Comparative analysis of snow parameter calibration in the mountainous euphrates Çoruh and Aras basins using the swat hydrological model

In mountainous basins, snow is a critical component of the water cycle. Snow accumulation in eastern Turkey is particularly important for the Euphrates, Coruh and Aras rivers. The snow that accumulates in winter melts in spring and summer, providing a constant water supply for rivers and lakes. In this study, four mountainous upstream sub-basins of the Euphrates, Coruh and Aras basins were selected as the study area and hydrological modeling was performed with SWAT. Model outputs were calibrated with the SWAT-CUP automatic calibration program. Flow, meteorological and snow measurements were used in the modeling process. Snow depth data were distributed at the sub-basin scale with the developed SNOlaps snow depth change rate parameter and calibrated with the snow outputs of the model. In the snow calibration process, average NSE values of 0,70, 0,82, 0,81 and 0,24 were obtained for basins E21A019, E23A016, E230A29 and D24A029, respectively. In the validation process, average NSE values of 0,60, 0.60, 0.25 and 0.64 were obtained respectively. According to the findings, snow falls earlier in Kemah and Coşkunlar Basin, while snowfall is observed later in İspir and Karakurt Basins After the snow parameterization process, the flow outputs of the basins were calibrated and NSE values of 0,73, 0,63, 0,61, 0,73 were obtained for calibration and 0,58, 0,50, 0,32, 0,36 for validation, respectively.