Ground water availability assessment for a data-scarce river basin in Nepal using SWAT hydrological model

Mountainous river basins are expected to experience significant seasonal fluctuations in water supply due to climate change. Thus, hydrological modeling becomes further challenging while accounting for data-scarce mountainous basins observing climate change impacts. In this study, Soil and Water Assessment Tool (SWAT) was used to predict hydrological flow in the Sunkoshi River Basin (SRB) based on daily rainfall and temperature data spanning 36 years. The specific objectives of this study were: (i) to use the SWAT model to simulate the long-term hydrological response, (ii) to generate spatially distributed rainfall–runoff and subbasin-wise water balance components using well-established performance indicators. Calibration and validation at the outlet of the study area were successful, with the values of R2/Nash–Sutcliffe efficiency (NSE) calculated as 0.91/0.82 for monthly data and 0.79/0.73 for daily data. In the validation phase, the values of R2/NSE were 0.91/0.84 for monthly data and 0.82/0.75 for daily data, respectively. This study predicted the average yearly flow and precipitation at the SRB outlet to be 279 m3/s and 368.25 mm, respectively. Approximately, 30% of water loss was attributed to evapotranspiration, 18% to runoff, and 30% to lateral flow. The findings of this study will contribute to water resource management.