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.
