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 northern 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.
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.
The Sahel is a tropical hot steppe and certainly represents the best example of a semi-arid area. The Sahel has a tropical, hot steppe climate (Köppen climate classification BSh). The climate is typically hot, sunny, dry and somewhat windy all year long. The Sahel has in fact the same climate as the Sahara desert, located just at the north but less extreme.
The Sahel mainly receives a low to a very low precipitation amount annually. The steppe has a very long, prevailing dry season and a short rainy season. The precipitation is also extremely irregular, and vary a lot from season to season and the major part of the rain can fall in only one, or two months while the others may remain absolutely dry. The entire Sahel region generally receives between 100 mm and 600 mm of rain yearly. Besides, a system of subdivisions based on annual rainfall is often adopted for the Sahelian climate is as follows: the Saharan-Sahelian climate, with a mean annual precipitation between around 100 and 200 mm (such as Khartoum, Sudan), the strict Sahelian climate, with a mean annual precipitation between around 200 and 400 mm (such as Kiffa, Mauritania) and the Sahelian-Sudanese climate, with a mean annual precipitation between around 400 and 600 mm (such as Niamey, Niger). The relative humidity in the steppe is low to very low, often being between 10% and 25% during the dry season and between 25% and 75% during the rainy season. The least humid places can have a relative humidity always lower than 35%.
The Sahel is characterized by constant, intense heat and the temperatures don't really vary. The climate is very hot year-round and the Sahel doesn't normally know the cold. During the hottest period, the average high temperatures are generally between 36 °C (96.8 °F) and 42 °C (107.6 °F) (and even more in the hottest regions), often for more than 3 months, while the average low temperatures are easily around 25 °C (77 °F) and 31 °C (87.8 °F). During the "coldest period", the average high temperatures are between 27 °C (80.6 °F) and 33 °C (91.4 °F) and the average low temperature are between 15 °C (59 °F) and 21 °C (69.8 °F). Everywhere in the Sahel, the average mean temperature is over 18 °C (64.4 °F) because the climate is tropical.
The Sahel is a very sunny place, for a steppe and has a high to a very high sunshine duration year-round, between 2,700 hours (about 61% of the daylight hours) and 3,500 hours (more than 79% of the daylight hours). The sunshine duration in the Sahel approaches the desert levels, and is comparable to the Arabian Desert for example whereas the Sahel in only a steppe, not a desert. The cloud cover is low to very low in the sky. For example, Niamey, Niger has 3,082 hours of bright sunshine; Gao, Mali has near 3,385 hours of sunshine; Timbuktu, Mali has 3,409 sunny hours, N'Djamena, Chad possesses 3,205 hours of sunlight.
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.
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.
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 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 time.
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