The Sahel[p] is the ecoclimatic and biogeographic zone of transition, in Africa, between the Sahara desert to the north and the Sudanian Savanna to the south. Having a semi-arid climate, it stretches across the southernmost extent of Northern Africa between the Atlantic Ocean and the Red Sea. The Arabic word sāḥil (ساحل) literally means "shore, coast", describing the appearance of the vegetation found in the Sahel as being akin to that of a coastline delimiting the sand of the Sahara.
The Sahel covers parts of (from west to east) the Gambia, Senegal, southern Mauritania, central Mali, Burkina Faso, southern Algeria and Niger, northern Nigeria and Cameroon, central Chad, southern Sudan, northern South Sudan and Eritrea.
The Sahel spans 5,400 km (3,360 mi) from the Atlantic Ocean in the west to the Red Sea in the east, in a belt that varies from several hundred to a thousand kilometers (620 miles) in width, covering an area of 3,053,200 square kilometers (1,178,850 sq mi). It is a transitional ecoregion of semi-arid grasslands, savannas, steppes, and thorn shrublands lying between the wooded Sudanian savanna to the south and the Sahara to the north.
The topography of the Sahel is mainly flat, and the region mostly lies between 200 and 400 meters (660 and 1,310 ft) in elevation. Several isolated plateaus and mountain ranges rise from the Sahel, but are designated as separate ecoregions because their flora and fauna are distinct from the surrounding lowlands. Annual rainfall varies from around 100 mm (4 in)-200 mm (8 in), in the north of the Sahel, to around 600 mm (24 in) in the south.
Flora and fauna
The Sahel is mostly covered in grassland and savanna, with areas of woodland and shrubland. Grass cover is fairly continuous across the region, dominated by annual grass species such as Cenchrus biflorus, Schoenefeldia gracilis, and Aristida stipoides. Species of acacia are the dominant trees, with Acacia tortilis the most common, along with Acacia senegal and Acacia laeta. Other tree species include Commiphora africana, Balanites aegyptiaca, Faidherbia albida, and Boscia senegalensis. In the northern part of the Sahel, areas of desert shrub, including Panicum turgidum and Aristida sieberana, alternate with areas of grassland and savanna. During the long dry season, many trees lose their leaves, and the predominantly annual grasses die.
The Sahel was formerly home to large populations of grazing mammals, including the scimitar-horned oryx (Oryx dammah), dama gazelle (Gazella dama), Dorcas gazelle (Gazella dorcas), red-fronted gazelle (Gazella rufifrons), the giant prehistoric buffalo (Pelorovis) and Bubal Hartebeest (Alcelaphus busephalus buselaphus), along with large predators like the African wild dog (Lycaon pictus), cheetah (Acinonyx jubatus), and lion (Panthera leo). The larger species have been greatly reduced in number by over-hunting and competition with livestock, and several species are vulnerable (Dorcas gazelle and red-fronted gazelle), endangered (Dama gazelle, African wild dog, cheetah, lion), or extinct (the Scimitar-horned oryx is probably extinct in the wild, and both Pelorovis and the Bubal Hartebeest are now extinct.
- It is tropical because the mean monthly temperature of the "coldest" month is equal to or greater than 18°C.
- It is semi-arid because of low annual precipitation, below about 600 mm in a tropical climate (and above about 100–150 mm), characterised by irregular and unpredictable short rainy seasons through the years. The dry season generally lasts from about 8 to 11 months a year.
Though erratic, the rainy season in a Sahelian climate zone usually occurs during the warm season but not during the very hottest months.
For instance, the mean annual precipitation in Khartoum, 156.8 mm, is distributed as follows: 151.3 mm during the "warm" season (warmest six months of the year, April to September), and only 5.5 mm during the "cold" season (the coldest six months, October to March). Therefore 96.5% of the precipitation falls during the "warm" season. In the latter the hottest months are May and June with however only 0.9 and 1.2 mm respectively of precipitation: the rainy season occurs later in the warm season, from July to September with August being the single truly wet month (according to F. Bagouls and Henri Gaussen's definition, which considers that a month is wet when the mean monthly precipitation in millimeters exceeds twice the mean monthly temperature in °C).
A system of subdivisions often adopted for the Sahelian climate is as follows:
- The Saharan-Sahelian climate, with a mean annual precipitation between around 100 and 200 mm (Khartoum)
- The strict Sahelian climate, with a mean annual precipitation between around 200 and 400 mm (Kiffa)
- The Sahelian-Sudanese climate, with a mean annual precipitation between around 400 and 600 mm (Niamey)
The Sahelian climate, with variations, also appears in (a) north-central Australia and more precisely in the north of the Great Sandy Desert in (the Pilbara region: Marble Bar, Port Hedland, and in the north of the Tanami Desert to Tennant Creek); (b) the southern Sindh around Karachi; and (c) a small region where the states of Pernambuco, Ceará, Piauí, and Bahia meet in the continental northeast of Brazil.
Since the threshold values of semi-aridity here (100–200 to 600 mm) are clearly lower than in the Köppen climate classification (390 to 780 mm for stations with mean annual temperature of 25°C and dry season centered in "winter", and even 440 to 880 mm at 30°C), the tropical semi-arid Sahelian climate, incidentally the hottest climate on Earth, is on the borderline of Köppen's hot semi-arid climates (BSh) and Köppen's hot arid climates (BWh).
Traditionally, most of the people in the Sahel have been semi-nomads, farming and raising livestock in a system of transhumance, which is probably the most sustainable way of utilizing the Sahel. The difference between the dry north with higher levels of soil-nutrients and the wetter south is utilized so that the herds graze on high quality feed in the North during the wet season, and trek several hundred kilometers down to the south, to graze on more abundant, but less nutritious feed during the dry period. Increased permanent settlement and pastoralism in fertile areas has been the source of conflicts with traditional nomadic herders.
The first instances of domestication of plants for agricultural purposes in Africa occurred in the Sahel region circa 5000 BC, when sorghum and African rice began to be cultivated. Around this time, and in the same region, the small Guineafowl were domesticated.
Around 4000 BC the climate of the Sahara and the Sahel started to become drier at an exceedingly fast pace. This climate change caused lakes and rivers to shrink rather significantly and caused increasing desertification. This, in turn, decreased the amount of land conducive to settlements and helped to cause migrations of farming communities to the more humid climate of West Africa.
The Sahelian kingdoms were a series of monarchies centered in the Sahel, between the 9th and 18th centuries. Their wealth of the states came from controlling the trans-Saharan trade routes across the desert, especially the slave trade with the Islamic world. Their power came from having large pack animals like camels and horses that were fast enough to keep a large empire under central control and were also useful in battle. All of these empires were also quite decentralized with member cities having a great deal of autonomy. The first large Sahelian kingdoms emerged after AD 750, and supported several large trading cities in the Niger Bend region, including Timbuktu, Gao, and Djenné.
The Sahel states were limited from expanding south into the forest zone of the Ashanti and Yoruba as mounted warriors were all but useless in the forests and the horses and camels could not survive the heat and diseases of the region.
The western Sahel fell to France in the late 19th century, as part of French West Africa. Chad was added in 1900 as part of French Equatorial Africa. The French territories were decolonialized in 1960.
The eastern Sahel (the part in what is now Sudan) did not fall to the European powers but was annexed by Muhammad Ali of Egypt in 1820. It came under British administration as part of the Sultanate of Egypt in 1914. The Sudanese Sahel became part of independent Sudan in 1956 and entered a lasting period of political instability and warfare, still ongoing in the War in Darfur.
The extreme east of the Sahel came under Italian control as Italian Eritrea in 1890. Eritrea was annexed by Haile Selassie of Ethiopia in 1962, and became independent in 1993, after the long Eritrean War of Independence.
For hundreds of years, the Sahel region has experienced regular droughts and megadroughts. One megadrought, from 1450 to 1700, lasted 250 years. There was a major drought in the Sahel in 1914, caused by annual rains far below average, that caused a large-scale famine. From 1951 to 2004, the Sahel experienced some of the most consistent and severe droughts in Africa. The 1960s saw a large increase in rainfall in the region, making the northern drier region more accessible. There was a push, supported by governments, for people to move northwards. As the long drought-period from 1968 through 1974 began, the grazing quickly became unsustainable, and large-scale denuding of the terrain followed. Like the drought in 1914, this led to a large-scale famine, but this time it was somewhat tempered by international visibility and an outpouring of aid. This catastrophe led to the founding of the International Fund for Agricultural Development.
In June to August 2010, famine struck the Sahel. Niger's crops failed to mature in the heat, and famine occurred. 350,000 faced starvation, and 1,200,000 were at risk of famine. In Chad, the temperature reached 47.6 °C (117.7 °F) on 22 June in Faya-Largeau, breaking a record set in 1961 at the same location. Niger tied its highest temperature record set in 1998, also on 22 June, at 47.1°C in Bilma. That record was broken the next day, when Bilma hit 48.2 °C (118.8 °F). The hottest temperature recorded in Sudan was reached on 25 June, at 49.6 °C (121.3 °F) in Dongola, breaking a record set in 1987. Niger reported on 14 July that diarrhea, starvation, gastroenteritis, malnutrition, and respiratory diseases had sickened or killed many children. The new military junta appealed for international food aid and took serious steps to call on overseas help. On 26 July, the heat reached near-record levels over Chad and Niger, and about 20 had reportedly died in northern Niger of dehydration by 27 July.
Desertification and soil loss
Major dust storms are a frequent occurrence, as well. During November 2004, a number of major dust storms hit the Chad, originating in the Bodélé Depression. This is a common area for dust storms (occurring, on average, 100 days every year).
On 25 August 2008, heavy dust storms passed over the eastern plains of Somalia and the northeast of a still drought-hit Kenya. On 23 March 2010, a major sandstorm hit Mauritania, Senegal, the Gambia, Guinea Bissau, Guinea, and inland Sierra Leone. Another struck in southern Algeria, inland Mauritania, Mali, and northern Côte d’Ivoire at the same ?
- [p] ^ The word "Sahel" is pronounced as "suh-Hail" or "suh-Heel".
- "Sahel: $1.6 billion appeal to address widespread humanitarian crisis". United Nations Office for the Coordination of Humanitarian Affairs. Retrieved 24 June 2013.
- "Sahelian Acacia savanna". Terrestrial Ecoregions. World Wildlife Fund. Retrieved 2009-12-07.
- O'Brien, Patrick K., ed. (2005). Oxford Atlas of World History. New York: Oxford University Press. pp. 22–23.
- Brahic, Catherine. "Africa trapped in mega-drought cycle". New Scientist. Retrieved 17 December 2012.
- Scholl, Adam. "Map Room: Hidden Waters". World Policy Journal. Retrieved 17 December 2012.
- "Drought threatens African humanitarian crisis - Channel 4 News". Channel4.com. 2010-07-01. Retrieved 2010-07-28.
- Foy, Henry (2010-06-21). "Millions face starvation in west Africa, warn aid agencies". The Guardian (London).
- Masters, Jeff. "NOAA: June 2010 the globe's 4th consecutive warmest month on record". Weather Underground. Jeff Masters' WonderBlog. Retrieved 21 July 2010.
- "Niger: famine on the horizon?". France 24. 2010-07-14. Retrieved 2012-10-25.
- "wonder Blog: Weather Underground". Wonder-ground.com. Retrieved 2010-07-28.
- Schmidt, Laurie J. (18 May 2001). "From the Dust Bowl to the Sahel". NASA.
- "Dust Storm in the Bodele Depression". NASA. Retrieved 19 June 2010.
- "Pronunciation of Sahel - Oxford Dictionaries", OxfordDictionaries.com, March 2013, web: ODae.
- Azam (ed.), Conflict and Growth in Africa: The Sahel, Organisation for Economic Co-operation and Development (1999), ISBN 92-64-17101-0.
- (French) Lagha CHEGROUCHE, "L'arc géopolitique de l'énergie : le croissant énergétique, in Le Soir d'Algérie, 19/12/2010 hi
- Dai, A.; Lamb, P.J.; Trenberth, K.E.; Hulme, M.; Jones, P.D.; Xie, P. (2004). "The recent Sahel drought is real". International Journal of Climatology 24 (11): 1323–1331. doi:10.1002/joc.1083.
- Moseley, W.G. 2008. “Strengthening Livelihoods in Sahelian West Africa: The Geography of Development and Underdevelopment in a Peripheral Region.” Geographische Rundschau International Edition, 4(4): 44-50. http://works.bepress.com/cgi/viewcontent.cgi?article=1069&context=william_moseley
- Simon, L., A. Mattelaer and A. Hadfield (2012) "A Coherent EU Strategy for the Sahel". Brussels: European Parliament (DG for External Policies).
|Wikimedia Commons has media related to Sahel.|