The Kalahari Desert (in Afrikaans: Kalahari-woestyn) is a large semi-arid sandy savannah in southern Africa extending 900,000 square kilometres (350,000 sq mi), covering much of Botswana, parts of Namibia (previously South West Africa), and South Africa. A semi-desert, with huge tracts of excellent grazing after good rains, the Kalahari supports more animals and plants than a true desert, such as the Namib Desert to the west. There are small amounts of rainfall and the summer temperature is very high. The driest areas usually receive 110–200 millimetres (4.3–7.9 in) of rain per year,[1] and the wettest just a little over 500 millimetres (20 in). The surrounding Kalahari Basin covers over 2,500,000 square kilometres (970,000 sq mi) extending farther into Botswana, Namibia and South Africa, and encroaching into parts of Angola, Zambia and Zimbabwe. The Kalahari is home to many migratory birds and animals. Previously havens for wild animals from elephants to giraffes, and for predators such as lions and cheetahs, the riverbeds are now mostly grazing spots, though leopards and cheetahs can still be found. The area is now heavily grazed and cattle fences restrict the movement of wildlife. Among deserts of the southern hemisphere, the Kalahari most closely resembles some Australian deserts in its latitude and its mode of formation. The Kalahari Desert came into existence approximately sixty million years ago along with the formation of the African continent. Despite its aridity, the Kalahari supports a variety of flora. The native flora includes acacia trees and many other herbs and grasses. The Kiwano fruit, also known as the Horned melon, melano, African horned cucumber, jelly melon, or hedged gourd, is endemic to a region in the Kalahari Desert (specific region unknown). Even where the Kalahari "desert" is dry enough to qualify as a desert in the sense of having low precipitation, it is not strictly speaking a desert because it has too dense a ground cover. The main region that lacks ground cover is in the southwest Kalahari (southeast of Namibia, northwest of South Africa and southwest of Botswana) in the south of the Kgalagadi Transfrontier Park. For instance in the ZF Mgcawu District Municipality of South Africa, total vegetation cover may be as low as 30.72% on non-protected (from cattle grazing) farmlands south of Twee Rivieren Rest Camp and 37.74% in the protected (from cattle grazing) South African side of the Kgalagadi Transfrontier Park: these southernmost Kalahari xeric savanna areas are truly semi-deserts. However, in all the remaining Kalahari, except on salt pans during the dry season, the vegetation cover can be clearly denser, up to almost 100% in some limited areas. In an area of about 600,000 km² in the south and west of the Kalahari, the vegetation is mainly xeric savanna. This area is the ecoregion identified by World Wide Fund for Nature as Kalahari xeric savanna AT1309. Typical savanna grasses include (Schmidtias, Stipagrostis, Aristida, and Eragrostis) interspersed with trees such as camelthorn (Acacia erioloba), grey camelthorn (Acacia haematoxylon), shepherd’s tree (Boscia albitrunca), blackthorn (Acacia mellifera), and silver cluster-leaf (Terminalia sericea). In certain areas where the climate is drier, it becomes a true semi-desert with ground not entirely covered by vegetation: "open" as opposed to "closed" vegetation. Examples include the north of the Siyanda District, itself in the north of South Africa, and the Keetmanshoop Rural in the southeast of Namibia. In the north and east, there are dry forests covering an area of over 300,000 km² in which Rhodesian teak and several species of acacia are prominent. These regions are termed Kalahari Acacia-Baikiaea woodlands AT0709. Outside the Kalahari "desert", but in the Kalahari basin, a halophytic vegetation to the north is adapted to pans, lakes that are completely dry during the dry season, and maybe for years during droughts, such as in Etosha (Etosha Pan halophytics AT0902) and Makgadikgadi (Zambezian halophytics AT0908). A totally different vegetation is adapted to the perennial fresh water of the Okavango Delta, an ecoregion termed (Zambezian flooded grasslands AT0907). North and east, approximately where the dry forests, savannahs and salt lakes prevail, the climate is sub-humid rather than semi-arid. South and west, where the vegetation is predominantly xeric savanna or even a semi-desert, the climate is "Kalaharian" semi-arid. The Kalaharian climate is subtropical (average annual temperature greater than or equal to 18 °C, with mean monthly temperature of the coldest month strictly below 18 °C), and is semi-arid with the dry season during the "cold" season, the coldest six months of the year.

• published: 15 Oct 2015
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