The Sahel, here defined as the portion of Africa between 12°N and 20°N, is a semi-arid eco-region that separates the Sahara desert from the Sudanian tropical savanna. This flat region is known to be particularly vulnerable to natural variability as most of the human activities in the region depend on the highly volatile single annual rainfall season, June through September with the maximum in August. The severe droughts that hit the region in the late seventies and early eighties act to remind us of the direct consequences of these events. This has been arguably the longest and the most geographically extended drought recorded anywhere in the world during the 20th century.