East African Climate Prediction: Shorter Long Rains and Longer Short Rains

Regional climate model predictions for mid-century indicate that the East African long rain in boreal spring will become significantly weaker, and the short rains in boreal fall will become stronger and persist longer as climate warms. Over Kenya and Tanzania, the weakening of the long rains, which almost disappear in some regions in the simulation, is associated with anomalous mid-tropospheric moisture divergence that is coupled with the Congo basin's response to Atlantic warming. Over Ethiopia and Somalia, the partial collapse of the long rains season is accompanied by a northward shift of rainfall over the eastern Sahel as the thermal low forms earlier in the year. The short rains (boreal fall) growing season is extended as the Indian Ocean warms, bringing more intense rainfall as well as a rainy season that extends later in the year. Current trends and modes of variability in the region are compared with the model predictions. Model validation, analysis of ensemble spreads, and comparisons with CMIP5 simulations are used to evaluate confidence in the projections.