Botswana and 30°E. The country is predominantly flat, tending toward gently rolling tableland. Botswana is dominated by the Kalahari Desert, which covers up to 70% of its land surface. The Okavango Delta, one of the world's largest inland deltas, is in the northwest. The Makgadikgadi Pan, a large salt pan, lies in the north. The Limpopo River Basin, the major landform of all of southern Africa, lies partly in Botswana, with the basins of its tributaries, the Notwane, Bonwapitse, Mahalapye, Lotsane, Motloutse and the Shashe, located in the eastern part of the country. The Notwane provides water to the capital through
Kalahari Desert annual rainfall ranging from around 110 mm (close to aridity) to more than 500 mm in some areas of the north and east. During summer time in all regions rainfall may go with heavy thunderstorms. In the driest and sunniest parts of the Kalahari, over 4,000 hours of sunshine are recorded annually on average. In the Kalahari, there are two main mechanisms of atmospheric circulation, dominated by the Kalahari High anticyclone: There are huge subterranean water reserves beneath parts of the Kalahari; the Dragon's Breath Cave, for example, is the largest documented non-subglacial underground lake on the planet. Such reserves