The Problem of Assessing the Erosive Power of Rainfall from Meteorological Observations

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Abstract
A number of rainfall parameters have been proposed in the past as bases for indexes of erosivity. Values for three such parameters—momentum, kinetic energy, and kinetic energy per unit horizontal area of the drop—were calculated from drop‐size data and relationships between rainfall intensity and the parameter values were developed. Examination of these relationships showed that both raintype and geographic location influenced the parameter values. This suggests that the detachment ability of rainfall, at a given rainfall intensity, may vary between raintypes and geographic locations. However, the degree and direction of the influence depended on which parameter was being considered. The ordering of five raintypes at Miami, Florida, determined by values obtained at given rainfall intensity from the intensity‐parameter regressions for momentum and kinetic energy was reversed for kinetic energy per unit horizontal area of the drop. Therefore, in the absence of data on the rate of soil detachment, it is not possible at present to classify the raintypes at a geographic location according to their detachment power. In the view that runoff is a major factor in controlling the transport phase of soil erosion, the observations indicate that rainfall parameters may only be evaluated as indexes of the detachment power of rainfall if they are determined directly and simultaneously with soil loss, and provided that the influence of runoff on soil loss is taken into account.

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