The Sahel drought mechanism: insights from two contrasting extreme events during boreal summer July-August-September (JAS) is investigated in this study using the standardized precipitation index (SPI). Empirical orthogonal function (EOF) and composite analyses were deployed in this study, where the global precipitation climatology center (GPCC) rainfall data is used. The SPI shows large widespread decreasing rainfall trend in the Sahel in the mid-1980s; thereafter, Sahel rainfall have recovered somewhat through the late 1990s, even though the drought conditions have not ended in the region. Although the region is still yet to fully recover from the early 1980s devastating droughts, but in recent decades the Sahel is not as dry as it used to be in the 1980s. An EOF analysis of Atlantic and Indian Ocean sea surface temperatures (SSTs), SPI reveal a fairly linear trend resulting from trends in SSTs and precipitation induced mode of inter-annual variations as the two leading patterns, respectively. Our results from analysis of the two Oceans’ SSTs refute the conclusion of earlier studies that southward shift of tropical Atlantic SSTs, and steady warming in the Indian Ocean which enhances subsidence over the Sahel through Ross-by waves caused the severe Sahel drought. The results of this study may only be useful in this context and should not imply that SSTs variability in the Atlantic and Indian Ocean solely explains rainfall variability over the Sahel, but rather that the combined SST forcing can, at least in certain years, be an important driving force of Sahel rainfall variability. Composite analyses show that the Sahel drought is usually accompanied by easterly winds, and moisture transport from the continent into the Atlantic Ocean.
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Tags: Drought ; Extreme weather event ; Sahel ; West Africa ; Region I - Africa ; Thesis - WMO Fellowship Division ; Standardized Precipitation Index (SPI) Add tag