Investigation on the 1970s and 1980s droughts in four tributaries of the Niger River Basin (West Africa).

Abstract

West Africa has experienced severe droughts during 1970s and 1980s. On the other hand, the region is characterized by high inter-annual rainfall variability and there seems to be a recent recovery. But has the drought stopped? To answer this question, we evaluated spatio-temporal pattern of rainfall and runoff in four tributaries (Sota, Alibori, Mekrou and Kompa-gorou) of the Niger River basin, covering a total area of 40,000km2 for the period 1971 to 2010. First, decadal rainfall variability was investigated using Kriging-based isohyets. Cross entropy method was then applied to detect breakpoints in rainfall and runoff series. Additionally, the rainfall-runoff relationship was assessed via Spearman's rank correlation coefficients. Yet the drought started in 1970s peaked in 1980s, but the wetness of the last two decades led to an overall increase of both rainfall and runoff over the study area. Though a moderate to strong (0.57-0.66) rainfallrunoff correlation was obtained for three of the four investigated catchments, the breakpoints in rainfall and runoff series were not per se consistent probably due to gaps in discharge data. Rainfall depicted a shift around 1992 but runoff around 1983. The wetness of the decades, 1990s and 2000s and the manifold floods records of this first half of 2010s over West Africa are evidences that the droughts of 1970s and 1980s have stopped.