Assessing the impact of climate change on snowmelt runoff and monthly streamflow in an Upper Himalayan River Basin using the SWAT model

The research aimed to explore the impact of climate change on average monthly streamflow and snowmelt-induced runoff for the Upper Alaknanda River Basin (UARB) in the Garhwal Himalayas. The Soil and Water Assessment Tool (SWAT) hydrological model was developed using historical climate and discharge data, and the model was then used for future projections. An average of thirteen bias-corrected Global Climate Models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), covering three key Shared Socioeconomic Pathways (SSPs): SSP2-4.5, SSP3-7.0, and SSP5-8.5, were provided as input into the SWAT model. Simulations were conducted on a monthly scale for three time periods: historical (1985-2014), imminent future (2030-2059), and extended future (2060-2089). Comparisons of the future periods with the historical period were investigated to analyze the change in monthly streamflow and snowmelt induced runoff. The highest increase for projected maximum and minimum temperatures are 4.02 degrees C and 4.24 degrees C, respectively, by the end of the century. The highest increase of projected precipitation (46.52%) by the end of this century is observed during the monsoon period. It was observed that rising temperature will have a greater impact in the pre-monsoon season in terms of increased ice melt induced discharge whereas precipitation played a more significant role during the monsoon period which was observed in terms of monthly streamflow. The average monthly projected streamflow is found to increase significantly during pre-monsoon period by the end of this century. There is an increase in melting dominated discharge due to rising temperatures in pre-monsoon period and winter season due to increased proportion of liquid precipitation.