Spatial teleconnections in African rainfall: A comparison of 19th and 20th century patterns

Abstract

Rainfall variability over the African continent is remarkably coherent on large-spatial scales. The continent as a whole has exhibited marked fluctuations of rainfall on scales from decades to millennia. A newly created data set commencing in 1800 allows for the comparison between patterns of spatial variability that prevailed on modern and historical time scales. The results show the dominance of a small number of spatial patterns, one of the most common being anomalies of the same sign over most of the continent. Two other common modes are an opposition between equatorial and subtropical regions and an east–west opposition in the equatorial region and in southern Africa. In these modes, the shift between negative and positive poles can be abrupt. These patterns remain stable over time. That is, the spatial patterns and their degree of dominance are markedly similar during the 19th and 20th centuries. On the other hand, the large-scale factors governing the rainfall regime appear to vary on decadal time scales. This is particularly true for ENSO and the Indian Ocean Zonal Mode. The associations with large-scale wind regimes are more stable over time. The robustness of these patterns and varying importance of large-scale factors have implications for the interpretation of paleoclimate data.