investigation of the effect of storm occurrence time on prioritization of factors affecting on erosion using wepp model sensitivity analysis (case study: shanganeh watershed, khorasan razavi province)

wepp model needs a great deal of input data.  identifying the model’s sensitive parameters and their prioritization increases the accuracy and efficiency of the model. on the other hand, wepp model can simulate processes affecting on runoff, erosion and sediment throughout the year. thus, model sensitivity must vary based on the storm occurrence time and parameters value in different sections of the year. to prove this assumption, two spring and autumn storm events related to 2008 were selected and sensitivity analysis of the wepp model was done in three plots with different conditions in sanganeh watershed. for sensitivity analysis, the oat method was used and sensitivity degree of parameters was calculated. obtained results show that the rate of sand is the most sensitive parameter of wepp model. this parameter was followed by other parameters like clay percent, effective hydraulic conductivity, height and intensity of rainfall, day degree of growing, growing season and percent of growing season when leaf area index decreases. most variations are observed in prioritization of sensitive parameter in the plant/ management file. in most cases, sensitivity degree of these parameters in autumn event comparing to the spring event has significantly reduced in all plots. in general, obtained results show that the rate of sensitivity of the wepp model to different parameters varies during the time. hence, for using this complex model in regions with data limitation, the user must be aware to this issue that regarding storm time, which parameter is more sensitive in the pilot area and need to be carefully measured in the field.