Simulation of the effects different rangeland improvements scenarios on evapotranspiration of Gorganrud Watershed-Golestan

In water efficiency studies, the values of runoff, evapotranspiration and range production are the main variables. Rangelands of Golestan province, Iran, have a high potential of run-off due to the geographical location, climate, and destruction of these resources as well as drastic land use change from forests and rangelands to agricultural lands. Therefore, in the present study, in order to determine the best management of rangelands, we developed a rangeland improvement model using the Soil and Water Assessment Tool (SWAT) in the Gorganrud Watershed, Golestan Iran. Calibration and validation of model was performed using Sequential Uncertainty Fitting Program (SUFI-2) in the eco-hydrological model SWAT. For this purpose, the SWAT was calibrated and validated for a 31-year period of discharge and 5-year period of range production and then the model was executed for different scenarios of rangeland management. The results showed that the model performance was satisfactory for predicting discharge. The values of Nash-Sutcliffe coefficient were calculated to be 0.72, 0.71 and 0.64 in calibration period and 0.59, 0.48 and 0.53 in validation period for Basirabad, Tilabad and Haji Ghoshan stations, respectively. As well, four range improvement scenarios (mechanical, biological, biomechanical and livestock grazing management) were defined in this study. On average, by applying mechanical, biological, biomechanical, and grazing management scenarios evapotranspiration was increased to 2.3%, 12.8%, 15.5% and 2.8%, respectively, in comparison with actual evapotranspiration. According to the obtained results, the biomechanical scenario was identified as the best one in increasing evapotranspiration in poor and moderate rangelands.