Modeling Seasonal Rainfall Erosivity on a Regional scale: A case Study from Northeastern Iran

There is a need to analyze and map rainfall erosivity to assess soil erosion at the regional scale. The objectives of this study were to develop a regional model to estimate seasonal erosivity from seasonal rainfall data and to study temporal and spatial distribution of rainfall erosivity for the Gorganrood drainage basin in the northeast of Iran. Six gauging stations with a high temporal resolution (15 min) and eleven monthly totals stations located into the study area have been used. Regression models for pluviograph stations indicated that storm rainfall explained 22-51% of the variation in storm erosivity. But, at the seasonal scale, the explained variation increased to 62-86% and modified coefficient of efficiency increased from 0.12-0.29 to 0.38-0.64. Also, the results of ANOVA showed that EI30 values have significant difference between autumn/summer seasons and winter/spring seasons. Interpolation surfaces were created from all 17 stations seasonal values using the local polynomial algorithm. The results showed, during the wet season, erosivity varied from 438 Mj/mm/h (west) to 1015 Mj/ mm/h (Middle). But, in the dry season, values of erosivity were lower than from values in wet season and the highest values were at the middle parts of the study area and the lowest were at the eastern and the western parts of the study area. Our findings provide good guidance to integrate pluviograph and pluviometric data for rainfall erosivity assessment in regional scales, where short duration rainfall intensity data, usually are not available.