3.1: Africa's Natural Environments

Learning Objectives

1. Describe Africa's latitudinal situation and how it shapes its major biome regions.
2. Explain the mechanisms of the Intertropical Convergence Zone and how it shapes climate and seasonability in tropical regions.
3. Identify the major river basins of Africa South of the Sahara and their significance.
4. Explain the tectonic dynamics of the Great Rift Valley and some of its geographical features.

 

Correcting Mental Misplacements

Even though most people know that the African continent is a large landmass, its size is sometimes underestimated. As we discussed in Chapter 1, geography students may have shaped their mental maps of the world based on the Mercator projection that was widely used in many geography classrooms in the United States. This projection exaggerates the size of northern regions, contributing to misconceptions by distorting the relative size of Africa. Africa is the second largest continent after Asia - as large as the US, China, India, Japan, Mexico, and many European countries combined. It is a massive landmass that is positioned further north than what most people think, with most of its land area located north of the equator. The northernmost latitudes are as far north as San Francisco and the southernmost about as far south as Buenos Aires. It is the only continent that is crossed by both the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S) making it the most tropical continent in the world. This latitudinal range shapes important climate mechanisms and life regions in Africa South of the Sahara.

 

Figure \(\PageIndex{1}\): These maps help us correct some geographical misconceptions about the African continent: it is larger and further north than most people imagine it. [left] This map is part of "Misconceptions," a storymap by John Nelson debunking some common mental geographical misplacements. Nelson highlights the northern portion of Africa on the map to illustrate that two thirds of it is located north of the equator (Copyrighted; used with permission of cartographer John Nelson). [right] This map shows the actual relative size of Africa in comparison to the land areas of other countries, illustrating that the US, China, India, the UK, Japan, and many European countries could "fit" in the African continent (Public Domain; Kai Krause).

 

The Dynamic Intertropical Convergence Zone (ITCZ)

Given that the African continent lies within tropical and subtropical latitudes, most of the continent experiences more direct solar radiation throughout the year than regions outside of the tropics. Recall (from Chapter 1) that as the Earth rotates around the sun, the northern and the southern hemisphere are either tilted towards or away from the sun in their respective solstices. Thus, in July, the northern hemisphere is tilted towards the sun, exposing the Tropic of Cancer to direct rays of the sun. July is when the Northern Hemisphere experiences its summer. Conversely, the Southern Hemisphere is tilted towards the sun in December and experiences summer at that time.

The relationship between the Earth and the sun shapes global pressure systems and air circulation patterns. Direct solar radiation warms up the lands and oceans and their adjacent air masses – the tropical Atlantic Ocean, for example, is a major source of moisture as warm Atlantic waters eventually evaporate into the adjacent warm air mass. This moist warm air rises, as it rises it cools, and as it cools it is less able to hold moisture. Thus, the tropics are marked by the presence of an enveloping cloud, a warm rising air mass that generates abundant rainfall in tropical regions. This tropical low-pressure system (characterized by rising air and rain) is called the Intertropical Convergence Zone (ITCZ). The ITCZ shifts north and south of the equator with the seasons, following the direct rays of the sun. Therefore, in July it shifts north and in December it shifts south. The presence and seasonality of the ITCZ shapes Africa’s tropical biomes.

 

Figure \(\PageIndex{2}\): [top] Satellite image showing the cloud formations of the ITCZ over the Atlantic Ocean, Northern South America, and West Africa (CC BY 4.0; Christoph Kersen via GEOMAR). [bottom] Two maps display the seasonal shifts of the ITCZ (red band) with the colors quantifying the seasonal rainfall: a) the ITCZ positioned in south of the equator in January, bringing high precipitation to regions near the Tropic of Capricorn and b) the ITCZ positioned north of the equator in August, bringing high precipitation to regions near the Tropic of Cancer (CC BY 3.0; Ziegler et al. via Nature Communications).

 

Major Biomes South of the Sahara

African Tropical Rainforests

Tropical rainforests typically exist near the equator (5-10° north and south of the equator) due to the prominence of the ITCZ. They are characterized by their tropical climates, or climates that are warm (average annual temperatures range from 68°-81°F) and wet (exceeding 80 inches per year). Tropical rainforests have dense tree cover and a high diversity of plant and animal species, many of which exist exclusively within the region. African rainforests are concentrated in the Congo Basin - most notably in the Democratic Republic of Congo but also in the Republic of the Congo, Gabon, Equatorial Guinea, Cameroon, and the The forests in the Congo Basin are the heart of African tropical biodiversity. Only second to the Amazon in their geographical size, the Congo Basin is home to 70 percent of forest cover in Africa. It displays diverse environments in differential topography, from swampy rainforests along riverine floodplains to higher elevation forests. Topographical differences in the Congo Basin provides for differential environments that are home to diverse flora and fauna, including the endangered forest elephant, lowland gorillas, bonobos, and chimpanzees.^[1] Rainforests can also be found in parts of Liberia, Sierra Leone, Nigeria and in eastern Madagascar, for example. Tropical rainforests have a long history of human settlement. The African rainforests has been intertwined with local peoples for more than 50,000 years. Today, it provides resources and sustenance for more than 75 million people of diverse ethnic identities.^[2]

 

Tropical Savannas

Savannas are grassy plains with sparse trees that represent transitional zones between the wetter tropical rainforests and the drier grasslands. This biome represents a noticeable climatic shift north and south from central Africa. Unlike tropical rainforests, which experience abundant rain year-round, tropical savannas experience warmer temperatures, less rain, and more seasonality. Most of the rain comes in a pronounced wet season (summer) followed by a pronounced dry (winter) season – a biproduct of the shifts of the ITCZ. This is the most prominent biome of Africa South of the Sahara, covering more than half of the African continent. Given its abundance of grasses, African savannas are known for its large populations of herbivores and the predators that hunt them - the wildebeest, zebras, elephants, and African buffalos and the hyenas, lions, and cheetahs. The most familiar example of the African savanna is the famous Serengeti Plains in Tanzania (and, to a less extent, Kenya). Other examples are found in Zimbabwe, Botswana, South Africa, and Namibia, where large swaths of savanna have been designated for wildlife protection or as hunting reserves.

From the Maa word meaning "endless plains", the Serengeti is an ecoregion with most of its extent in northern Tanzania. It is host to an extraordinary diversity of animals and is known to have the highest concentration of large mammals in the world. These are migratory species that march by the millions following seasonal rains and escaping dry conditions. Every fall and spring, as many as two million wildebeests, antelopes, and other grazing animals and the predators that hunt them migrate from the northern hills to the southern plains in search of grass and food. The Serengeti National Park and the Ngorongoro Conservation Area are both listed as UNESCO World Heritage Sites based on their natural importance. Both governments of Tanzania and Kenya maintain national parks, national game reserves, and wildlife sanctuaries protecting 80 percent of the Serengeti. Several ethnic groups live in and depend on the Serengeti ecosystem, namely the Maasai, the largest cattle herding group living in Eastern Africa whose villages are concentrated on the eastern edges of the Serengeti National Park.

 

The Serengeti

The Serengeti, from the Maa word meaning "endless plains", is a transboundary ecoregion extending from northern Tanzania to southern Kenya. It is host to an extraordinary diversity of fauna and known to have the highest concentration of large mammals in the world. It is here that the largest migration of land animals in the world occurs as local fauna follow the seasonal rains and escape dry conditions. Every fall and spring, as many as two million wildebeests, antelope, and other grazing animals and the predators that hunt them migrate from the northern hills to the southern plains in search of grass and food. The Serengeti National Park and the Ngorongoro Conservation Area are both listed as UNESCO World Heritage Sites based on their natural importance. Both governments of Tanzania and Kenya maintain national parks, national game reserves, and wildlife sanctuaries protecting nearly 80 percent of the Serengeti. Several ethnic groups live in and depend on the Serengeti ecosystem, namely the Maasai, the largest cattle herding group living in Eastern Africa whose villages are largely concentrated on the eastern edges of the Serengeti National Park.

Figure \(\PageIndex{3}\): [top] The Serengeti is a tropical savanna in Tanzania (mostly) and Kenya. This picture of the Serengeti shows the replete populations of zebras and wildebeest and a towering giraffe among the grasses and acacia trees in the background (CC BY-SA 4.0; Fuhrmann via Wikimedia Commons). [bottom] A picture of the Maasai, the pastoralists of the Serengeti, taken in Tanzania (CC BY 2.0; Smith via Flickr).

 

Arid Environments

Deserts are usually found in areas 15-30° north and south of the equator. They outline latitudes north and south of the savanna, and major deserts exist in the northernmost and southernmost regions of the African continent. Deserts are marked by low precipitation (less than 10 inches of rain a year) and wide daily and annual temperature ranges, with summer temperatures often exceeding 100°F in hot deserts. The Sahara Desert, the world’s largest hot desert, is an extensive and pronounced physical feature dividing the continent’s regions. The Sahel sits at the southern edge of the Sahara Desert, and it is a pronounced natural region that transverses Africa. This semi-arid belt crosses the continent from Senegal to Djibouti and supports many subsistence farmers and semi-nomadic herders. South of the Sahel, environments become more verdant until the next dry region takes place in the southern part of the African continent.

The Namib Desert, a costal desert in southwestern Africa extends through Angola, Namibia, and South Africa. It is one of the world’s driest deserts receiving less than 1 inch of moisture per year. This is influenced by three factors: First, the desert is located within a dry latitudinal range, where dry air masses are compressing and sinking (a high-pressure system). Secondly, it is a cold-water desert because of the adjacent Benguela current, a cold oceanic current carrying Antarctic waters north to southwest Africa. The cold water chills the air above resulting in fog and precipitation over water, thus the incoming cold air masses hold little moisture. Third, the desert is found in the rain shadow of the Great Escarpment and Central Plateau, a topographic feature that blocks moisture carrying air masses from reaching the Namib Desert.^[3]

The Kalahari Desert in Botswana is an extensive desert region. When there is adequate rainfall, the grasslands provide excellent grazing for wildlife. Precipitation varies from three to ten inches per year. Large areas of dry salt pans stretch over ancient lake beds fill with water after heavy rainfall but are dry the remainder of the year. It is replete with unique resilient life forms like meerkats, pangolins, and cheetahs, all of which are adapted to its harsh hot and dry conditions that are only relieved by brief flash seasonal rains.

 

Water Towers and the Great Rift Valley

Elevation is another principal factor shaping Africa’s biomes since higher altitudes experience cooler temperatures and even snow peaks. The highest mountain in Africa, Mt. Kilimanjaro (19,340 ft), is in Tanzania near the border with Kenya. The second highest peak, Mt. Kenya (17,058 feet), is located just north of the country’s capital of Nairobi, near the equator. Both mountains are inactive volcanoes and are high enough to have permanent snow at their peaks. Another high range is the Rwenzori Mountains (upwards of 16,000 ft) on the Congo–Uganda border. It is referred to as “Africa’s botanical big game” due to its distinctive snow-capped peaks, glaciers, valleys, biodiversity, waterfalls, fast flowing rivers, and overall natural beauty.^[4] Lastly, the Ethiopian Highlands average more than 5,000 feet in altitude. Although its territory represents only 4 percent of the African land surface, Ethiopia contains 80 percent of the continent’s high terrain (over 10,000 feet).^[5] Its highest peak, Ras Dashan, reaches up to 14,928 feet. The Ethiopian Highlands are home to Lake Tana, the source of the Blue Nile, the main tributary of the Nile River. Highlands and mountain peaks create distinctive ecosystems that vary depending on their elevation and situation to incoming air masses.

The highlands and volcanic mountains of East Africa surround the Great Rift Valley, a geological region of tectonic diversion where the African Plate has been splitting for at least the past 30 million years. It is dividing into two smaller tectonic plates: the Somalian Plate and the Nubian Plate. It is not one continuous fracture but a complex system, a series of rifts of the same geological origin. It extends from southern Mozambique to Lebanon. The region is dotted with lakes, notably Lake Victoria, Lake Tanganyika, Lake Albert, and Lake Malawi which are among the world’s largest lakes. Lake Victoria is the primary reservoir and the inland starting point for the White Nile River (white in color due to carried clay), a river that flows northward to the Blue Nile connection. The Western side of the Rift, also called Albertine Rift, is among the most biodiverse regions in Africa featuring dramatic peaks and valleys, lakes, highland forests, savannas, and wetlands. The Rift Valley’s fertile volcanic soils have a long history of human settlement and sustain the highest population densities in rural Africa today.^[6]

High Africa contributes disproportionately to the total stream flow of Africa’s major rivers. These areas receive more rainfall than their lower surroundings and tend to lose less water to evapotranspiration because temperatures are cooler. Downstream areas often benefit from the abundant runoff. These important, high-elevation watersheds are the water towers of Africa, for their role in storing water in glaciers, permafrost, snow-packs, soil, and groundwater and for supplying millions of people with water. These water towers are important sources for many of Africa’s transboundary rivers, river systems that permeate political borders. This means that upstream communities can influence the management of water resources downstream, a reality that shapes tensions and cooperation in Africa and everywhere where transboundary rivers exist.

The main rivers of Africa include the Nile, Niger, Congo, and Zambezi. The Nile River competes with the Amazon River for its ranking as the world's longest river. The White Nile branch begins in Lake Victoria in East Africa, and the Blue Nile branch starts in Lake Tana in Ethiopia. The water collected from tropical rains in the Ethiopian highlands eventually flows north through arid landscapes. For half of its course, the Nile runs without added water until it discharges into the Mediterranean Sea. In West Africa, the Niger River flows drains West Africa. Its delta is in Nigeria where the Niger’s waters flow out into the Atlantic Ocean through Benin. The Congo River is Africa’s most voluminous river, crossing the equator with a large tropical drainage basin that creates a flow of water second only to the Amazon in volume. The Zambezi River in the south is famous for the extensive Victoria Falls on the Zambia and Zimbabwe border. Victoria Falls is considered to be one of the largest waterfalls in the world, an astonishing natural wonder. All these rivers have long histories of human settlement. Their basins were sites of great ancient African civilizations and their tributaries important waterways for trade. To this day, they remain important sources of livelihood and mobility supporting high population densities.

 

Figure \(\PageIndex{4}\): [top] The majority of countries in East Africa have land that is over 1,500 m above sea level, and therefore classified as a highland. East Africa is home to some of Africa’s most prominent mountains, including Mount Kilimanjaro, Rwenzori, Virunga, Kenya and Elgon, as well as highland regions such as the Ethiopian Highlands and the East Africa Arc. The East Africa Rift Valley is also a major geological feature of East Africa (CC BY-NC-SA 2.0; Isquierdo via Flickr). [top right] Africa's major river basins, lakes and reservoirs, and water towers (UNEP, Water Atlas - permitted educational use). [bottom right] A map of the Nile River system, including its primary source as the Blue Nile flowing out of Lake Tana and the White Nile out of Lake Victoria (CC BY SA 3.0; Hel Hama via Wikimedia Commons).

 

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References:

[1] UNESCO World Heritage Sites Datasheet. Salonga National Park.

[2] World Wildlife Fund. From Rainforests to Reefs.

[3] UNESCO World Heritage Site Datasheet. Namib Sand Sea.

[4] UNESCO World Heritage Sites. Rwenzori Mountains National Park.

[5] Reader, J. 1999. Africa: A Biography of the Continent. pp 210.

[6] McNulty, W. et al. 2022. Africa’s Great Lakes. National Geographic Society

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Attributions:

"Peaks, Valleys and Lakes" and "The Serengeti" is adapted from East Africa, World Regional Geography by the University of Minnesota, CC BY-NC-SA.

"Water Towers" is adapted from Water Atlas by the United Nations Environmental Programme, within terms of use for non-commercial educational purposes.

"African Rivers" is adapted from World Regional Geography by University of Minnesota, CC BY-NC-SA.