Remember: 1. What weather characteristic of tropical and subtropical climate zones? 2. How does the cold sea current affect the climate of the coast? Why do coastal deserts arise? 3. What is physical weathering?

Tropical deserts and semi-deserts. Where the dry season lasts sometimes all year round, and short-term rains fall irregularly, the natural zone of tropical deserts and semi-deserts is located. It occupies the largest area in Africa in the Northern Hemisphere. From Atlantic Ocean The Sahara Desert stretches 5,000 km from the Red Sea in a wide strip from west to east. In the southern part of Africa, deserts occupy significantly smaller areas: the harsh Namib Desert stretches in a narrow strip along the coast of the Atlantic Ocean, and the Kalahari semi-desert is located a little further inland.

The Sahara is the largest desert in the world by area. In its interior regions there is no rain for years, even decades. Often, even rain does not reach the surface of the earth: it evaporates in the air due to the high temperature. Great heat during the day gives way to piercing cold at night, and sandy and dusty browns sweep away all living things in their path. During the day, the surface of the rocks heats up to +70 °C, and at night the temperature drops sharply by 20-30 °C. Even stones cannot withstand such sudden changes. Sometimes at noon, in the heat of the day, you can hear a loud crash. It cracks and shatters into fragments of stones, it has overheated.

Due to varying degrees of surface destruction, three types of deserts have formed in the Sahara: rocky, sandy and clayey. Rocky deserts (hamadas) are common in highlands, plateaus and elevated plains formed by hard rocks. Sandy deserts (ergs) occupy mainly low-lying plains and basins (Fig. 30). They amaze with the endless “sea” of dunes and dunes that are blown by the wind. Clay deserts (seriri) are less common.

The insignificant amount of precipitation has led to the fact that there are no permanent watercourses in the desert (except for the Nile River), and dry riverbeds - wadis - are stored. They fill with water briefly only when it rains. The sun quickly evaporates the water, and after a few hours the river disappears.

Since desert vegetation is sparse, there is little organic matter in the soil. Desert tropical soils formed here.

They are poor in nutrients and form a very thin layer. Only in clay deserts does it linger in the soil more water and there are mineral salts needed by plants.

All life in the Sahara is concentrated in oases. They arise where groundwater comes close to the earth's surface (Fig. 31). There are wells or springs, temporary lakes in hollows. Acacias grow in the oases, ducks, turtle doves, pigeons, hazel grouse, desert lark, runners, and falcons are found. The hospitable hostess of desert oases is the date palm, which provides people with shade and tasty fruits. Cool juice flows from a cut on the trunk. The leaves of the tree are used to weave baskets and shoes.

Explain why the areas of tropical deserts and semi-deserts are different in northern and southern Africa.

Explain why rocks break down in the desert. Remember what this process is called.

Rice. 30. Sandy desert in the Sahara

Rice. 31. Scheme of formation of an oasis in the desert

However, such landscapes are extremely rare. There is almost no vegetation in vast areas of the Sahara. Ephemerals, plants with a short period of active existence, have adapted to the harsh desert climate. The rain will rustle - and leaves and flowers will immediately appear on them. Ephemerals ripen, bloom and wither so quickly that their seeds ripen by the next rain and are just waiting for water to germinate quickly.

Thanks to its long root system, camel thorn receives moisture from groundwater. Its leaves are modified into short needles, which reduces water evaporation.

Animals that survive in the desert are those that can quickly run from one oasis to another (antelope), accumulate water in their bodies (camels), or some types of predators that hardly drink water, receiving it with the blood of their victims (fennec fox) (Fig. 32 ). Reptiles are best adapted to life in the desert: snakes, lizards, turtles. They have dry, scaly skin that evaporates little water. These animals hide from the sun in sand or crevices and feed on insects.

The Namib Desert is located in southern Africa. The climate here is extremely harsh, as evidenced by the name - “That which is avoided.” It rains quite rarely here, so most of the desert is devoid of vegetation. Only rocks, stones, sand and salt. Tall sand dunes, not anchored by plant roots, move in the direction of the prevailing wind.

Only along the rivers do acacias and tamarix grow. The most amazing plant of the Namib Desert is Welwitschia (Fig. 33). This tree has a short (10-15 cm) and thick (up to 1 m in diameter) trunk, from which emerge two leathery leaves up to 3 m long. Welwitschia leaves absorb moisture from the fog. The plant lives up to 2 thousand years and never sheds its leaves, which constantly grow and spread along the ground.

Rice. 32. Fennec fox

Rice. 33. Velvichia

Rice. 34. Kalahari Semi-Desert

The most severe nature of the desert ocean coast. It’s not for nothing that this area was called the Skeleton Coast. Diamond seekers and passengers of shipwrecks often died of thirst here.

The Kalahari semi-desert is covered with huge sand dunes, colored pink, red and dark red, almost brown, because the soil contains a lot of iron (Fig. 34).

There is more rainfall here than in the Namib Desert, so the Kalahari has vegetation cover. In some places the desert resembles a steppe. Tough grass grows on the tops of the dunes, which turns green during rains and fades during drought. Low shrubs covered with thorns can also grow on the slopes of dunes. In the Kalahari there are euphorbias, aloe and other plants that accumulate moisture in the stems, leaves and trunks. Kalahari is the birthplace of watermelons. Wild watermelons still replace water for people and animals.

Animal world deserts and semi-deserts in southern Africa are lizards, snakes and turtles. There are lions, cheetahs and jackals. Even elephants sometimes enter the Namib Desert to escape poachers. There are a lot of insects here: various beetles, locusts, scorpions and the like.

The population of the desert zone of Africa is engaged in nomadic animal husbandry, and in the oases - farming. Industrial settlements for mining appear. A trans-Saharan highway has been built, and caravan routes have been preserved between the oases.

Human economic activity leads to the expansion of deserts due to semi-deserts and savannas.

Zone of evergreen hardwood forests and shrubs. This zone is located in the extreme north and south of Africa. In winter, it is under the influence of cyclones, which bring coolness and moisture. In summer, cyclones displace the dry and hot air of the tropics. It has a typical Mediterranean climate: enough rainfall for plant development (about 500 mm) and at the same time not so much as to wash nutrients from the soil. Therefore, the brown soils that formed in this zone are quite fertile because they contain a lot of humus.

The plants have small, hard, yellow-skinned leaves, which make them easy to withstand heat. Therefore, these forests are called hard-leaved forests. Coniferous trees- Lebanese cedar, pine, cypress - dry air in summer also does not harm.

Think about what the main economic sectors are typical for the desert zone of Africa. Name the areas of their distribution.

In South Africa subtropical forests and shrubs occupy a small area. Laurel olive, southern beech, ebony, euphorbia, heather, daffodils, tulips, and gladioli grow here.

Large areas of the zone of evergreen hardwood forests and shrubs have been developed by humans: citrus fruits, grapes, olives and the like are grown here.

Briefly about the main thing!

Deserts and semi-deserts of Africa are located in areas of dry and hot tropical climate. The most big desert world - the Sahara - occupies most of North Africa. In the southern part of the continent, the coastal Namib desert and the Kalahari semi-desert formed.

Tropical desert soils are infertile. The vegetation cover is very poor. Common animals include lizards, snakes, turtles, and insects.

Evergreen hardwood forests and shrubs are found in northern and southern Africa, in areas of subtropical climate. The fertile brown soils here grow Lebanese cedar, pine, cypress, olive, southern beech and other evergreen trees and shrubs.

1. Name and show on the map the largest deserts and semi-deserts in Africa.

2. Tell how plants and animals of tropical deserts are adapted to harsh living conditions.

3. What are oases? In what places and why are they formed?

4. Compare the natural conditions of savannas and tropical deserts. How are they similar, what are their significant differences?

5. Why is there food in Africa? different types deserts: rocky, sandy, clayey?

6. Which natural areas of Africa are best developed by humans? Explain why.

Where the dry period sometimes lasts all year round, and short-term rains fall irregularly, lies the natural zone of tropical deserts and semi-deserts. It occupies the largest area in Africa in the Northern Hemisphere. Here, from the Atlantic Ocean to the Red Sea, the Sahara Desert stretches in a wide strip from west to east for 5000 km. In southern Africa, deserts occupy much smaller areas. Here, the harsh Namib Desert stretches in a narrow strip along the shore of the Atlantic Ocean. In the interior of the mainland is the Kalahari semi-desert.

Sahara - the largest desert in the world by area. In its interior regions there is no rain for years, or even decades. And rain often does not reach the surface of the earth: it evaporates in the air due to the high temperature. Intense heat during the day gives way to piercing cold at night, and sandy and dusty browns sweep away all living things in their path. The surface of the rocks during the day heats up to + 70 °C, and at night the temperature rapidly drops by 20-30 °C. Even stones cannot withstand such sudden changes. At midday, during the hottest period, you can sometimes hear a loud and sharp crackling sound. These are overheated stones cracking and flying into pieces. In the Sahara they are called “shooting”. Desert inhabitants say: “The sun in our country makes even the stones scream.”

Due to varying degrees of surface destruction, three types of deserts were formed in the Sahara: rocky, sandy and clayey. Rocky deserts (hamadas) are common in highlands, plateaus and elevated plains consisting of hard rocks. Sandy deserts (ergs) occupy mostly low-lying plains and basins (Fig. 73). They amaze with the endless “sea” of dunes and dunes blown by the wind. Clay deserts are less common.

Rice. 73. Sandy desert in the Sahara

The insignificant amount of precipitation has led to the fact that there are no permanent watercourses in the desert (except for the Nile), but dry riverbeds remain - wadi They fill with water only when it rains, but not for long. The sun quickly evaporates the water, and after a few hours the river disappears.

Since the desert has sparse vegetation, there is little organic residue in the soil. Formed here desert tropical soils. They are poor nutrients and form very thin elephants. Only in clay deserts does the soil retain more water and contain mineral salts needed by plants.

All life in the Sahara is concentrated in oases. They occur where groundwater comes close to the surface of the earth (Fig. 74). There are wells or springs, temporary lakes formed in basins. They grow in oases acacias, found ducks, doves, pigeons, hazel grouse, desert lark, runners, falcons. The hospitable “hostess” of desert oases is date palm (Fig. 75), giving people cozy shade and tasty fruits. Cool juice flows out of the cut in the trunk. The leaves of the tree are used to weave baskets and shoes.

But oases are extremely rare. There is almost no vegetation on the vast expanses of the Sahara. They have adapted to the harsh desert climate ephemera plants with a short period of active existence. The rain will rustle - and immediately leaves and flowers appear on them. Ephemera ripen, bloom and wither so quickly that their seeds ripen by the next rain and are just waiting for water to germinate quickly.

Thanks to the long root system, it receives moisture from groundwater camel thorn (Fig. 70). Its leaves are modified into short needles to reduce water evaporation.

Of the animals that survive, those who are able to quickly run from one oasis to another (antelope), accumulate water in your body ( camel-people) (Fig. 77), or some predators that hardly drink water, getting it with the blood of their victims (fennec fox). Reptiles are best adapted to life in the desert: snakes, lizards, turtles. They have dry, scaly skin that evaporates little water. These animals hide from the sun in sand or crevices and feed on insects.

Coastal desert in southern Africa Namib (Fig. 78). The climate here is extremely harsh. The very name of the desert speaks about this: “that which is avoided.” Rainfall is extremely rare, so most of the desert is devoid of vegetation - only rocks, stone, sand and salt. High sand dunes, not anchored by plant roots, move in the direction of the prevailing wind. Only along the rivers do acacias and ta-marisco trees grow. The most amazing plant of the Namib Desert - Velvichia (Fig. 79). This tree has a short (5-10 cm) and thick (up to 1 m in diameter) trunk, from which two leathery leaves up to 3 m long extend. Welwitschia is supplied with moisture by leaves that absorb it from the fog. The plant lives up to 2000 years and never sheds its leaves, which grow all the time.

The most severe nature is the ocean coast of the desert. It is no coincidence that this area was called the Skeleton Coast. Diamond seekers and shipwrecked people have died here more than once from thirst.

Semi-desert Kalahari covered with huge sand dunes, which one after another, like giant waves, rush onto its surface. The dunes are colored pink, red and dark red, almost brown, as the soil contains a lot of iron. There is more precipitation than in the Namib Desert, so the Kalahari has vegetation cover. In some places the desert resembles a steppe. Tough grass grows on the tops of the dunes, which turns green during rains and becomes faded during drought.

Low bushes with thorns can also grow on the slopes of dunes. Found in the Kalahari milkweed, aloe and other plants that accumulate moisture in stems, leaves, and trunks. Kalahari - homeland watermelons Wild watermelons still replace water here for people and animals.

The fauna of deserts and semi-deserts in southern Africa is presented lizards, snakes, turtles. Lots of insects: different types beetles, locusts, scorpions etc. Meet lions, cheetahs, jackals. Even elephants sometimes enter the Namib Desert to escape poachers.

The population of the desert zone of Africa is nomadic livestock farming, in oases - agriculture. Industrial settlements for mining are appearing. A trans-Saharan highway has been built, and caravan routes between the oases have been preserved.

Human economic activity leads to the expansion of the desert zone due to semi-deserts and savannas.

Deserts and semi-deserts are a natural area characterized by almost complete absence vegetation and very poor fauna. All this is due to the extremely harsh climatic conditions of the planet where they are located. Deserts, in principle, can form in almost any climate zone. Their formation is primarily associated with low rainfall. This is why deserts are primarily found in the tropics. Tropical deserts occupy the territory of most of tropical Africa and Australia, the western coast of the tropical zone of South America, as well as the territory of the Arabian Peninsula in Eurasia. Here their formation is associated with the year-round dominance of tropical air mass, the influence of which is enhanced by the terrain and cold currents off the coast. Also a large number of Deserts are located in the subtropical and temperate zones of the Earth. This is the territory of Patagonia South America, where their formation is due to the isolation of the southern tip of the continent from penetration humid air cold currents, as well as in inland areas North America And Central Asia. Here, the formation of deserts is already associated with a strong continental climate due to the great distance from the coast, as well as mountain systems that prevent the penetration of moisture from the ocean. The formation of deserts may also be associated with extreme low temperatures on the planet, this type of desert, called Arctic and Antarctic deserts, is considered by us separately.
Natural conditions deserts are exceptionally harsh. The amount of precipitation here does not exceed 250 mm per year, and in large areas it is less than 100 mm. The driest desert in the world is the Atacama Desert in South America, where there has been no rainfall for 400 years. The largest desert in the world is the Sahara, located in North Africa (pictured). Its name is translated from Arabic as “desert”. The most recorded heat air on the planet +58°C. Under the scorching rays of the sun in the summer months, when it reaches its zenith at noon, the sand under your feet heats up to enormous temperatures, and sometimes you can even fry eggs on the stones. However, with sunset the temperature in the desert drops sharply, the differences reach tens of degrees during the day, and winter night There are even frosts here. This is due to the constantly clear sky due to the downward flows of dry air from the equator; because of this, almost no clouds form here. The vast open spaces of deserts do not at all prevent the movement of air along the surface of the Earth, which leads to the emergence of strong winds. Dust sandstorms come unexpectedly, bringing clouds of sand and streams of hot air. In spring and summer the Sahara rises strong wind- samum, which can be literally translated as “poisonous wind.” It can last only 10-15 minutes, but the hot dusty air is very dangerous for humans, it burns the skin, the sand does not allow you to breathe freely, many travelers and caravans died in the deserts under this deadly wind. Also, at the end of winter - beginning of spring in North Africa, a seasonal wind begins to blow from the desert almost every year - khamsin, which in Arabic means “fifty”, since on average it blows for fifty days.
Temperate deserts, unlike tropical deserts, are also characterized by strong temperature changes throughout the year. Hot summer gives way to cold, harsh winter. Air temperature fluctuations over the year can be about 100°C. Winter frosts in the deserts of the temperate zone of Eurasia drop to -50°C, the climate is sharply continental.
Vegetable world deserts in particularly difficult climatic conditions may be completely absent; where moisture remains sufficient, some plants grow, but the flora is still not diverse. Desert plants usually have very long roots - more than 10 meters - in order to extract moisture from groundwater. In the deserts Central Asia A small shrub grows - saxaul. In America, a significant part of the flora is made up of cacti, in Africa - milkweed. The fauna of deserts is also not rich. Reptiles predominate here - snakes, monitor lizards, scorpions also live here, and there are few mammals. One of the few that was able to adapt to these difficult conditions was the camel, which was not accidentally called the “ship of the desert.” By storing water in the form of fat in their humps, camels are able to travel long distances. For the indigenous nomadic peoples of the deserts, camels are the basis of their economy. Desert soils are not rich in humus, however, they often contain a lot minerals and suitable for conducting Agriculture. The main problem for plants remains water shortage.

Sandstorm in Australia

Africa is the hottest of all the continents on our planet. The largest desert on Earth, the Sahara Desert, is located in northern Africa, and the Kalahari Desert in the south. The main reason for Africa's hot and dry climate lies in its geographical location.

The entire territory of the mainland is in hot climatic zones. In Africa, in northern Ethiopia, in the Afar Basin, the highest temperature on Earth was recorded at +58.4 °C. The abandoned settlement of Dallol located there is recognized as the hottest place on Earth.

Sahara (North Africa).

The Sahara (Arabic الصحراء الكبرى, aṣ-ṣaḥrā´ Al Kubra, "The Great Desert") is the largest hot desert in the world. Situated over more than 9,400,000 square kilometers, it covers most of North Africa. It is almost equal in territory to Europe or the United States of America. There is only one other place in the world where precipitation is as low - Antarctica.

The Sahara extends from the Red Sea, including parts of the Mediterranean coast, to the Atlantic Ocean. To the south, it is separated by the Sahel, a belt of semi-arid tropical savanna that lies in northern central and western sub-Saharan Africa. Some of the Sahara sand dunes can reach up to 180 meters in height.

White Desert (Egypt).

The White Desert (Sahara El Beida) is located in Egypt. The word sahara means desert. It is famous for its small oasis - Farafra ( Arabic: الفرافرة) located in the Western Desert of Egypt, approximately midway between Dakhle and Bahariya. About 5,000 people live in Farafra. The village is inhabited mainly by local Bedouins. Near Farafra there are hot springs and Lake El Mufid.

Tenere (Niger)

Tenere (Berber: Tiniri, literally: desert) is a desert in the south-central Sahara. It includes vast plains of sand stretching from northern Niger to western Chad. Tenere covers an area of ​​more than 400,000 km²). Its borders are the Aïr Mountains in the west, the Hoggar Mountains in the north, the Djado Plateau in the northeast, the Tibesti Mountains in the east and the Lake Chad basin in the south. The name Tenere comes from the Tuareg language and means "desert", much like the Arabic word sahara - "desert", which refers to the region as a whole. Tenere is an arid, very hot and dry desert with virtually no plants.

Kalahari Desert (South Africa)

The Kalahari (Dorsland in Afrikaans) is a vast desert of arid sandy areas in southern Africa. Its area of ​​900,000 square kilometers covers most of Botswana, Namibia and South Africa. After heavy rains, the adjacent semi-deserts turn into green meadows and provide excellent conditions for grazing livestock. The Kalahari Desert is geographically part desert and plateau. The Kalahari is home to some animals and plants because parts of it are semi-arid sandy areas. In summer there is little rainfall and temperatures are very high. The Kalahari typically receives 76–190 mm of precipitation per year. Surrounding the Kalahari Desert are semi-arid areas covering an area of ​​over 2,500,000 square kilometers. These are parts of Botswana, Namibia, South Africa, Angola, Zambia and Zimbabwe.

Namib Desert (Namibia).

The Namib Desert is a desert located in Namibia and southwest Angola. Part of it is included in national park Namib-Naukluft, which is the largest nature reserve in Africa. The name "Namib" means "place of significance". It has had an arid or semi-arid climate for at least 55 million years. The Namib Desert is considered the oldest desert in the world and covers an area of ​​approximately 80,900 km², stretching from the Usiab River (north) to the city of Lüderitz (south) and from the Atlantic Ocean (west) to the Namib Escarpment (east). This is about 1600 km. from north to south and 50-160 km from east to west.

The famous plant of the Namib Desert is tumboa, or Welwitschia mirabilis. During its 1000 year life, tumboa grows two giant leaves, which are more than 3 meters long. These 2 leaves extend from a stem, which is shaped like a huge radish with a diameter of up to 120 centimeters. Its root extends 30 cm out of the ground. Tumboa roots are up to 3 m long. But the main source of moisture for it is dew and fog. Tumboa is endemic. Her image appears on state emblem Namibia.

Another famous plant of the Namib Desert is the endemic nara (Acanthosicyos horridus). It grows in slightly wetter desert areas on sand dunes. Nara fruits are food and a source of moisture for many African animals, such as elephants, antelopes, etc.

Deserts and semi-deserts are located mainly in tropical zones. Largest area they occupy North Africa. Dry tropical air prevails here throughout the year. Annual precipitation is everywhere less than 100 mm. It happens that annual rate falls in a few hours, and then for many years there is no precipitation at all.

In a tropical continental (desert) climate, when the temperature at night is less than +10 °C, and during the day exceeds +50 °C in the shade, rocks quickly collapse, turning into stones and sand. Due to weathering, different types of deserts are formed. Most of the Sahara (Fig. 75) and the Namib Desert are occupied by rocky deserts. In addition to them, sandy and clayey deserts and semi-deserts, such as the Kalahari, are common here.

How did the Sahara Desert appear? To the north of the Ahaggar plateau, in the mountains, a drawing was found on sandstone that is about eight thousand years old. The picture shows hunters and wild animals. This indicates that the Sahara, oddly enough, was once a steppe covered with rich vegetation. The increasing dryness of the climate and the depletion of soils by agriculture led to the formation of the largest desert in the world.

Rice. 75. Sahara Desert

Desert tropical soils, in conditions of dryness and lack of vegetation cover, are poorly developed and often saline. They contain little organic matter and there is almost no humus in such soils.

The vegetation of deserts and semi-deserts is poor and very sparse, although individual plants are well adapted to the harsh growing conditions. These are camel thorn, aloe, euphorbia, wild watermelons, wormwood, etc. Some plants emerge only after rain, grow quickly, bloom, and then dry out. A unique plant of the Namib Desert is Welwitschia, which lives for about 100 years (Fig. 76).

Rice. 77. Oasis

At springs and in river valleys, where groundwater rises close to the surface, rich vegetation develops - palm trees, various shrubs. People live here. Such places are called oases (Fig. 77). The largest oasis in the world is the Nile Valley.

The main plant of the oases is the date palm. The tasty and nutritious fruits of palm trees are eaten, drinks are made from the juice, the tree is used for construction, and the roofs of homes are covered with tree foliage. About 100 kg of fruits are harvested from each tree annually. Africa accounts for 40% of world date production. Material from the site

Animals have also adapted to life in deserts (Fig. 78). Antelopes and gazelles travel hundreds of kilometers in search of water. Predators - hyena, jackal, fennec fox, cheetah - obtain moisture from food. Turtles, lizards and snakes can go without water for a long time, hiding in burrows. There are many birds in the deserts: ostriches, bustards, larks. Dangerous for humans poisonous bites scorpion and phalanx.

In tropical conditions continental climate deserts and semi-deserts are formed.