Capability of hillslope version of WEPP model in prediction of runoff and soil erosion dynamic in different type of semi-arid rangeland

The WEPP physically model is able to dynamically simulate runoff and soil erosion using physical concepts of erosion and hydraulic of overland flow science considering plant growth، residue decomposition، winter process. Determination of the capability of this model in runoff and erosion estimation in different range type with investigation the effects of management were the main objectives of this research. This research was conducted in the Kabode placed across the Gharasoo watershed by installing erosion plot with dimension of 10×3 meter and three replications in three range types at the slopes of 25، 35 and 45%. Climate data including rainfall and air temperature was recorded in the site and additional data including wind velocity and direction، solar radiation and dew point temperature was prepared from Kermanshah synoptic climate station. Event based erosion and runoff was simulated in each plot by the v2008. 9 version of the model. Results from model assessment for prediction of runoff indicated that the maximum model accuracy was in 45% slope. Also، mode relative error in runoff in 25 and 35% slope was about 0. 61 liter. Overall، model performance in runoff estimation was sought in all three slopes، so that Nash-Sutcliff index was 0. 96 to 0. 73. Minimum and maximum estimation error in erosion prediction was occurred in 35 and 45% slope، respectively. Model prediction results indicated under-estimation in all the slopes. Negative amounts of Nash-Sutcliff index indicated confirms the low efficiency model especially in conditions prevailing in two slopes of 25 and 35%.