Appointment and estimation of appropriate rainfall erosivity index in Khorasan Razavi province

The rainfall erosivity index is one of the important factors that affect soil erosion. Therefore، evaluation of the accuracy of rainfall erosivity indices is important for different climatic regions. The objective of this research was to investigate different rainfall erosivity factors and determine the appropriate ones in Khorasan Razavi province. For this reason، 15 rainfall events resulted in runoff were recorded from 2006 to 2009 at the Sanganeh soil erosion research station، and associated sediment amounts gauged from 92 soil erosion plots in 25 groups of 2 m width and 5، 10، 15، 20، and 25 m length. Then، 63 different intensity-based rainfall erosivity indices and their regression relationships with associated soil loss amounts were computed for recorded rainfall events. The statistical analysis demonstrated that index had the most significant correlation of 0. 740 (P < 0. 01). Then، long-term average of selected rainfall intensity-based index and 7 rainfall-amount based indices and their regression relations were also computed for 15 recorded rain gauge stations. The results showed that mean annual rainfall displayed a significant correlation with selected rainfall intensity-based index (r =0. 99، P < 0. 01). Selected regression relation was recommended to estimate the rainfall intensity-based index at stations without rainfall intensity data in the studied provinces.