Evaluating the Performance of Soil and Water Assessment Tool (SWAT) in a Snow-Dominated Climate (Case Study: Azna–Aligoudarz Basin, Iran)

This study aims to investigate the capability of the SWAT (Soil and Water Assessment Tool) model in hydrologic simulation of a cold and mountainous climate, the Azna–Aligoudarz Basin, Iran. For this purpose, daily climatic data from the Aligoudarz synoptic station, discharge data from the Marbare hydrometric station, soil and land use maps, and a 10 m digital elevation model of the study area were used. The results demonstrated that the model exhibited poor performance due to poor simulation of runoff generated from snowmelt. To enhance the model’s performance, the calibration period was split into warm and cold seasons using a temperature threshold of 3.6 °C. As a result, the model’s performance improved, with the Nash–Sutcliffe Efficiency (NSE) increasing from 0.28 to 0.60 and R2 rising from 0.32 to 0.61. The research indicated that refining the conceptual and theoretical framework of the SWAT model is essential to reduce uncertainty and achieve reliable accuracy, particularly in snow-dominated and mountainous areas.