9.1.1 Geographic Diversity on the African Continent

Owing to its position across the equatorial and subtropical latitudes of both the northern and southern hemispheres, Africa is home to a range of climates, including searing deserts, frozen glaciers, sweltering rainforests, and lush grasslands. These divergent environments exist because most of the continent lies between the Tropic of Cancer and the Tropic of Capricorn, in the tropical climate zone. Only its northernmost and southernmost fringes are beyond the tropical area.

Across the center of Africa, stretching like a band from Guinea in the northwest to parts of Mozambique in the southeast, lies a swath of wet, tropical land subject to extremely heavy rainfall. Here we find the deep canopy and undergrowth of Africa’s equatorial rainforest (Figure 9.4). Centered on the Congo River Basin, the rainforest is densest in the present-day central state of the Democratic Republic of Congo. Here there is very little space between trees, resulting in thick layers of leaf covering that prevent much sunlight from reaching the forest floor. Approximately 386,000 square miles in extent, the Congo rainforest is the second largest in the world. Overall, it receives between sixty-three and seventy-eight inches of rain every year.

The Congo River, which forms the heart of the rainforest region, is the second-longest river in Africa; only the Nile is longer. The geographic differences between the environments of these rivers produced vastly different societies. The Nile River and its predictable flood patterns allowed Egyptian civilization to flourish for centuries. Large cities and grand architecture were features of the region due to readily available and plentiful food supplies, and hieroglyphs remained that left a clear and permanent record of key moments of its history. The Congo, however, flows through a tropical region, where dense forests created a very different kind of society, and the moist environment did not allow for recorded history but rather oral stories passed down through generations. Thus, while both regions had a human past, we know far more about one than we do about the other.

Africa’s tropical band is further divided into the monsoon area and the tropical savanna. Wetter than temperate savannas, tropical savannas are characterized by tall grasses, sparse trees, and greater rainfall and are found bordering the equator. The monsoon area is subject to seasonal wind changes that produce wetter and drier periods in isolated locations of the West African coast and the Central African interior. In the tropical savanna, on the other hand, rainfall diminishes considerably, and the dense stands of thickly layered trees that characterize the rainforest give way to forested pockets and lush grasslands.

The savanna is a grassy plain that constitutes another of Africa’s immense biomes. A biome is a community of vegetation and wildlife adapted to a particular climate. At around five million square miles in size, the savanna covers almost half the surface of the continent and has been home to more people and history than any other part of Africa. Stretching from the warm and humid reaches of the rainforest to the torrid zone of the Sahara, it is wetter than the desert but drier than the rainforest and presents a striking geographic contrast to the landscapes of the desert and rainforest. Unlike those areas, the savanna landscape encompasses snow-capped mountains, vast expanses of grassy plains dotted with trees, and marshy tropical areas.

Geographers consider the savanna a region of transitions, with three successive belts running east–west: the Sahel, the tropical grassland savanna, and the woodland savanna. The Sahel, the northernmost band, is a semiarid belt between the Sahara and the grassland savannas to the south (Figure 9.5). It is the driest part of the savanna and experiences rain only periodically during six months of the year.

The people of the Sahel have historically been seminomadic—that is, they have adopted a mixed-farming system of crop production and the breeding and raising of livestock. Although the soil of the Sahel lacks sufficient nutrients to grow forests of trees, it is rich in the kind of nutrients that support the growth of plants in gardens as well as those that allow for small-scale farming and foster the growth of abundant grasses for the grazing of larger animals, particularly cattle and sheep. These herding animals also provide a key ingredient to help African farmers grow crops: manure. With the use of manure and the process of composting, the people of the region successfully navigate the challenges posed by their environment. Its conditions have tended to produce limited agriculture and smaller homesteads that are spaced farther apart to accommodate livestock. Many people of the region continue to live a seminomadic lifestyle rooted in animal husbandry. They do not cling to the past, a recurring myth about Africa; rather, their lifestyle is still the best way to harness what their climate provides.

The Sahel gradually gives way in the south to a grassland savanna carpeted by short grasses and studded by scattered trees. At the extreme, this area can see as much as forty-eight inches of rain per year (the rainy season lasts from May to October). The most famous of all Africa’s tropical savannas is the Serengeti. Located in northern Tanzania, the Serengeti is a tremendously diverse ecosystem that witnesses some of the world’s largest mass migrations of animals. In January each year, for example, nearly 1.75 million wildebeests begin migrating out of the Ngorongoro Conservation Area at the southern extreme of the Serengeti, following the rainfall in search of food (Figure 9.6).

Moving clockwise in a northerly direction toward the Masai Mara Reserve in Kenya, along the way these wildebeests encounter hundreds of thousands of other animals, including zebras and gazelles, that preceded them on their migration. They confront many obstacles and dangers on their trek, including rivers that hide dangerous hippopotamuses and crocodiles, not to mention numerous predators they face on land. When they finally arrive in Kenya, the female wildebeests birth around half a million calves. Their migration comes to an end in early November, after months spent grazing in the savanna grasslands of the Masai Mara Reserve. The herds then migrate south on their return trip to northern Tanzania from Kenya.

The woodland savanna is the last of the belts separating the great northern desert from the equatorial rainforest. It is characterized by tall grasses occasionally interrupted by scattered trees, and corridors of gallery forests along streams and rivers. The area receives plentiful rainfall, usually nine months of the year, and farmers in the region cultivate palm oil trees and root crops such as yams.

As distance from Africa’s tropical zone increases, so too does the unpredictability of the rainfall. Progressively, to the north and south of this region, the bands of tropical and temperate climate give way to increasingly drier environments. Limits on resource availability in the more arid parts of Africa, as elsewhere in the world, have necessarily restricted the growth and expansion of civilizations. Regions that lack accessible supplies of water in the form of underground aquifers or wells, rivers, or lakes or that receive little rainfall are ill-suited to farming. Because only farming can support larger human population centers, the lack of accessible water is a barrier to human settlement. This helps explain why no large civilizations emerged in the more obviously arid parts of Africa, such as the Sahara and the Kalahari Desert and also why certain of the drier transitional zones between savanna and desert remain so thinly populated.

The Sahel transitions to desert in the extreme north of the savanna belt. Deserts are the sunniest and driest parts of the continent. Africa’s largest desert—in fact, the world’s—is the Sahara. At 3.6 million square miles, about the size of the United States, the Sahara covers much of North Africa (excluding the fertile coastal zones along the Mediterranean and the Nile delta) and stretches from the Red Sea in the east to the Atlantic Ocean in the west. The Sahara has not always been a vast desert, however. In the period following the last Ice Age, this was a lush region that experienced monsoon-like weather conditions and was home to pastoralists and large herds of cattle. In fact, the earliest evidence we have of the domestication of cattle was discovered on Saharan rock art. But between 6000 and 2500 BCE, the region witnessed a great drying, which resulted in the retreat of the rainforest and the expansion of desert zones. These changes prompted crises for the human inhabitants of the formerly tropical zones, who found their old hunting and gathering techniques no longer suitable in the changed environment.

This desertification is what produced the modern Sahara, which receives less than an inch of precipitation per year with variations of some regions experiencing up to four inches per year, while other places go decades with no rain(Figure 9.7). The average daytime high is 99°F, and average nighttime lows are as cool as 68°F, but highs can reach up to 120°F during the warmer months from April to June, and lows can dip below 37°F in the cooler period between December and January. The only plants that can survive in this hostile environment rely on the water that collects in dry riverbeds during the exceptional periods of rain, but they are few.

Among the Sahara’s thousand-foot-tall sand dunes, hard stony surfaces, and vast mountain ranges with peaks as high as eleven thousand feet are oases, green dots of civilization formed around underground water sources that reach the surface via wells or springs. Although together these oases take up only eight hundred square miles—about 0.02 percent of the desert’s total landmass—they are home to some three-quarters of the people living in the desert. The remainder of the population are nomads, including the Tuareg and Teda. These peoples engage in a range of economic activities, such as farming and herding, but on a severely restricted basis. Pasturage, for example, exists only in marginal areas such as mountain borders and the somewhat moister areas to the west, limitations that govern the herders’ nomadic lifestyle.

As famous as it is, the Sahara is not Africa’s only desert; there is also a desert region in the African Horn (the area corresponding to Somalia, Ethiopia, and northern Kenya), as well as the Namib and the Kalahari Desert, Africa’s great southwestern desert (Figure 9.8). The Kalahari Desert presents perhaps the most interesting contrast to the extremes of the Sahara.

The Kalahari is a semiarid sandy savanna some 350,000 square miles across. Occasionally referred to as the southern African equivalent of the Sahel, it stretches south from modern-day Namibia into South Africa’s Northern Cape province, extends deep into the interior of the South African veld or grassland, and covers almost the whole of Botswana. While Saharan sand dunes are typically large, in the Kalahari they are much smaller, ranging between twenty and two hundred feet high and measuring at least one mile in length and several hundred feet in width. The landscape is also distinguished by numerous “dry lakes” or pans, evidence of a wetter period earlier in the region’s history. Even today, some of the northeastern parts of the Kalahari receive more than ten inches of water per year and thus climatically do not qualify as “desert.” However, they do lack surface water. When they experience rain, it drains instantly through the deep sands, leaving the soil completely devoid of moisture.

Precipitation in the Kalahari depends largely on weather patterns influenced by the Indian Ocean and is highly variable. While the northeastern part receives comparatively abundant rainfall, the southern fringe of the desert sees less than five inches of rain per year. This rainfall accompanies severe thunderstorms, which often appear suddenly and produce violent downpours that deluge the landscape. Still, for six to eight months of the year, the region receives no rainfall. As a result, there is very little ecologically to distinguish the southwestern landscape beyond flat sand plains—aside from a few drought-resistant shrubs and bushes. On the other hand, the central Kalahari, which enjoys more rain, is dotted with scattered trees, shrubs, and grasses. At the extreme end, the northern reaches of the Kalahari appear to be an entirely different biome with woodlands, palm trees, and forests.

The final major climate in Africa is the Mediterranean climate, found only on the northernmost and southernmost fringes of the continent in the coastal regions of Morocco, Algeria, and Tunisia in the north, and in South Africa. The combination of dry summers with lower humidity (relative to the tropical band) and mild rainy winters makes them ideal environments for the growing of olive trees, cereal grains, and grapes—the so-called Mediterranean triad of crops that dot the landscapes of both regions. The temperatures there are pleasant, with average daily highs of 77°F and average nightly lows hovering around 60°F.

Africa also offers regional climates, each with its own local variations. East Africa, for example, straddles the equator and includes Kenya, Uganda, and Tanzania. Along the coast and around Lake Victoria, hot and humid conditions prevail, but there are much cooler climates in the highlands and mountains (Figure 9.9). Many areas of the region experience extreme amounts of rainfall. Coastal islands and the tropical area around Lake Victoria, for example, receive upward of fifty-nine inches of rain per year. To the north, the Ethiopian highlands form a drier climate region, thanks to the influence of the eastern desert. Locally, Africa’s diverse microclimates belie the continent’s broad regional climate patterns and suggest the impressive variety of ecosystems that span it—and to which people have adapted over the millennia.

A staggering variety of wildlife has also adapted to these climates. Because of the abundance there of grasses as sources of food, Africa’s savannas are home to a range of large grazing mammals including gazelles, wildebeests, elephants, ostriches, and zebras. Large herds of these animals are commonly seen in the savanna, none more spectacular than the wildebeests on their annual migration in East Africa. Although giraffes, elephants, hippopotamuses, and rhinoceroses can be found in many places on the continent, including modern-day Botswana, Zimbabwe, and Zambia in the interior of south-central Africa and East Africa, one of the greatest concentrations of these animals on the continent is found in the sub-Saharan savanna.