Multi-decadal Variability in the Sahel and Guinea Coast Regions of Africa

The recent update of an historical rainfall archive for Africa has allowed for the production of gauge-based time series commencing in 1847 and for the Guinea Coast, to the south, in 1883.  While a common pattern of inter-annual variability in these regions is an out-of-phase relationship, rainfall in the two regions tends to vary in-phase on decadal and multia-decadal time scales.  Both regions experienced an abrupt decline in rainfall in 1968 and the rainfall regime has never recovered to its pre-1968 state.  The decline was most evident in the boreal summer, which tends to be a dry season along the Guinea Coast.  Correlation between the two regions in this season changed from negative to positive after 1968.  Teleconnections to sea-surface temperatures and ENSO changed markedly after 1968 as well.  The driver of variability in that season along the Guinea Coast was consistently (i.e., throughout the analysis period) SSTs in the Gulf of Guinea, while ENSO played a major role in the Sahel prior to 1968.  After 1968, ENSO’s influence decreased over the Sahel but increased over the Guinea Coast, while the relationship between Sahel rainfall and Gulf of Guinea SSTs became more positive.