Assessment of future hydrology in the Gandaki River Basin under climate change using a multi-site calibration with the SWAT model

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This study assesses the future hydrology of the Gandaki River Basin, Nepal, using the Soil and Water Assessment Tool and bias-corrected CMIP6 climate projections under the SSP2-4.5 and SSP5-8.5 scenarios. The SWAT model demonstrated high performance at Naryanghat station, with R2 and NSE values exceeding 0.9 for both calibration and validation periods, providing confidence in future hydrological simulations. Results show that substantial hydrological changes occur under the SSP5-8.5 Warm Warm-Wet scenario: rainfall rises from 1961 to 4068 mm, surface runoff from 556 mm to 1838 mm, and groundwater flow from 309 to 600 mm, while snowfall decreases from 392 to 231 mm, reflecting a significant shift from snow to rainfall. This study emphasizes the spatial variability and importance of robust multi-site calibration in data-scarce Himalayan regions to address spatial and hydrological uncertainties. The finding highlights the need for adaptive water management and climate-resilient planning in high-altitude Himalayan basins. An advanced multi-site calibration approach improves hydrological model performance and spatial representation in complicated, data-sparse Himalayan terrain.Several climate scenarios for SSP2-4.5 and SSP5-8.5 are considered, integrating a bias-corrected CMIP6 climate model to enhance future hydrological projections.The results indicate that reduced snowfall, altered runoff and diminished groundwater recharge are key hydrological processes through which climate change significantly affects water resources.There is a high significance of snowfall in the hydrology of the basin, and snowfall is highly susceptible to warming temperatures.Findings demonstrate practical implications of altered hydrology for water resource planning and hydropower sustainability in mountainous regions under climate change. An advanced multi-site calibration approach improves hydrological model performance and spatial representation in complicated, data-sparse Himalayan terrain. Several climate scenarios for SSP2-4.5 and SSP5-8.5 are considered, integrating a bias-corrected CMIP6 climate model to enhance future hydrological projections. The results indicate that reduced snowfall, altered runoff and diminished groundwater recharge are key hydrological processes through which climate change significantly affects water resources. There is a high significance of snowfall in the hydrology of the basin, and snowfall is highly susceptible to warming temperatures. Findings demonstrate practical implications of altered hydrology for water resource planning and hydropower sustainability in mountainous regions under climate change.

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