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E. Linacre and B. Geerts |
12/'98 |
The Kalahari plateau lies at about 1000 metres elevation in southern Africa, and is about the size of France, i.e. 260,000 km2. It is mostly flat, and together with Namibia's Skeleton Coast, it is the world’s largest body of sand. (The Sahara is larger but it only has pockets of sand dunes.) It comprises both windblown sand and, in the north, sand from river deposition. The sandy soil soaks up any rain even in the wetter north and east, so that surface water is rare. The Okavango river in the north drains from the Angolan highlands but spreads in an inland delta (the Okavango Delta), where most water evaporates. After a particularly wet summer some Delta water will fill the Boteti river which discharges in the Makgadikgadi plains, a series of salt pans some 900 km from the sea.
The Kalahari plateau is well covered by vegetation, mostly deciduous trees, low scrub and tussocky grass, adapted to the erratic rainfall. Most rain falls in the late summer, however occasionally the northern fringes of a cold front may bring some rain to the southwestern Kalahari in winter. Up to 660 mm/a falls in the north, 400-450 mm/a in the east but less than 200 mm/a in the southwest. The number of species of plants decreases with the rainfall, and eventually plants are only found in the ephemeral river valleys.
The dryness, especially in the south, leads to large annual and daily ranges of temperature, with up to 47ºC in summer and frosts in winter.