Sahara

The Sahara is the largest desert in the world and occupies approximately 10 percent of the African Continent. The ecoregion includes the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Although species richness and endemism are low, some highly adapted species do survive with notable adaptations. Only a few thousand years ago the Sahara was significantly wetter, and a large mammal fauna resided in this area. Climatic desiccation over the past 5000 years, and intense human hunting over the past 100 years, has obliterated these faunas. Now only rock, sand and sparse vegetation exist over huge areas. The remnant large mammal fauna is highly threatened by over-hunting.

From the Atlantic Ocean in the west, the greater Sahara stretches across Africa to the Red Sea and down to the highlands of Ethiopia, encompassing an area 9,100,000 square kilometers (km2). This ecoregion covers the central Sahara Desert, between 18° and 30° N, and has an area of 4,619,260 km2. The northern and southern margins of the Sahara, which receive more rainfall and have greater vegetation cover, are described separately.

The Sahara is located in a climatic divide. The Intercontinental Convergence Zone moves up from the south, but stops before the center of the Sahara, and consequently hardly carries any rain. Similarly, the winter rainfall of North Africa does not reach far south enough to regularly bring rain to the central Sahara. Consequently, the rainfall, albeit extremely rare, can fall in any season. The annual rainfall is below 25 millimeters (mm), and in the eastern part of the desert it is less than 5 mm per annum. The scarcity of rainfall in this ecoregion is aggravated by its irregularity, as no rain may fall for many years in some areas, followed by a single intense thunderstorm.

The Sahara is one of the hottest regions in the world, with mean annual temperatures exceeding 30°C. In the hottest months, temperatures can rise over 50°C, and temperatures can fall below freezing in the winter. A single daily variation of -0.5°C to 37.5°C has been recorded. The Sahara is also extremely windy. Hot, dust-filled winds create dust devils which can make the temperatures seem even hotter.

The extreme aridity of this area is a relatively recent feature. Much larger areas of the Sahara had adequate water only 5000 to 6000 years ago. It is not clear how much of this ecoregion was covered with vegetation, but in other parts of the Sahara the vegetation was closer to the savanna woodlands of eastern and southern Africa. Currently the ecoregion is in a "hyper arid" phase, with high summer temperatures, lower winter temperatures and rainfall between 0 and 25 mm per annum.