WEPP model efficiency in estimation of runoff and soil loss in stony rangelands of Khamesan watershed, Kurdistan

The aim of this study was to evaluate the efficiency of WEPP model in estimation of runoff and soil loss under natural events at plot scale in rangelands of Khamesan watershed, Kurdistan. Runoff and sediment induced by events leading to runoff were measured over three years (2011 to 2013) at eighteen plots of 24 m long by 1.8 m wide (6 Hillslopes-three plots in each hillslope). At the same time, the input data including soil characteristics, vegetation and ground cover were evaluated and recorded during this period. In overall, 24 events were investigated. Model validation was performed with 16 remaining events, after calibration the model with eight events data based on the single event section of the model. The model estimated runoff and soil loss with acceptable accuracy under natural events in rangeland hillslopes containing significant amounts of rock fragment. The soil loss estimations were somewhat better than total runoff. In general, the model efficiency was lower in the hillslopes with higher rock fragment (especially rock cover) and higher percentage of lime, than the other hillslopes. It seems that rainfall intensity pattern during each event also had a significant effect on the model estimations. In WEPP model for single event estimations, just some of storm characteristics are used as input, and intra-storm variations are not considered which may have a significant impact on the amounts of runoff and sediment.