Application of SWAT model and SWAT-CUP software in simulation and analysis of sediment uncertainty in arid and semi-arid watersheds (case study: the Zoshk–Abardeh watershed)

This research aimed to appraise the performance of the Soil and Water Assessment Tool (SWAT) model in sediment flow simulation and also to investigate the uncertainty of the model in the watershed areas of arid and semi-arid regions. In this survey, we used the Sequential Uncertainty Fitting ver.2 (SUFI-2) algorithm to assess the uncertainty and calibrate the model. Different factors of water resources are simulated, and we consider the crop yield and water quality at the Hydrological Response Units (HRU) level. Besides, to quantify the water resources, we implemented monthly time intervals. Also, we used monthly time intervals to quantify the water resources. The results showed that in a 3-year validation period (2007–2010), the P-factor and the r-factor were 0.28 and 0.38 respectively, while in the 7-year calibration period (2000–2006), these two factors were 0.29 and 0.39, respectively. The findings of this study proved that in the validation period, statistical indicators of model evaluation comprise R2, bR2, and the Nash–Sutcliffe efficiency (NSE) coefficients were 0.85, 0.23, and 0.47, respectively, while in the calibration period, these coefficients were 0.46, 0.14, and 0.37, respectively. The results of uncertainty and calibration analysis were acceptable, but in the validation phase, the model has been more applicable and useful. These results show the acceptable efficiency of the SWAT model in simulating the sediment load of the study area. To assess the sensitivities of 22 input parameters, we used SWAT Calibration Uncertainties Program (SWAT-CUP) and achieved three of the most sensitive parameters comprising CN2, SOL_BD, and USLE_P. In contrast, the parameters with the least sensitivity were SLSUBBSN, GW_DELAY, and ESCO. We can use the calibrated model as inputs for SWAT, to assess the impact of climate change on soil erosion.