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Africa
The African continent is an immense plateau, broken by a few mountain ranges and bordered in some areas by a narrow coastal plain. It is a land of striking contrasts and great natural wonders. In the tropical rain forests of western and central Africa, the towering treetops form a thick green canopy. The world's largest desert, the Sahara, stretches across northern Africa. It covers an area almost as large as the United States. Africa also has the world's longest river—the Nile. It flows more than 4,000 miles (6,400 kilometers) through northeastern Africa. Grasslands make up about a third of the continent. Elephants, giraffes, lions, zebras, and many other animals live in the vast grasslands in eastern and southern Africa.
Africa is divided into 53 independent countries and several other political units. The largest country, Sudan, has an area of 967,500 square miles (2,505,813 square kilometers). The smallest, Seychelles, has a land area of only 176 square miles (455 square kilometers). The most heavily populated African nation, Nigeria, has more than 155 million people. However, about one-third of all African countries have fewer than 5 million people each. About 835 million people—about 80 percent of Africa’s total population—live south of the Sahara in the vast region called sub-Saharan Africa.
There are several hundred ethnic groups throughout Africa, each with its own language or dialect and way of life. The large number and various sizes of ethnic groups has made it difficult for some African countries to develop into unified, modern nations. In some African countries, national boundaries cut across traditional ethnic homelands. As a result, people may feel closer ties to neighbors in another country than to other ethnic groups within their own country. Ethnic and religious differences have led to civil wars in several countries.
Africa has great mineral wealth, including huge deposits of copper, diamonds, gold, and petroleum. It also has valuable forests. In addition, many African rivers and waterfalls could be used to produce hydroelectric power. Africa produces most of the world's cassava, cocoa beans, and yams. But Africa has the least developed economy of any continent except Antarctica.
Agriculture is the leading economic activity in Africa, but most farmers use outdated tools and methods to farm thin, poor soil. About two-thirds of all Africans live in rural areas, where they make a living growing crops or raising livestock. Since the mid-1900's, however, millions of rural Africans have flocked to cities and have adopted a more urban lifestyle. The development of manufacturing has been handicapped by a lack of money to build factories, a shortage of skilled workers, and competition from industries on other continents. Many African countries depend on only one or two farm or mineral products for more than half their export earnings. In case of crop failures or drops in world market prices, a country's economy suffers. The majority of African nations rely to some extent on aid from countries outside the continent.
One of the world's first great civilizations—ancient Egypt—arose along the banks of the NileRiver more than 5,000 years ago. Later, other powerful and culturally advanced kingdoms and empires developed in Africa. Even so, for many years Westerners referred to Africa as the "Dark Continent." They used this name because they knew little about Africa's interior geography, and they mistakenly believed that the people of the interior had not developed any important cultures.
Sahara, «suh HAR uh or suh HAHR uh», is the world's largest desert. It covers about 3 1/2 million square miles (9 million square kilometers), an area roughly equal to that of the United States. The landscape of this vast African desert includes mountain ranges, rocky plateaus, gravelly plains, and sandy wastes. The barren desert is broken only by the cultivated land along the NileRiver and in the scattered oases.
The Sahara extends more than 3,500 miles (5,630 kilometers) across northern Africa from the Atlantic Ocean to the Red Sea. It stretches more than 1,200 miles (1,930 kilometers) from north to south. The desert spreads over all of Western Sahara and the African part of Egypt. In addition, the Sahara covers parts of Morocco, Algeria, Tunisia, Libya, Sudan, Chad, Niger, Mali, and Mauritania. The word Sahara comes from the Arabic word sahra', meaning desert. Parts of the Sahara have separate names, such as the Arabian, Libyan, Nubian, and Egyptian Western deserts.
Land and climate. Mountains and uplands cover the central portion of the Sahara. The AhaggarMountains in Algeria rise 9,573 feet (2,918 meters) high. The uplands of a region called the Tassili-n-Ajjer lie northeast of those mountains, and to the south are the main mountain ranges of the Aïr, the Ennedi, and the Adrar des Iforhas. The TibestiMountains in Chad reach a height of 11,204 feet (3,415 meters).
Scattered areas of barren, rocky plateaus and of gravelly plains called regs make up most of the Sahara. Only about 15 percent of the desert is sand, but dunes are found throughout the desert. Vast sand seas called ergs lie within large basins and are shifted and shaped by strong winds. In some places, the flowing sands of the ergs form dunes as high as 600 feet (180 meters).
Oases lie throughout the Sahara. The water in these fertile areas comes mainly from wells or springs. The Sahara has about 90 large oases, where people live in villages and grow grains such as barley and millet and fruits such as dates and melons. There are many small oases, some of which support only one or two families.
Major deposits of oil and natural gas lie under the Sahara in Algeria and Libya. These countries rank among the largest producers of the two vital fuels. The Sahara also contains valuable deposits of copper, iron ore, phosphates, uranium, and other minerals, but many of them have not been mined.
The Sahara has a dry, hot climate. The annual rainfall—which often comes in a single storm—averages less than 4 inches (10 centimeters). Large areas of the eastern and western Sahara receive less than 1 inch (2.5 centimeters) of rain yearly. The mountainous central Sahara gets slightly more rain, and snow sometimes falls on the mountaintops. Some wetlands exist near the AhaggarMountains of Algeria.
The Sahara is extremely hot during the day, but it turns cool at night. Daily summer temperatures often average above 90 °F (32 °C), and parts of the desert have daytime temperatures higher than 110 °F (43 °C). The highest official temperature in the world—136 °F (58 °C)—was recorded at Al Aziziyah, Libya, in September 1922. Daily winter temperatures in the Sahara average from 50 to 60 °F (10 to 16 °C), while winter night temperatures can fall below freezing.
People. The Sahara has a population of about 2 million. Large areas of the desert, such as the Great Western Erg and the desolate, pebbly plains of the Tanezrouft in Algeria, have no permanent settlements. Most Saharan people are of Arab or Berber origin. Berbers are the indigenous peoples of the northern coast. The chief inhabitants of the Sahara include the Moors, the Tuareg, and the Toubou. The Moors have mixed Arab and Berber ancestry and live in the northwestern Sahara. The Tuareg, who speak a Berber-related language, occupy the central mountains and uplands. The Bérabiche, a Tuareg people, are the traditional caravanners of the desert. The Toubou are a people of mixed ancestry who live in Chad's TibestiMountains.
Most of the Saharan people live in villages and oases or in mining settlements. Only about a third retain the traditional nomadic life, tending herds of sheep, goats, camels, and cattle. Nomads usually occupy fairly distinct areas and travel systematically to use seasonally available water and pastures. Some tribes of nomads own land in the oases but employ other people to farm it.
Most oases settlements have fewer than 2,000 inhabitants, but some have evolved into desert cities. Some oases have thousands of date palm trees, but in areas where water is scarce, a single tree may be shared by several owners.
The Saharan people traditionally use camels for transportation in the desert, though trucks and highways are becoming more common. The Trans-Saharan Highway crosses part of the desert from north to south in Algeria. In some other areas—especially in Egypt and Libya—paved roads connect the principal oases.
Sahel,«sah HEHL», is a dry grassland in Africa. The Sahel lies south of the Sahara and extends through large parts of Senegal, Mauritania, Mali, Burkina Faso, Niger, Nigeria, Chad, and Sudan. Some geographers also consider certain desertlike regions in Eritrea, Ethiopia, Kenya, and Somalia to be part of the Sahel. A number of serious droughts (dry periods) have struck the Sahel. The area has been especially dry since 1968. Millions of people in the Sahel have died as a result of crop failures caused by the droughts.
Farmers in the Sahel face many problems. During some seasons, the area either receives no rain, or the rains come too late for the growing season. Occasionally, the Sahel receives heavy rainfalls that wash away the farmers' seeds. Other problems include livestock epidemics, attacks by locusts that destroy crops, and erosion, the wearing away of soil by wind and rain. Much of this erosion results from the overgrazing of the grassland. Agricultural experts have developed methods to improve farming in drought-stricken areas such as the Sahel. But more economic assistance and cooperation by the
A still drier savanna zone, with 15 to 25 inches (380–635 mm) of rainfall per year, has drought-resistant scrubby acacias, thorn bushes, and desert grasses. Except for periods of rain it has a dry and almost steppelike appearance. This dry savanna occurs in a belt south of the Sahara, in parts of the Eastern Horn region, and on the west coast of Southern Africa, where it widens toward the south. Gum arabic is obtained from the Acacia senegal in the north. In many places the grasses provide grazing for cattle and sheep, and goats browse on some of the shrubs. The low rainfall, hot summers, and sparse vegetation discourage tsetse flies. Whereas the dry savanna has many domesticated grazing animals, the tree savannas, because of tsetse flies, have almost none.
The dry savanna merges into a steppe zone, with about 10 inches (250 mm) of rainfall, as it nears the Sahara, the Somali desert in the Eastern Horn, and the Namib desert along the southwest coast. After periods of rain, grass and shrub growth is sufficient for the animals of nomadic peoples. The northern dry savanna lies within the marginal region known as the Sahel, receiving between 4 and 24 inches (100–600 mm) of rainfall a year. area's governments are needed before these methods can be widely applied.
Savanna,«suh VAN uh», also spelled savannah, is a grassland with widely scattered trees and shrubs. Most savannas are in the tropics and lie between deserts and rain forests. Certain grasslands in temperate areas are also sometimes called savannas. This article discusses tropical savannas.
Savannas cover more than two-fifths of Africa and large areas of Australia, India, and South America. They occur in regions that have both rainy and dry seasons.
Most savannas receive from 30 to 40 inches (76 to 100 centimeters) of rain annually. But some get as little as 10 inches (25 centimeters) of rain, and others get as much as 60 inches (150 centimeters). Grasses on the driest savannas, where trees are widely scattered, grow only a few inches high. On more humid savannas, grasses grow several feet tall, and trees are more abundant. Grasses on the wettest savannas may reach heights of 10 feet (3 meters) or more.
Most savanna grasses grow in clumps and do not form a continuous cover of sod. Other nonwoody plants, including members of the composite and legume families, grow among the grasses. Acacias, baobabs, and palms are some common savanna trees.
The growth of trees on savannas is limited by the dry season, which may last up to five months. When the dry season begins, grasses stop growing and turn brown, and most trees shed their leaves. Only the most drought-resistant trees can survive. During the dry season, frequent brush fires destroy many young trees. Grasses have extensive root systems that survive the fires and send up fresh shoots as soon as the rains return. On some savannas, poor drainage and other soil conditions also favor the growth of grasses instead of trees.
A wide variety of animals live on savannas. Large herds of antelope and zebras graze on the African savannas. Cheetahs, hyenas, lions, and other meat-eaters prey on these animals. Many rodents, birds, reptiles, and insects also inhabit savannas.
Savanna and Tropical Steppe Zones.
The savanna and steppe zones south of the Sahara, in eastern Africa, and in south-central Africa form an almost continuous belt enclosing the tropical rain forest on the north, east, and south. Savanna and steppe cover more than a third of the continent's surface.
In the north and south these zones are transitional between the equatorial forests and the deserts. Rainfall usually occurs in the warmer months. It is abundant on the forest margins but decreases toward the deserts until, in the steppe areas, it is very light and irregular. Winters are generally without rainfall.
Along much of the Indian Ocean coast there are two rainy seasons, caused by monsoon winds that blow from the southwest toward Asia during the Northern Hemisphere summer and from the northeast during the winter. A major cause of the monsoons is the change from great heat and low atmospheric pressure in interior Asia in summer to cold and high pressure in winter. The changing pressure system alternately attracts and repels air masses from eastern Africa.
Temperatures in the drier parts of the northern savanna-steppe zone are very high, reaching well over 100° F (38° C) during March, April, and May, just before the summer rains. The rainy period has slightly lower temperatures, and in the winter temperatures are commonly in the 70°–90° F range (21°–32° C). Because of elevation and marine influences from the ocean, the eastern and southern zones are less hot. Many plateaus with savanna in East Africa have average temperatures in the 70's F (21°–26° C). Average temperatures in the southern savannas are intermediate between those of the north and those of the east.
Average annual rainfall in the savanna and steppe zones ranges from more than 40 inches (1,020 mm) on the forest margins to about 10 inches (250 mm) near the deserts, but it is often highly variable from year to year. The rainy season in the northern savannas occurs usually in June, July, and August, and in the Southern Hemisphere savannas in December, January, and February.
Recent studies indicate that Africa is likely to suffer the most serious consequences of global warming, even though it has contributed very little in terms of the greenhouse gases responsible for climate change. Dry areas are already becoming drier, while wet areas have become wetter, with many experiencing devastating floods. This is expected to have dramatic effects on a continent where food sustainability is often marginal, at best.
Savanna grasslands near the rain forest have a luxuriant growth, with patches of forest. These combined forest and grassland areas, or tree savannas, occur where rainfall is between 35 and 50 inches (890–1,070 mm) and the dry season lasts three months or less. One band, about 500 miles (800 km) in width, extends across the northern savanna zone. Within this band is a gradation from dense to lighter growth as the length of the dry season increases northward. The vegetation varies also with slope, drainage, and soil types. In the south, much of another broad band has open stands of trees, so that it is often called woodland instead of savanna. Part of this open woodland and savanna has replaced the original forest as a result of burning, cutting, and cultivation. In East Africa are patches of tree savanna varying from grassland with scattered trees and a parklike appearance to scrubby areas with mixed palms and acacias and wooded areas with grasses and low shrubs. Several useful trees occur in these savanna areas. Oil palms grow in moister regions of West and Equatorial Africa. Some trees yield rubber, and the iroko and African ebony are used for timber. The kernels of the shea tree provide a solid white fat (shea butter), and the fruits of some trees are edible.