ENSO Teleconnections to East African Summer Rainfall: A Process-Based Study of Climate Models

There has been limited improvement in climate modeling for Africa in recent decades, as compared to the rest of the world. We focus on the East African region where most of the rainfall occurs in summer, a region that is crucial to the Ethiopian Highlands and that feeds the flow of the Blue Nile River. This region is known for its high vulnerability to droughts, with El Nino Southern Oscillation (ENSO) being a leading cause of interannual variability in rainfall. Unfortunately, this region also suffers from a lack of consensus in future projections generated by global climate models (GCMs), which is a hindrance for planning and adaptation. Adequate understanding and accurate representation of climate features that influence regional variability is an important but often neglected issue when evaluating models. First, we perform a process-based evaluation of coupled GCMs, focusing on the atmospheric teleconnections of ENSO to East African summer rainfall, at the upper level (Tropical Easterly Jet) as well as the lower level (Somali Jet). We find that most of the models have an ENSO-Jet coupling similar to observed, but the models diverge in their representation of Jet-East African rainfall coupling. The models perform similarly for both jets in their couplings. Second, we test previously hypothesized mechanisms of influence in a regional climate modeling experiment, to elucidate the sensitivity of rainfall to different combinations of magnitudes and locations of these atmospheric jets.