Evaluation of Hydrological Modelling Using a New Calibration Approach in a Snow-Dominated Climate

This study aims to investigate the capability of the SWAT (Soil and Water Assessment tools) model in hydrologic simulation of a cold and mountainous climate, Azna-Aligoudarz Basin, Iran. Daily climatic data from synoptic Aligoudarz Station for the period 1991-2023, discharge data from Marbare hydrometric station for the period 1991-2021, soil and land use maps, and a 10-meter digital elevation model of study area were used. 1991-1992, 1993-2016, and 2017-2021 were considered for the warm-up, calibration, and validation of the model, respectively. The results demonstrated that the model had a poor performance due to poor simulation of runoff generated from snowmelt if the complete dataset was used for the calibration. To enhance the model 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.