Despite the fact that its very name "desert" comes from words such as "empty", "emptiness", this amazing natural object is filled with diverse life. The desert is very diverse: in addition to the sand dunes that our eyes habitually draw, there are saline, rocky, clayey, as well as snowy deserts of Antarctica and the Arctic. Taking into account the snowy deserts, this natural zone belongs to one fifth of the entire surface of the Earth!

Geographical object. The meaning of deserts

The main distinguishing feature of the desert is drought. The reliefs of the deserts are very diverse: island mountains and complex highlands, small hills and stratal plains, lake depressions and dried up centuries-old river valleys. The formation of the relief of deserts is greatly influenced by the wind.

Man uses the deserts as pastures for livestock and areas for growing some crops. Plants for livestock thrive in the desert thanks to a horizon of condensed moisture in the soil, and desert oases, bathed in sun and fed by water, are extremely favorable places for growing cotton, melons, grapes, peach and apricot trees. Of course, only small areas of deserts are suitable for human activity.

Desert characteristics

Deserts are located either next to the mountains, or almost on the border with them. High mountains impede the movement of cyclones, and most of the precipitation they bring falls in the mountains or foothill valleys on one side, and on the other side - where the deserts lie - only small remnants of rain reach. The water that manages to reach the desert soil flows down the surface and underground streams, collecting in springs and forming oases.

Deserts are characterized by various amazing phenomena that are not found in any other natural zone. For example, when there is no wind in the desert, the smallest grains of dust rise into the air, forming the so-called "dry fog". Sandy deserts know how to "sing": the movement of large layers of sand generates a high and loud slightly metallic sound ("singing sands"). Deserts are also known for their mirages and terrible sandstorms.

Natural areas and types of deserts

Depending on the natural zones and type of surface, there are such types of deserts:

• Sandy and sandy-crushed stone... They differ in a wide variety: from chains of dunes devoid of any vegetation, to areas covered with shrubs and grass. The sandy desert is extremely difficult to navigate. Sands do not occupy most of the deserts. For example: the sands of the Sahara make up 10% of its territory.

• Stony (hamadas), gypsum, gravelly and gravelly-pebble... They are combined into one group according to the characteristic feature - a rough, hard surface. This type of desert is the most widespread on the globe (the hamads of the Sahara occupy 70% of its territory). Succulents and lichens grow in tropical rocky deserts.

• Saline... In them, the concentration of salts prevails over other elements. Salt deserts can be covered with a hard cracked salt crust or salt bog that can completely suck in a large animal and even a person.

• Clayey... Covered with a smooth clay layer stretching for many kilometers. They are characterized by low mobility and low water properties (the surface layers absorb moisture, preventing it from penetrating deeper, and dry quickly during heat).

Desert climate

Deserts occupy the following climatic zones:

• moderate (Northern Hemisphere)
• subtropical (both hemispheres of the Earth);
• tropical (both hemispheres);
• polar (icy deserts).

The deserts are dominated by a continental climate (very hot summers and cold winters). Precipitation is extremely rare: from once a month to once in several years and only in the form of showers, because small precipitation does not reach the ground, evaporating in the air.

The daily temperature in this climatic zone varies greatly: from +50 o C during the day to 0 o C at night (tropics and subtropics) and up to -40 o C (northern deserts). The desert air is particularly dry: from 5 to 20% during the day and from 20 to 60% at night.

The largest deserts in the world

Sahara or Queen of the Deserts - the largest desert in the world (among hot deserts), the territory of which covers over 9,000,000 km 2. Located in North Africa, famous for its mirages, which happen here on average 150 thousand per year.

Arabian Desert (2,330,000 km 2). Located on the territory of the Arabian Peninsula, also capturing part of the land of Egypt, Iraq, Syria, Jordan. One of the most capricious deserts in the world, known for particularly sharp fluctuations in daily temperature, strong winds and dust storms. From Botswana and Namibia to South Africa stretches more than 600,000 km 2 Kalahari, constantly increasing its territory due to alluvium.

Gobi (more than 1,200,000 km 2). It is located in the territories of Mongolia and China and is the largest desert in Asia. Clay and stony soils occupy almost the entire territory of the desert. In the south of Central Asia lie Karakum ("Black Sands"), covering an area of \u200b\u200b350,000 km 2.

Victoria Desert - occupies almost half of the Australian continent (over 640,000 km 2). Famous for its red sand dunes, as well as a combination of sandy and rocky areas. Also located in Australia Great Sandy Desert (400,000 km 2).

Two South American deserts are very remarkable: Atacama (140,000 km 2), which is considered the driest place on the planet, and Salar de Uyuni (more than 10,000 km 2) - the largest salt desert in the world, the salt reserves of which are more than 10 billion tons.

Finally, the absolute champion in terms of occupied territory among all world deserts is Icy desert Antarctica(about 14,000,000 km 2).

The desert may seem like a lifeless territory only at first glance. In fact, it is inhabited by unusual representatives of the animal and plant world, who have managed to adapt to difficult climatic conditions. The natural zone of the Desert is very extensive and occupies 20% of the land of the world.

Description of the natural area of \u200b\u200bthe Desert

The desert is a vast flat area with a uniform landscape, sparse soil, flora and fauna. Such land areas are found on all continents, with the exception of Europe. The main sign of the desert is drought.

The features of the relief of the natural complex Desert include:

• plains;
• plateaus;
• arteries of dry rivers and lakes.

This type of natural zone extends over most of Australia, a relatively small part of South America, located in the subtropical and tropical zones of the Northern Hemisphere. On the territory of Russia, deserts are located in the south of the Astrakhan region in the eastern regions of Kalmykia.

The largest desert in the world is the Sahara, which is located on the territory of ten countries on the African continent. Life here is found only in rare oases, and on an area of \u200b\u200bover 9000 thousand square meters. km only one river flows, communication with which is not available to everyone. It is characteristic that the Sahara consists of several deserts, similar in their climatic conditions.

Figure: 1. The Sahara Desert is the largest in the world.

Desert types

Depending on the type of surface, the desert is divided into 4 classes:

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• Sandy and sandy-crushed stone ... The territory of such deserts is distinguished by a variety of landscapes: from sand dunes without a single hint of vegetation, to plains covered with small bushes and grass.

Even the very word "desert" evokes associations of emptiness and lack of life, but for the people who live on these lands, it seems beautiful and unique. The natural area of \u200b\u200bthe desert is an area very complex, but life. Distinguish between sandy, clayey, stony, saline and snowy (yes, in the Arctic and Antarctica - the Arctic desert) deserts. The most famous is the Sahara, it is also the largest in area. In total, deserts occupy 11% of the land, and if you count with Antarctica - more than 20%.

See the geographical location of the natural desert zone on the natural zones map.

Deserts are located in the temperate zone of the Northern Hemisphere and the subtropical and tropical zones of the Northern and Southern Hemispheres (they are characterized by special moisture conditions - the amount of precipitation per year becomes less than 200 mm, and the moisture coefficient is 0-0.15). Most deserts were formed on geological platforms, occupying the most ancient land areas. Like other landscapes of the Earth, deserts have arisen naturally, due to the peculiar distribution of heat and moisture over the earth's surface. In simple terms, deserts are located in places where very little or no moisture gets in. The reasons for this are mountains that close the deserts from the oceans and seas or the close location of the desert to the equator.

The main symptom of semi-arid and desert lands is drought. Arid, arid zones include lands where the life of people, plants and animals is completely dependent on it. Arid lands make up almost a third of the entire land mass of the planet.

The relief of the desert zone is very diverse - complex highlands, hummocks and island mountains, stratal plains, ancient river valleys and closed lake depressions. The most common are aeolian landforms, which were formed under the influence of wind.

Sometimes the territory of the deserts is crossed by rivers (Okavango is a river that flows into the desert, the Yellow River, the Syr Darya, the Nile, the Amu Darya, etc.), there are many dry streams, lakes and rivers (Chad, Lop Nor, Eyr).

Soil poorly developed - water-soluble salts prevail over organic substances.
Groundwater is often mineralized.

Features of the climate.

The climate in the deserts is continental: winters are cold and summers are very hot.

It rains once a month or only once in several years, in the form of heavy downpours. Light rains simply do not reach the surface of the earth, evaporating under the influence of high temperatures. The driest regions of the world are the deserts of South America.

Most deserts receive major precipitation in spring and winter, and only in some deserts the maximum amount of precipitation falls in summer in the form of showers (in the large deserts of Australia and the Gobi).

The air temperature in this natural zone can fluctuate greatly - during the day it rises to + 50 ° С, and at night it drops to 0 ° С.
In the northern deserts, the temperature in winter drops to -40 ° C.

One of the most important features is the dryness of the air - in the daytime humidity is 5-20%, and at night within 20-60%.

Winds are of great importance in deserts. Each of them has its own name, but they are all hot, dry, carrying dust and sand.

The sandy desert is especially dangerous during a hurricane: sand turns into black clouds and obscures the sun, the wind carries sand over long distances, destroying absolutely everything in its path.
Another feature of the deserts is the mirages created by the sun's rays, which refract to create very amazing pictures on the horizon.

Deserts and semi-deserts are characterized by severe weather conditions and unique natural phenomena. Here there are animals and plants that practically do not use water, moving hills - dunes, evidence of the existence of ancient civilizations.

Deserts are natural areas with an arid climate. However, not all of them are characterized by hot weather and an abundance of sunlight, there are areas that are recognized as the coldest on planet Earth. Semi-deserts represent an average landscape between desert, steppe or savanna and are formed in arid (dry) climates on all continents, excluding Antarctica.

How are formed

The predisposing factors for the emergence of deserts and semi-deserts are individual for each of them and include the territorial location (continental or oceanic), the peculiarities of the atmosphere and land structure, the uneven distribution of heat and moisture.

The reasons for the formation of such natural zones are high levels of solar radiation and radiation, a small amount or lack of precipitation.

Cold deserts appear for other reasons. In the Arctic, Antarctica, snow mainly falls on the coast; clouds with precipitation practically do not reach the inner regions. In this case, the annual rate can fall out at a time. As a result, snow deposits form over hundreds of years.

The relief in hot desert zones is varied. They are open to the wind, the gusts of which carry small stones and sand, creating undulating sediments.

They are called dunes, their common type is a dune, the height of which reaches 30 meters. Ridge dunes grow up to 100 meters and are up to 100 meters long.

Location: location on the map

Deserts and semi-deserts are located in the tropical, subtropical and temperate zones. Natural areas on planet Earth are represented on a map with names.

The world

In the northern latitudes, there are deserts and semi-deserts of the subtropical and temperate zones. At the same time, there are tropical ones - in Mexico, on the Arabian Peninsula, the southwestern United States, and the Indo-Gangetic lowland.

Arabian Peninsula

United States of America

In Eurasia, desert zones are located in the Caspian lowlands, on the Central Asian and South Kazakh plains, Central Asia, and the Near Asian highlands.

Natural areas are less common in the southern hemisphere. This includes a list of names: Namib in the Republic of Namibia, the desert zones of Peru and Venezuela, Gibson, Atacama, Victoria, Kalahari, Patagonia, Gran Chaco, Big Sandy, Karoo in Southwest Africa, Simpson.

Namib and Kalahari

Venezuela

Victoria Desert, Gibson, Big Sandy, Simpson

Patagonia

Gran Chaco

One of the largest deserts in the world, Rub al-Khali, occupies a third of the Arabian Peninsula. Tourists visiting Dubai often opt for a hot spot safari.

The vast deserts of Israel are represented on the map - these are the Judean and Negev.

Polar natural zones are located in the glacial regions of Eurasia, on the islands of the Canadian archipelago, in the north of Greenland.

Greenland

Desert regions of Asia, Africa, Australia are located at 200-600 meters above sea level, in Central Africa and North America - 1000 meters. Borders of deserts with mountains are widespread. They impede the movement of cyclones. Most of the precipitation falls only on one side of the mountainous area; on the other, it is absent or present in small amounts.

Sources of information about how many deserts there are on earth call the number 51, while 49 are real (not ice).

Of Russia

The country occupies a vast area with different types of climate, so the answer to the question whether there are deserts in Russia is in the affirmative. There are not only hot zones, but also cold ones. On the territory of Russia, deserts and semi-deserts are widespread from the Caspian lowland to China, in the east of Kalmykia and in the southern part of the Astrakhan region. In the area of \u200b\u200bthe left bank of the Volga, deserts and semi-deserts extend to Kazakhstan. The Arctic zone is located in the area of \u200b\u200bthe northern islands.

As you can see in the picture, semi-deserts are located in the northern part, they are characterized by a steppe landscape. To the south, the climate becomes arid, the vegetation cover is thinning. The desert zone begins.

The largest desert in Russia, Europe is called Ryn-Peski, located in the Caspian region.

Kinds

Depending on the type of soil and soil, there are types of deserts:

• Sandy and sandy-crushed stone - are formed on loose deposits of ancient alluvial plains. In different territories, they are called differently: in Africa - ergs, in Central Asia - kums, in Arabia - nefuds. Moreover, the sands do not occupy the largest part of the desert zone. For example, in the Sahara they are only 10%.

  

  Sandy deserts

  

  Sand-gravel deserts

• Stony (hamadas), gypsum, gravelly, gravelly-pebble - their location in mountain ranges, hills, low mountains, and so on. The formation of a hard surface is due to the physical weathering of material from cracked rocks, which fills the depressions. This type is the most common - in the Sahara 70% of the territory belongs to it.

  

• Saline. They are characterized by a high concentration of salts. Territories are covered with a crust or bog that can suck in humans or animals.

  

• Clayey - the surface of the territory is a clay layer characterized by low mobility and low water properties (they dry quickly, do not allow moisture to penetrate under the clay).

  

• Loess - are formed in the areas of accumulation of dusty, porous particles. They are characterized by an inhomogeneous relief, the presence of a network of ruts and ravines.

  

• Arctic - distinguish between snowy and snowless (dry). The former occupy 99% of the area of \u200b\u200bthe Arctic deserts.

  

  Arctic snow deserts

  

  Arctic snowless deserts

Depending on the nature of precipitation, deserts are distinguished:

Driest desert - Atacama

Atacama is located on the west coast of South America in Chile. The coastal desert is at the foot of the mountains, covering it with ridges from the rain, cold sea \u200b\u200bwaters wash hot shores.

The Atacama is considered the driest natural area, with an average rainfall of 1 millimeter per year. In some localities, rain is observed once every several decades. There was no significant rainfall from 1570 to 1971. Some weather stations in the desert zone have never recorded rain.

In 2010, an anomalous phenomenon occurred there - snow fell, covering several cities with snowdrifts.

In the Atacama, there is the famous 11-meter sculpture "Hand of the Desert", depicting a human palm, which protrudes three-quarters of the sand. It symbolizes loneliness, grief, injustice, helplessness.

Atacama is known for a mysterious find - a humanoid mummy, discovered in 2003 in the village of La Noria. Its size is 15 centimeters, instead of the usual 12 ribs, there are only 9, the skull has a pronounced elongated shape. For its external resemblance to an alien creature, she was named "Atacama humanoid".

However, scientists in their reports after the research are inclined towards the earthly origin of the mummy girl. She probably suffered from Progeria (rapid aging) and died either in the womb or after birth. There is a version that she lived for 7 years - this is due to the age of the skeleton.

In the desert on Mount Sierro Unica, there is the largest anthropomorphic geoglyph - a drawing 86 meters long, which is about 9 thousand years old. They call him Tarapaca, the Giant. The creators are unknown, it is possible to fully view the image from an airplane.

The largest hot desert - Sahara

The natural zone is located on the territory of 10 states: Algeria, Egypt, Morocco, Libya, Mali, Niger, Mauritania, Chad, Sudan.

Her definition of "Queen of the Desert" is due to the huge area of \u200b\u200bthe territory (9,065,000 square kilometers). Many areas of the zone are not inhabited, settlements are observed only at reliable sources of water and vegetation.

The Sahara is full of secrets and mysteries.

It is known for its mirages that knock travelers off the right path and doom them to death. People see oases, lakes and even entire cities, but it is impossible to get close to them - they move away until they dissipate at all.

The version that explains the phenomenon calls the mirage a kind of lens that visually brings objects closer to them, which are actually much further away.

For tourists, special maps have been drawn up, indicating the places where phantom images are likely to appear.

In the Sahara, on the territory of Mauritania, astronauts discovered an amazing object - a ring 50 kilometers in diameter, called the "Eye of Africa" \u200b\u200bor "Rishat Structure".

Its age is estimated at 500-600 million years, its origin is unknown.

The largest cold desert - Antarctic

In terms of the area occupied by the territory, it is recognized as the leader among all desert places, ahead of even the Sahara. According to Wikipedia, the area of \u200b\u200bthe polar zone is 13,828,430 square kilometers. Located on the island and mainland land of Antarctica.

In winter, the air temperature drops to -70 degrees, in summer, the characteristic level is from -30 to -50 (not higher than -20). On the coast of the Antarctic Peninsula, an increase in summer rates up to 10-12 degrees is possible.

Precipitation is presented in the form of snow, their amount is from 30 mm to 1000 mm per year. Strong winds, storms, blizzards are characteristic. Nature is poor, flora and fauna are poor and monotonous.

The most popular desert is the Mojave

Located in the southwestern United States of America, most of the area is uninhabited.

However, the desert is popular with tourists; the major cities of Lancaster, St. George, Henderson and, of course, gambling Las Vegas are located here.

Famous museums, national parks, nature reserves in the Mojave. Among them, Death Valley stands out. This is a national park, where bizarre shapes of salt flats, canyons, sand dunes, valleys are presented.

Even an experienced tourist finds it difficult to navigate in such a variety. Poisonous snakes, spiders, scorpions, coyotes will not let you lose your guard.

Description of desert places

Natural zones are characterized by a variety of landscape and climate. Despite the harsh conditions, adapted species of animals, plants, insects live in deserts and semi-deserts.

People also inhabit hot areas, farm, find ways to interact with nature. However, in vast areas, due to the harsh conditions of the external environment, life is absent, the existence there for almost all organisms becomes impossible.

The soil

In desert zones, a weak development of soils was noted, in which water-soluble salts predominate over organic components. Vegetation cover is less than 50% of the surface or is completely absent.

The gray-brown soil is typical of the high plains.

In deserts and semi-deserts, salt marshes with 1% concentration of readily soluble salts are often found.

Ground waters are predominantly mineralized. Upon reaching the surface, the soil is located in its upper layer, forming salinity.

The soil in subtropical deserts and semi-deserts is orange and brick-red. This soil is called red soil and yellow soil.

In northern Africa, South and North America, gray soils are found in deserts.

Climate

The climate in deserts and semi-deserts depends on its location. It is dry, hot, the air is slightly humidified, and practically does not protect the soil from solar radiation.

The average temperature is +52 degrees, the maximum is +58. Excessive heating is associated with the absence of clouds and, therefore, protection from direct sunlight. For the same reason, temperatures drop markedly at night, since heat is not stored in the atmosphere.

The daily amplitudes in the deserts of the tropical zone are up to 40 degrees, in the moderate - up to 20. The latter are characterized by significant seasonal fluctuations. There are hot summers with temperatures in the range of +50 degrees and severe winters, when the thermometer drops to -50, while the snow cover is small.

In hot deserts, rains are rare, but sometimes heavy showers occur, in which water is not absorbed into the soil. It flows down into dry channels called wadis.

A characteristic feature of deserts is strong winds at a speed of 15-20 meters per second, sometimes more.

They carry surface material to form sand and dust storms.

The desert zones of Russia are characterized by a sharply continental climate: dry and harsh with strong daily and seasonal temperature drops. In summer, the level reaches more than +40 degrees, in winter it drops to -30.

Evaporation of precipitation exceeds the amount of precipitation; it is mainly observed in spring and summer.

Strong winds, dust storms and dry winds are characteristic.

There are no transitional seasons in arctic deserts. The polar night lasts 90 days, winter comes with temperatures down to -60 degrees. Then summer comes with the polar day. It does not last long, while the temperature is within +3 degrees. Snow cover is constant, winter comes in 1 night.

Animal world

Living organisms living in deserts and semi-deserts have managed to adapt to harsh conditions.

From cold or heat, they hide in burrows, feed on insects, underground parts of plants.

Jungle cat

The fennec fox, jungle cats, cougars, and coyotes are among the carnivores of the desert zones.

You can meet a tiger in the semi-desert.

Some representatives of the animal world have a developed thermoregulation system. They withstand the loss of fluid up to a third of their own body weight (camel, gecko), and certain types of invertebrates - up to two thirds of their weight.

North America and Asia are inhabited by a large number of reptiles: lizards, snakes, insects, including poisonous ones, are present.

The large mammal, the saiga, is also considered an inhabitant of hot natural areas.

In the Chihuahua Desert, located on the border of Texas, New Mexico and the Mexican states, the pronghorn is often found, feeding on all plants, including poisonous ones.

In the hot natural zone Danakil, where the air temperature can rise up to +60 degrees, wild donkeys, Grevy's zebra, Somali gazelle live, feeding on scarce vegetation.

Wild donkey

In the deserts and semi-deserts of Russia, there are sandstone hares, hedgehogs, kulan, gazelles, snakes, jerboas, ground squirrels, mice, and voles.

Sandstone hare

Among the predators, the steppe fox, ferret, and wolf are distinguished.

Steppe fox

Spiders also live in natural areas: karakurt and tarantula. Among the birds are the steppe eagle, the white-winged lark, the egret and so on.

Steppe eagle

In the polar deserts, the animal world is scarce. Its representatives feed on seafood and vegetation. Polar bears, musk ox, arctic fox, seals, walruses, reindeer, hares live here.

Polar bear and walruses

Reindeer

Among the birds, eiders, gulls, terns, penguins and so on stand out.

Penguins

Plants

In deserts and semi-deserts, the flora is not rich and includes thorny cactus, date palm, stiff-leaved cereals, acacia, saxauls, psammophyte shrubs, ephedra, soap tree, edible lichen.

Date palm

Shrubs-psammophytes

Sandy natural zones are characterized by oases - "islets" with rich vegetation and water bodies.

In Russian deserts and semi-deserts there are white and black wormwood, fescue, Sarepta feather grass, viviparous bluegrass. The soil is not fertile.

Sarepta feather grass

The semi-deserts serve as pastures for livestock from April to November.

In some periods, natural areas flourish, filling with rich vegetation. For example, the Kyzylkum desert ("red sands"), which belongs to Uzbekistan, Kazakhstan, and partly Turkmenistan, blooms in spring with a bright carpet of flowers and herbs.

Subsequently, they disappear under the rays of the scorching summer sun.

In the Takla-Makan Desert in western China, most of the territory is generally devoid of vegetation, only in rare areas of groundwater occurrence are thickets of tamarisk, reed, camel thorn, saxaul, and poplar grow along river valleys.

Camel-thorn

In the Arctic desert, vegetation is practically absent. In summer, the surface of the earth is covered with moss and lichens, sedges and grasses, polar poppy, saxifrage, buttercup and so on are found.

Locals

People living in hot natural areas are forced to adapt to environmental conditions. In economic activities, grazing cattle is distinguished.

Agriculture is used only in the valleys of large rivers, irrigation is used.

Oil and gas are produced in many natural areas. This is especially true in Asia.

In the deserts and semi-deserts of Russia, irrigated agriculture is practiced in the floodplains and deltas of large rivers (Volga, Syrdarya, Amu Darya). A large number of wells and boreholes have been created for livestock watering, places for their wintering.

The most severe conditions for economic activity are noted in rocky and gravelly deserts; agriculture is practically absent here.

When there is a shortage of water, local residents develop different ways for its extraction. For example, in the driest Atacama Desert, aborigines use "mist catchers" - cylinders the size of a person to collect moisture. Mist condenses on the nylon filament walls of the vessel and flows into the barrel. With its help, it is possible to collect up to 18 liters of water per day.

The nomadic inhabitants of Arabia, the Near and Middle East are called Bedouins.

Their culture is based on the invention of the tent and the domestication and breeding of camels. The Bedouin roams with his family on a camel, which carries portable housing and utensils.

Nature reserves

Human intervention is recognized as the main threat to deserts and their inhabitants. In addition to hunting rare and endangered species of animals and birds, natural resources - oil and gas - are mined in these zones.

Technological progress increases the demand for them, which leads to an increase in field development. The mining pollutes the surrounding area, causing an ecological disaster.

Anthropogenic impact in the Arctic contributes to the melting of ice, reducing the territory of cold deserts. Her disappearance will cause doom a large number representatives of flora and fauna of the natural zone.

In Russia and around the world, nature conservation work is underway, national parks and reserves are being created.

Geographic features of deserts

Most of the world's deserts were formed on geological platforms and occupy the most ancient land areas. Deserts in Asia, Africa and Australia are usually located at altitudes of 200-600 m above sea level, in Central Africa and North America - at an altitude of 1,000 m above sea level.

Deserts are one of the landscapes of the Earth, which arose just as naturally as all others, due primarily to the peculiar distribution of heat and moisture over the earth's surface and the associated development of organic life, the formation of biogeocenotic systems. A desert is a certain geographic phenomenon, a landscape that lives its own special life, has its own laws, which, during development or degradation, has its inherent features, forms of change.

Speaking of the desert as a planetary and naturally occurring phenomenon, one should not mean by this concept something monotonous, of the same type. Most deserts are surrounded by mountains or, more often, bordered by mountains. In some places, deserts are located adjacent to young high mountain systems, in others - with ancient, heavily destroyed mountains. The first include the Karakum and Kyzyl Kum, the deserts of Central Asia - Alashan and Ordos, the South American deserts; the second should include Northern Sahara.

Mountains for deserts are areas of formation of liquid runoff, which comes to the plain in the form of transit rivers and small, with “blind” mouths. The underground and under-channel runoff that feeds their underground waters is also of great importance for deserts. Mountains are areas from where the products of destruction are carried out, for which deserts serve as places of accumulation. Rivers supply a mass of loose material to the plain. Here it is sorted out, ground into even smaller particles and lines the surface of the deserts. As a result of centuries-old work of the rivers, the plains are covered with a multi-meter layer of alluvial deposits. The rivers of the waste areas carry out a huge mass of blown and debris into the World Ocean. Therefore, the deserts of the waste areas are distinguished by an insignificant distribution of ancient alluvial and lacustrine deposits (Sahara, etc.). On the contrary, the closed areas (Turan lowland, Iranian highlands, etc.) are distinguished by thick strata of deposits.

The surface deposits of deserts are peculiar. They owe this to the geological structure of the territory and natural processes. According to MP Petrov (1973), the surface deposits of deserts are the same type everywhere. These are “stony and gravelly eluvium on Tertiary and Cretaceous conglomerates, sandstones and marls that make up structural plains; pebble, sandy or loamy-clayey proluvial deposits of foothill plains; sandy strata of ancient deltas and lacustrine depressions and, finally, aeolian sands ”(Petrov, 1973). Deserts are characterized by some of the same type of natural processes that are prerequisites for morphogenesis: erosion, water accumulation, blowing out and aeolian accumulation of sand masses. It should be noted that the similarities between the deserts are found in a large number of features. The lines of difference are less noticeable and limited to a few examples, to a fairly sharp one.

The differences are mostly related to the geographical position of deserts in different thermal zones of the Earth: tropical, subtropical, temperate. The first two zones contain the deserts of North and South America, the Near and Middle East, India, and Australia. Among them are continental and oceanic deserts. In the latter, the climate is mitigated by the proximity of the ocean, which is why the differences between heat and water balances, precipitation and evaporation are not similar to the corresponding values \u200b\u200bthat characterize continental deserts. However, for oceanic deserts great importance have washing continents ocean currents - warm and cold. The warm current saturates the air masses coming from the ocean with moisture, and they bring precipitation to the coast. The cold current, on the contrary, intercepts the moisture of the air masses, and they enter the mainland dry, increasing the aridity of the coasts. Oceanic deserts are located off the western shores of Africa and South America.

Continental deserts are located in the temperate zone of Asia and North America. They lie inside the continents (deserts of Central Asia) and are distinguished by arid and extra-arid conditions, a sharp discrepancy between the thermal regime and precipitation, high volatility, and contrasts of summer and winter temperatures. The differences in the nature of deserts are also influenced by their altitude position.

Mountain deserts, like those located in intermontane depressions, are usually characterized by an increased climate aridity. The variety of similarities and differences between deserts is primarily associated with their location in different latitudes of both hemispheres, in the hot and temperate zones of the Earth. In this regard, the Sahara may have more similarities with the Australian desert and more differences with the Karakum and Kyzyl Kum in Central Asia. Equally, the deserts formed in the mountains may have a number of natural anomalies among themselves, but even more differences with the deserts of the plains.

Differences are in average and extreme temperatures during the same season of the year, in the time of precipitation (for example, the eastern hemisphere of Central Asia receives more precipitation in summer from monsoon winds, and the deserts of Central Asia and Kazakhstan in spring). Dry channels are a prerequisite for the nature of deserts, but the factors of their occurrence are different. The thinness of the cover largely determines the low humus content in desert soils. This is also facilitated by the dryness of the air in summer, which prevents active microbiological activity (in winter, rather low temperatures slow down these processes).

Desert Formation Patterns

The “mechanism” of the formation and development of deserts is primarily subject to the uneven distribution of heat and moisture on the Earth, the zoning of the geographic shell of our planet. The zonal distribution of temperatures and atmospheric pressure determines the specifics of winds and the general circulation of the atmosphere. Above the equator, where the greatest heating of the land and water surface occurs, ascending air movements dominate.

An area of \u200b\u200bcalm and weak variable winds is formed here. The warm air that has risen above the equator, cooling somewhat, loses a large amount of moisture, which falls in the form of tropical showers. Then, in the upper atmosphere, the air flows north and south, towards the tropics. These air currents are called anti-trade winds. Under the influence of the rotation of the earth in the northern hemisphere, the anti-trade winds deflect to the right, in the southern - to the left.

Approximately above latitudes of 30-40 ° С (near the subtropics), the angle of their deflection is about 90 ° С, and they begin to move along the parallels. At these latitudes, air masses descend to the heated surface, where they heat up even more, and move away from the critical saturation point. Due to the fact that in the tropics all year round, atmospheric pressure is high, and at the equator, on the contrary, it is low, at the surface of the earth there is a constant movement of air masses (trade winds) from the subtropics to the equator. Under the influence of the same deflecting influence of the Earth in the northern hemisphere the trade winds move from the north-east to the south-west, in the south - from the south-east to the north-west.

The trade winds cover only the lower troposphere - 1.5-2.5 km. The trade winds prevailing in the equatorial-tropical latitudes determine the stable stratification of the atmosphere, prevent vertical movements and the associated development of clouds, and precipitation. Therefore, the cloudiness in these belts is not very significant, and the inflow of solar radiation is the greatest. As a result, the air is extremely dry here (relative humidity in the summer months is about 30% on average) and extremely high summer temperatures. The average air temperature on the continents in the tropical zone in summer exceeds 30-35 ° C; here is the highest air temperature on the globe - plus 58 ° С.The average annual amplitude of air temperature is about 20 ° С, and the daily temperature can reach 50 ° С, the soil surface sometimes exceeds 80 ° С.

Precipitation falls very rarely, in the form of showers. In subtropical latitudes (between 30 and 45 ° C of northern and southern latitudes), the total radiation decreases, and cyclonic activity contributes to moisture and precipitation, mainly confined to the cold season. However, sedentary depressions of thermal origin develop on the continents, causing severe aridity. Here, the average temperature of summer months is 30 ° C and more, the maximum can reach 50 ° C. In subtropical latitudes, the intermontane depressions are the most dry, where the annual precipitation does not exceed 100-200 mm.

In the temperate zone, conditions for the formation of deserts arise in inland regions such as Central Asia, where precipitation is less than 200 mm. Due to the fact that Central Asia is fenced off from cyclones and monsoons by mountain rises, a baric depression forms here in summer. The air is very dry, high temperature (up to 40 ° C and more) and dusty. Air masses from the oceans and from the Arctic, which rarely penetrate here with cyclones, quickly warm up and dry up.

Thus, the nature of the general circulation of the atmosphere is determined by planetary features, and local geographic conditions create a kind of climatic situation that forms a desert zone to the north and south of the equator, between 15 and 45 ° C latitude. To this is added the influence of cold currents in tropical latitudes (Peruvian, Bengal, Western Australian, Canary and California). By creating a temperature inversion, cool, moisture-saturated sea air masses from the eastern constant baric winds lead to the formation of coastal cool and foggy deserts with even less precipitation in the form of rain.

If the land covered the entire surface of the planet and there were no oceans and high mountain rises, the desert belt would be continuous and its borders would exactly coincide with a certain parallel. But since land occupies less than 1/3 of the earth's area, the distribution of deserts and their sizes depend on the configuration, size and structure of the surface of the continents. So, for example, the Asian deserts spread far to the north - up to 48 ° С N. In the southern hemisphere, due to the vast expanses of the oceans, the total area of \u200b\u200bthe continental deserts is very limited, and their distribution is more localized. Thus, the emergence, development and geographical distribution of deserts on the globe are conditioned by the following factors: high values \u200b\u200bof radiation and radiation, little or no precipitation. The latter, in turn, is determined by the latitude of the area, the conditions of the general circulation of the atmosphere, the peculiarities of the orographic structure of the land, the continental or oceanic location of the area.

Aridity of the territory

By the degree of aridity - aridity, many territories are not the same. This gave rise to the division of arid lands into extra-arid, arid and semi-arid, or extremely arid, arid and semi-arid. At the same time, extra-arid areas include areas where the probability of permanent droughts is 75-100%, arid ones - 50-75% and semi-arid ones - 20-40%. The latter include shrouds, pampas, pashtas, prairies, where organic life takes place in a natural setting, in which, apart from certain years, drought is not a determining condition for development. Rare droughts with a probability of 10-15% are also characteristic of the steppe zone. Consequently, not all areas of land where droughts occur, but only those where organic life has been largely under their influence for a long time, belongs to the arid zone.

According to MP Petrov (1975), deserts include territories with an extremely arid climate. Precipitation falls less than 250 mm per year, evaporation exceeds precipitation many times, agriculture is impossible without artificial irrigation, the movement of water-soluble salts and their concentration on the surface prevail, there are few organic substances in the soil.

The desert is characterized by high summer temperatures, low annual precipitation - more often from 100 to 200 mm, lack of surface runoff, often a predominance of sandy substrate and a large role of aeolian processes, salinity of groundwater and migration of water-soluble salts in the soil, uneven amount of precipitation, which determines the structure , yield and forage capacity of desert plants. One of the features of the distribution of deserts is the insular, local nature of their geographical location. Desert lands do not form a continuous strip on any continent, like the arctic, tundra, taiga or tropical zones. This is due to the presence within the desert zone of large mountain structures with their greatest peaks and significant expanses of water. In this respect, deserts do not fully obey the law of zoning.

In the northern hemisphere, the desert territories of the African continent lie between 15 ° C and 30 ° C N, where the largest desert in the world - the Sahara - is located. In the southern hemisphere, they are located between 6 and 33 ° C S, covering the Kalahari, Namib and Karoo deserts, as well as the desert territories of Somalia and Ethiopia. In North America, deserts are confined to the southwestern part of the continent between 22 and 24 ° C N, where the Sonoran, Mojave, Hila, etc. deserts are located.

Significant areas of the Great Basin and the Chihuahua Desert are naturally quite close to the conditions of the arid steppe. In South America, deserts, located between 5 and 30 ° C S, form an elongated strip (more than 3 thousand km) along the western, Pacific coast of the mainland. Here from north to south the deserts of Sechura, Pampa del Tamarugal, Atacama stretch, and beyond mountain ranges Patagonian. The deserts of Asia are located between 15 and 48-50 ° C north latitude and include such large deserts as Rub al-Khali, Bolshoi Nefud, Al-Khasa on the Arabian Peninsula, Deshte-Kevir, Deshte-Lut, Dashti-Margo, Registan , Haran in Iran and Afghanistan; Karakum in Turkmenistan, Kyzyl Kum in Uzbekistan, Muyunkum in Kazakhstan; Tar in India and Thal in Pakistan; Gobi in Mongolia and China; Takla Makan, Alashan, Beishan, Tsaidasi in China. Deserts in Australia occupy a vast area between 20 and 34 ° C S. and are represented by the deserts of Great Victoria, Simpson, Gibson and Big Sandy.

According to Meigle, the total area of \u200b\u200barid territories is 48810 thousand square meters. km, that is, they occupy 33.6% of the earth's land, of which the extra-arid account for 4%, arid - 15 and semi-arid - 14.6%. The area of \u200b\u200btypical deserts, with the exception of semi-deserts, is about 28 million square meters. km, that is, about 19% of the earth's land area.

According to the data of Shants (1958), the area of \u200b\u200barid territories classified by the nature of the vegetation cover is 46,749 thousand square meters. km, that is, about 32% of the earth's land area. At the same time, the share of typical deserts (extra-arid and arid) is about 40 million square meters. km, and the share of semi-arid lands - only 7044 thousand square meters. km per year, arid (21.4 million sq. km) - with precipitation from 50 to 150 mm and semi-arid (21.0 million sq. km) - with precipitation from 150 to 200 mm.

In 1977, UNESCO compiled a unified new picture on a scale of 1: 25,000,000 in order to clarify and establish the boundaries of the arid regions of the world. Four bioclimatic zones are identified on the map.

Extraarid zone. Precipitation less than 100 mm; devoid of vegetation, excluding ephemeral plants and shrubs along the stream beds. Farming and animal husbandry (except for oases) is impossible. This zone is a very pronounced desert with possible droughts for one or several years in a row.

Arid zone. Precipitation 100-200 mm. Sparse, sparse vegetation, represented by perennial and annual succulents. Rain-fed agriculture is impossible. Zone of nomadic cattle breeding.

Semi-arid zone. Precipitation is 200-400 mm. Shrub communities with discontinuous herbaceous cover. A zone of cultivation of rainfed agricultural crops (“dry” farming) and animal husbandry.

Zone of insufficient moisture (sub-humid). Precipitation is 400-800 mm. Includes some tropical savannas, Mediterranean communities such as maquis and chaparral, black earth steppes. Zone of traditional rainfed agriculture. For highly productive agriculture, irrigation is necessary.

According to this map, the area of \u200b\u200barid territories is about 48 million square meters. km, which is equal to 1/3 of the entire land surface, where moisture is a decisive factor that determines the biological productivity of arid lands and the living conditions of the population.

Desert classification

In arid territories, despite their seeming monotony, there is not at least 10-20 square meters. km of area, within which the natural conditions would be exactly the same. Even if the relief is the same, the soils are different; if the soil is of the same type, then the water regime is not the same; if there is a single water regime, then different vegetation, etc.

Due to the fact that the natural conditions of vast desert territories depend on a whole complex of interrelated factors, the classification of desert types and their regionalization is a difficult matter. There is still no unified and satisfactory from all points of view classification of desert territories, drawn up taking into account all their geographical diversity.

In Soviet and foreign literature there are many works devoted to the classification of desert types. Unfortunately, almost all of them do not have a single approach to solving this issue. Some of them base the classification on climatic indicators, others on soil, third on floristic composition, fourth on lithoedaphic conditions (that is, the nature of soil and vegetation growth conditions on them), etc. Few of the researchers in their classification proceeds from a complex of signs of the nature of deserts. Meanwhile, on the basis of generalization of the components of nature, it is possible to correctly identify the ecological features of the region and quite reasonably assess its specific natural conditions and natural resources from an economic point of view.

MP Petrov in his book "Deserts of the Globe" (1973) suggests ten lithoedaphic types for the world's deserts on a multi-stage classification:

* sandy on loose deposits of ancient alluvial plains;

* sandy-pebble and pebble on gypsum tertiary and lilac structural plateaus and foothill plains;

* rubble, gypsum on the Tertiary plateaus;

* rubble on the foothill plains;

* stony in low mountains and small hills;

* loamy on slightly carbonate mantle loams;

* loess on the foothill plains;

* clayey on low mountains, composed of saline marls and clays of various ages;

* salt marshes in saline depressions and along sea coasts.

Different classifications of the types of arid territories of the globe and individual continents are also available in foreign literature. Most of them are compiled on the basis of climatic indicators. There are comparatively few classifications for other elements of the natural environment (relief, vegetation, fauna, soils, etc.).

Desertification and nature conservation

In recent years, alarming signals have been heard from different parts of the world about the growing desert offensive in human-inhabited territories. For example, according to the UN, in North America alone, the desert annually takes away from people about 100 thousand hectares of useful land. The most probable reasons for this rather dangerous phenomenon are considered to be unfavorable weather conditions, destruction of vegetation cover, irrational use of natural resources, mechanization of agriculture, transport without compensation for damage caused to nature. In connection with the intensification of desertification processes, some scientists talk about the possibility of an aggravation of the food crisis.

According to UNESCO, over the past 50 years, an area of \u200b\u200bjust under half of South America has been turned into barren deserts. This happened as a result of excessive grazing of pastures, predatory deforestation, unsystematic farming, road construction and other engineering structures. The rapid growth of population and technical means is also leading to the intensification of desertification processes in several parts of the world.

There are many different factors leading to desertification in arid regions of the world. However, among the bottom there are common ones that play a special role in intensifying the processes of desertification. These include:

destruction of vegetation cover and destruction of soil cover in industrial, irrigation construction;

degradation of vegetation cover by overgrazing;

destruction of trees and shrubs as a result of fuel harvesting;

deflation and erosion of soils during intensive rainfed agriculture;

secondary salinization and waterlogging of soils in conditions of irrigated agriculture;

destruction of the landscape in the mining areas due to industrial waste, waste and drainage water discharge.

Among the natural processes leading to desertification, the most dangerous are:

climatic - an increase in aridity, a decrease in moisture reserves caused by changes in the macro- and microclimate;

hydrogeological - precipitation becomes irregular, groundwater recharge - episodic;

morphodynamic - geomorphological processes become more active (erosion, deflation, etc.);

soil - drying out of soils and their salinization;

phytogenic - degradation of the soil cover;

zoogenic - a decrease in the population and number of animals.

The fight against desertification processes is carried out in the following directions:

early identification of desertification processes in order to prevent and eliminate them, orientation towards the formation of conditions for rational nature management;

creation of protective forest belts along the outskirts of oases, borders of fields and along canals;

creation of forests and green "umbrellas" from local species - psamophytes in the depths of the deserts to protect livestock from strong winds, scorching rays of the sun and strengthen the forage base;

restoration of vegetation cover in the areas of open mining, along the construction of the irrigation network, roads, pipelines and all places where it has been destroyed;

consolidation and afforestation of mobile sands for the purpose of protection from sand drifts and blowing out of irrigated lands, canals, settlements, railways and highways, oil and gas pipelines, industrial enterprises.

The main lever for a successful solution to this global problem is international cooperation in the field of nature conservation and combating desertification. The life of the Earth and life on Earth largely depends on how timely and urgent the tasks of monitoring and managing natural processes will be solved.

The problem of combating adverse events observed in the arid zone has existed for a long time. It is believed that of the 45 identified causes of desertification, 87% are due to the irrational use of water, land, vegetation, fauna and energy by humans, and only 13% are related to natural processes.

Nature protection is a very broad concept. It includes not only measures to protect specific areas of the desert or certain species of animals and plants. In modern conditions, this concept also includes measures for the development of rational methods of environmental management, restoration of ecosystems destroyed by humans, forecasting of physical and geographical processes in the development of new territories, the creation of manageable natural systems.

firstly, because its flora and fauna are unique. To keep the desert intact means to leave its indigenous inhabitants out of economic progress, and the national economy without very many, including unique, types of raw materials and fuel.

Secondly, because the desert itself is wealth, in addition to what is hidden in its depths or in the fertility of irrigated land.

Rich in various natural resources, the desert is very attractive, especially in early spring, when its short-lived plants bloom, and in late autumn, when cold rains with wind are pouring almost everywhere in our country, and warm sunny days are in the desert. The desert is attractive not only for geologists and archaeologists, but also for tourists. It is also curative, its dry air, long warm period, outcrops of medicinal mud, hot mineral springs allow to treat kidney diseases, rheumatism, nervous and many other diseases.