The Sahel is a narrow region in West Africa, lying between the Sahara desert at 18¿N and savannah and equatorial forest at about 15¿N. The climate and atmospheric dynamics of this region are determined by the West African monsoon resulting from the alternating southwesterly and northwesterly winds, corresponding to a north-south migration of the Intertropical Convergence Zone (ITCZ). During the northward shift of the ITCZ, rainfall occurs over Sahel during a short but intense wet season, between late June and mid-September, which induces fast vegetation growth. The dry season that follows this rainy period produces a rapid drying of the vegetation.