Thus, climate is not only driving land use and land cover change, but to some extent is also driven by it. The current understanding is that variations in sea surface temperatures in the global oceans play the largest role in Sahelian rainfall variability, amplified by land cover (Giannini, 2016). Are they part of the normal variability of this semiarid climate, or harbingers of human-induced climate change? Understanding the climatological processes behind the droughts is a prerequisite for attributing them to natural or human causes and to eventually predicting the impacts of future climate change on rainfall in the region. However, for lack of an observational rainfall record before the 20th century, or sufficient proxy indicators, it remains unclear how unique these droughts have been at time scales of centuries and millennia (Hulme, 2001). The great Sahelian droughts provide the most dramatic worldwide example of multi-decadal climate variability that has been directly measured. Heavy rainstorms also cause severe soil erosion, particularly on cleared cultivated land. Too much rain at once can damage crops or change pasture composition in unfavorable ways. Moreover, for agro-pastoralists not only annual rainfall totals are important, but also the frequency and distribution of rainfall events throughout the wet season. The great Sahelian droughts forced the abandonment of agriculture at the arid margin, triggered a famine crisis that killed thousands of people and their livestock, and has been blamed for widespread environmental degradation in the region.Īverage annual rainfall has recovered some from the low point of the early 1970s, however it has not been enough to erase the long-term drying trend since 1900 - the earliest available rainfall records (Nicholson, 2005). These droughts followed a period of more favorable rainfall in the 1950s and early 1960s, which had encouraged government planners and farmers to expand agriculture northward (Glantz, 1994). From the late 1960s through the 1980s, the Sahel zone experienced droughts of unprecedented spatial extent and duration (Hulme, 2001). Drought is a recurring phenomenon in semiarid West Africa, where average rainfall conditions seldom prevail, and rainfall is skewed to dryness, i.e., a few heavy rainfall years are balanced out by a larger number of below-average rainfall years. Thus, year-to-year rainfall variability ranges from 10 to 20 percent in the coastal areas to over 40 percent in the northern Sahel (FAO, 1983). Not only scarcity of rainfall, but also its variability and unpredictability become more significant with latitude. Standardized rainfall anomalies in the Sahel region (10–20ºN, 20ºW–10✮) derived from station dataįlooded village along the Niger River south of Niamey in 2012. Dust storm, Winde Mborni, Mauritania, July 2008. In the Sahel, maximum temperatures can reach above 40☌. Temperatures in the lowlands of West Africa are high throughout the year, with annual means usually above 18☌. Along the south–north gradient of decreasing rainfall, Abidjan, Côte d’Ivoire (5° north latitude) records a mean annual rainfall of 1,600 mm Ouagadougou, Burkina Faso (12° northern latitude) 700 mm within a 5-month rainy season and Agadez, Niger (18° northern latitude) 165 mm annually in a short 2.5-month rainy season. the Guinean Highlands and the Jos Plateau in central Nigeria, receiving more precipitation than lowlands of the same latitude. This latitudinal pattern is somewhat modified by altitude, with higher mountain elevations, e.g. At higher latitudes, precipitation decreases and is limited to a wet season of decreasing duration. At the Gulf of Guinea, precipitation is abundant year-round without a marked dry season. In summer, moist equatorial air masses originating over the Atlantic Ocean bring annual monsoon rains (Nicholson, 2013).Īs a result of these interacting air masses, West Africa’s precipitation regime is characterized by latitudinal belts of decreasing rainfall and wet season length. Hot, dry continental air masses originating from the high pressure system above the Sahara Desert give rise to dusty Harmattan winds over most of West Africa from November to February. West Africa’s climate is controlled by the interaction of two air masses, the influence of which varies throughout the year with the north-south movement of the Intertropical Convergence Zone (ITCZ). Mean annual rainfall 1981–2014, with number of months of 50 mm or more of rainfall.
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