Projected alterations in snowmelt streamflow with climate change in Shiyang River Basin of Northwest China using modified SWAT model

Abstract

The timing and magnitude of snowmelt are changing due to global warming, posing significant implications for irrigated agricultural areas reliant on snowmelt streamflow. By taking the Shiyang River Basin (SRB) in Northwest China as the study area, this study focuses on accurately quantifying the snowmelt derived streamflow and its variation under the impacts of future climate change. Based on the observation data, we modified the snowmelt factor seasonal variation formula in the source code of the Soil and Water Assessment Tool (SWAT) to improve the simulation capability. Results show that the original SWAT model tends to overestimate streamflow, whereas the enhanced model (SWAT-s) aligns more closely with measured streamflow during both calibration and validation periods. The SWAT-s improves the snowmelt streamflow simulation performance and outperforms SWAT in capturing the monthly streamflow peak, especially in springtime. Furthermore, we integrated SWAT and SWAT-s with the bias-corrected 6th International Coupled Model Comparison Program (CMIP6) under four Shared Socio-economic Pathways (SSP) scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) to investigate the projected alteration in future streamflow, evapotranspiration, snowmelt, and soil water content. Compared with the baseline period (1985–2014), a decrease in annual streamflow but an increase in snowmelt streamflow in early spring was projected in the upper reaches of the SRB over the next 78 years (2023–2100). Evapotranspiration showed a significantly increasing trend, while snowmelt and soil water content showed a significantly decreasing trend (P < 0.05) under the SSP5-8.5 scenario. The study provides the scientific basis for developing streamflow management plans to ensure the sustainable development of arid areas in Northwest China.