Drying Versus Wettening of the East African Climate

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This project considers changes in East African precipitation during the March to May "long rains" season, which has received less attention in the literature than the October to December "short rains". While the short rains season has stronger interannual variability and stronger links to El Nino, the long rains have experienced a decline between the periods 1999-2009 and 1980-1998. This decadal trend in rainfall has been linked to increasing SST in the Indian Ocean, which in turn has been attributed to anthropogenic climate change. However, climate change simulations from the Coupled Model Intercomparison Project version 3 (CMIP3) show a robust projection that East Africa will become wetter over the 21st century. The climate processes which drive the long rains and their interannual variability are not well understood, and a better understanding of these processes could help to determine whether the model projections are credible, and what factors lead to the dichotomy between long-term model projections and the shorter-term observed trend. The research is divided into three tasks: 1) Identifying the key features of the anomalous large- and regional-scale atmospheric and sea surface temperature (SST) patterns that are linked to observed seasonal rainfall variability and its recent decline in East Africa; 2) Employing climate model simulations and idealized climate model experiments to discern the main drivers of the observed features and changes; and 3) Identifying dynamical and thermodynamical processes in climate model projections associated with changes in long rains precipitation in East Africa during the twenty-first century in the CMIP5 experiments, contrasting results with those found in analysis of CMIP3 experiments.East Africa is one of the most food-insecure regions of the globe, and a better understanding of the causes of drought and the likelihood of future rainfall change could play a critical role for the development of the region. Work under this award will be highly relevant to organizations including the Famine Early Warning Systems Network (FEWSNET) and the International Federation of the Red Cross (IFRC), both of which have close ties to the PIs' home institution. The work thus has important broader impacts in addition to its scientific merit.