The Sahara desert ecoregion, as defined by the World Wide Fund for Nature (WWF), includes the hyper-arid center of the Sahara, between 18° and 30° N. It is one of several desert and xeric shrubland ecoregions that cover the northern portion of the African continent.
The Sahara is the world's largest hot desert, located in northern Africa. It stretches from the Red Sea to the Atlantic. The vast Sahara encompasses several ecologically distinct regions. The Sahara desert ecoregion covers an area of 4,619,260 km² (1,791,500 square miles) in the hot, hyper-arid center of the Sahara, surrounded on the north, south, east, and west by desert ecoregions with higher rainfall and more vegetation
The North Saharan steppe and woodlands ecoregion lies to the north and west, bordering the Mediterranean climate regions of Africa's Mediterranean and North Atlantic coasts. The North Saharan steppe and woodlands receives more regular winter rainfall than the Sahara desert ecoregion. The South Saharan steppe and woodlands ecoregion lies to the south, between the Sahara desert ecoregion and the Sahel grasslands. The South Saharan steppe and woodlands receives most of its annual rainfall during the summer. The Red Sea coastal desert lies in the coastal strip between the Sahara desert ecoregion and the Red Sea.
Some mountain ranges also rise up from the desert, and receive more rainfall and cooler temperatures. These Saharan mountains are home to two distinct ecoregions; the West Saharan montane xeric woodlands in the Ahaggar, Tassili n'Ajjer, Aïr, and other ranges in the western and central Sahara, and the Tibesti-Jebel Uweinat montane xeric woodlands in the Tibesti and Jebel Uweinat of the eastern Sahara.
The surface of the desert ranges from large areas of sand dunes (erg), to stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. The only permanent river that crosses the ecoregion is the Nile River, which originates in central Africa and empties northwards into the Mediterranean Sea. Some areas encompass vast underground aquifers resulting in oases, while other regions severely lack water reserves.
The Sahara desert generally features an arid climate. The Sahara desert is one of the hottest regions of the world, with a mean temperature over 30 °C (86 °F). Variations may also be huge, from over 50 °C (120 °F) during the day during the summer, to temperatures below 0 at night in summer . Daily variations are also very important. The Sahara also receives very little rain (The Inter-Tropical Convergence Zone moves up from the south, but stops are observed and full-blown wind and sand storms occur as soon as early spring. Local inhabitants protect themselves from heat, cold and mostly wind and sand by covering their heads (see the cheche worn by Tuareg).
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