Rainfall Erosivity Factor (R)

 It refers to the rainfall erosion index, which expresses the ability of rainfall to erode the soil particles from an unprotected field. It is a function of the physical characteristics of rainfall. Since the measurement of R is complicated, it is best estimated from certain indices called Erossivity indices viz EI30, KE>25 mm/hr, and AIm.

EI30: Studies have shown that soil loss by splash, overland flow, and rill erosion is related to a compound index of kinetic energy and the maximum 30 minutes rainfall intensity. The I30 is the greatest average intensity experienced in any 30 minute period during a storm.

KE> 25 mm/hr: It is based on the fact that little erosion takes place at low intensities. At low intensity, rain is composed mainly of small drops, falling with low velocity, and hence low energy. The intensity of 25 mm/hr can be taken as a threshold value separating erosive and non-erosive rain.

AIm: It is the product of the amount of rain (A) and maximum intensity (Im) over a 7.5 minute period. For NW India, the 15 minute period of rain intensity has been observed to be best correlated to soil loss, especially for tropical rain.

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