Temporal and spatial variations of rainfall erosivity in Southwest of Iran

Rainfall erosivity index is the most important factor which impacts soil erosion. The objective of this research was mapping spatial and temporal variations of rainfall erosivity in the southwest of Iran. Properties of 10,000 rain storms belonging to 27 climatological stations were analyzed and their synthetic energy (E) and maximum 30 minute rainfall intensity (I30) were calculated. The mean annual and monthly rainfall erosivities were calculated for all station's data. Mapping spatial variations was carried out using Spline algorithm. The results showed that the monthly erosivity index values decrease from the north to the south and from the west to the east of the region. Maximum and minimum values of annual erosivity were equal to 26.39 and 6.11 MJ.mm.ha-1.h-1.yr-1 belonging to Ivan (Ilam province) and Brojen stations (Chaharmal Va Bakhtiari province), respectively. Temporal studies of rainfall erosivity index indicated that maximum rainfall erosivity was equal to 183.7 MJ.mm.ha-1.h-1.yr-1 and occured in winter. Existence of significant correlation coefficients between the means of monthly and annual rainfall values and their corresponding rainfall erosivities were 0.94 and 0.93, respectively and such significant correlation coefficients facilitate indirect estimations of monthly and annual rainfall erosivities through rainfall values and simple or multiple regression models. The results revealed higher reliability of multiple regression models consist of both means of annual rainfall and rain storm intensities than simple regression models for estimation of annual rainfall erosivity.