Evaluating the Spatial-Temporal Variations of Rainfall Erosivity and Erosivity Density (A Case Study: Menderjan Watershed, Isfahan Province)

Rainfall erosivity is one of the factors determining the amount of water erosion in the soil. Rainfall erosivity is determined by the  total rainstorm energy and the maximum intensity in 30 minutes (I30). Since rainfall erosivity is closely related to the amount and intensity of rainfall, it is expected that the rainfall erosivity would change monthly and seasonally throughout the year. The main objective of this study was the  spatial and temporal variation modeling of rainfall erosivity, erosivity density and their impacts on the soil erosion in Menderjan watershed. In this research, by using rainfall data with 1 minute from the rain gauge in the proximity of the basin during the 11-year statistical period (2005-2015), the rainfall erosivity factor (R) was calculated on a monthly average; then it was mapped using geostatistical technologies. Comparison of the monthly, seasonal and annual rainfall erosivity maps showed the highest rainfall erosivity occur in autumn (about 41 percent), while  the lowest one was recorded in summer (less than 1%), respectively. According to the results obtained the maximum amount of erosivity was observed in November, which was 65 (MJ.mm.ha-1.h-1.month-1), while the lowest amount was observed in August. This study showed that the highest risk of soil erosion was  expected to occur in November, because this month  is not only the time of rainfall erosion, but also involves a high erosion density.