Africa

C

Drainage and Water Resources

Africa contains some of the world's greatest rivers. In all, six major networks drain Africa. With the exception of those draining into the Lake Chad basin, and those surrounding the Kalahari, all have outlets to the sea. The River Nile drains north-eastern Africa, and, at 6,695 km (4,160 mi), is the longest river in the world. It is formed from the Blue Nile, which originates at Lake Tana in Ethiopia, and the White Nile, which originates at Lake Victoria. The two converge at Khartoum in Sudan, from where the Nile flows west and north before emptying into the Mediterranean Sea. The River Congo, some 4,375 km (2,720 mi) long, drains much of central Africa. It originates in Zambia, in southern Africa, and flows north, west, and south to empty into the Atlantic Ocean in the Democratic Republic of the Congo. The third longest African river, the Niger in west Africa, is about 4,180 km (2,600 mi) long; its upper portions are navigable only during rainy seasons. The Niger rises in the highlands of the Fouta Djallon and flows north and east before turning south to empty into the Gulf of Guinea. The River Zambezi, about 3,540 km (2,200 mi) long, originates from tributaries that begin in Zambia and Angola, and converge in Zambia; it then flows south and east to empty into the Indian Ocean in Mozambique. The Zambezi is cut by numerous rapids, the most spectacular being the Victoria Falls. Draining southern Africa are the Limpopo and Orange rivers. The Orange River, with its tributary, the River Vaal, has a length of about 2,090 km (1,300 mi). It rises in the Drakensberg and flows west to the Atlantic. The River Limpopo originates in South Africa and runs 1,610 km (1,000 mi), east and south to drain into the Indian Ocean in southern Mozambique.

The Rift Valley contains a series of great lakes. This equatorial lake system includes lakes Turkana, Albert, Tanganyika, and Malawi. Lake Victoria, the largest lake in Africa and the third-largest in the world, is, however, not part of this system; it occupies a shallow depression in the Eastern Highlands. Lake Chad, a shallow freshwater lake with an average depth of only about 1.2 m (4 ft), drains nearby rivers and constitutes the largest inland drainage system on the continent.

Achieving effective control of water supplies is a major problem in Africa. Vast areas suffer low rainfall; still larger areas receive only irregular rainfall and must store water as insurance against drought or poor rains. Other areas have an over-abundance of water: there are great swamps, like the Sudd of southern Sudan, and large areas suffer from periodic flooding. Since the 1950s many dams and reservoirs have been built to channel water for irrigation and for hydroelectric power. The continent's numerous rivers and their abrupt descent over the coastal escarpments have led to estimates that Africa has approximately 40 per cent of total world hydroelectric power potential.

D

Climate

The climate of Africa is the most generally uniform of any of the continents. This results from the position of the continent in the Tropical Zone, the impact of cool ocean currents, and the general absence within the continental plateau of mountain chains serving as climatic barriers.

Seven main African climatic zones can be distinguished. The central portion of the continent and the eastern coast of Madagascar have a tropical rainforest climate. Here the average annual temperature is about 26.7° C (80° F), and the average annual rainfall is about 1,780 mm (70 in). The climate of the Guinea coast resembles the equatorial climate, except that rainfall is concentrated in one season; no months, however, are rainless.

To the north and south the rainforest climate is supplanted by a tropical savannah climate zone that encompasses about one-fifth of Africa. Here the climate is characterized by a wet season during the summer months and a dry season during the winter months. Total annual rainfall varies from 550 mm (20 in) to more than 1,550 mm (60 in). Away from the equator, to the north and south, the savannah climate zone grades into the drier steppe climate zone. Average annual rainfall varies between 250 and 500 mm (10 and 20 in) and is concentrated in one season.

Africa has a proportionately larger area in arid, or desert, climate zones than any continent except Australia. Each of these areas—the Sahara in the north, the Horn of Africa in the east, and the Kalahari and Namib deserts in the south-west—has less than 250 mm (10 in) of rainfall annually. In the Sahara, daily and seasonal extremes of temperatures are great; the average July temperature is more than 32.2° C (90° F); during the cold season the night-time temperature often drops below freezing.

Mediterranean climate zones are found in the extreme north-west of Africa and in the extreme south-west. These regions are characterized by mild, wet winters and warm, dry summers. In the highlands of eastern Africa, particularly in Kenya and Uganda, rainfall is well distributed throughout the year, and temperatures are equable. The climate on the high plateau of southern Africa is temperate.

E

Vegetation

African vegetation can be classified according to rainfall and climate zones. The tropical rainforest zone, where the average annual rainfall is more than 1,270 mm (50 in), has a dense surface covering of shrubs, ferns, and mosses, above which tower evergreens, oil palms, and numerous species of tropical hardwood trees. A mountain forest zone, with average annual rainfall only slightly less than in the tropical rainforest, is found in the high mountains of Cameroon, Angola, eastern Africa, and parts of Ethiopia. Here a ground covering of shrubs gives way to oil palms, hardwood trees, and primitive conifers. A savannah woodland zone, with annual rainfall of 890 to 1,400 mm (35 to 55 in), covers vast areas with a layer of grass and fire-resistant shrubs, above which are found deciduous and leguminous fire-resistant trees. A savannah grassland zone, with annual rainfall of about 500 to 890 mm (20 to 35 in), is covered by low grasses and shrubs, and scattered, small deciduous trees. The thornbush zone, a steppe vegetation, with an annual rainfall of about 300 to 510 mm (12 to 20 in), has a thinner grass covering and a scattering of succulent or semi-succulent trees. The sub-desert scrub zone, with an annual rainfall of 130 to 300 mm (5 to 12 in), has a covering of grasses and scattered low shrubs. The zone of desert vegetation, found in areas with an annual rainfall of less than 130 mm (5 in), has sparse vegetation or none at all.

F

Animal Life

Africa has two distinct faunal zones: the North and North-western zone, including the Sahara; and the Ethiopian zone, including all of sub-Saharan Africa. The North and North-western zone is characterized by animals similar to those of Eurasia. Sheep, goats, horses, and camels (introduced by the Romans) are common. Barbary sheep, African red deer, and two types of ibex are native to the north African coast. Desert foxes are found in the Sahara, along with hares, gazelles, and the jerboa, a small leaping rodent. The Ethiopian zone is famous for its great variety of distinctive animals and birds, although many of these are now under threat of extinction from loss of habitat and poaching. The woodland and grassland areas are the traditional habitats of numerous species of antelope and deer, of zebra, giraffe, buffalo, the African elephant, rhinoceros, and the baboon and various monkeys. Carnivores, or meat-eating animals, include the lion, leopard, cheetah, hyena, jackal, and mongoose. The hippopotamus is found in the rivers, emerging at night to graze. The gorilla, the largest ape in the world, inhabits the rainforests of equatorial Africa, as do monkeys, flying squirrels, bats, and lemurs. However, many of these species, notably the elephant, rhinoceros, leopard, lion, and gorilla, are now found only in specially delineated game reserves.

Most bird life belongs to Old World groups. The guinea fowl is a leading game bird. Water birds, notably pelicans, goliath herons, flamingos, storks, and egrets, congregate in great numbers. The ibis is common in the Nile region, and the ostrich is found in eastern and southern Africa. Reptiles are also mainly of Old World origin and include lizards, crocodiles, and tortoises. A variety of venomous snakes, including the mamba, are encountered throughout the Ethiopian zone. Among the constricting snakes, pythons are found mainly in western Africa. Boa constrictors are indigenous only to Madagascar, which has a large number of unique species. Freshwater fish abound, with more than 2,000 known species. The continent has a variety of highly destructive insects, notably mosquitoes, driver ants, termites, locusts, and tsetse flies. The tsetse transmit sleeping sickness (or trypanosomiasis) to humans and animals.

G

Mineral Resources

Africa is very rich in mineral resources, possessing almost all types of the known minerals of the world, many of which are found in significant quantities, although the geographic distribution is uneven. Fossil fuels are abundant, including major deposits of coal, oil, and natural gas. Africa has some of the world's largest reserves of gold, diamonds, copper, bauxite, manganese, nickel, platinum, cobalt, radium, germanium, lithium, titanium, and phosphates. Other important mineral resources include iron ore, chromium, tin, zinc, lead, thorium, zirconium, vanadium, antimony, and beryllium. Also found in exploitable quantities are clays, mica, sulphur, salt, natron, graphite, limestone, and gypsum.