Recent East African Droughts and the Global Climate Shift of 1998–99

Observational data and climate model simulations and experiments are utilized to demonstrate that the recent increase in East African drought during boreal spring is primarily related to a global climate shift that occurred in 1998-99. This shift is associated with multidecadal sea surface temperature (SST) variability in the Pacific Ocean. Emphasizing the March-May season over roughly the last 110 years, the observational analysis reveals a pattern of SST variability that is correlated with the Pacific Decadal Oscillation. Examination of observed March-May precipitation variations since 1901 indicates the recent drying in East Africa (1999-2010) is part of a robust, global anomaly pattern that includes drought in central-southwest Asia, parts of eastern Australia and the southwestern US. In addition, the recent global precipitation anomaly pattern is remarkably similar to earlier anomaly patterns when SSTs in the Pacific were in a similar configuration (1914-1925, 1946-1977). Simulations using an atmospheric climate model forced with observed, global SSTs capture many of the salient precipitation and atmospheric circulation features associated with the observed shift in 1999, including the drying in East Africa. Further, when the model is forced only with observed SSTs from the tropical Pacific it also captures the drought in East Africa and many of the large-scale atmospheric circulation changes and the abrupt shift in 1999. Overall, the observational analysis and climate model results provide strong evidence that the recent droughts in East Africa are driven primarily by natural multidecadal climate variability in the tropical Pacific, not anthropogenic forcing.