DISCONTINUITIES IN PRECIPITATION SERIES IN THE WEST AFRICAN SAHEL

Sequential application of the single shift Normal Homogeneity Test (NHT) to the time series of Sahel rainfall revealed three clusters of discontinuities or breakpoints separating climatically stationary periods: 1933–1944, 1955–1974, and 1980–1989. At least one breakpoint was detected in 33 of the 55 series analyzed, while two breakpoints occurred in 12. The breakpoints of 1933–1944 marked the termination of spatially localized droughts in western Burkina Faso and southern Mali. Generally speaking, the Sahel drought that began in the late 1960s, persisted into 1998. However, abrupt positive shifts that occurred during the late 1980s restored mean annual rainfall to pre-drought levels at isolated locations. The stationarity of the periods between breakpoints suggests that the abrupt shifts are the dominant source of inhomogeneity in Sahel rainfall. Unlike the widely used climatic normal periods (CNPs), stationary periods are suitable for calculating various empirical indices for application in agriculture and rural water-resources planning in the area. The large number of breakpoints detected at different time periods suggests that Sahel rainfall series are prone to sudden transitions between quasi-stable climatic regimes; much like the onset, drought may terminate abruptly through a sudden shift in the mean annual rainfall. Key words: Sahel, West Africa, drought, rainfall.]