Characteristics of African rainfall – An update

Each year during 1901-1990 was characterized as having an El Nino (EN) or Southern Oscillation minimum (SO) or warm (W) or cold (C) waters in east equatorial Pacific sea surface or any combination of these, or none (non-events). In contrast to Indian summer monsoon rainfall which showed a very good association between ENSOW type years and droughts, none of the African regions showed any significant, consistent relationship with any combination, except S. Africa where a slight bias for droughts was observed during El Nino years. When departures in specific regions were compared, often there was lack of coherence within regions. For years when departures in every region could be classified as positive or negative, all type of teleconnections between W. Africa, E. Africa and S. Africa were seen and no preponderance was observed for continental scale floods or droughts, nor for opposite depart for equator and subtropics. Five-year running averages indicated long intervals of positive departures preceded or followed by long intervals of droughts, with average spacings of -24 years for W. Africa and E. Africa (but phases not matching) and of -17 years for S. Africa. This seems to be a basis feature of African rainfall variability.

The El Niño–Southern Oscillation and the Transatlantic Slave Trade

The relationship between the El Niño-Southern Oscillation (ENSO) and the Transatlantic Slave Trade (TAST) is examined using the Slave Voyages dataset and a reconstructed ENSO index. The ENSO index is used as a proxy for West African rainfall and temperature. In the Sahel, the El Niño (warm) phase of ENSO is associated with less rainfall and warmer temperatures, whereas the La Niña (cold) phase of ENSO is associated with more rainfall and cooler temperatures. The association between ENSO and the TAST is weak but statistically significant at a two-year lag. In this case, El Niño (drier and warmer) years are associated with a decrease in the export of enslaved Africans. The response of the TAST to El Niño is explained in terms of the societal response to agricultural stresses brought on by less rainfall and warmer temperatures. ENSO-induced changes to the TAST are briefly discussed in light of climate-induced movements of peoples in centuries past, and in the drought-induced movement of peoples in the Middle East today.