Evaluation of SWAT Model for Simulation of Runoff and Soil Moisture in Doiraj Basin of Ilam Province

Different models have been proposed to describe and predict the hydrology of the watershed which are different in terms of objectives and spatial and temporal scales. In this study, the SWAT model was used to simulate the hydrologic response of the doiraj basin. The main inputs of the model, which include meteorological data, a basinchr('39')s elevational digital model map, a soil map and land use map, are entered into the model. The model was implemented according to the curve number method, then, using the SWAT_CUP model, the performance of the model increased with entering the observation data of the discharge from the basin and performing the calibration steps during the period from 1996 to 2008. And then the validation step from 2009 to 2012 confirmed the modelchr('39')s ability to simulate rainfall-runoff and its use for study purposes. Long-term mean soil moisture in 1996, 2008, and 2013 was 524.24, 337.59, and 468.77 mm, respectively. The study of the simulated water balance components showed that for 1996, despite heavy rainfall, the water balance was almost zero, indicating a loss of water in the basin in the basin, with major evapotranspiration losses. The water balance is positive for 2008 and 2013 because the sum of evapotranspiration, river flow, lateral flow, infiltration and surface runoff are lower than the sum of precipitation.