Characteristics of African rainfall – An update

Abstract

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.