Africa is the hottest of all the continents on our planet. In the north of Africa is the largest desert on Earth, the Sahara, in the south - the Kalahari Desert. The main reason for the hot and arid climate of Africa lies in its geographical location.
The entire territory of the mainland is in hot climatic zones. In Africa, in the north of 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, "Great Desert") is the largest hot desert in the world. Spread over 9,400,000 square kilometers, it covers most of North Africa. It is almost equal in area to Europe or the United States of America. There is only one other place in the world with such little rainfall - Antarctica.
The Sahara extends from the Red Sea, including parts mediterranean coast to the Atlantic Ocean. In the south, it is separated by a belt of semi-arid tropical savannah Sahel, which is located in the northern part of Central and West Africa south of the Sahara. Some of the sand dunes of the Sahara 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 known for its small oasis - Farafra ( Arabic: الفرافرة) located in the Western Desert of Egypt, approximately halfway between Dakhla and Bahariya. About 5,000 people live in Farafra. The village is inhabited mainly by local Bedouins. Near Farafra are hot springs and lake El Mufid.
Tenere (Niger)
Tenere (Berber: Tiniri, literally: desert) is a desert in south-central Sahara. It includes vast plains of sand that stretch from northern Niger to western Chad. Tenere covers an area of more than 400,000 km²). It is bordered by the Aïr Mountains to the west, the Hoggar Mountains to the north, the Djado Plateau to the northeast, the Tibesti Mountains to the east, and the Lake Chad basin to the south. The name Tenere comes from the Tuareg language and means "deserts", in much the same way as the Arabic word for sahara, "desert", which refers to the region as a whole. Tenere is arid, with a very hot and dry climate, a desert in which there are practically no plants.
Kalahari Desert (South Africa)
The Kalahari (Dorsland in Afrikaans) is a vast desert of arid, sandy land in southern Africa. Its area of 900,000 square kilometers covers most of Botswana, Namibia and South Africa. The semi-deserts adjacent to it, after heavy rains, turn into green meadows and provide excellent conditions for grazing. The Kalahari Desert is geographically part of the desert and plateau. Some animals and plants live in the Kalahari, as part of it is semi-arid sandy areas. In summer, there is little rainfall and the temperature is very high. The Kalahari typically receives 76–190 mm of precipitation per year. Around the Kalahari Desert are semi-arid regions covering 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 southwestern Angola. Part of it is included in national park Namib-Naukluft being the largest reserve Africa. The name "Namib" means "significant place". For at least 55 million years, an arid or semi-arid climate has reigned here. The Namib Desert is considered the oldest desert in the world and covers an area of about 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 (Welwitschia mirabilis). For my 1000 summer life tumboa grows two giant leaves that are over 3 meters long. These 2 leaves extend from the stem, which is shaped like a huge radish with a diameter of up to 120 centimeters. Its root comes out of the ground by 30 cm. 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 is present on the state emblem of Namibia.
Another famous Namib desert plant is the endemic nara (Acanthosicyos horridus). She grows in a little more wet places desert on sand dunes. Nara fruits are food and a source of moisture for many African animals, such as elephants, antelopes, etc.
Where the dry period lasts sometimes all year round, and short-term rains fall irregularly, lies the natural zone of tropical deserts and semi-deserts. Most large areas in Africa it ranks in the Northern Hemisphere. Here, from the Atlantic Ocean to the Red Sea, the Sahara desert stretches for 5000 km in a wide strip from west to east. In southern Africa, deserts occupy much smaller areas. Here, the harsh Namib Desert stretches in a narrow strip along the coast of the Atlantic Ocean. In the depths of the mainland is the Kalahari semi-desert.
Sahara - largest desert in the world. In her interior areas it doesn't 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. Heatwave during the day it is replaced by piercing cold at night, and sandy and dusty brown ones 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 drops rapidly by 20-30 ° C. Even stones cannot withstand such sharp changes. At noon, during the hottest period, you can sometimes hear a loud and sharp crackling. It cracks and shatters into pieces overheated stones. They are called "shooters" in the Sahara. The inhabitants of the desert say: "The sun in our country makes even the stones scream."
Due to varying degrees surface destruction in the Sahara formed three types of deserts: rocky, sandy and clayey. Stony deserts (hamads) are common in highlands, plateaus and elevated plains, consisting of solid rocks. Sandy deserts (ergs) occupy for the most part low plains and basins (Fig. 73). They amaze with an endless "sea" of dunes and dunes blown by the wind. Clay deserts are less common.
| Rice. 73. Sandy desert in the Sahara |
An insignificant amount of precipitation has led to the fact that there are no permanent watercourses in the desert (except for the Nile), but dry channels 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 is sparsely vegetated, there are few organic remains in the soil. Here formed desert tropical soils. They are poor in nutrients and form very thin elephants. Only in clay deserts does it linger in the soil more water, and contains mineral salts necessary for 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 the basins. grow in oases acacia, found ducks, doves, pigeons, hazel grouses, desert larks, runners, falcons. The hospitable "mistress" of the desert oases is date palm (fig. 75), giving people a cozy shade and tasty fruits. Cool juice flows from the incision of the trunk. Baskets and shoes are woven from the leaves of the tree.
But oases are extremely rare. There is almost no vegetation on the vast expanses of the Sahara. Adapted to the harsh climate of the desert ephemera plants with short period active existence. The rain will make a noise - and immediately leaves and flowers appear on them. Ephemera ripen, wither and wither so quickly that their seeds are ripe by the next rain and are just waiting for water to germinate quickly.
Due to the long root system of groundwater gets moisture camel thorn (Fig. 70). Its leaves are modified into short needles to reduce water evaporation.
Of the animals, those who are able to quickly run from one oasis to another survive. (antelopes), accumulate water in your body ( camel people) (Fig. 77), or some predators who hardly drink water, getting it from the blood of their prey (Fennec fox). Pre-crouching are best adapted to life in the desert: snakes, lizards, turtles. They have dry, scaly skin that evaporates little water. From the sun, these animals hide in the 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 of this: "that which is bypassed." Rains fall extremely rarely, so most of the desert is devoid of vegetation - only rocks, stone, sand and salt. Unfastened by plant roots, high sand dunes move in the direction of the prevailing wind. Only along the rivers do acacias and ta-marisk grow. Most amazing plant 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. Moisture is supplied to Velvichia by leaves that absorb it from the fog. The plant lives up to 2000 years and never sheds leaves that grow all the time.
The most severe is the nature of the ocean coast of the desert. It is no coincidence that this area was called the Skeleton Coast. From thirst, diamond seekers and shipwrecked died here more than once.
semi-desert Kalahari covered with huge sand dunes, which one after another, as if giant waves, run up to its surface. The dunes are pink, red and dark red, almost brown, because the soil contains a lot of iron. Precipitation is higher than in the Namib Desert, so the Kalahari has vegetation cover. In some places the desert resembles the steppe. The tops of the dunes grow tough grass, which turns green during the rains and fades during the drought. material from the site
On the slopes of the dunes, low shrubs with thorns can also grow. meet in the Kalahari spurges, aloe and other plants that accumulate moisture in stems, leaves, trunks. Kalahari - home watermelons. Wild watermelons still replace water for people and animals here.
The fauna of deserts and semi-deserts in southern Africa is represented by lizards, snakes, turtles. Lots of insects different kind beetles, locusts, scorpions etc. lions, cheetahs, jackals. Fleeing from poachers, even elephants sometimes enter the Namib Desert.
The population of the desert zone of Africa is nomadic animal husbandry, in the oases agriculture. There are industrial settlements for mining. A trans-Saharan road was laid, caravan routes between oases were preserved.
Human economic activity leads to the expansion of the desert zone due to semi-deserts and savannahs.
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On this page, material on the topics:
- essay on tropical deserts
- information about the tropical deserts of africa
- tropical deserts and semi-deserts of Africa
- essay on the theme of the desert of africa grade 3
Geographical position. tropical desert occupy a vast territory in northern Africa. Desert and semi-desert landscapes are distributed all the way from the Atlantic Ocean to the Red Sea, from the foot of the Atlas Mountains and the Mediterranean coast to a line running approximately from the lower reaches of the Senegal River through Lake Chad to Khartoum on the Nile (see map of the physiographic zoning of Africa with links to photographs of the nature of this region). This vast expanse of about 7 million km 2 is united under a common geographical name- Sahara.
The geographic boundaries of the Sahara are quite definite. Only in the south. where natural conditions change more or less gradually from semi-deserts to savannahs, the physical-geographical boundary is somewhat blurred and separates areas with a pronounced rainy period.
geological structure. Most of the Sahara is a plateau, composed at the base of crystalline and volcanic rocks and overlain by layers of horizontal sedimentary deposits. In some places, an ancient folded foundation protrudes to the surface, forming high uplands, or ancient intrusions emerge in the form of domed hills.
In the extreme east, between the Red Sea and the Nile, the crystalline basement is uplifted and in places overlain by layers of Mesozoic sandstones. Table plateaus up to 2000 m high rise there, crossed by deep dry gorges, indicating strong erosional dissection in the previous wetter era. This part of the region is known as the Arabian and Nubian deserts.
West of the Nile stretches the plateau of the Libyan Desert with the world's greatest accumulations of sand. In the north, the surface of the Sahara is gradually lowered, some deep depressions are located below sea level. The Kattara depression with an absolute bottom mark of 133 m below sea level is one of the deepest dry depressions on Earth.
In the central part of the Sahara, high uplands and plateaus rise, composed of crystalline and volcanic rocks: the Tibesti, Ahaggar, Iforas, etc. highest peak Tibesti highlands - dormant volcano Emi Kushi (3415 m) with a crater 12 km in diameter; it is the highest peak in the Sahara. The relief of the massifs is strongly dissected, their slopes are steep and rocky, masses of coarse clastic material have accumulated at the foot.
The surface of the rest of the Sahara with prevailing heights of 300-400 m is covered with strata of limestones, sandstones and clayey rocks of various ages.
Relief. Many sections of the Sahara have a monoclinal structure and form well-defined cuesta ledges. This type of relief is typical for the Tassilin-Adjer plateau, bordering the Ahaggar highlands from the northeast, for the Tademait plateau located to the north and the Bani plateau adjacent to the Anti-Atlas, etc. Tectonics and erosion processes, which manifested themselves in the postglacial, wetter than the modern era.
The surface of the desert plateaus of the Sahara is crossed by a network of channels bearing the Arabic name "wedd" or "wadi". Only after rare rains do they fill with water, which dries up after a few days, and sometimes even after a few hours. Most of the water diverges radially along the slopes of the Central Saharan massifs, which served as watersheds during the pluvial period, when the network of erosional troughs in the Sahara narrowed. Their bottoms are currently covered with alluvial sandy material, and sometimes they represent a hard clay surface.
Many wadis end at closed depressions of various sizes and depths, which are also one of the features of the Sahara relief. After the rains, the hollows are filled with water for a short time. The bottoms of some depressions (sebkhs) are covered with a crust of salts, but those that have an underground runoff are usually not saline. The origin of depressions is due to tectonics, underground erosion processes, karst processes and blowing out of weathering products.
With a high intensity of weathering processes and the absence of removal in the Sahara, clastic material accumulated in huge quantities. For some part of the desert, especially for depressions between cuesta plateaus and for vast closed basins, huge accumulations of dune sands, the so-called ergs, are characteristic. Along with areas of immobile, "dead" sands large territories occupied by sand dunes constantly moving in the direction prevailing winds. Especially powerful accumulations of sands are noted in the Libyan Desert. The relative height of the dunes there reaches 300 m. In the Sahara, there are often extensive flat areas with a layer of pebble material, sometimes covered from the surface with sand (“reg”, or “serir”). Large spaces are cluttered with rubble formed as a result of the destruction of crystalline rocks. Such rocky deserts are called "hamada". Among the gravelly accumulations of hamad, isolated plateaus with steep rocky slopes rise - "gara".
climatic conditions. The continental deserts of the Sahara owe their existence to the year-round dominance of dry tropical air. The climate of most of its parts is sharply continental, and the annual precipitation is almost everywhere less than 50 mm (Fig. 114).
Rice. 114. annual course temperature, precipitation and relative humidity in Algerian Sahara
In inland areas, precipitation is sometimes absent for several years in a row and rainfall is random. At the same time, sometimes showers cause floods. It is known that drowned in the Sahara more people than died from the heat. Caravan routes usually passed along the bottoms of dry channels, and people did not have time to escape from sudden heavy rains.
A certain increase in precipitation is observed only on the slopes of high uplands, but even there their annual amount does not reach 100 mm. On the northern and southern fringes of the desert, more constant precipitation is confined to certain periods of the year. In the north, they fall in autumn, winter and spring, and in the south - in summer. These bands with more or less constant rainfall serve as a transition from the Sahara to the Atlas country in the north and the natural region of Sudan in the south. The air in the Sahara is always dry and saturated with dust; relative humidity it is very small, sometimes below 25%. On hot days, with strong and uneven heating of the air, visibility conditions can be distorted, mirages appear with non-existent rivers, lakes or mountains on the horizon. Along with low rainfall, the Sahara has the strongest evaporation in the world. During the year, a layer of water up to 6 m thick can evaporate in this hot desert. Strong winds increase evaporation. The most constant summer winds are the trade winds, which carry dry and hot air from the north and northeast. Atmospheric depressions passing in summer cause the strongest sandy and dust storms- one of the main disasters in the Sahara.
The course of temperatures is characterized by sharp diurnal and annual contrasts. AT summer time the heat reaches 30 ... 50 ° C, it is aggravated by constant hot and dry winds carrying dust and sand. The absolute maximum of 58 °C observed in the Sahara in the shade is the absolute maximum for the entire Earth. The soil surface is heated up to 60...80 °C. In summer, even at night, the temperature usually does not fall below 30 ° C, but daily jumps of 30 ... 50 ° C are possible.
AT winter months the air is cooler and more stable as anticyclonic weather sets in. During the day, the temperature is about 20 ... 25 ° C, at night, due to strong heat transfer, the air cools to 0 ° C, and sometimes there are such severe frosts that water freezes in vessels and artificial reservoirs. In the mountains, frosts down to -18 °С were observed.
The western outskirts of the Sahara, located on the coast of the Atlantic Ocean with its cold Canary Current, is already a different type of desert - coastal. Due to the proximity of the ocean, temperatures become more moderate, relative humidity reaches 75-80%, refreshing breezes blow on the coast, but it rains a little more than in the interior of the Sahara.
Natural water. There is almost no surface water in the Sahara, the source of water supply is groundwater, the proximity of which depends on the existence of people, animals and plants. Sandy deserts are the richest in underground water. Quite powerful groundwater horizons lie under the sand in places, giving rise to springs. Underflow streams are characteristic of many wadis. Most of the water in the Sahara comes from wells. Recently, deep artesian wells and boreholes equipped with pumps pumping out the most reliable and constant water from pressure horizons have begun to play a significant role in water supply. There is evidence of huge reserves artesian waters in the bowels of the Sahara and other regions of North Africa.
In the marginal parts of the Sahara and some mountainous regions there are lakes with clear water, preserved from the time of the last pluvial and fed by groundwater.
The only major permanent watercourse within the region is the Nile. This river, flowing for many hundreds of kilometers through the barren desert and enlivening it, is one of the most remarkable natural phenomena in Africa. But the existence of the Nile is sustained by the waters it receives outside the desert.
Vegetation. The soils of the Sahara do not form a continuous cover. Vast areas of sandy and rocky deserts are almost completely devoid of soil. However, when irrigated, the Sahara lands can become very fertile, as they contain a lot of salts necessary for plants. But the rise in groundwater levels is often associated with excessive salinization and the appearance of salt marshes.
AT vegetation cover The Sahara contains 1200 plant species. The vast majority of them are xerophytes or ephemera. Only relatively few areas, mostly rocky, seem completely lifeless. But even on them there are plants that amaze with the ability to adapt to the harsh conditions of the desert. For example, among the stones or on the sand you can find the Jericho rose - a plant with a short stem and branches bent like fingers with seeds clamped. When it rains, the branches open up, the seeds fall to the ground and germinate very quickly, using every drop of moisture. Seeds or tubers of other plants are stored in the ground and also germinate quickly after rains that occur once every few months or even several years. In places on sands and stones there are prickly squat or creeping plants with small leaves or thorns. Sometimes the stones are covered with a thick crust of lichens. In some places, tree-like spurges rise. The vegetation cover is dominated by gray-green, gray and yellow tones, which gives it a particularly sad, lifeless appearance.
At southern border Sahara appear communities of shrubs and some hard grasses. In the north, along the border with the Atlas mountain country, there are wild pistachios, oleanders and jujubes.
Animal world. Poor in species, but rather rich in individuals, the fauna of the Sahara includes animals that are hardy and fast moving in search of water and food, or permanently living near water sources. The most typical for the Sahara are the addax and oryx antelopes, the gazelle dorcas, the gazelle lady, and mountain goats. They are exterminated for their meat and hides, some of them have almost disappeared.
Of the predators, the most famous are jackals, hyenas, foxes, cheetahs. There are birds, both migratory and permanent. Among the latter, the desert raven is especially characteristic. Of the reptiles, lizards predominate, snakes and turtles are found. Relics of pluvial eras - crocodiles - have been preserved near rare reservoirs in strictly localized habitats.
The existence of relict fauna, as well as many other facts (for example, dry erosional hollows, terraces on the slopes of lake basins) indicate that in the recent geological past the climate of the Sahara was more humid than at present. Particularly convincing are the rock paintings found in the caves of the Central Sahara massifs depicting plants and animals that are now absent in the Sahara, hunting scenes, etc. It is assumed that during the last pluvial, i.e. 10-15 thousand years ago, the Sahara was watered and quite densely populated.
Population and environmental issues. The modern population of the Sahara is concentrated mainly in oases. Oases - one of the sights of the Sahara, green spots among the vast desert spaces. They occur where there is water on or near the surface. In some oases, water is taken from springs, sometimes feeding small rivers, in others - from wells. The largest oases of the Sahara are formed near artesian wells. Many of them exist for a relatively short time, and then disappear if the source dries up or the well dries up. But there are oases dating back hundreds and even thousands of years. The largest and most ancient oasis of the Sahara is the Nile Valley, irrigated by Nile water and representing one of the oldest centers of agricultural culture.
As in the oases of Southwest Asia, the main cultivated plant of the Saharan oases is the date palm, in the shade of which fruit trees and shrubs are grown, and cereals are sown. In some oases there is no permanent population, the Arabs come there only at certain times of the year to collect dates. Noting the close connection date palm with the Sahara, some scientists consider it possible to draw the border of the Sahara as a geographical region along the border of the date palm.
On the outskirts of the Sahara, some tribes of Berber-Arabs lead a nomadic or semi-nomadic lifestyle, breeding camels and sheep. They live in large tents and dress in loose, long clothes that protect the body from overheating.
In some regions of the Sahara, salt has been mined and exported for a long time, iron and other metals are smelted. But the real use of natural resources in the Sahara is just beginning. And the riches of this desert territory are incalculable, first of all, these are the reserves of its bowels. After World War II, large deposits of oil and gas were discovered in Libya, Algeria and other countries. There are also large reserves of iron, manganese, copper ores, uranium.
Great amount solar energy, which receives the surface of the Sahara, presents inexhaustible opportunities for agriculture; Soils are rich in mineral nutrients. Mention has already been made of the supposed enormous reserves of groundwater that make it possible to use the climatic and land resources of the Sahara.
In the decades that have passed since the formation of North Africa independent states, paved roads were laid across the Sahara, new cities and towns arose in the places of mining, the number of people engaged in agriculture. But these essentially positive developments, given the extremely vulnerable nature of the Sahara, have also led to undesirable phenomena. Currently, the area of deserts in northern Africa is increasing. The observed process of the advance of the desert to the south, towards the savannas, is very fast. The trampling of the soil by cattle, the burning and cutting down of shrubs and woody vegetation along the border of the desert contribute to the destruction of the soil cover, the winding of sands and the drying up of reservoirs.
in the North and southern hemispheres, between 15 and 30 latitudes there is a zone of tropical deserts. Some deserts are located inside the continents, while others stretch along the western coasts of the continents. These are very hot and dry areas. the globe with poor flora and fauna. There are no permanent rivers here, and vast areas are occupied only by waving sands, heaps of stones and clay surfaces cracked from the heat.
tropical desert
Tropical or as they are also called trade wind deserts include the deserts of Arabia, Syria, Iraq, Afghanistan and Pakistan; the exceptionally peculiar Atacama Desert in Chile; the Thar Desert in northwest India; vast deserts of Australia; Kalahari in South Africa; and finally, the greatest desert in the world - the Sahara in North Africa.
Tropical Asian deserts
Tropical Asian deserts, together with the Sahara, form a continuous arid belt stretching for 7200 km from Atlantic coast Africa to the east, with an axis approximately coinciding with the Tropic of the North; in some areas inside this belt it almost never rains. patterns general circulation atmospheres lead to the fact that these places are dominated by downward movements air masses, which explains the exceptional aridity of the climate. Unlike the deserts of America, Asian deserts and the Sahara has long been inhabited by a man who has adapted to these conditions, but the population density here is very low.
The most beautiful deserts in the world
Atacama, Chile
Presumably the oldest dry desert in the world (only 3-15 mm of precipitation per year) consists of salt lakes, sand and solidified lava. The composition of its soil is as close as possible to Martian. By the way, they filmed "Space Odyssey" here. In autumn, when the rains fall, the desert is covered with flowers.
Great Sandy Desert, Australia
In the Uluru-Kata Tjuta nature reserve, the people of the wild dog dingo, there is the 8.6 km² red rock Uluru, sacred to the Anangu aborigines. It takes about an hour to climb it, and it is better to make it at dawn or at night to admire the stars.
Gobi, Mongolia
Asia's largest and coldest (up to -40 °C) desert is famous for its fossils: it is here that paleontologists have found dinosaur eggs. The Gurvansaikhan Park is famous for the Khongoryn-Els sandy massif stretching for 180 km, which means “singing sands”.
Namib, Namibia
High sand dunes come close to the ocean, where the cold Benguela current forms fog, creating obstacles to navigation. South of the Kunene River is the Skeleton Coast - a graveyard of dead ships, which is covered with sand more and more every year.
Death Valley, California
In the depression of the Mojave Desert, southeast of the Sierra Nevada, the highest air temperature in the world, +57 ° C, is recorded. Ghost hunters come to abandoned gold digging towns, and Antonioni fans come to Zabriskie Point. Five million years ago there was a lake in this place.
In the northern and southern hemispheres, approximately between 15 and 30 latitudes, there is a zone of tropical deserts. Some deserts are located inside the continents, while others stretch along the western coasts of the continents. These are very hot and dry regions of the globe with poor flora and fauna. There are no permanent rivers here, and vast areas are occupied only by waving sands, heaps of stones and clay surfaces cracked from the heat. Although many believe that all deserts are made of sand, this is actually not the case.
On Earth, rocky deserts, or hamads, are more common, as a rule, located on a plateau or in the mountains. Tropical deserts are located in an area of high atmospheric pressure where descending air currents predominate. Hot air contains an insignificant amount of water vapor, and throughout the year its absolute and relative humidity is close to zero - approx .. Precipitation in desert regions is rare, usually in the form of short showers, and in some places there is no rain for several years. The annual amount of precipitation is 50-200 mm.
Desert air is so hot and dry that rain often evaporates before it reaches the ground, and the moisture that does hit the surface disappears instantly. After heavy rain, the groundwater level rises, while soil capillaries ground water are pulled to the surface and evaporate, and the salts dissolved in them accumulate in the near-surface soil layer, salinizing it.
Since desert air contains very little moisture, it provides little protection against solar radiation. The value of total solar radiation averages 200-220 kcal/cm2 per year, which is more than in equatorial belt where there is a lot of cloudiness. During the day, the sun shines brightly over the desert and there is sizzling heat (in the Sahara, for example, about 50 ° C - approx. °C.
Strong (80-100 km/h) winds are constantly blowing in deserts, they capture loose material and carry it over long distances, causing sand and dust storms. Dust from the Sahara Desert, for example, has been found more than 3,000 km from where it formed, in northwestern Europe. And the dust from the Australian deserts is found on the coast of the island. New Zealand, distant from them by 2400 km.
The primitive soils of tropical deserts are very poor in humus, and gray soils form only in relatively humid areas. ground cover in tropical deserts, as a rule, is absent. Vast areas are covered with sands or placers of rubble and pebbles, on the surface of which a characteristic shiny dark crust forms, the so-called desert tan, which protects rocks from rapid weathering and destruction.
AT sandy deserts eolian landforms are formed: dunes, dunes, etc. Not fixed by vegetation, they move tens of meters a year. However, most of the sand is immobile: it is held by the long roots of shrubs and grasses, which have adapted to the conditions of constant moisture deficiency.
Deserts can only grow plants that can develop under extreme conditions of drought and high temperatures. There are many xerophytes, ephemers and ephemeroids that do not form a dense vegetation cover, unusual shrubs and semi-shrubs of the "tumbleweed" type. Leafless shrubs (white saxaul, sand acacia) are common in the sandy deserts of Asia, succulents (cacti, agaves, aloe, etc. - note) are common in America and Africa. A variety of wormwood and saltwort are characteristic of clay deserts. , also have vegetation cover - lichens.
Where groundwater comes close to the surface, oases are located. The largest of them are in river valleys. Irrigated agriculture and horticulture are developing here, cotton, wheat, barley, sugarcane, olive, etc. are cultivated. In the Arabian and North African deserts, the date palm grows - a beautiful, slender tree up to 30 m high. dried. The apical buds, flower shoots of palm trees - palm cabbage, as well as the powdery core of young palm trees are eaten.
Behind recent decades the area of deserts has increased - this is the result of the active influence of man on the fragile natural environment. Sahara annually takes 100 thousand hectares of arable land and pastures, Atacama moves at a speed of 2.5 km per year, Tar - 1 km per year. For many peoples of the North and East Africa, South Asia and tropical America this is a real threat.
Clay deserts are found on all continents. AT dry time their surface cracks into polygons, and after the rains swell and become almost watertight. AT Central Asia clayey deserts are called takyrs, in the Gobi - toyrims.
The rocky deserts of the hamada (translated from Arabic - “barren” - approx.) Are very widespread on Earth. For example, in the world's greatest desert, the Sahara, sands occupy only 20% of the area, clay deserts - 10% of the surface, and about 70% are sand and pebble deserts and hamads.
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