Rainfall erosivity mapping for Lorestan province

Rainfall erosivity is usually represented by indices based on rainfall characteristics. So far، many rainfall erosivity indices have been developed، out of which the R index (EI30 in the model of RUSLE) is the most acceptable one. By calculating the EI30 in various points، erosivity maps can be produced for the country، some provinces or any other parts of the country. In this study، erosivity map for Lorestan Province was produced using this index. In order to estimate this index for regions lacking data from recording rain gauges، regression analysis was used. Thus the EI30 index and a few easily obtainable rainfall erosivity indices were calculated for 13 recording rain gauges with long term and intensive rainfall data. A regression analysis was then carried out between EI30 index and other indices. The best regression equation was established using Modified Fournier index (MF) with determination coefficient and standard error of estimate of 0. 955 and 112، respectively. To mapping rainfall erosivity، all of rain gauges (both having rainfall intensity and daily rainfall depth records) existed in the province and that of the surrounding regions were then assessed، and 61 rain gauges having more than 15 year daily rainfall data were selected. The EI30 were then estimated for the selected ones using the regression equation. Mean، Maximum، Minimum and coefficient of variation of the rain gauges were 594. 94، 2257. 3، 98. 54 Mj-mm-ha-1hr-1year-1 and 66. 38 percent. For converting point erosivity data to a map، a number of common interpolation methods were assessed and in order to select the suitable one، cross- validatin method were used. from the interpolation methods، Co Kriging was found to be the most suitable in terms of low error measures based on cross validation. Therefore rainfall erosivity map were produced for Lorestan Province using Co Kriging.