Evaluation of main factors affecting soil erosion in FAO method using TOPSIS technique

In this study evaluation of erosion rate in Bolhasan area locating in south Zagros wasperformed using six-factor FAO method. Inthis method estimation of soil erosion rate was done based on evaluating 6 factors including geology, soil, topography and slope, soil cover, land use, the current state of erosion and sediment production in the watershed. After grading all the factors in hydrologic units in study area, using the sum of these grades, the intensityof soil erosion was determined and was classified into six classes. The results showed that approximately 42% of soils of the study area are in class III and 58% in class IV that revisions in the management strategy in both classes is necessary. In order to analyze the most important factors of erosion in the study area TOPSIS method was used. Results confirmed that the current situation of erosion with the weight of 0.5855 is the most important factor of erosion in the study site. Then the next important factors of erosion were soil cover with score 0.4143, geology with score0.4141,land use with score0.4140, slope with score0.4138 and soil with score0.4135.In this study, combining the field observations with application of GIS caused a higher accuracy in evaluationprocess.