This study tries to investigate relationship between rainfall parameters and USLE R factor. To gain R-factor, at first, shower kinetic energy was calculated and then its erosivity computed by using maximum 30 minutes rainfall intensity. Therefore 3 meteorological stations in Khuzestan province and one station per Kohgiloyeh & BoyerAhmad and Boushehr provinces were selected and their recorded hyetographs of 13 years were analyzed. For any hyetographs, rainfall erosivity was computed in any one month, season, or year and corresponding rainfall parameters were extracted too. Temporal and spatial variation of rainfall erosivity was studied and relationships between R factor and rainfall characteristics were investigated by using regression analysis. It was resulted that February to March and winter season has the most erosivity risk. Spatial analysis of rainfall erosivity in selected area showed that Dezful and Ramhormuz have the maximum erosivity factor. Mean annual erosivity factor of Khuzestan province was computed 28.07 ton.m/ha.h. Regression analysis showed strong relationships between rainfall amount (mm) and maximum 30 minutes rainfall intensity (cm/h) with R factor. A model that computes R-factor by means of rainfall amount was suggested.
