Where are the tropical deserts located and which ones are worth seeing? The desert and semi-desert zone of Russia: where it is located, map, climate, flora and fauna. Why do deserts exist?

19.10.2023

The desert may seem like a lifeless area 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 desert natural zone is very vast and occupies 20% of the world's landmass.

Description of the Desert natural area

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

The relief features of the Desert natural complex 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, and is 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 in ten countries of the African continent. Life here is found only in rare oases, and on an area of over 9,000 thousand square meters. There is only one river flowing km, communication with which is not accessible to everyone. It is characteristic that the Sahara consists of several deserts, similar in their climatic conditions.

Rice. 1. The Sahara Desert is the largest in the world.

Desert types

Depending on the type of surface, deserts are divided into 4 classes:

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Sand and sand-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.

More than 20%.

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general characteristics

Deserts are common in the temperate zone of the Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres. They are characterized by moisture conditions (annual precipitation is less than 200 mm, in extra-arid areas - less than 50 mm, and in some deserts there has been no precipitation for decades; the moisture coefficient, reflecting the ratio of precipitation and evaporation, is 0-0.15). The relief is a complex combination of highlands, small hills and island mountains with structural strata plains, ancient river valleys and closed lake depressions. The erosional type of relief formation is greatly weakened; aeolian relief forms are widespread. For the most part, the territory of the deserts is drainless, sometimes they are crossed by transit rivers (Syr Darya, Amu Darya, Nile, Yellow River and others); There are many drying up lakes and rivers, often changing their shape and size (Lop Nor, Chad, Eyre), and periodically drying up watercourses are typical. Groundwater is often mineralized. The soils are poorly developed, characterized by a predominance of water-soluble salts over organic substances in the soil solution; salt crusts are common. The vegetation cover is sparse (the distance between neighboring plants is from several tens of cm to several meters or more) and usually covers less than 50% of the soil surface; in extra-arid conditions it is practically absent.

Sandy deserts are inhabited by plants mainly by thorny bushes, and by animals - reptiles and small steppe animals. In sandy deserts above areas where groundwater occurs, there are oases - “islands” with dense vegetation and ponds. Snowy deserts are mainly located in the Arctic Circle and are inhabited by animals that are resistant to cold.

Formation and distribution of deserts

The formation, existence and development of deserts is based on the uneven distribution of heat and moisture, as well as the geographical zonation of the planet.

The zonal distribution of temperature and atmospheric pressure determines the specificity of the circulation of atmospheric air masses and the formation of winds. Trade winds, prevailing in equatorial-tropical latitudes, determine the stable stratification of the atmosphere, preventing vertical movements of air currents and the associated formation of clouds and precipitation. Cloud cover is extremely low, while the influx of solar radiation is greatest, resulting in extremely dry air (relative humidity in the summer months is about 30%) and exceptionally high summer temperatures. In the subtropical zone, the amount of total solar radiation decreases, but on the continents sedentary depressions of thermal origin develop, causing severe aridity. The average temperature in the summer months reaches + 30 °C, maximum + 50 °C. The dryest areas in this belt are the intermountain depressions, where the annual precipitation does not exceed 100-200 mm.

In the temperate zone, conditions for the formation of deserts occur in inland regions such as Central Asia, where precipitation does not exceed 200 mm/year. Central Asia is fenced off from cyclones and monsoons by mountain uplifts, which entails the formation of pressure depression in the summer months. The air is very dry, high temperature (up to + 40 °C or more) and very dusty. Occasionally, air masses with cyclones from the oceans and the Arctic penetrate here and quickly warm up and dry out.

It is the nature of the general circulation of the atmosphere, together with local geographical conditions, that creates the climatic conditions that form the desert zone north and south of the equator, between 15° and 45° latitude. To this is also added the influence of cold currents of tropical latitudes (Peruvian Current, California Current, Benguela Current, Canary Current, West Australian Current). Cool, moisture-laden maritime air masses that cause temperature inversions result in the formation of cool, foggy coastal deserts with even less rainfall.

The emergence, development and geographical distribution of deserts is determined by the following factors: high values of solar radiation and radiation, low amounts of precipitation or their complete absence. 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, and the continental or oceanic position of the area.

Geographical features

Most deserts were formed on geological platforms and occupy the oldest land areas. Deserts located in Asia, Africa and Australia are usually located at altitudes of 200-600 meters above sea level, in Central Africa and North America - at an altitude of 1000 meters above sea level. Many deserts border or are surrounded by mountains. The presence of high mountains always prevents the advancement of cyclones, and most of the precipitation falls on one side of the mountains, while either little or no precipitation falls on the other side.

Deserts are located either next to young high mountain systems (Karakum and Kyzylkum, deserts of Central Asia - Alashan and Ordos, South American deserts), or with ancient mountains (Northern Sahara).

Surface deposits of deserts are heterogeneous and different, depending on the geological structure of the territory and the natural processes affecting it.

Climate

Climate type - warm, dry (arid). The temperature regime of the desert depends, first of all, on its geographical location. Desert air, having extremely low humidity, practically does not protect the soil surface from solar radiation. The usual temperature is +50 °C, and the maximum temperature recorded in the Sahara is +58 °C. At night, the temperature is much lower, since the heated soil quickly loses heat (the weather in the desert is almost always clear, and at night after a hot day even frosts are sometimes possible). Daily temperature amplitudes in deserts of the tropical zone can be 30-40 ° C, in deserts of the temperate zone - usually about 20 ° C. Temperate desert temperatures exhibit significant seasonal variations. Summers in such deserts are usually warm, even hot, and winters in deserts of temperate latitudes are very severe, frosts can reach −50 °C, but snow cover is insignificant.

One of the characteristic features of all deserts is constantly blowing winds, sometimes reaching speeds of 15 - 20 m/s, sometimes more. The reasons for their occurrence are excessive heating and associated convective air flows, as well as landforms. Desert winds capture and transport loose material on the surface. This is how sand and dust storms are formed.

Relief

The formation of desert relief occurs under the influence of wind and water erosion. Deserts are characterized by a number of similar natural processes that are prerequisites for their morphogenesis: erosion, water accumulation, blowing and aeolian accumulation of sand masses.

Shapes created by water erosion

In other areas of the desert, wind-blown sand and dust accumulate. This is how sand dunes are formed. The sand that forms these dunes is predominantly composed of quartz particles, but the sand dunes at White Sands National Monument in New Mexico in the United States are composed of white gypsum. Dunes form in places where the air flow encounters an obstacle in its path. Sand accumulation begins on the leeward side of the obstacle. The height of most dunes ranges from meters to several tens of meters; dunes reaching a height of 300 m are also known. If the dunes are not fixed by vegetation, then over time they shift in the direction of the prevailing winds. As the dune moves, sand is carried by the wind up the gentle windward slope and falls off the crest of the leeward slope. The speed of dune movement is on average 6 - 10 meters per year.

A special type of dunes is called dunes. They are crescent-shaped, with a steep and high leeward slope and pointed “horns” elongated in the direction of the wind. In all areas of dune relief, there are many irregularly shaped depressions. Some of them are created by vortex air currents, others were formed simply as a result of uneven sand deposition.

Main geographical characteristics of the world's deserts

Name	Area, thousand sq. km.	Prevailing absolute heights, m.	Absolute maximum temperature, °C	Absolute minimum temperature, °C	Average annual precipitation, mm.
Central Asia and Kazakhstan
Karakum	350	100 - 500	+ 50	−35	70 - 100
Ustyurt and Mangyshlak	200	200 - 300	+ 42	−40	80 - 150
Kyzylkum	300	50 - 300	+ 45	−32	70 - 180
Aral Karakum	35	400	+ 42	−42	130 - 200
Betpak-Dala	75	300 - 350	+ 43	−38	100 - 150
Muyunkum	40	100 - 660	+ 40	−45	170 - 300
Central Asia
Taklamakan	271	800-1500	+ 37	−27	50 - 75
Alashan	170	800 - 1200	+ 40	−22	70 - 150
Beishan	175	900 - 2000	+ 38	−24	40 - 80
Ordos	95	1100 - 1500	+ 42	−21	150-300
Tsaidam	80	2600 - 3100	+ 30	−20	50 - 250
Gobi	1050	900 - 1200	+ 45	−40	50 - 200
Iranian Plateau
Dasht-Kevir	55	600 - 800	+ 45	−10	60 - 100
Dasht-Lut	80	200 - 800	+ 44	−15	50 - 100
Registan	40	500 - 1500	+ 42	−19	50 - 100
Arabian Peninsula and Middle East
Rub al-Khali	650	100 - 500	+ 47	−5	25 - 100
Big Nefood	80	600 - 1000	+ 54	−6	50 - 100
Dekhna	54	450	+ 45	−7	500 - 100
Syrian Desert	101	500 - 800	+ 47	−11	100 - 150
Negev	12	600 - 800	+46	−5	50 - 300
North Africa
Sahara	8600	200 - 500	+ 59	−5	25 - 200
Libyan Desert	1934	100 - 500	+ 58	−4	25 - 100
Nubian Desert	1240	350 - 1000	+ 53	−2	25
South Africa
Namib	150	200 - 1000	+ 40	−4	2 - 75
Kalahari	600	900	+ 42	−9	100 - 500
Karoo	120	450 - 750	+ 44	−11	100 - 300
Peninsula Hindustan
Tar	300	350 - 450	+ 48	−1	150 - 500
Thal	26	100 - 200	+ 49	−2	50 - 200
North America
Large Pool	1036	100 - 1200	+ 41	−14	100 - 300
Mojave	30	600 - 1000	+ 56,7	−6	45 - 100
Sonora	355	900 - 1000	+ 44	−4	50 - 250
Chihuahua	100	900 - 1800	+ 42	−6	75 - 300
South America
Atacama	90	300 - 2500	+ 30	−15	10 - 50
Patagonian	400	600 - 800	+ 40	−21	150 - 200
Australia
Great Sandy Desert	360	400-500	+ 44	+ 2	125 - 250
Gibson Desert	240	300 - 500	+ 47	0	200 - 250
Great Desert Victoria	350	200 - 700	+ 50	−3	125 - 250
Simpson	300	0 - 200	+ 48	−6	100 - 150

Desert classification

According to the nature of soils and soils:

Sandy- on loose sediments of ancient alluvial plains;
Loess- on loess deposits of piedmont plains;
Loamy- on low-carbonate cover loams of the plains;
Clay takyr- on piedmont plains and ancient river deltas;
Clayey- on low mountains composed of salt-bearing marls and clays,
Pebble and sand-pebble- on gypsum plateaus and foothill plains;
Crushed gypsum- on plateaus and young piedmont plains;
Rocky- in low mountains and small hills;
Salt marshes- in saline depressions and along sea coasts.

According to the dynamics of precipitation:

Coastal- develop where cold sea currents approach hot coasts (Namib, Atacama): there is almost no precipitation; life, respectively, too.
Central Asian type(Gobi, Betpak-Dala): the rate of precipitation is approximately constant throughout the year - and therefore there is life here all year, but it barely glimmers.
Mediterranean type(Sahara, Kara-Kum, Great Sandy Desert in Australia): there is the same amount of precipitation here as in the previous type, but they all pour out at once, in two to three weeks; here there is a brief and vigorous flourishing of life (various ephemera), which then passes into a latent state - until next year.

Flora and fauna

The species composition of desert vegetation is very unique. Frequent changes in plant groups and their complexity are often observed, which is due to the structure of the desert surface, the diversity of soils, and frequently changing moisture conditions. Along with this, in the nature of the distribution and ecology of desert vegetation of different continents there are many common features that arise in plants in similar living conditions: strong sparseness, poor species composition, sometimes traced over large areas.

For inland deserts of temperate zones, plant species of the sclerophyll type are typical, including leafless shrubs and subshrubs (saxaul, juzgun, ephedra, solyanka, wormwood, etc.). An important place in the phytocenoses of the southern subzone of deserts of this type is occupied by herbaceous plants - ephemerals and ephemeroids.

The subtropical and tropical inland deserts of Africa and Arabia are also dominated by xerophilous shrubs and perennial herbs, but succulents also appear here. The massifs of dune sands and areas covered with a salt crust are completely devoid of vegetation.

The vegetation cover of the subtropical deserts of North America and Australia is richer (in terms of the abundance of plant mass, they are closer to the deserts of Central Asia) - there are almost no areas devoid of vegetation here. The clayey depressions between the sand ridges are dominated by low-growing acacia and eucalyptus trees; The pebble-gravel desert is characterized by semi-shrub hodgepodges - quinoa, prutnyak, etc. In subtropical and tropical oceanic deserts (Western Sahara, Namib, Atacama, California, Mexico) succulent-type plants dominate.

The phytocenoses of oases, tugai, large river valleys and deltas differ significantly from the main vegetation of deserts. The valleys of the desert-temperate zone of Asia are characterized by thickets of deciduous trees - turango poplar, jida, willow, elm; for river valleys in subtropical and tropical zones - evergreens - palm, oleander.

Living conditions in deserts are very harsh: lack of water, dry air, strong insolation, winter frosts with very little or no snow cover. Therefore, mainly specialized forms live here (with adaptations both morpho-physiological and in lifestyle and behavior).

Deserts are characterized by fast-moving animals, which is associated with the search for water (watering holes are removed) and food (grass cover is sparse), as well as with protection from pursuit by predators (there are no shelters). Due to the need for shelter from enemies and harsh climatic conditions, a number of animals have highly developed adaptations for digging in the sand (brushes made of elongated elastic hair, spines and bristles on the legs, used for raking and throwing away sand; incisors, as well as sharp claws on the front paws - in rodents). They construct underground shelters (burrows), often very large, deep and complex (great gerbil), or are able to quickly burrow into loose sand (round-headed lizards, some insects). There are fast running forms (especially ungulates). Many desert reptiles (lizards and snakes) are also capable of moving very quickly.

The fauna of deserts is characterized by a protective “desert” coloring - yellow, light brown and gray tones, which makes many animals inconspicuous. Most of the desert fauna is nocturnal in summer. Some hibernate, and in some species (for example, ground squirrels) it begins at the height of the heat (summer hibernation, directly turning into winter) and is associated with burning of plants and lack of moisture.

Lack of moisture, especially drinking water, is one of the main difficulties in the life of desert inhabitants. Some of them drink regularly and a lot and, therefore, move long distances in search of water (grouse) or move closer to the water during the dry season (ungulates). Others rarely use watering holes or do not drink at all, limiting themselves to moisture obtained from food. Metabolic water, formed during the metabolic process (large reserves of accumulated fat), plays a significant role in the water balance of many representatives of the desert fauna.

The desert fauna is characterized by a relatively large number of species of mammals (mainly rodents, ungulates), reptiles (especially lizards, agamas and monitor lizards), insects (Diptera, Hymenoptera, Orthoptera) and arachnids.

Economic use of deserts

Pasture livestock farming is developed in deserts. Agriculture is possible only with the help of irrigation and is practiced mainly in the valleys of large rivers. Many deserts are rich in mineral resources (especially in Asia), and oil and gas production occurs.

In the floodplains and deltas of large rivers crossing deserts (Volga, Akhtuba, Syr Darya, Amudarya), irrigated agriculture (vegetable growing, rice growing, cotton growing, and in some places viticulture) is widely practiced.

Favorable conditions for grazing livestock (sheep farming, camel farming) are available in sandy deserts (Karakum, Kyzylkum, Aral Karakum, Saryesik-Atyrau, etc.), since due to the high level of groundwater (precipitation seeps into the soil without having time to evaporate), vegetation here richer than in adjacent clay deserts. There are a large number of wells and artesian wells for watering livestock, numerous livestock wintering grounds are organized near them, and inter-barchan depressions serve as shelter from strong winds, dust storms, and blizzards. Thus, sandy deserts are actively used for grazing livestock all year round.

Pasture farming is also practiced in clay deserts, although in general the conditions here are less favorable: groundwater is deeper, there are fewer wells, but there are temporary watercourses and drying up rivers that fill with water in the spring.

The most severe natural conditions are observed in rocky and gravelly deserts (Ustyurt Plateau, Mangyshlak Peninsula, western Turkmenistan): groundwater is practically inaccessible here, the number of wells is very small, and there is no river network. Therefore, in such regions there is practically no agriculture, and the population density is the lowest compared to other types of CIS deserts.

Ecological signs

Due to their remoteness from civilizational progress and stable climate, deserts have preserved unique ecological systems. In some countries, desert areas are included in national nature reserves. On the other hand, human activities near deserts (deforestation, damming of rivers) have led to the expansion of deserts. Desertification is one of the most formidable, global and fleeting processes of our time. In the 1990s, desertification began to threaten 3.6 million hectares of the most arid lands. Desertification can occur in different climatic conditions, but it occurs especially rapidly in hot, arid regions. In the 20th century, attempts were made to stop desertification through landscaping and the construction of water pipelines and canals. Nevertheless, desertification remains one of the most pressing environmental problems in the world.

Climate features, desert classification

This natural area occupies about 25% of the planet's land area. There are 51 deserts in total, 2 of which are icy. Almost all deserts were formed on ancient geological platforms.

General signs

The natural zone called “desert” is characterized by:

flat surface;
critical volume of precipitation(annual norm - from 50 to 200 mm);
rare and specific flora;
peculiar fauna.

Deserts are often found in the temperate zone of the Earth's Northern Hemisphere, as well as in the tropical and subtropical zones. The relief of such an area is very heterogeneous: it combines highlands, island mountains, small hills and strata plains. Basically, these lands are drainless, but sometimes a river can flow through part of the territory (for example, the Nile, Syr Darya), and there are also drying lakes, the outlines of which are constantly changing.

Important! Almost all desert areas are surrounded by or near mountains.

Classification

There are different types of deserts:

Sandy. Such deserts are characterized by dunes and often experience sandstorms. The largest is the Sahara, characterized by loose, light soil that is easily blown by the winds.
Clayey. They have a smooth clay surface. They are found in Kazakhstan, the western part of Betpak-Dala, on the Ustyurt plateau.
Rocky. The surface is represented by stones and rubble, which form placers. For example, Sonora in North America.
Salt marshes. The soil is dominated by salts, and the surface often looks like a salt crust or quagmire. Distributed on the coast of the Caspian Sea, in Central Asia.
Arctic— located in the Arctic and Antarctica. They can be snowless or snowy.

Climatic conditions

The desert climate is warm and dry. The temperature depends on the geographical location: the maximum +58°C was recorded in the Sahara on September 13, 1922. A distinctive feature of the desert area is a sharp temperature drop of 30-40°C. During the day the average temperature is +45°C, at night - +2-5°C. In winter, the deserts in Russia can be frosty with light snow.

In desert lands it has low humidity. Strong winds with a speed of 15-20 m/s or more often occur here.

Important! The driest desert is the Atacama. There has been no rainfall on its territory for more than 400 years.

Semi-desert in Patagonia. Argentina

Flora

The desert flora is very sparse, consisting mainly of sparse shrubs that can extract moisture deep into the soil. These plants are specially adapted to live in hot and dry habitats. For example, a cactus has a thick waxy outer layer to keep water from evaporating. Sagebrush and desert grasses need very little water to survive. Desert and semi-desert plants have adapted to protect themselves from animals by growing sharp needles and thorns. Their leaves are replaced by scales and spines or covered with hairs that protect the plants from excessive evaporation. Almost all sand plants have long roots. In sandy deserts, in addition to herbaceous vegetation, there is also shrub vegetation: zhuzgun, sand acacia, teresken. Shrub plants are low and poorly leafy. Saxaul also grows in deserts: white on sandy soils, and black on saline soils.

Flora of desert and semi-desert

Most desert and semi-desert plants bloom in the spring, reproducing flowers until the hot summer begins. During wet winter and spring years, semi-desert and desert plants can produce a surprising amount of spring flowers. Pine trees, junipers and sage grow in desert canyons and rocky mountains. They provide shelter from the scorching sun for many small animals.

The least known and underestimated species of desert and semi-desert plants are lichens and cryptogamous plants. Cryptogamous or secretogamous plants - spore fungi, algae, pteridophytes, bryophytes. Cryptogamous plants and lichens need very little water to survive and live in dry, hot climates. These plants are important because they help stop erosion, which is very important for all other plants and animals because it helps keep the soil fertile during high winds and hurricanes. They also add nitrogen to the soil. Nitrogen is an important nutrient for plants. Cryptogamous plants and lichens grow very slowly.

Annual ephemerals and perennial ephemeroids grow in clay deserts. In solonchaks there are halophytes or solyankas.

One of the most unusual plants that grow in this area is saxaul. It often moves from place to place under the influence of the wind.

Fauna

The fauna is also sparse - reptiles, spiders, reptiles or small steppe animals (hare, gerbil) can live here. Among the representatives of the order of mammals, the camel, antelope, wild ass, steppe sheep, and desert lynx live here.

To survive in the desert, animals have a specific sandy coloration, can run fast, dig holes and live for a long time without water, and are preferably nocturnal.

Among the birds you can find the raven, saxaul jay, and desert chicken.

Important! In sandy deserts there are sometimes oases - this is a place that is located above the accumulation of underground water. There is always dense and abundant vegetation and ponds here.

Leopard in the Sahara desert

Characteristics of the climate, flora and fauna of the semi-desert

Semi-desert is a type of landscape that is an intermediate option between desert and steppe. Most of them are located in the temperate and tropical zones.

General signs

This zone is distinguished by the fact that there is absolutely no forest on it, the flora is quite unique, as is the composition of the soil (very mineralized).

Important! Semi-deserts exist on all continents except Antarctica.

Climatic conditions

They are characterized by hot and long summers with temperatures of approximately 25°C. Evaporation here is five times higher than precipitation levels. There are few rivers and they often dry up.

In the temperate zone they run in an unbroken line across Eurasia in an east-west direction. In the subtropical zone they are often found on the slopes of plateaus, highlands and plateaus (Armenian Highlands, Karoo). In the tropics these are very large areas (Sahel zone).

Fennec foxes in the desert of Arabia and North Africa

Flora

The flora of this natural zone is uneven and sparse. It is represented by xerophytic grasses, sunflowers and wormwood, and ephemerals grow. On the American continent, the most common are cacti and other succulents; in Australia and Africa, xerophytic shrubs and low-growing trees (baobab, acacia) are most common. Here the vegetation is often used to feed livestock.

In the desert-steppe zone, both steppe and desert plants are common. The vegetation cover mainly consists of fescue, wormwood, chamomile, and feather grass. Often wormwood occupies large areas, creating a dull, monotonous picture. In some places, kochia, ebelek, teresken, and quinoa grow among the wormwood. Where groundwater comes close to the surface, thickets of shin weed are found on saline soils.

The soil, as a rule, is poorly developed; its composition is dominated by water-soluble salts. Among the soil-forming rocks, ancient alluvial and loess-like deposits, which are reworked by winds, predominate. Gray-brown soil is typical for elevated flat areas. Deserts are also characterized by salt marshes, that is, soils that contain about 1% of easily soluble salts. In addition to semi-deserts, salt marshes are also found in steppes and deserts. Groundwater, which contains salts, when reaching the soil surface is deposited in its upper layer, resulting in soil salinization.

Fauna

The fauna is quite diverse. To the greatest extent it is represented by reptiles and rodents. Mouflon, antelope, caracal, jackal, fox and other predators and ungulates also live here. Semi-deserts are home to many birds, spiders, fish and insects.

Protection of natural areas

Some desert areas are protected by law and recognized as nature reserves and national parks. The list of them is quite long. From the deserts man guards:

Etosha;
Joshua Tree (in Death Valley).

Among semi-deserts the following are subject to protection:

Ustyurt Nature Reserve;
Tiger beam.

Important! The Red Book includes such desert inhabitants as the serval, mole rat, caracal, and saiga.

Chara desert. Transbaikal region

Economic activity

The climatic features of these zones are unfavorable for economic life, but throughout history entire civilizations developed in the desert zone, for example, Egypt.

Special conditions forced us to look for a way to graze livestock, grow crops and develop industry. Taking advantage of the available vegetation, sheep are usually grazed in such areas. Bactrian camels are also bred in Russia. Farming here is possible only with additional irrigation.

The development of technological progress and the unlimited supply of natural resources have led to the fact that man has reached the deserts. Scientific research has shown that in many semi-deserts and deserts there are considerable reserves of natural resources, such as gas, precious minerals. The need for them is constantly increasing. Therefore, equipped with heavy equipment and industrial tools, we are going to destroy previously miraculously untouched territories.

The two largest deserts on planet Earth: Antarctica and the Sahara.
The height of the highest dunes reaches 180 meters.
The driest and hottest area in the world is Death Valley. But, nevertheless, more than 40 species of reptiles, animals and plants live in it.
Approximately 46,000 square miles of arable land turns to desert each year. This process is called desertification. According to the UN, the problem threatens the lives of more than 1 billion people.
When passing through the Sahara, people often see mirages. To protect travelers, a mirage map was compiled for caravan drivers.

Natural zones of deserts and semi-deserts are a huge variety of landscapes, climatic conditions, flora and fauna. Despite the harsh and cruel nature of the deserts, these regions have become home to many species of plants and animals.

Geographical features of deserts

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

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

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

Mountains and deserts are areas of formation of liquid runoff, which comes to the plain in the form of transit rivers and small, “blind” mouths. Underground and sub-channel flow, which feeds their groundwater, is also of great importance for deserts. Mountains are areas from which destruction products are removed, for which deserts serve as a place of accumulation. Rivers supply a lot of loose material to the plain. Here it is sorted, ground into even smaller particles and lines the surface of deserts. As a result of centuries-old work of rivers, the plains are covered with a multi-meter layer of alluvial sediments. The rivers of the sewage areas carry a huge mass of blown and debris material into the World Ocean. Therefore, the deserts of drainage areas are characterized by an insignificant distribution of ancient alluvial and lacustrine sediments (Sahara, etc.). On the contrary, drainage-free regions (Turanian Lowland, Iranian Plateau, etc.) are distinguished by thick thicknesses of sediments.

Surface deposits of deserts are unique. They owe this to the geological structure of the territory and natural processes. According to M.P. Petrov (1973), surface deposits of deserts are of the same type everywhere. This is “rocky and gravelly eluvium on Tertiary and Cretaceous conglomerates, sandstones and marls that make up the structural plains; pebbly, sandy or loamy-clayey proluvial sediments of piedmont plains; sandy strata of ancient deltas and lake depressions and, finally, aeolian sands” (Petrov, 1973). Deserts are characterized by some similar natural processes that are prerequisites for morphogenesis: erosion, water accumulation, blowing and aeolian accumulation of sand masses. It should be noted that similarities between deserts are found in a large number of characteristics. The differences are less noticeable and are limited to a few examples, quite sharply.

The differences are most associated with the geographical location 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 moderated 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 that characterize continental deserts. However, for oceanic deserts, the ocean currents washing the continents - warm and cold - are of great importance. 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 air masses, and they arrive on the mainland dry, increasing the aridity of the coasts. Oceanic deserts are located off the western coasts 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 evaporation, and contrasts in summer and winter temperatures. The differences in the nature of deserts are also influenced by their altitude.

Mountain deserts, like those located in intermountain depressions, are usually characterized by increased climate aridity. The variety of similarities and differences between deserts is primarily due to their location at 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 Kyzylkum in Central Asia. Equally, deserts formed in the mountains may have a number of natural anomalies among themselves, but there are even more differences with the deserts of the plains.

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

Patterns of desert formation

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

An area of calms and weak variable winds forms here. Warm air rising 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 antitrade winds bend to the right, in the southern hemisphere - to the left.

Approximately above latitudes of 30-40° C (near the subtropics), their deviation angle is about 90° C, and they begin to move along 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 there is high atmospheric pressure all year round, and at the equator, on the contrary, it is low, a constant movement of air masses (trade winds) occurs at the surface of the earth from the subtropics to the equator. Under the influence of the same deflecting influence of the Earth, trade winds move from northeast to southwest in the northern hemisphere, and from southeast to northwest in the southern hemisphere.

Trade winds cover only the lower layer of the troposphere - 1.5-2.5 km. The trade winds that dominate in equatorial-tropical latitudes determine the stable stratification of the atmosphere and prevent vertical movements and the associated development of clouds and precipitation. Therefore, cloudiness in these belts is very insignificant, and the influx of solar radiation is the greatest. As a result, the air here is extremely dry (relative humidity in the summer months averages about 30%) and extremely high summer temperatures. The average air temperature on continents in the tropical zone in summer exceeds 30-35° C; here the highest air temperature on the globe occurs - plus 58 ° C. The average annual amplitude of air temperature is about 20 ° C, and the daily temperature can reach 50 ° C; the soil surface sometimes exceeds 80 ° C.

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

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

Thus, the nature of the general circulation of the atmosphere is determined by planetary features, and local geographical conditions create a unique climatic situation that forms a desert zone to the north and south of the equator, between 15 and 45 ° C latitude. Added to this is the influence of cold currents of tropical latitudes (Peruvian, Bengal, Western Australian, Canary and Californian). By creating a temperature inversion, cool, moisture-laden maritime air masses and easterly persistent wind pressure highs lead to the formation of coastal cool and foggy deserts with even less rainfall.

If land covered the entire surface of the planet and there were no oceans or high mountain rises, the desert belt would be continuous and its boundaries would exactly coincide with a certain parallel. But since land occupies less than 1/3 of the area of the globe, the distribution of deserts and their size depend on the configuration, size and structure of the surface of the continents. For example, Asian deserts spread far to the north - up to 48° N latitude. In the southern hemisphere, due to the vast water expanses of the oceans, the total area of the continents' deserts is very limited, and their distribution is more localized. Thus, the emergence, development and geographical distribution of deserts on the globe are determined by the following factors: high values of radiation and radiation, low amounts of precipitation or their complete absence. 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, and the continental or oceanic position of the area.

Aridity of the territory

In terms of the degree of aridity - aridity, many territories are not the same. This gave grounds to divide arid lands into extra-arid, arid and semi-arid, or extremely arid, arid and semi-arid. At the same time, areas where the probability of constant droughts is 75-100% are considered extra-arid, arid – 50-75% and semi-arid – 20-40%. The latter include savannas, pampas, pashtos, and prairies, where organic life occurs in a natural environment in which, except for some 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, the arid zone does not include all areas of land where droughts occur, but only those where organic life is largely under their influence for a long time.

According to M.P. 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 predominates and their concentration on the surface, there is little organic matter in the soil.

The desert is characterized by high summer temperatures, low annual precipitation - usually from 100 to 200 mm, lack of surface runoff, often the predominance of sandy substrate and the large role of aeolian processes, groundwater salinity and migration of water-soluble salts in the soil, uneven amount of precipitation, which determines the structure , yield and feeding capacity of desert plants. One of the features of the distribution of deserts is the island, local nature of their geographical location. On no continent do desert lands form a continuous strip, 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 completely obey the law of zonation.

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

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

According to Meigl, the total area of arid territories is 48,810 thousand square meters. km, that is, they occupy 33.6% of the earth's land, of which extra-arid accounts for 4%, arid - 15 and semi-arid - 14.6%. The area of typical deserts, excluding semi-deserts, is about 28 million square meters. km, that is, about 19% of the earth's land area.

According to Shants (1958), the area of arid territories, classified according to the nature of 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) falls on about 40 million square meters. km, and the share of semi-arid lands is 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 world's arid regions. Four bioclimatic zones are highlighted on the map.

Extra-arid zone. Precipitation less than 100 mm; deprived of vegetation cover, excluding ephemeral plants and shrubs along the beds of watercourses. Agriculture and animal husbandry (except in oases) is impossible. This zone is a 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. Nomadic cattle breeding zone.

Semi-arid zone. Precipitation 200-400 mm. Shrub communities with intermittent herbaceous cover. Area of cultivation of rain-fed agricultural crops (“dry” farming) and livestock raising.

Zone of insufficient moisture (subhumid). Precipitation 400-800 mm. Includes some tropical savannas, Mediterranean communities such as maquis and chaparral, and black soil steppes. Zone of traditional rain-fed farming. To conduct highly productive agriculture, irrigation is necessary.

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

Desert classification

In arid territories, despite their apparent 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 topography is the same, the soils are different; if the soil is 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 zoning is a complex matter. There is not yet a unified and satisfactory from all points of view classification of desert territories, compiled taking into account all their geographical diversity.

There are many works in Soviet and foreign literature devoted to the classification of desert types. Unfortunately, in almost all of them there is no uniform approach to solving this issue. Some of them base their classification on climatic indicators, others on soil, others on floristic composition, others on lithoedaphic conditions (i.e. the nature of the soil and conditions for vegetation growing on them), etc. Rarely do any researchers base their classification on from a complex of characteristics of desert nature. Meanwhile, based on a generalization of the components of nature, it is possible to correctly identify the ecological features of the region and quite reasonably evaluate its specific natural conditions and natural resources from an economic point of view.

M.P. Petrov in his book “Deserts of the Globe” (1973) proposes ten lithoedaphic types for the deserts of the world on a multi-stage classification:

* sandy on loose sediments of ancient alluvial plains;

* sand-pebble and pebble on gypsum tertiary and lilac structural plateaus and piedmont plains;

* crushed stones, gypsum on tertiary plateaus;

* gravelly on foothill plains;

* rocky in low mountains and small hills;

* loamy on low-carbonate cover loams;

* loess on piedmont plains;

* clayey ones in low mountains, composed of salt-bearing marls and clays of various ages;

* solonchaks in saline depressions and along sea coasts.

Various classifications of 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 climate indicators. There are relatively few classifications for other elements of the natural environment (relief, vegetation, wildlife, soils, etc.).

Desertification and nature conservation

In recent years, alarming signals have been heard from different parts of the globe about the increasing advance of desert into territories inhabited by humans. For example, according to the UN, in North America alone, the desert annually robs people of about 100 thousand hectares of usable land. The most likely causes of this rather dangerous phenomenon are considered to be unfavorable weather conditions, destruction of vegetation, irrational environmental management, mechanization of agriculture, and 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 just 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, construction of roads and other engineering structures. The rapid growth of population and technology also leads to intensifying desertification processes in some areas of the world.

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

extermination of vegetation cover and destruction of soil cover during industrial and irrigation construction;

degradation of vegetation cover due to overgrazing;

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

deflation and soil erosion due to intensive rainfed agriculture;

secondary salinization and waterlogging of soils under irrigated farming conditions;

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

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 macro- and microclimate;

hydrogeological – precipitation becomes irregular, groundwater recharge becomes episodic;

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

soil – drying out of soils and their salinization;

phytogenic – degradation of soil cover;

zoogenic - reduction 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, focusing on the formation of conditions for rational environmental management;

creation of protective forest strips along the edges of oases, field boundaries and along canals;

creation of forests and green “umbrellas” from local species - psamophytes in the depths of deserts to protect livestock from strong winds, scorching rays of the sun and strengthen the food supply;

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

consolidation and afforestation of moving sands in order to protect irrigated lands, canals, settlements, railways and highways, oil and gas pipelines, and industrial enterprises from sand drifts and blowing out.

The main lever for successfully solving 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 urgently the tasks of monitoring and managing natural processes are solved.

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

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

firstly, because its flora and fauna are unique. Preserving the desert intact means leaving its indigenous inhabitants outside of economic progress, and the national economy without 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 late autumn, when cold rains and wind fall almost everywhere in our country, and there are warm sunny days in the desert. The desert is attractive not only for geologists and archaeologists, but also for tourists. It is also healing, its dry air, long warm period, medicinal mud and hot mineral springs make it possible to treat kidney diseases, rheumatism, nervous and many other diseases.

The desert and its inhabitants

Deserts belong to the arid zone. In summer the desert is extremely hot and there is very little rainfall. Because of this, there is little moisture there. Air temperature in the shade is 40-45 0 C, and the sand heats up to 70 0 WITH.

Usually the desert is covered with sand. Its surface is made up of dunes - sand waves that move slowly

Among the hot dunes, there are very rarely “paradises”, shady palm trees and some clean cool water - “Oases”.

Desert animals include mammals, reptiles and birds. All of them are adapted to live in its climate.

Camel 1. Thick coat (protects against overheating, maintaining body temperature). 2 Fat reserves in the humps (helps to go without water for a long time)

3. Rough digestive system (camel eats thorns).

5. 4. Narrow foot (helps you move easily on the sand and not get burned). 5.Large nostrils (help cool the air). 6.Filters in the nose (protect from sand).

6 . Jerboa .

Has a long tail. To escape the heat, he leads a twilight lifestyle

7. Dancing lizard Membranous lizard.

This small lizard often dances to lower its temperature. During intense heat, hides in the sand

8. African pygmy viper

What is a desert without snakes? This small viper (25 cm) hides from the sun in the sand. Only the eyes remain visible. She can wait like this for many days until her victim approaches her.

9. Birds also live in deserts: desert sparrows, larks, nightjars, and predators.

10. Lamb vulture. This bird has learned to break skeletons. She climbs to a height and throws bones onto flat stones so that they break. And then it eats the bone marrow, which contains a lot of water.

11. Plants live in any ecosystem. Desert inhabitants: saxaul, camel thorn, seline. They have adapted to life in the desert

They acquired long roots, turned the leaves into thorns or covered them with wax, and stored water in thick stems. This is such an amazing living world in the desert. Over millions of years, all its inhabitants have learned to survive in its climate and obtain water for themselves.