Climate change impact on water availability in the Himalaya: Insights from Sunkoshi River basin, Nepal

Changing streamflow is one of the most visible consequences of climate change. In this study, the Soil and Water Assessment Tool (SWAT) model was used to investigate the significant effects of climate change on streamflow in a Himalayan River. We incorporated information from several Global Climate Models (GCM), considering two climate scenarios: SSP 2.45 and SSP 5.85, which are part of Shared Socioeconomic Pathways (SSPs) for the future periods of 2022–2030 and 2031–2050. Substantial patterns in temperature and rainfall changes were identified using ensemble modeling. Under both SSPs 2.45 and 5.85, the results indicated a rising trend in temperatures from January to June, a decline from June to September, and a marginal increase from October to December. Additionally, annual rainfall, real evapotranspiration, and river flow are anticipated to rise by 17.67–21.79%, up to 0.93%, and 23–53%, respectively in the upper region of the study basin. Conversely, across the two future periods and scenarios, the lower region is depicted to have a decline in rainfall of 20.84–36.34%, evapotranspiration of up to 4.35%, and river flow of 38–65%. These findings will be invaluable for the design and construction of climate-resilient water resources related projects in the Himalayan regions, such as Nepal.