Water balance simulation for the Ghare-Sou Watershed, Golestan, using the SWAT model

In this study, water balance of Ghare-sou watershed, was simulated using the SWAT model. The main objective of the study was to test the performance of SWAT and the feasibility of using this model as a water balance simulator for Ghare-sou watershed. The required input data were collected and the model was run. A parameters sensitivity analysis was performed using OAT method to determine the most important parameters. Model calibration was first performed manually and then automatically using SUFI2 algorithm. In order to reduce uncertainty, a number of hydrological components as well as a number of subcatchments were used simultaneously in the calibration and validation. The results showed that, the SWAT model performance for simulation of Ghare-sou watershed hydrology is satisfactory. During calibration, the simulated monthly flows in Syah-ab station (outlet of the watershed) matched the observed values with a Nash-Sutcliffe coefficient of 0. 6 and a coefficient of determination (R2) 0.65. These values were 0.36 and 0.62 during the validation. The values obtained for uncertainty assessment indicators were also satisfactory. P-factor and R-factor for the calibration period were 0.77 and 1.23 respectively and for the validation period were 0.97 and 1.73 respectively. Based on the model simulation, about 67% of the precipitation returns to the atmosphere through evapotranspiration process, about 17% runs off over land and moves toward the stream networks, about 16% percolates to the aquifer. This study provides useful information about water balance of the Ghare-sou watershed and helps better water resources planning for this watershed.