Assessment of Climate Change on Water Availability in Central Himalayas, Nepal

The Kaligandaki River Basin (KRB) in Nepal, as one of the Himalayan River Basins, is experiencing severe impacts of climate change on its water resources. In this study, future climate projections from downscaled CMIP6 GCM models were used to evaluate the potential effects of climate change on the hydrological regime of the KRB by developing a hydrological model soil and water assessment tool (SWAT). Multi-site validation approaches were used to address the high spatial heterogeneity of the basin. The performance of the model was excellent, achieving a consistently very good ranking throughout the study, as evidenced by calibration and validation results. Under the intermediate emission pathways SSP245 scenario, the average annual temperature in the basin is projected to increase by 1.5C, with a maximum rise of 2.8C during the pre-monsoon season in the far future. In the high emission pathways SSP585 scenario, the average annual temperature is projected to increase by 2.2C, with a maximum rise of 4.3C expected during the winter season in the far future. Precipitation is anticipated to increase across all future time windows, with higher magnitudes under the SSP585 scenario. The combined effect of temperature and precipitation increases is expected to increase the discharge of the river. Specifically, discharge is projected to increase by 6% (under SSP245) and 12% (under SSP585) for 2025-49, 14% (under SSP245) and 24% (under SSP585) for the 2050-74, and 23% (under SSP245) and 40% (under SSP585) for the 2075-99 timeframes. The projected changes indicate an overall increase in average annual discharge, with greater increases expected under the high-emission scenario. These findings highlight the significant influence of climate change on the water balance components and hydrological regime of the KRB. Keywords: SWAT, Climate Change, Water Availability, Kaligandaki