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The Sahel has long experienced a a series of historic droughts, dating back to at least the 17th century. The Sahel region is a climate zone sandwiched between the African Savannah grasslands to the south and the Sahara desert to the north, across West and Central Africa. While the frequency of drought in the region is thought to have increased from the end of the 19th century, three long droughts have had dramatic environmental and societal effects upon the Sahel nations. Famine followed severe droughts in the 1910s, the 1940s, and the 1960s, 1970s and 1980s, although a partial recovery occurred from 1975-80. The most recent drought occurred in 2012. While at least one particularly severe drought has been confirmed each century since the 17th century, the frequency and severity of recent Sahelian droughts stands out. Famine and dislocation on a massive scale—from 1968 to 1974 and again in the early and mid-1980s—was blamed on two spikes in the severity of the 1960-1980s drought period.〔(The Sahel region; assessing progress twenty-five years after the great drought ). Simon Batterbury, republished paper from 1998 RGS-IBG conference. Global Environmental Change (2001) v11, no 1, 1-95.〕 From the late 1960s to early 1980s famine killed 100,000 people, left 750,000 dependent on food aid, and affected most of the Sahel's 50 million people.〔(AFRICA ENVIRONMENT OUTLOOK. Past, present and future perspectives ). United Nations Environmental Programme (2002). Retrieved 2009-02-13.〕 The economies, agriculture, livestock and human populations of much of Mauritania, Mali, Chad, Niger and Burkina Faso (known as Upper Volta during the time of the drought) were severely impacted. As disruptive as the droughts of the late 20th century were, evidence of past droughts recorded in Ghanaian lake sediments suggest that multi-decadal megadroughts were common in West Africa over the past 3,000 years and that several droughts lasted far longer and were far more severe.〔(Severity, Length of Past Megadroughts Dwarf Recent Drought in West Africa ). Jackson School of Geosciences Online, April 16, 2009.〕 Since the 1980s, summer rainfall in the Sahel has been increasing; this has been associated with an increase in vegetation, forming what has been called a 'greening' of the Sahel. The observed increase in rainfall is accounted for by enhancements in the African easterly jet, which is known to induce wet anomalies. A (2011 study ) found that the positional shifts in the African easterly jet and African easterly waves accompanied the northward migration of the Sahel rainband.〔Wang and Gillies (2011) http://www.hindawi.com/journals/ijge/2011/259529/abs/〕 ==History== Because the Sahel's rainfall is heavily concentrated in a very small period of the year, the region has been prone to dislocation when droughts have occurred ever since agriculture developed around 5,000 years ago. The Sahel is marked by rainfalls of less than 100 mm a year, all of which occurs in a season which can run from several weeks to two months. Despite this vulnerability, the history of drought and famine in the Sahel do not perfectly correlate. While modern scientific climate and rainfall studies have been able to identify trends and even specific periods of drought in the region, oral and written records over the last millennium do not record famine in all places at all times of drought. One 1997 study, in attempting to map long scale rainfall records to historical accounts of famine in Northern Nigeria, concluded that "the most disruptive historical famines occurred when the cumulative deficit of rainfall fell below 1.3 times the standard deviation of long-term mean annual rainfall for a particular place."〔Aondover Tarhule1 and Ming-Ko Woo. Towards an Interpretation of Historical Droughts in Northern Nigeria. Climatic Change, no 37, 1997. pp.601-613〕 The 1982-84 period, for instance, was particularly destructive to the pastoral Fula people of Senegal, Mali and Niger, and the Tuareg of northern Mali and Niger. The populations had not only suffered in the 1968-74 period, but the inability of many to rebuild herds destroyed a decade earlier, along with factors as various as the shift of political power to settled populations with independence in the 1960s, Senegalese-Mauritanian border relations, and Niger's dependence upon falling world uranium prices coinciding in a destructive famine.〔David Tenenbaum. (Traditional drought and uncommon famine in the Sahel ). Whole Earth Review, Summer, 1986.〕〔J Swift. Sahelian Pastoralists: Underdevelopment, Desertification, and Famine. Annual Review of Anthropology Vol. 6: 457-478〕〔Timberlake L. The Sahel: drought, desertification and famine. Draper Fund Report, 1985 Sept(14):17-9.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sahel drought」の詳細全文を読む スポンサード リンク
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