Determining the appropriate rainfall erosivity index by soil erosion plots in Semnan

The rainfall erosivity factor is one of the important parameters for the correct prediction of soil loss amount by water. However، the used rainfall erosivity indices in any region must be accurate. The aim of this research was studying the regression relations between rainfall erosivity indices and related soil losses from experimental plots after individual rainfall event in order to investigate the appropriate rainfall erosivity index in Semnan province. For this reason، rainfall events were recorded from a recording raingauge at the Jashloobar Researches Station in Semnan province، from 2008 to 2010. Also، soil loss amounts after any rainfall events were collected and determined from 6 plots with standard dimensions in two slopes، 3 and 15 percentage and 3 replications. Then، daily rainfall amounts، maximum intensities in different base times، total kinetic energy and other rainfall parameters for calculation of different indices were calculated and relations between these indices and related sediment amounts were studied. With statistical analysis of mentioned relations، 2 P. (I60) index، showed strongest correlation، r=0. 651 and significant at 0. 001 level. Also، long-term average of selected index and seven rainfall amount-based indices at 10 stations with raingauge in Semnan province for periods of 1 to 25 years were calculated. The regression relationships between 2 P. (I60) and readily available indices were investigated. Mean annual rainfall، standard deviation of annual rainfall and maximum monthly rainfall، showed good correlations (r=0. 83، 0. 82 and 0. 81، respectively) at 0. 001 level.