Interpretting Projected Changes in the Large Scale Circulation Relevant to the Climate of East Africa

This paper reports on recent results obtained from an analysis of CMIP5 model simulations and projections of sea surface temperature and atmospheric circulation features relevant to the climate of East Africa. Most CMIP5 model simulations of the current climate exhibit substantial errors in capturing the observed amplitude and phase of the annual cycle of Indian Ocean sea surface temperatures as well as fundamental aspects of the the regional and large scale atmospheric circulation. Fundamental consequences of these simulation errors is to reverse the observed intensity of the two main rainy seasons in East Africa and for a one-month lag in the peak intensity of the March-May "long rains." For the March-May season these errors are in turn related to a substantial phase lag in the timing of the South Asia monsoon.

In projections, several of the errors identified in the model simulations are found to be amplified, including the spatial distribution of sea surface temperatures across the Indian Ocean. In East Africa, this results in substantially enhanced rainfall in the October-December rainy season and a more muted response in March-May. Erroneous phase lags in the annual cycle of the regional and large scale atmospheric circulation in simulations are found to persist. Overall, the study finds that the inability of the CMIP5 models to properly capture key aspects of the regional and large scale circulation calls into question the reliability of current projections of the climate of East Africa.