Rainfall erosivity and variability in the Northern Ethiopian Highlands

• Published in: Journal of hydrology (Amsterdam) 2005-09, Vol.311 (1), p.172-187
• Main Authors: Nyssen, J., Vandenreyken, H., Poesen, J., Moeyersons, J., Deckers, J., Haile, Mitiku, Salles, C., Govers, G.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Erosivity; Ethiopia; Exact sciences and technology; geographical variation; highlands; Hydrology; Hydrology. Hydrogeology; Intensity; Marine and continental quaternary; mountains; Rain; Rain drop size; rain intensity; Rain kinetic energy; rainfall energy; Spatial variation; Surficial geology; water erosion
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2004.12.016

The Ethiopian Highlands are subjected to important land degradation. Though spatial variability of rain depth is important, even at the catchment scale, this variability has never been studied. In addition, little is known on rain erosivity for this part of the world. The objectives of this study are (a) to assess the spatial variation of rain in a 80 km 2 mountain area (2100–2800 m a.s.l.) in the Northern Tigray region, and how this variation is influenced by topography, geographical position and lithology, (b) to analyse the temporal variations and (c) to quantify rain erosivity and the different factors determining it, such as rain intensity, drop size and kinetic energy. Spatial variation of rain was measured over a 6-y period by installing 16 rain gauges in the study area. Topographical factors, especially general orientation of the valley and slope gradient over longer distances, determine the spatial distribution of annual rain, which is in the order of 700 mm y −1. Precipitation is highest nearby cliffs and other eminent slopes, perpendicular to the main valleys which are preferred flow paths for the air masses. Rain intensity is smaller than expected: 88% falls with an intensity