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Drop size distribution and kinetic energy load of rainfall events in the highlands of the Central Rift Valley, Ethiopia

Meshesha, Derege Tsegaye, Tsunekawa, Atsushi, Tsubo, Mitsuru, Haregeweyn, Nigussie, Adgo, Enyew
Hydrological sciences journal 2014 v.59 no.12 pp. 2203-2215
energy, erodibility, fallow, highlands, rain, rain intensity, soil erosion, soil types, Ethiopia
Knowledge of rainfall characteristics is important for estimating soil erosion in arid areas. We determined basic rainfall characteristics (raindrop size distribution, intensity and kinetic energy), evaluated the erosivity of rainfall events, and established a relationship between rainfall intensity I and volume-specific kinetic energy KE ᵥₒₗ for the Central Rift Valley area of the Ethiopian highlands. We collected raindrops on dyed filter paper and calculated KE ᵥₒₗ and erosivity values for each rainfall event. For most rainfall intensities the median volume drop diameter (D ₅₀) was higher than expected, or reported in most studies. Rainfall intensity in the region was not high, with 8% of rain events exceeding 30 mm h ⁻¹. We calculated soil erosion from storm energy and maximum 30-min intensity for soils of different erodibility under conditions of fallow (unprotected soil), steep slope (about 9%) and no cover and management practice on the surface, and determined that 3 MJ mm ha ⁻¹ h ⁻¹ is the threshold erosivity, while erosivity of >7 MJ mm ha ⁻¹ h ⁻¹ could cause substantial erosion in all soil types in the area.