Rainfall variability in subequatorial America and Africa and relationships with the main sea-surface temperature modes (1951-1990)

The rainfall variability of subequatorial South America and Africa is poorly documented owing to the scarcity of data. We present a new land-only data set of monthly precipitation from 1951 to 1990, focusing on subequatorial South America and Africa, which improves the knowledge of rainfall variability and allows comparisons with GCM outputs. The results of multivariate analyses are compared with those performed on the best actual global rainfall data set developed by Mike Hulme. The main modes of bimonthly rainfall variability are not located in the major rain-forest basins of Zaire and Amazonia, but rather on the tropical margins, such as Venezuela or Sudan, and near-coastal equatorial areas, such as Guyana, Nordeste, Guinea, and Gabon. A regionalization into 13 homogeneous areas selected from the multivariate analyses is proposed. The statistical links between the rainfall variability and the four main sea-surface temperature modes indicate a strong influence of the El Nino-Southern Oscillation (ENSO) phenomenon upon South America (less/more rainfall during an El Nino/La Nina event) and a weaker impact, modulated by the Atlantic thermal state, upon Africa. The impact of ENSO events seems stronger since 1965 than before.