Rainfall erosivity and variability in the Northern Ethiopian Highlands

Rain intensity is smaller than expected: 88% falls with an intensity <30 mm h−1. High intensities have a short duration; maximum recorded rain depth over 1 h (32 mm) is only 2 mm less than that over 24 h. Using the blotting paper method 65,100 rain drops were sampled. For all observed rain intensities, the median volume drop diameters (D50) are significantly larger than those reported for other regions of the world. A relation between rain intensity (I) and volume specific kinetic energy (Ekvol) was developed for the Ethiopian Highlands:Ekvol=36.65(1−(0.6/I))(R2=0.99,n=18),(EkvolinJm−2mm−1,Iinmmh−1).Due to the occurrence of large drop sizes, probably linked to the prevailing semi-arid to subhumid mountain climate, this relation yields, within the intensity range [0.6-84 mm h−1], larger values for Ekvol than elsewhere in the world. It is recommended to use this new relationship for calculating Ekvol of rain in the Ethiopian Highlands, as well as for the computation of Universal Soil Loss Equation's rain erosivity factor on yearly basis.