Common Mechanism for Interannual and Decadal Variability in the East African Long Rains

Abstract

The East African long rains constitute the main crop-growing season in the region. Interannual predictability of this season is low in comparison to the short rains, and recent decadal drying contrasts with climate projections of a wetter future (the “East African climate paradox”). Here, we show that long rains rainfall totals are strongly correlated with 700 hPa zonal winds across the Congo basin and Gulf of Guinea ((Formula presented.)). Westerly anomalies align with more rainfall, with the same mechanism controlling covariability on interannual and decadal time scales. On both time scales wind anomalies are linked to geopotential anomalies over the Sahel and Sahara, and warming there. Rainfall and wind are significantly correlated with the Madden-Julian Oscillation (MJO) amplitude, and around 18% of the decadal drying can be explained by MJO amplitude variability. This work shows that predictions of East African rainfall across time scales require robust prediction of both zonal winds and MJO activity.