Botswana's geography: a river that ends in the Kalahari

How the Kalahari sand covers the country

Botswana sits in the middle of a basin, and its relief is gentle by any measure. Britannica describes the country as having a mean altitude of 3,300 feet, about 1,000 metres, and consisting largely of a sand-filled plain that rises gently towards highlands in the neighbouring states. Wikipedia's country article puts about 70% of the territory inside the Kalahari. The sand is deep enough that Britannica calls geological exploration limited by it: the rock under most of the west is the least known in the country.

Three environmental regions follow from that. The hardveld is the east, a belt of rocky hill ranges and shallow sand where the basement rock, older than two and a half billion years in Britannica's account, comes to the surface. The sandveld is the deep Kalahari sand that covers the rest. The third region is a set of ancient lake beds lying on the northern sandveld in the lowest part of the basin, which is where the Okavango Delta and the Makgadikgadi Pans are.

The Kalahari is not a desert in the sense of bare dunes. Britannica notes that it has often been called thirstland to separate it from true desert, and that even in the south-west, where some bare dunes stand, the vegetation is closer to dry steppe. Wikipedia's geography article describes the land as flat to gently undulating tableland with some hilly country, and the hilly country is where the mines are.

Soils divide the same way. On the hardveld plains Britannica lists red loamy mokata soils, mixed chalky and sandy chawana soils, and brownish rocky seloko soils around the hills, which are considered best for grain. The old lake beds carry grey loams in the wetlands, grey-green saline soils on the pans and black cracking clay in former wet areas such as Pandamatenga. On the sandveld, rainfall rather than soil is the limit, and Britannica says it is regularly too low to support any cultivation at all.

Where the highest and lowest ground lies

The sources disagree on both ends of the country's small range of height, and the disagreement is mostly about which hill and which point on the Limpopo is meant. The record beside this article names Otse Hill and the Limpopo River.

All three place the high ground in the south-east hills near Lobatse and the low ground on the Limpopo in the east. Between them lies less than a thousand metres of relief over the whole territory.

Why the Okavango floods in the dry season

Where the water comes from

The Okavango River is formed in Angola by the Cubango and the Cuito, crosses the Caprivi Strip of Namibia and enters Botswana near Mohembo. UNESCO's statement for the World Heritage property, inscribed in 2014, gives the river a length of 1,500 kilometres and describes the delta as a low-gradient alluvial fan whose waters drain into the sands of the Kalahari Basin, an endorheic delta with no outlet to any sea. The trough it fills is part of the African rift system; UNESCO describes the river as captured by that geology.

The rain that feeds the flood falls in the Angolan highlands in January and February. Wikipedia's article on the delta says the surge travels about 1,200 kilometres in roughly a month and then takes four more months, from March to June, to spread across the fan. Flood levels peak between June and August, which is the middle of Botswana's dry winter, and the delta then swells to about three times its permanent size. UNESCO names June and July as the peak of the dry season in which the flood arrives, and notes that the plants and animals of the flooded grasslands have timed their breeding to it.

Where the water goes

About 11 cubic kilometres of water a year spreads over the delta, in Wikipedia's figure, and almost all of it is lost to evaporation, transpiration and seepage. The same article gives 96 to 98% lost in that way and only a small share leaving through the Thamalakane and Boteti rivers. The land is very flat, with less than 2 metres of variation in height across 15,000 square kilometres, while the water falls about 60 metres between Mohembo and Maun.

UNESCO puts the permanent swamps at about 600,000 hectares and the seasonally flooded grassland at up to 1.2 million hectares, and the inscribed property at 2,023,590 hectares with a buffer zone of 2,286,630 hectares. Distributary channels named in Wikipedia's article include the Boro, Maunachira, Thaoge, Santantadibe, Nqoga and Jao.

The delta builds its own islands. Its water carries little mud, so plants catch the sand and make the banks. Wikipedia's article says about 70% of the islands began as termite mounds on which a tree took root, and that salt left by evaporation gathers around the roots at the centre of many islands until they are white and bare. Chief's Island was raised along a fault over 70 kilometres long and 15 kilometres wide, and was once reserved as a chief's hunting ground.

Which rivers reach the sea and which do not

Wikipedia's geography article divides the country into four drainage regions, which are sometimes indistinct because of the dry climate. The Chobe on the Namibian border and a small swamp beside it belong to the Zambezi basin, and Britannica notes that the Chobe joins the Zambezi above the Victoria Falls. Most of the north and centre drain inward to the Okavango basin. The far east drains to the Limpopo. The south and south-west, the driest part, belong in theory to the Orange River basin through the Molopo and the Nossob, but neither normally flows that far, and the last recorded confluence was in the 1880s.

Most rivers are ephemeral. Wikipedia's geography article lists the Chobe, Okavango, Boteti and Limpopo as the exceptions that keep flowing outside the rains, and Britannica describes the others as channels that do not flow above ground except in the summer rainy season. Britannica adds that the Molopo and its Ramatlhabama tributary today rarely flood more than 80 kilometres from their sources.

The north-centre holds the dried beds of a much larger system. Wikipedia's country article describes a vast palaeolake, Lake Makgadikgadi, which began to shrink about 50,000 years ago. The Makgadikgadi Pans that remain are salt pans of about 4,000 square miles, roughly 10,000 square kilometres, in Britannica's estimate, made up of Nwetwe, Sua and Nxai pans among others, and the Nata River from the Zimbabwe highlands floods the eastern pans each year. Floodwater from the Okavango reaches down the Boteti towards Lake Xau and the pans only sporadically. Lake Ngami, 180 square kilometres and famous a century before Britannica's account, received less and less water through the western side of the delta during the twentieth century and is described there as dry and almost unrecognisable.

How rain and drought set the year

Britannica gives annual rainfall an average of 460 millimetres, ranging from about 635 millimetres in the far north-east to less than 127 millimetres in the far south-west, almost all of it falling in summer downpours between December and March. Summer runs from October to March, with temperatures reaching about 34 °C in the far north and south-west. Winter runs from April to September, with frequent frost at night. Dust-laden winds from the Kalahari announce summer from late August to early October.

The World Bank's Climate Change Knowledge Portal gives an annual mean temperature of 21.94 °C and annual precipitation of 461.83 millimetres for the period 1995 to 2014. Since 1970, on the portal's ERA5 series, temperatures have risen by 0.25 °C a decade and precipitation has changed by minus 3.16 millimetres a decade. Its projection for 2040 to 2059 under the high-emission scenario SSP3-7.0 is a median warming of 1.79 °C and a median change in precipitation of minus 20.03 millimetres against 1995 to 2014.

Drought is the recurring event. Britannica describes cyclic droughts lasting up to five or six years in every two decades, which can wipe out harvests and starve livestock. Wikipedia's country article says less than 5% of agriculture can be sustained by rain, and its geography article records a study predicting that by 2050 the cycle of mild drought in one district may shorten from two years to 18 months. Veld fires burn in the winter dry season.

What grows and lives on the Botswana savanna

Britannica describes the vegetation as savanna grassland with woody plants, changing from acacia shrub savanna in the south-west through thornbush and tree savanna into denser woodland towards the north and east. Mopane woodland covers most of the northern and eastern third. Croton and Combretum grow on the rocky eastern hills. Wikipedia's geography article puts forest cover at about 27% of the land in 2020, or 15,254,700 hectares, against 18,803,700 hectares in 1990.

Britannica counts about 150 species of mammals in the country, from 30 species of bats and 27 of rodents to more than 30 large mammals, and more than 460 species of birds. UNESCO's statement for the Okavango Delta, written for the inscription in 2014, lists 1,061 plants, 89 fish, 64 reptiles, 482 birds and 130 mammals within the delta, and puts the national elephant population at around 130,000 with the delta as its core area. Wikipedia's article on the delta estimates about 88,000 red lechwe there and records that about 150 rhinoceroses lived in the northern delta by 2019, that poachers killed 92 between 2020 and 2021, and that the government then moved the remaining animals out.

The protected land is large. About 40% of the World Heritage property lies inside the Moremi Game Reserve, according to UNESCO, and the rest is divided into 18 Wildlife Management Areas and controlled hunting areas run by community trusts or concession holders. Britannica lists the Central Kalahari Game Reserve, Chobe National Park, the Makgadikgadi Pans Game Reserve and the Kgalagadi Transfrontier Park, shared with South Africa, among the parks and reserves.

How cattle and boreholes use the land

Livestock and water decide how the land is used. Wikipedia's country article gives a livestock population of 1.7 million in 1966 and 5.5 million in 1991, about 71% of the land under communal grazing, and three-quarters of the human and animal population dependent on groundwater from boreholes. Overgrazing, desertification and limited fresh water are the environmental issues its geography article lists. Wikipedia's geography article records that the common practice of overstocking cattle to cover drought losses depletes the scarce plant cover and leaves the land more exposed to the next drought. UNESCO's statement adds the veterinary cordon fences, built to keep disease from passing between wildlife and cattle, to the causes of declining wildlife numbers in the delta.

The borders follow nineteenth-century treaties and several rivers. Wikipedia's geography article gives a total land boundary of 4,347.15 kilometres.

The Zambian border is a few hundred metres of river; Britannica gives it as only several hundred yards long. The point at which Botswana, Namibia, Zambia and Zimbabwe meet in the river has never been fixed precisely, according to both Britannica and Wikipedia. The channel of the Chobe near Sedudu Island was disputed with Namibia until a ruling of the International Court of Justice in December 1999 placed the island in Botswana.