely due to an increase in climatic variables. By the end of the 21st century, the SSP 8.5 scenario predicts a rise in average annual temperature and precipitation. The SSP 8.5 scenario shows a more pronounced and rapid increase in total runoff, snow melt, and glacier melt compared to SSP 4.5. Our simulations suggest significant impacts on the hydrological regime and water balance of the region, particularly at Devprayag, where an increase of 63.21% in total flow is expected compared to 2015. Despite initial fluctuations, our analysis indicates a substantial increase in total runoff under SSP 8.5 by 2100, over 60% higher than the base year levels. This reflects a marked escalation in runoff rates over time, in line with the expected intensification of the hydrological cycle under this scenario.