A study on the west Sahel rainfall variability: The role of the intertropical convergence zone (ITCZ)

This article provides a report of rainfall analysis results supporting the hypothesis that rainfall variability in the Western Sahel is associate with temporal variability of the incursions of ITCZ over West Africa. It is pointed out that the most significant climatic rainfall changes in Sahel most probably occurred between 1950 and 1975 with the decrease of the annual rainfall totals, a high reduction (about 70%) over the whole region. One of the most significant climatic variations has been the rainfall persistent decline in the Sahel since late 1960’s. Remarkable latitudinal shift of ITF mean position towards the South seems to generate an overall reduction of annual rainfall. In the last two decades covered in this research (1985–2004), rainfall showed some improvement, particularly in the 1990–1999 decade. However, the more humid conditions of the 1950’s and 1960’s were not reestablished yet. The trend was abruptly interrupted by a return of adequate rainfall conditions in 1994. This was considered to be the wettest of the past 30 years and was thought to indicate the end of the drought perhaps. However, the 1994 rainfall total barely exceeded the long-term mean. The 1994 rainy season was unusual in the sense that the anomalously wet conditions occurred in the end of the rainy season and the months following. The temporal characteristics of the series, such as variance, were evaluated using principal components regression.