The main characteristic of deserts. Desert Formation The main factor in the formation of a desert is

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 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 the land and water surface occurs, ascending air movements dominate.

An area of calm and weak variable winds is formed here. Warm air that has risen above the equator, cooling somewhat, loses a large amount of moisture, which falls out 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 are heated even more, and move away from the critical saturation point. Due to the fact that in the tropics the atmospheric pressure is high all year round, 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 northeast to the southwest, in the southern - from the southeast to the northwest.

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 here is extremely dry (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 ° 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 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, on the continents, sedentary depressions of thermal origin develop, causing severe aridity. Here the average temperature of the summer months is 30 ° C and more, the maximum can reach 50 ° C. In the 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 north and south of the equator, between 15 and 45 ° C latitude. Added to this is the influence of the cold currents of tropical latitudes (Peruvian, Bengal, Western Australian, Canary and California). By creating a temperature inversion, the cool, moisture-saturated sea air masses of 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 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 boundaries 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 north latitude. In the southern hemisphere, due to the vast expanses of the oceans, the total area of the continental 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, little or no precipitation. The latter, in turn, is determined by the latitude of the terrain, 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 terrain.

Once upon a time, herds of elephants roamed in tropical forests and leopards hunted. A dense network of rivers and lakes covered the steppes, and caravans laden with gold, slaves and ostrich feathers crossed the sands. And all in the same territory! Sahara Desert occupied a third of Africa, almost all of its north. In terms of area, the Sahara is only slightly inferior to the United States; a dozen countries are now freely located on it. But the population here is half as much as in St. Petersburg.

On maps, the Sahara Desert is depicted as a huge yellow spot, and, perhaps, that is why most people imagine it as a boring plain with sands without end and edge. In fact, the Saharan landscapes are surprisingly varied. There are mountains, massifs of bushes, rubble and gravel, steppes and burnt clay plains. There are oases where life is in full swing, and around are dry river valleys, salt marshes and lakes, scattered huge stones and rocky hills. And, of course, sands, from which the wind forms bizarre reliefs - labyrinths, wavy fields and dunes as high as a 60-storey (!) Skyscraper. Here you can hear the "singing sands": while moving, dry hot grains of sand create sounds reminiscent of squeak, rattling, rattling, grunt of a dog, a vibrating rumble that can be heard 10 km away.

"Sugar pump"

The climate of the Sahara is controlled by an invisible conductor - the wind. Above the equator, the air heats up strongly, rises and goes towards the poles. On the way, it cools down, descends in the north of the Sahara and returns to the equator, replacing heated, rising portions of air. This scheme is called the "Saharan pump", and the air currents that constantly rush from the tropics to the equator are called trade winds.

Flying over the north of the continent, the dried up trade wind carries away the remnants of moisture from the surface of water bodies and land. Already at a speed of 10 m / s, it pulls it out even from the soil, and the roots of the plants are deprived of nutrition. And when the wind gets stronger, it carries away the fertile soil itself. In addition to the trade winds, local winds - khamsin, ghibli, sirocco - walk here. They carry sand and heat at a hurricane speed (up to 40 m / s) to the north, to Spain and Italy. In the calm over the Sahara, "dry fogs" - fine dust - hang.

Sahara climate.

In the Sahara, the summer air temperature is about + 50 ° C - a common thing. On stones and sand, you can fry eggs without lighting a fire. Daytime heat is replaced by night cold (up to + 15 ° С). Stones burst from such drops!

In the hot air, mirages are frequent - imaginary reflections of what lies beyond the horizon. Since stable caravan routes have developed in the Sahara, mirages are often seen in the same places. Even maps have been compiled, where the places of appearance of 1500 mirages are indicated, and conventional icons show where it can be seen: an oasis, the ruins of a fortress, a well, mountains, etc.

Receiving with an excess of solar heat, the Sahara languishes from a lack of moisture. Many regions wait for rain for years. Sometimes its drops do not reach the ground, drying out along the way.

Snow happens in the Sahara, but it is always a worldwide sensation. It happened in 2016, and before that - in 1979!

Through the sands, rainwater easily seeps into the ground, and over millions of years, real freshwater lakes have formed above the water-resistant layers. In some places, underground water is squeezed out closer to the surface. In such places, oases have long been formed - with drinking springs, palm trees, etc.

The Sahara has the driest air in the world. Clouds in the sky here are rare guests. For this reason, the heat is even greater, and Eastern Sahara is one of the most illuminated places in the world. Here the Sun shines on average 11 hours daily throughout the year.

How did the Sahara Desert come about?

Millions of years ago, the land from Spain to Mongolia was flooded with the Tétis ocean. Whales frolicked in it, dinosaurs roamed along the shores. Then, when mountain systems began to rise from the depths, the ocean receded. Its remains formed the Mediterranean, Black, Azov seas, the Caspian and the Aral. And the current Sahara is the former bottom of the Tethys. It is not surprising that skeletons of extinct animals have long been found in the desert from Morocco to Egypt. For example, 45-ton paralititans, egyptosaurs and other monsters.

Approximately 9000 years ago, the local coastal forests were replaced by the African steppes - savannas: deep rivers and lakes, a carpet of dense grasses, woodlands. Herds of giraffes, elephants, antelopes, buffaloes, rhinos, flocks of ostriches and lions roam. People quickly mastered the fertile land - they hunted, fished, kept livestock, settled along the rivers. On the rocks, now lost in the sands, whole galleries of graffiti have been discovered - images and inscriptions that confirm this. Why is everything wrong now? There is no unity among scientists here. Some people explain everything by the arrival of aliens. But there are also more realistic assumptions.

Hypothesis 1. The climate has become "not the same". It was once hotter and higher sea levels. The air above the equator was warming up more, which means it retained heat longer and cooled further than it is now, over the Mediterranean Sea. Having descended, the trade winds were saturated with its moisture, rushed to Africa and brought rains and fogs. They also created the prosperity of the Sahara.

Hypothesis 2. The earth swung in the wrong direction. During the movement of the Earth around the Sun, the inclination of its axis is not constant. As a result, the planet receives a different amount of solar heat and light, and the seasons alternate. Over the millennia, this tilt and the orbit itself have changed markedly. Therefore, global climate changes are coming. It is possible that a grand drought in northern Africa is just such a case.

Hypothesis 3."Global flood". Fossilized bones of whales, sharks, rays, turtles, shells of molluscs are found shallow in the Sahara. And the ocean has existed for millions of years, over the bones must have been kilometer-long layers of marine sediments. Where are they? It is possible that they were carried away by a real flood, the traditions of which are kept in the Bible and folklore. Streams of ocean water washed away the topsoil and brought back animal remains. The primary cause of the flood could be the fall of a huge meteorite, which caused a tsunami and turned mountains into dust and sand.

Hypothesis 4. With your own hands. Perhaps the formation of the Sahara is the first ecological catastrophe in the history of mankind. The nomadic way of life does not focus on the preservation and renewal of the natural environment. A nomad - he is here today, there tomorrow. Together with their herds, which eat and trample the greens. Deprived of a network of roots, the soil is easily blown out and washed off. The bare soil and the air above it warms up more, a zone of increased pressure arises, and the winds blow not here, but from here, not allowing clouds to come close.

Most likely, the Sahara arose under the influence of several natural factors, which aggravated the unreasonableness of man. And even now ... Laying of routes, exploration and production of oil and gas, motor rallies - all this destroys the fragile ecosystems of the desert.

Sahara Desert. Plants. The land of dates and féncs.

Our ancestors invented the word "desert" to denote the property of the vast landscape that amazed them - its "emptiness", that is, uninhabitedness. It is, indeed, almost impossible to live here permanently. But there are extremists both among plants and among animals.

For plants, the Sahara could become a paradise - a lot of light, heat, mineral salts. But without water, you understand ... Nevertheless, about 3000 species of plants have been found in the desert, and one in four cannot be found outside of it. Many species live only where there is water, in oases - with date palms, cypresses, vegetables, citrus fruits, pomegranates, and cereals. And in those that grow outside the oases, botanists have identified a lot of devices that allow you to overcome the moisture deficit:

a dense and extensive network of surface roots - allows you to effectively absorb moisture from rare rains, morning fogs and dew before everything dries;
deep (up to 30 m!) roots - they reach underground waters, penetrate through cracks into the thickness of rocks;
leaves are narrow, small, covered with hairs (wormwood), wax, turned into thorns (cacti) or scales (saxauls) - to evaporate less moisture;
thickening of stems and leaves that turn into fleshy pantry water (aloe);
storage of moisture and nutrient reserves underground - in rhizomes, bulbs, tubers;
the roots are covered with thick bark or a case of hardened sap and sand and do not dry out when the soil is blown off them by the wind;
the stem grows very quickly and / or the roots grow in any place - protection from falling asleep with sand;
a very short period of life - sometimes in a few spring days the plants have time to bloom, form seeds, and even they lie and wait (sometimes for years) until "life gets better";
the development of salt marshes - here from the depths moisture and salts are constantly pulled up through the capillaries of the soil;
withstand almost complete drying, but recover very quickly after rains.

The Sahara Desert and Wildlife.

Desert animals also have to deal with the problem of water scarcity. Some hide during the day, but are active during cool hours, from dusk to dawn. Thicker body covers protect against moisture loss from scorpions and beetles. There are many species that may not drink for a long time (or even never) - they have enough scarce moisture, which is always in food.

Reptiles feel good in the Sahara - cobras, vipers, chameleons and others. Densely covered with scales, they are protected from moisture loss. The skink lizard can literally "swim" in the sand: diving into it in an instant, it paddles with its feet and makes its way through the sand at a speed of up to 90 cm per minute.

Many people prefer to dwell not among clay and rubble, but in the sands, where it is easier to dig, make underground burrows and wait out the heat there (jerboas and other small rodents). The Sahara's business card could be a funny fének fox - smaller than our usual cat, but with huge ears. The ears allow to give off excess heat faster (protection against overheating). And, of course, together with big eyes, they help hunt mice and beetles at night. The Sahara is also home to the smallest animal of the cat family - the sand cat. There are also antelopes - gazelles, and lizards similar to small crocodiles.

Believe it or not, but ... toads also live here. And not off the banks of the Nile, but in Central Sahara. They doze, burrowing deeper into the clay soil, eating nothing and barely breathing, But as soon as a good rain passes, every large puddle teems with toads. They lay eggs, there is an accelerated development of tadpoles, and when the puddle dries up, a new generation of toads is already settling in the dungeon. Desert snails can remain in underground hibernation for more than one year.

The Sahara is home to some of the most heat-resistant animals - the satin runner ants. They are active at air temperatures up to + 70 ° С. Their long legs allow them to keep their bodies high above the hot ground. Their bodies are covered from above with silvery hairs that reflect sunlight. And the hairs of the bottom, like radiator fins, remove excess heat from the body. Runners get out of their burrows to the surface when their enemies - lizards are hiding from the heat. Insects scurry, collecting food for 10 minutes, and then go underground too - it gets hot for them too.

And for man, the most important desert animals have been camels for centuries. True, there are no wild ones in the Sahara for a long time, but caravans of domesticated camels slowly cross it constantly.

The Sahara Desert is turning ... turning ...

In the 19th and 20th centuries, Europe was hatching plans to change the Saharan climate, to restore the lost prosperity of these lands. For example, more than once it was proposed to create a "Sahara Sea": to lay a canal that would connect the Mediterranean Sea with the relief depressions in the north of the desert. They say that a man-made reservoir will increase the humidity of the air, and the trade winds will carry this moisture, pouring rain over the desert. The project "did not go" - calculations showed that the lowlands are small, most of the desert lies above sea level, so it will not be possible to create a stable reservoir.

In 2008, the Sahara Forest project was born. British engineers suggested not just planting greenery in the desert, but placing powerful solar power plants and a network of seawater greenhouses between the forest plantations. According to the plan, at the stations, circular mirrors will collect sunlight, heat water with it in a boiler, the steam of which will turn the turbines. They will provide energy for desalination plants, fresh water will go to greenhouses. And the population will receive water for drinking and irrigation, electricity and agricultural products. The project has attracted interest in the Middle East, in the Arabian Emirates, but the political situation in North Africa does not yet give hope for the transformation of the Sahara.

The same can be said about the "Great Man-Made River" project, which Libya undertook to implement: the supply of underground fresh water through a network of pipes that covers almost the entire country. Water came to cities and villages, in the south, in the desert, date palm groves, gardens and fields turned green, but all work was interrupted by the civil war (2011–2014).

Meanwhile, the Sahara continued its offensive, advancing inexorably towards the equator. Back in 1974, the Green Wall program was launched in Algeria. Here they began to plant strips of trees along the roads and oases. Eucalyptus and pine trees formed a 1500 km long belt. He kept the soil from weathering, reduced the speed of dry winds. The expansion of the Sahara in this area has slowed down.

Assessing this success, the African Union took on the Great Green Wall project in 2010. In fact, it is an extended continuation of the Algerian program. Across the entire continent, from Somalia to Senegal, a continuous green ribbon, 15 km wide and 7775 km long, began to be planted. Of course, huge costs. Of course, there is no guarantee that the planted will take root, that local residents will not cut trees for firewood, etc. But you have to do something!

Meanwhile, satellite imagery (2002) showed that the Sahara Desert began to recede in the west. Thick grass returns to pastures, acacias grow, ostriches and antelopes have appeared. Environmentalists do not exclude that this is the result - oddly enough - of global warming. The warmer the air, the more water vapor it can hold. As a result, the winds bring more abundant and more frequent rains. Whether the trend will continue is unknown. Sahara Desert after all, it is also famous for being able to present surprises.

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SPECIES AND ORIGINDESERT LAND

Introduction

Chapter 1. General information about the desert

1.1 Patterns of formation and distribution of deserts

1.2 Geographic features of the desert

1.3 Desert relief

1.4 Desert classification

1.5 Desert Biota

Chapter 2. Characteristics of the largest deserts in the world

2.2 Deserts of Central Asia and Kazakhstan

2.3 Deserts of Central Asia

2.4 Deserts of the Indian subcontinent

2.5 Deserts of the Arabian Peninsula

2.6 Desert of North Africa

2.7 Deserts of South Africa

2.8 Deserts of North America

2.9 Deserts of South America

2.10 Deserts of Australia

Chapter 3. Desert and man

3.1 Ecological-geographical and socio-economic aspects of the problem "desert and man

3.2 Desert development

3.3 Desertification and nature conservation

Conclusion

Literature

Introduction

The problem of studying and developing the deserts of the world has recently attracted special attention of geographers of all countries. The activities of the commission on the arid zone contributed a lot to this. Since 1951, with the assistance of the International Geographical Union, she has held a number of symposia devoted to the most important problems of the study and development of the arid regions of the world, they were held in Ankara (1952) Karachi (1957) Madrid and Canberra (1959) and other cities.

The proceedings of the UNESCO Arid Zone Commission and symposia have been published in 30 issues of the Arid Zone Research series, containing valuable materials on the study and development of the world's deserts.

International conferences were convened at the initiative of individual countries: the International Conference on Arid Areas in the Developing World (Tusan, Arizona, June 1969), the International Conference on Arid Areas in Mexico in 1970.

In 2000, the United Arab Emirates hosted a major international conference on the problem of combating the advance of deserts, in which representatives of government public organizations from 70 countries of the world took part. 125 reports were heard and final recommendation documents were adopted. The reports indicated that the threat of drought and desertification of fertile lands really hung over 110 countries of the world. Many of them are experiencing considerable difficulties in the fight against the onset of the sands and rely on international support, without which the situation could lead to catastrophic consequences. The United Nations Environment Program (UNEP) is urgently developing global and regional projects to help developing countries and prevent environmental disasters. Such conferences are held annually, and mankind is approaching the achievement of the goal of rational, mutually beneficial use of deserts with the environment.

The task of this course robot is to give a comparative overview of the natural features of the deserts of the world, the results of the development of their natural resources, and also to discuss issues related to further plans for the study of arid territories.

The first chapter gives a general description of all types of deserts. One can notice the similarity of their geostructures, geomorphological processes and climatic features, as well as note significant differences in their flora and fauna.

The second chapter evaluates the specific features of the natural conditions of deserts, mainly sandy. It describes the nature, genesis of aeolian relief and processes of sand movement, gives a characteristic of the habitat in sandy deserts, and environmental factors that determine organic life: the temperature and water regime of the sands, the geochemical features of arid regions.

The third chapter provides an overall assessment of the natural resources of deserts and the ways in which they are used. The problems of geographical study of the world's deserts are also highlighted. In this work, 16 sources of literature were used.

desert sandy geostructure natural

Chapter 1.General information about the desert

1.1 Regularities of the formation and distribution of deserts

Desert is a type of landscape characterized by a flat surface, sparse or lack of flora and specific fauna.

The process of formation and development of deserts is based, first of all, on 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 the 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. Warm air that has risen above the equator, cooling somewhat, loses a large amount of moisture, which falls out 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 30-40C (near the subtropics), the angle of their deflection is about 90C, and they begin to move along the parallels. At these latitudes, air masses descend to the heated surface, where they are heated 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. Petrov MP .. Under the influence of the same deflecting influence of the Earth in the northern hemisphere the trade winds move from northeast to southwest, in the south - from southeast to northwest. 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 here is extremely dry (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 30-35C; here is the highest air temperature on the globe - plus 58C. The average annual amplitude of air temperature is about 20C, and the daily temperature can reach 50C, the soil surface sometimes exceeds 80C. Precipitation falls very rarely, in the form of showers. In subtropical latitudes (between 30 and 45C northern and southern latitudes), the amount of total radiation decreases, and cyclonic activity contributes to moisture and precipitation, mainly confined to the cold season. However, on the continents, sedentary depressions of thermal origin develop, causing severe aridity. Here, the average temperature of summer months is 30C and more, while the maximum can reach 50C. 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 40C 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 north and south of the equator, between 15 and 45C latitude. Added to this is the influence of the cold currents of tropical latitudes (Peruvian, Bengal, Western Australian, Canary and California). By creating a temperature inversion, the cool, moisture-saturated sea air masses of the eastern constant baric winds lead to the formation of coastal cool and foggy deserts with even less precipitation in the form of rain. Babaev A.G.

If 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 boundaries 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 48C N. In the southern hemisphere, due to the vast expanses of the oceans, the total area of the continental 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, little or no precipitation. The latter, in turn, is determined by the latitude of the terrain, 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 terrain.

According to M.P. Petrov, deserts include areas with an extremely arid climate. Precipitation falls less than 250 mm per year, evaporation exceeds precipitation many times, agriculture without artificial irrigation is impossible, 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 completely obey the law of zoning [Fig. 1.].

Rice. 1. Deserts of the world, M.P. Petrov

In the northern hemisphere, the desert territories of the African continent lie between 15C and 30C N, where the largest desert in the world - the Sahara - is located. In the southern hemisphere, they are located between 6 and 33N S, covering the Kalahari, Namib and Karoo deserts, as well as the desert territories of Somalia and Ethiopia. In North America, the deserts are confined to the southwestern part of the continent between 22 and 24C N, where the Sonoran, Mojave, Hila and other deserts are located. Significant areas of the Great Basin and the Chihuahua desert are by nature quite close to the conditions of the arid steppe. In South America, deserts, located between 5 and 30C S, form an elongated strip (more than 3 thousand km) along the western, Pacific coast of the mainland. Here, from north to south, the Sechura, Pampa del Tamarugal, Atacama deserts stretch, and beyond the Patagonian mountain ranges. The deserts of Asia are located between 15 and 48-50 NN 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 huge area between 20 and 34C S. and are represented by the Great Victoria, Simpson, Gibson and Great Sandy deserts.

According to P. Meigs, the total area of arid territories is 48810 thousand square meters. km [table 1], 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%. According to the table. 1, the area of typical deserts, with the exception of semi-deserts, is about 28 million square meters. km, that is, about 19% of the earth's land area.

Table 1. Areas of arid territories by continent, million sq. Km. I, P. Meigs

The ratio of arid areas to the area of continents is clearly shown in Fig. 2.

Fig. 2. Arid regions of the continents, P. Meigs

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 sharply defined, 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. The zone of cultivation of rainfed agricultural crops (“dry” farming) and animal husbandry.

According to the above data on the amount of precipitation in arid territories, we conclude. Moisture is a decisive factor that determines the biological productivity of arid lands and the living conditions of the population.

1.2 Geographic features of deserts

Most of the world's deserts are formed on geological platforms and occupy the most ancient land areas. Deserts in Asia, Africa and Australia are usually located at an altitude 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 definite geographical 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. Most deserts are surrounded by mountains or, more often, bordered by mountains. In some places, deserts are located adjacent to young high mountain ranges, 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. Fedorovich B.A.

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, which 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. As a result of centuries-old work of 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 material into the oceans. According to M.P. Petrov, the surface deposits of deserts are of the same type everywhere. 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 deserts are found in a large number of features. Differences are less common and limited to few examples. The differences are most associated with 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 that characterize continental deserts. However, for oceanic deserts, warm and cold ocean currents washing the continents 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 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.

In the temperate zone of Asia and North America, there are continental deserts. They lie inside the continents (the 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 occur 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). 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 the summer, which prevents active microbiological activity (in the winter, rather low temperatures slow down these processes).

Arctic desert(ice desert) - a natural (landscape) zone - a part of the Arctic geographic belt, confined to many islands in the Arctic Ocean basin and individual sections of the mainland coast. There are numerous glaciers (Greenland, Spitsbergen, Novaya Zemlya, the Canadian Arctic Archipelago, islands near Antarctica, and others). It has low air temperatures in winter (up to? 50 ° C), on average? 30? C in February and +1? C in July. It is formed not only due to the low temperatures of high latitudes, but also due to the reflection of heat (albedo) in the daytime from snow and ice. The annual amount of precipitation is up to 400 mm. The widespread distribution of permafrost. The spaces are covered with rubble and fragments of stones with crustose lichens. Soils are primitive, shallow (1 - 5 cm), low-humus, with spotty (island) distribution mainly only under vegetation. The flora and fauna are not rich. Small isolated areas with moss-lichen and herbaceous vegetation look like a kind of oases among polar snows and glaciers. In the conditions of the Arctic desert, there are some types of flowering plants: polar poppy, foxtail, buttercup, saxifrage, etc. Among animals, the lemming, arctic fox and polar bear are widespread, and in Greenland - the musk ox. Bird colonies are numerous. For the protection and study of the Arctic desert, a number of national parks and reserves have been created, including the Greenland National Park, Wrangel Island, etc. Ivanov N.N.

1.3. Desert relief

Features of the relief of deserts, according to N.P. Neklyukova, are determined by its formation in a climate characterized by a very small (no more than 200 - 250 mm) amount of precipitation with a huge evaporation rate and large daily amplitudes of air temperature fluctuations (30 - 35 °). Surface runoff is either absent at all, or occurs after short-term heavy showers that fall every few years. Temporary streams create channels that are devoid of water most of the time. On impervious rocks, streams of rainfall, being overloaded with detrital material, turn into mud-stone streams - mudflows. Large valleys have only "transit" rivers starting in the mountains or on neighboring plains with a humid climate. Erosional dissection of the surface is very weak. Streams flowing over the surface of the desert do not reach the sea, but end in lakes or are lost in the sands. Extensive drainless basins are characteristic. If the groundwater is shallow in the basin, springs come to the surface and oases appear.

Climatic conditions contribute to vigorous, physical weathering (mainly temperature), which plays a very important role in the formation of the relief of deserts in general, and especially of the relief of stony deserts. Intense weathering is accompanied by the activity of the wind blowing out loose products of destruction of rocks (deflation) and thus creating conditions for their further destruction. The air flow, lifting from the surface and moving dusty particles, sand, and sometimes small fragments of rocks, with their help grinds and grinds obstacles encountered on the way (corrosion process). Corrosion is most pronounced in the surface layer with a height of 1.5 - 2 m, i.e. where the number of particles carried is greatest. Therefore, various mushroom-shaped rocks often appear. The ability of the wind to carry particles depends on its speed and on the size of the particles. At a wind speed of up to 6.5 m / s, it is able to carry fingers and grains of sand up to 1 mm in diameter, at a speed of 20 m / s, the diameter of the carried particles increases to 4 - 5 mm, hurricane force winds raise small pebbles. Of all the particles carried by the wind, up to 90% rises to a height of no more than 11 cm above the surface.

The relief-forming activity of the wind consists of interconnected processes of destruction of irregularities, the transfer of loose sediments and the creation of new, accumulative forms of relief.

Wind activity is manifested to one degree or another everywhere, but it leads to the formation of a special aeolian relief only with a combination of intense weathering, a dry climate, the presence of loose sediments not fixed by vegetation, and constant or frequent winds of significant force. Deserts meet these conditions first of all.

Morphological types of deserts... Differences in the morphology of deserts depend on irregularities created by internal forces, on the lithological composition of surface sediments and on the effect of wind on this surface.

Stony, sandy and clayey deserts are distinguished.

Stony deserts developed mainly in mountainous desert areas. The surface of the flat stony deserts is covered with rubble - products of the destruction of uplands. Near the mountains, the rubble covering the surface of the desert can be brought in by water currents. The protrusions of hard rocks, individual rocks, cliffs under the influence of the wind and with the participation of weathering form bizarre shapes: cornices, columns, pillars, mushrooms, etc. Forms such as blowing pots and stone grates are not uncommon. The influence of the structure in the relief is very clear in the stony steps. Rocky deserts are common in North Africa (the Arabs call them "hamadas"), in Asia. Fedorovich B.A.

Sandy deserts- the most common type of flat desert. The sands are of various origins. These can be ancient alluvial deposits (for example, the sands of the Turkmen Karakum, deposited by the Amu Darya) and products of destruction of bedrocks (for example, the sands of the central part of Alashan). In sandy deserts, the role of the wind in the formation of the relief is especially significant; eolian sandy forms dominate in them. At the same time, the relief forms of loose (dune) and semi-fixed sands are distinguished.

The relief of loose sands is mainly the relief of subtropical deserts. The most characteristic form for him is the dunes. Dunes are asymmetric crescent-shaped sandy hills, located perpendicular to the prevailing wind direction, with sharp ends ("horns") forward. Their windward slopes are gentle (5-15?), Leeward - steep (30-35?). The height of the dunes ranges from 1 - 2 to 15 m, and in some places (the Libyan Desert), higher dunes are formed. The dunes in diameter reach 40-70 m, sometimes 140 and more meters. Dune chains are located perpendicular to the direction of the prevailing winds and have the form of asymmetric waves (gentle windward slope). The height of the sand dune chains in the deserts of Central Asia reaches 100m, in the deserts of Central Asia 60-70m, the length is from several hundred meters to 10-12 km. The distance between the ridges of adjacent chains is 150-3500 m. The relief influences the formation and direction of the dune chains; they can occur where the wind is reflected from an obstacle (from hills, from mountain ranges). A ridge with a height of 2-3 km affects the direction of sandy ridges at a distance of up to 100 km. Dune chains move noticeably in the event that the spruce winds displacing each other in opposite directions have unequal strength, but these chains are much less mobile than single dunes.

The ridges have an asymmetric shape with a slope steepness of no more than 20 °. Their height is very different and ranges from 1 - 3 m to hundreds of meters. Sand ridges reach large sizes in the Sahara. Longitudinal sand ridges arise as a result of the simultaneous processes of sand waving and its deposition. The air jets in the wind flow move in a corkscrew manner. This is mainly due to unequal heating of the slopes of the ridges. The air moves towards the heated slope, over which its ascending movement occurs. At the same time, it transfers sand particles from the inter-rows to the slopes of the ridge.

The area of the earth's surface under the sandy deserts is very large. In Africa alone, it is 1,000,000 square meters. km. Huge sandy massifs are located in the deserts of Asia: Karakum, Kyzylkum, Muyunkum, Balkhash sands, Sary-Ishikotrau, Takla-Makan, etc. Large areas are occupied by sandy deserts in Iran, India, on the Arabian Peninsula. Colossal areas of sandy deserts in Australia and South America.

Clay deserts are formed on a surface covered with fine earth deposits. Small clay particles are carried away by temporary streams and are deposited in relief depressions or foothill plains. When the water dries up, these particles form a crust, in places covered with efflorescence of crystallized salts. Clay deserts are most often located in separate areas within sandy deserts, but they can cover large areas all over (for example, in the northeastern and northwestern parts of Kyzyl Kum). They are usually sloping plains. The area of clay deserts on Earth is generally not much less than the area of sandy deserts. Significant areas of clayey deserts are found in North America, where they are occupied by depressions between ridges in mountainous regions. They occupy large areas in Central and Central Asia. Among clay deserts in negative forms of relief there are areas clayeysaline deserts. Salt marshes located in depressions with closely lying, highly mineralized groundwater are called sors (blinders). The litter is often subject to increased fluttering.

In Central Asia, areas of a clayey - saline desert with a waterproof surface cracked when drying into polygons are called takyrami... The sand brought to the surface of the takyr often forms single dunes. N.P. Neklyukova

The relief of the deserts, which at first glance seems simple, upon closer examination turns out to be very complex and varied.

1.4 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 are classifications of deserts according to their geographic characteristics, they are more informative. One of these is presented in the table. 4.

Table 4. The main geographic characteristics of the world's deserts, Ivanov N.N.

Name	Geographical position	Area, thousand sq. km.	Prevailing absolute heights, m	Absolute maximum temperature, С	Absolute minimum of temperatures, С	Average annual precipitation, mm Hg
Central Asia and Kazakhstan
Karakum	37-42С N; 57-65С v.d.
Ustyurt and Mangyshlak	42-45С N; 51-58С east longitude
Kyzylkum	42-44С N; 60-67С v.d.
Aral Kara-Kum	46-48С N; 57-65С v.d.
Betpak-Dala	44-46С N; 67-72С v.d.
	43-44С N; 67-73С v.d.
central Asia
Takla-Makan	37-42С N; 76-88С v.d.
	39-41С s.w .; 101-107С v.d.
	40-42С N; 91-100С v.d.
	38-40С N; 107-111С v.d.
	36-39С s.w .; 92-97С east longitude
	42-47С N; 98-118С v.d.
Iranian highlands
Deshte-Kevir	33-36С s.w .; 52-57С east longitude
Deshte-Lut	28-33С N; 56-60С v.d.
Registan	29-32С N; 64-66С v.d.
Peninsula Arabia
Rub al-Khali	17-23С N; 46-55С v.d.
Big Nefud	27-30С N; 39-41С v.d.
	21-28С N; 44-48С v.d.
Syrian Desert	31-34С N; 37-42С east longitude
North Africa
	15-28С N; 15 W-33С E
Libyan Desert	23-30С N; 18-30C east longitude
Nubian desert	15-23С N; 31-37С east longitude
South Africa
	19-29С S; 13-17C east longitude
Kalahari	21-27С S; 20-27С v.d.
	32-34C S; 18-26С east longitude
Hindustan Peninsula
	26-29С N; 69-74С east longitude
	30-32С N; 71-72С v.d.
North America
Great Pool	36-44С N; 112-119С w.d.
	35-37С N; 116-118С w.d.
	28-35С N; 109-113С w.d.
	22-30С N; 105-108С w.d.
South America
	22-29С S; 69-70С w.d.
Patagonian	39-53С S; 68-72С w.d.
Australia
Bolshaya Peschanaya	18-23C S; 121-128С east longitude
	23-25С S; 121-128С east longitude
Great Victoria Desert	25-29С S; 125-130С v.d.
	24-27С S; 135-138С v.d.

1.5 Desert Biota

All desert dwellers, no matter how diverse they are, have one thing in common: they are all more or less adapted to a lack of water, food, shelter and sharp fluctuations in temperature.

Fig. 3. Short-leaved yucca

Desert plants. Desert plants have a number of characteristic adaptations. For example, short-leaved Yucca [Fig. 3.] can dry without any harm to itself. Old leaves dry out completely and die off, but young ones, although they also dry out and turn brown, continue to grow with the next precipitation.

Drought tolerance is the most common protection method. Some plants shed their leaves, while others develop very long roots that draw moisture from the depths. On the contrary, some desert plants develop an extensive superficial root system, which quickly assimilates the moisture of short-term rains and early morning dew. Many plants store excess moisture in the leaves, like aloe, or in the stems, like cacti [Fig. 4.]. In cacti, the shape of the plant (cylindrical or spherical) and the reduction of leaves into thorns, lumps and villi protect against herbivores and reduce evaporation. Babaev A.G., Freikin Z.G.

Fig. 4. Cactus

Desert insects. Insects are very numerous in the desert and play an important role in the life of its inhabitants, who feed exclusively on insects, Zaletaev V.S. ... The adaptation of these small desert dwellers to arid conditions is varied. One of them, such as reaper ants, is not physiologically adapted to the conditions of the desert, they arrange nests deep underground, where the outside temperature does not reach them. They make only short-term raids to the surface to stock up on seeds.

Amphibians and reptiles. Dry desert conditions do not allow many species of amphibians to live in the desert, but the shovel frog is an example of adaptability. This is one of the very few desert amphibians that live most of their life in burrows, going out at night to hunt and waiting for rare rains to mate and lay eggs. Reptiles are another group of desert dwellers that probably do better here than others. When the daytime temperature rises, they hide either in burrows or on plants. But at night they seek shelter from the cold. Babaev A.G. ... Perhaps the most abundant desert reptiles are snakes, but since most of them are nocturnal, they are less visible than the lizards scurrying here and there throughout the day.

Fig. 5. Sichik-elf

Birds of the desert. Many birds are found in deserts - from tiny elf owl [Fig. 5.] to flightless giants ostriches. Desert birds feed on seeds or green plants (saxaul jay, shrub, budgerigar, desert lark, ostrich, and others). But among them there are many predators -

Mediterranean falcon, elf sychik (up to 15 cm), earthen cuckoo. Birds, as a more mobile type of animals, fly into the deserts from neighboring more favorable territories, especially during the rains and the autumn-spring period. Zaletaev V.S.

Desert mammals. Mammals, like birds, especially large ones, are fewer in deserts than in other zones, but still, surprisingly, many of them manage to survive in such harsh conditions thanks to adaptations in behavior, metabolism and structure.

Rodents are the most common small inhabitants of the desert. Most of them are active at night, and spend the day in burrows where the humidity is higher. Many of them do not drink water, but extract it from plant foods. It is also known that some rodents obtain moisture by oxidizing food carbohydrates stored as fat. Zaletaev VS .. Relatively few predators live in the deserts: the cat family is represented only by the cheetah [Fig. 6.]. Babaev A.G., Freikin Z.G.

Fig. 6. Cheetah

Chapter 2.NSCharacteristics of the largest deserts in the world

Aleshkovskysands- a sandy massif located in Ukraine, 30 km east of the city of Kherson. The massif is about 15 km in diameter. Aleshkovsky sands are the largest sandy massif in Europe. They consist of endless dunes, about 5 m high, and rare vegetation [Fig. 7.]

Fig. 7. Aleshkovsky sands

The name comes from the old (before 1925) name of the city of Tsyurupinsk - Alyoshka. Aleshkovsky sands in their present form appeared very recently. In the lower reaches of the Dnieper, sands have always existed, but their progress was restrained by the cover of steppe vegetation. In the 18th, as well as in the 19th century, sheep began to be brought here (only Baron Falz-Fein, the founder of the Askania-Nova reserve, owned huge herds of up to a million heads), which destroyed the grass, freed the sands, and wind erosion gave them the opportunity to expand. According to P. Kostychev, who studied the Aleshkovsky sands in the 1880s, no more than a hundred years before that time, the Aleshkovsky sands were completely fixed by vegetation, in places woody. The opinion that "the appearance of the sands came from a change in the climatic conditions of the area", Kostychev considers completely unfounded ("there is not the slightest evidence of this"). "The formation of loose sands and the obstacle to their consolidation are due to one reason:" intensively grazing cattle. " In the "Journal of General Useful Information" for 1837, it is indicated that the area of forests on the sands of the lower Dnieper, which in 1802 was more than 5000 hectares by 1832, had dropped to almost zero.) acquired in 1830-1840 in connection with the activities to intensify afforestation and the formation of the Aleshkovsky forestry. The period of general land surveying and the allotment of land to peasants (1859-1890) turned into a disaster for forests and the area of sand increased significantly. Now the sands are stopped at the edges by huge artificial forests, with a total area of about 100 thousand hectares. Actually the Dnieper sands occupy an area of 161,200 hectares, and with inter-arable lands - 210,000 hectares. Despite the fact that Aleshkovsky sands are often called a desert, this is not entirely true. According to the temperature regime and the amount of precipitation, they can be attributed rather to semi-deserts. However, the climatic conditions are such that the sand heats up to 75 degrees in summer. The air over the sands warms up more strongly than over the surrounding terrain, the humidity of the air decreases, so in the summer the raindrops evaporate quickly, and the intensity of the rains (according to some unconfirmed data) here is somewhat less than in Kherson itself, which is located on the other side of the Dnieper. Although the sands are now held back by forests, sometimes they sweep the outskirts of nearby villages.

The main factors affecting the ecological situation in the region are a decrease in the forest area and a decrease in the layer of sand. The decrease in the forest area is caused by felling, fires, natural death of pine plantations, which are incapable of self-reproduction and can lead to the expansion of the sandy massif. On the other hand, the uncontrolled use of sand for construction purposes and the placement of agricultural facilities in the region leads to a decrease in the level of groundwater and their pollution, which can deprive the inhabitants of the region of high-quality drinking water and negatively affect the forest.

http: //www.wiki.kherson .ua /

2.2 Deserts of Central Asia and Kazakhstan

The semi-deserts and deserts of Central Asia and Kazakhstan are located on the Turan plain. The deserts extend from the Kopetdag and Paropamiz mountains bordering the plain from the south to 48C north latitude. and to the east of the Kazakhstan Sea up to the foothills of the Dzhungarskiy Alatau, Tien Shan and Pamir-Altai. Within these vast limits, there are deserts of various types in geological and landscape terms: sandy deserts (Karakum, Kyzylkum, Moyinkum, Aral Karakum, Big and Small Barsuki, Volga-Ural), rocky (Betpak-Dala), rubble (Ustyurt), clayey steppe), Solonchakovaya (Kelkor, Dead Kultuk, etc.) Among the different types of deserts, remnant mountains rise, occupied by stony and clayey deserts. The Kazakh Upland, Betpak-Dala and the remnant mountains are the most ancient formations. The characteristic features of the desert relief include dry channels and drainless depressions, including very large ones. Some of them are hollow in shape (Sarykamysh, Barsakelmes, etc.). the deepest depression - Karagiye (-132 m below sea level) - is located on the territory of Western Kazakhstan; other depressions are linear: Unguz, Western Uzboy. The life of the sands, the natural processes occurring on their surface are closely related to the desert climate and most of all to the wind regime, to the moisture of the sand. The wind sets in motion bare sands, changes their shapes, creates areas of sand removal or deflation, areas of dragging and areas of accumulation - accumulation. Wet sands are immobile. Moving sands under the influence of winds of different speeds form diverse landforms that are genetically related to each other. Distinguish the following sequence: wind-sand flow, motionless accumulation of sand in the vortex zone and the formation of ripples on it, sand waves, ridges, dunes, dune chains and ridges, dune fields, etc. Petrov MP. ...

The climate of Central Asia is characterized by a relatively long duration of sunshine, aridity and continentality. This is due to its geographical location at the northern border of the subtropics, far from the oceans and inside the Eurasian continent, as well as atmospheric circulation, which contributes to the formation of predominantly cloudless and little cloudy weather. On the plains of Central Asia, the duration of sunshine is high - 2500-3000 hours per year. The climate of Central Asia is often divided into two periods: from mid-May to mid-October - warm and dry, the rest of the year - wet and cold. Deserts of Kazakhstan are located to the north, their climate is characterized by longer and colder winters, shorter summers; shorter vegetation and frost-free periods, more precipitation. Among the negative features of the desert climate, we note unstable weather in spring and winter, a small amount of precipitation, excessively high summer temperatures, at which agriculture is possible only with artificial irrigation. Depending on the conditions of formation, the water content, length, regime of rivers is not the same, as well as the possibilities of their economic use. The richest rivers are the central and western regions of Central Asia. In Central Asia, rivers of glacial-snow supply (Amurdarya, Syrdarya, Ili), snow-rain (Murgab, Atrek), spring-rain (small rivers flowing from the Kopetdag and other medium-high mountains) are distinguished. There are many small temporary rivers within the Turan Plain, which are formed in spring due to snow and rain supply. They are especially numerous in Kazakhstan. Some rivers, such as Turgai, Sarysu, do not dry up completely, but only in some places. Dry channels are a noticeable phenomenon in the relief of deserts, its hydrographic network and catchments. Dry channels in the deserts of Central Asia and Kazakhstan are very long and seem to be rivers left without water. Such are the Western Uzboy and Kelifskiy Uzboy in the Karakum Desert, Zhanadarya in the Aral Sea region. There are few large lakes in the desert. They only form where rivers with a large runoff carry their waters into deep basins.

Most desert plants belong to xerophytes, succulents, halophytes and are highly adaptable to local conditions due to their morphological and physiological characteristics. Desert plants are in conditions of waterlessness and low water and find a sufficient amount of moisture and protect themselves from excessive heating and desiccation; evaporation of moisture is reduced to a minimum.

The fauna of the deserts of Central Asia and Kazakhstan is very peculiar. It is distinguished by the great adaptability of animals to desert conditions, the protective coloration of the animal, a relatively poorer species composition, and the predominance of nocturnal activity of animals. When forming the structure of the animal world, it is important that the mountains and plains are here in the immediate vicinity and the animals freely move from one natural zone to another. In the deserts of Central Asia, there are a jackal, a hyena, a desert lark, a large lizard monitor lizard, a poisonous snake Efa, a sand boa, a cobra, an arrow-snake, many birds fly from Kazakhstan and Siberia. The fauna of the sandy desert is richer than the fauna of clay, gypsum, rubble. In the sandy desert there are desert crows, saxaul jays, desert warblers, desert shrikes, sandpipers, tolai hares, many rodents (gerbils, yellow and fine-fingered ground squirrels, comb-footed and fur-footed jerboas, many eared hedgehogs at night) butterflies fly - scoops, beetles, mosquitoes, solpugs, scorpions, tarantula spiders, snakes leave their traces on the sand. The wolf is heavily exterminated in the desert. During spring and autumn flights, flocks of ducks, geese, coots, cranes, etc. appear in the desert zone. Among the desert animals there are species that are gradually disappearing, these include: gray monitor lizard, gazelle, poisonous snakes and others. Zaletaev V.S.

2.3 Deserts of Central Asia

Central Asia is a region of high-lying plains and uplands, framed by high climatic-dividing ridges. The dry climate characteristic of arid regions is formed here at a great distance, often in isolation from the Atlantic and Pacific air masses. The surface of the deserts is composed of aeolian sands, loess, as well as sand and pebble deposits, on the foothill plains - proluvium. Central Asia is poor in surface waters. In many places, there are dry channels, or saury, confined to the basins. Within Central Asia, ancient alluvial plains are distinguished (Takla-Makan in the Tarim Basin, Alashan in North China, Kuzupchi sands in Ordos), deserts of Tertiary and Cretaceous structures (parts of Dzungaria, Tsaidam, Alashan, Ordos), rocky and stony deserts in the place of destroyed ancient mountains (Beishan, Gashun and Mongolian Gobi). In the west of Central Asia, sandy deserts prevail, in the central part - stony and sandy-pebble. Deserts do not represent one continuous territory, but are dissected by mountain rises. Petrov M.P.

Alashan Desert occupies a depression between Nanshan and Gobi Altai. The absolute height is 800 m and more. Along with tectonic forms in the form of separate ridges, there are accumulative forms - chalk sandy-pebble plains, as well as erosional ones - from dry channels and aeolian accumulative forms in the form of dune sands.

Dzungaria- a plain located in the east about 300 m. Here you can find small hills of ancient crystalline rocks, rubble-pebble plains, takyrs and takyr-like soils, salt marshes, hilly sands overgrown with desert vegetation, and dune sands subject to scattering. Sandy deserts are located in the center and in the south of Dzungaria; on the southern outskirts, fixed sands turn into mobile ones.

Gobi - located between the mountains of the Mongolian Altai and Khangai, Eastern Tien Shan, Altintag, Beishan and Inshan. It stretches from west to east for 1750 km with a width of 600 km. Although the gobi as a type of desert is quite common in Central Asia, nevertheless its own name refers to the Eastern Gobi, located in the north of Central Asia [Fig. 8.]

Fig. 8. Gobi Desert

The Eastern Gobi is a plain lying in the east with an average of about 1000 m. The flatness of the relief alternates with ridges and dry valleys. The precipitation is 200 mm. The underground waters are slightly saline, they are shallow, feeding lakes and springs. The landscape is dominated by deserts and semi-deserts, but where there is more rainfall, steppes are formed.

The deserts of Central Asia lie in the temperate zone and belong to arid regions with cold winters and maximum precipitation in summer. Average annual air temperatures in the deserts of Central Asia range from 2.5C in the high-mountainous Tsaidam to 11.6C in Kashgar. The average July temperature in Tsaidam is plus 17.9C, in Chechnya - plus 27.3C. In other deserts, the temperature fluctuates within these limits. Annual precipitation is less than 100 mm. The eastern part of Central Asia up to Beishan is weakly influenced by the eastern monsoons and therefore receives the most precipitation in summer (in Alashan, 219 mm).

The fauna of Central Asia is small in species composition; endemism at the species level is significant, there are also endemic species among rodents. Only in this region lives the only modern representative of the camelid family in the Old World - the bactrian camel. The basis of the world of rodents is the jerboa; on dense soils, earthen hares, the jerboa jumper, and the Mongolian jerboa are common. In addition to jerboas, gray and Dzungarian hamsters are widespread in the deserts of Central Asia. Two species of gerbils - midday and clawed - inhabit sandy deserts. A small tolai hare is common in the sandy deserts of the region. Ungulates are not numerous. Only gazelles are common, large herds of which are still found in sandy deserts. Over the past decade, Przewalski's horse has completely disappeared in its former habitats in the Western Gobi and Dzungaria. Predators in the deserts of Central Asia are also few in number (ferret - dressing, steppe cat, occasionally you can see the footprints of a fox and a wolf). The most notable birds are the larks (gray and larger Mongolian). Babaev A.G., Freikin Z.G.

2.4 Deserts of the Indian subcontinent

The deserts of Hindustan are confined to its western part and occupy significant areas. They are located in the vast ancient alluvial plain of the Indus and its tributaries, entering the Deccan plateau. There are two sandy deserts here - Tar and Thal and a small sandy-clay desert Pyat.

Thar Desert located on the border of India with Pakistan [Fig. 9.] Its area is about 300 thousand square meters. km. The desert belongs to the type of sandy deserts of the subtropical belt in the north and tropical in the south. Much of the desert is covered with loose sands that have formed patches of fixed or movable dunes. Aeolian sands occupy 90% of the territory. Dunes occupy 58% of the area. The climate of the Thar Desert is dry and continental. The average annual rainfall varies from 105 to 500 mm. The distribution of precipitation is uneven.

Fig. 9. Thar Desert

Precipitation falls to the west. If the summer monsoon is strong enough to penetrate most of the desert, light rain falls as a result of convective currents of moist rising air. And in winter, sometimes several tens of mm of precipitation falls as a result of the movement of cyclones. In summer, the average daily maximum temperature, as a rule, is 40C, in winter - plus 22-28C. The average minimum temperature varies from 24C in summer to 4C in winter.

Groundwater is too deep from the surface. Most of these waters are not suitable for water supply. V. N. Kunin Four types of soil formations prevail in the Thar Desert: powerful saline clay alluvium on vast, seasonally flooded plains; sandy masses north of Rann; loamy, often silty modern alluvium of the Indus River in the west. Strong monsoon winds of the south-west direction and powerful dust storms carry away fine-grained fractions of sand and dust, leaving larger particles in place, as a result of which, to the west of the Arabian Ridge, the soils are increasingly sandy.

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 sheet 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 the cultivation of some cultivated plants. Plants for livestock thrive in the desert thanks to the 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.

Characteristics of deserts

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 the type of surface, there are such types of deserts:

Sandy and sandy-crushed stone... They are very diverse: from chains of dunes devoid of any vegetation, to areas covered with shrubs and grass. Getting around in the sandy desert is extremely difficult. 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 a 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 going deep, 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 air of the deserts 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, it is 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 especially sharp fluctuations in daily temperature, strong winds and dust storms. From Botswana and Namibia to South Africa stretches over 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"), occupying an area of 350,000 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 noteworthy: 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 the world's deserts is Icy desert Antarctica(about 14,000,000 km 2).