What actions of people open the way to the desert. Desert: environmental problems, desert life

The easiest way to determine the distance to a given landmark is to count the number of breaths or leg strokes. You can more accurately determine the distance under water using a distance meter (lag), the operation of which is based on the use of high-speed water pressure on a special turntable.
Underwater navigation- a kind of sport in which the advantage of one athlete over another is achieved not only thanks to the best physical training, but also due to the technical skill of the athlete and the quality of his equipment. Underwater orienteering combines several underwater exercises:

• “straight” - swimming without changing course;
• “zones” - swimming with a change in course without landmarks;
• “landmarks” - sailing with a change in course according to landmarks; performing special group exercises. For example, swimming underwater “with a change of course according to landmarks” is that at a given control time the submariner must go through a certain route underwater and find 5 landmarks in succession, the distance between which is 100-200 m. This type of underwater orienteering requires a search a landmark representing a wooden cross 4 m high; it is attached to the anchor at the bottom with a hemp rope 2-3 cm thick using navigation instruments and special search devices.

• 1) informing about what is happening, pointing to something and insisting on doing something;
• 2) indicating a not entirely normal state of the diver or his equipment, conveying certain wishes and even orders;
• 3) reporting an emergency condition and assistance.

In populated areas

Deserts are dry spaces with high temperatures and low humidity. Researchers consider such places on earth to be territories of geographical paradoxes. Geographers and biologists argue that deserts themselves are the main environmental problem of the Earth, or rather desertification. This is the name given to the process of loss of permanent vegetation, the impossibility of natural restoration without human intervention. Let's find out what territory the desert occupies on the map. We will establish the environmental problems of this natural zone in direct connection with human activities.

Country of geographical paradoxes

Most dry areas globe is in tropical zone, they receive from 0 to 250 mm of rain per year. Evaporation is usually tens of times greater than the amount of precipitation. Most often, the drops do not reach the surface of the earth and evaporate while still in the air. In the Gobi and Central Asia, winter temperatures drop below 0 °C. Significant amplitude - characteristic desert climate. During the day it can be 25-30 °C, in the Sahara it reaches 40-45 °C. Other geographical paradoxes of the Earth's deserts:

• precipitation that does not wet the soil;
• dust storms and whirlwinds without rain;
• endorheic lakes with high salt content;
• springs that are lost in the sands, not giving rise to streams;
• rivers without mouths, waterless channels and dry accumulations in deltas;
• wandering lakes with constantly changing shorelines;
• trees, shrubs and grasses without leaves, but with thorns.

The largest deserts in the world

Vast areas devoid of vegetation are classified as drainage regions of the planet. It is dominated by trees, shrubs and grasses without leaves or completely absent vegetation, which is reflected in the very term “desert”. The photos posted in the article give an idea of ​​the harsh conditions of dry areas. The map shows that deserts are located in the Northern and Southern Hemispheres in hot climates. Only in Central Asia is this natural area is in temperate zone, reaches 50° N. w. The most large deserts world:

• Sahara, Libyan, Kalahari and Namib in Africa;
• Monte, Patagonian and Atacama in South America;
• Great Sandy and Victoria in Australia;
• Arabian, Gobi, Syrian, Rub al-Khali, Karakum, Kyzylkum in Eurasia.

Zones such as semi-desert and desert on the world map generally occupy from 17 to 25% of the total land area of ​​the globe, and in Africa and Australia - 40% of the area.

Drought on the sea coast

The unusual location is typical for the Atacama and Namib. These lifeless, arid landscapes are located on the ocean! The Atacama Desert is located in the west of South America, surrounded by the rocky peaks of the Andes mountain system, reaching a height of more than 6500 m. In the west, the territory is washed by Pacific Ocean with his cold

The Atacama is the most lifeless desert, with a record low rainfall of 0 mm. Light rains occur once every few years, but in winter fogs often move in from the ocean coast. This arid region is home to about 1 million people. The population is engaged in livestock farming: the entire high-mountain desert is surrounded by pastures and meadows. The photo in the article gives an idea of ​​the harsh landscapes of the Atacama.

Types of deserts (ecological classification)

1. Arid - zonal type, characteristic of tropical and subtropical zones. The climate in this area is dry and hot.
2. Anthropogenic - occurs as a result of direct or indirect human impact on nature. There is a theory that explains that this is a desert, ecological problems which are associated with its expansion. And all this is caused by the activities of the population.
3. Populated - a territory in which there are permanent residents. There are transit rivers, oases that form at the exit points groundwater.
4. Industrial - areas with extremely poor plant cover and fauna, which is due to industrial activity and disturbance natural environment.
5. Arctic - snow and ice expanses in high latitudes.

The environmental problems of deserts and semi-deserts in the north and in the tropics are in many ways similar: for example, there is insufficient rainfall, which is bad for plant life. But the icy expanses of the Arctic are characterized by extremely low temperatures.

Desertification - loss of continuous vegetation cover

About 150 years ago, scientists noted an increase in the area of ​​the Sahara. Archaeological excavations and paleontological studies have shown that this territory was not always only desert. Environmental problems then consisted of the so-called “drying” of the Sahara. Thus, in the 11th century, agriculture in North Africa could be practiced up to 21° latitude. Over the course of seven centuries, the northern border of agriculture moved south to the 17th parallel, to XXI century moved even further. Why does desertification occur? Some researchers explained this process in Africa by the “drying out” of the climate, others provided data on the movement of sands covering oases. Stebbing’s work “The Man-Made Desert,” published in 1938, became a sensation. The author cited data on the advancement of the Sahara to the south and explained the phenomenon by incorrect Agriculture, in particular, trampling of cereal vegetation by livestock and irrational farming systems.

Anthropogenic cause of desertification

As a result of studies of the movement of sands in the Sahara, scientists found that during the First World War, the area of ​​agricultural land and the number of livestock decreased. Tree and shrub vegetation then reappeared, that is, the desert retreated! Environmental problems are currently aggravated by the almost complete absence of such cases when territories are withdrawn from agricultural use for their natural restoration. Land reclamation and reclamation measures are being carried out on a small area.

Desertification is most often caused by human activity; the cause of “drying out” is not climatic, but anthropogenic, associated with excessive exploitation of pastures, excessive development of road construction, and irrational agricultural practices. Desertification under the influence natural factors may occur on the border of existing dry areas, but less frequently than under the influence of human activity. The main causes of anthropogenic desertification:

• open-pit mining (in quarries);
• without restoration of pasture productivity;
• cutting down forests that stabilize soils;
• improper irrigation systems;
• increased water and wind erosion:
• drying up of water bodies, as in the case of the disappearance of the Aral Sea in Central Asia.

Environmental problems of deserts and semi-deserts (list)

1. Lack of water - main factor, which increases the vulnerability of desert landscapes. Heavy evaporation and dust storms lead to erosion and further degradation of marginal soils.
2. Salinization is an increase in the content of easily soluble salts, the formation of solonetzes and solonchaks, which are practically unsuitable for plants.
3. Dust and sand storms are movements of air that lift a significant amount of small debris from the surface of the earth. On salt marshes, the wind carries salts. If sands and clays are enriched with iron compounds, then yellow-brown and red dust storms occur. They can cover hundreds or thousands of square kilometers.
4. “Devils of the Desert” are dusty sand whirlwinds that lift huge amounts of small debris into the air to a height of several tens of meters. Sand pillars have an extension at the top. They differ from tornadoes in the absence of cumulus clouds carrying rain.
5. Dust bowls are areas where catastrophic erosion occurs as a result of drought and uncontrolled plowing of the land.
6. Clogging, accumulation of waste - objects foreign to the natural environment that do not decompose for a long time or emit toxic substances.
7. Human exploitation and pollution from mining, livestock development, transport and tourism.
8. Reduction of the area occupied by desert plants, impoverishment of the fauna. Loss of biodiversity.

Desert life. Plants and animals

Harsh conditions, limited water resources and the barren desert landscapes change after the rains have passed. Many succulents, such as cacti and crassulas, are able to absorb and store bound water in stems and leaves. Other xeromorphic plants, such as saxaul and wormwood, develop long roots that reach the aquifer. Animals have adapted to obtain the moisture they need from food. Many representatives of the fauna switched to night image life to avoid overheating.

The environment in particular is negatively affected by the activities of the population. The destruction of the natural environment occurs, as a result of which man himself cannot use the gifts of nature. When animals and plants are deprived of their usual habitat, this also negatively affects the life of the population.

The journalist stayed at the hotel. In the morning I noticed a yellow layer of sand on the windowsill.

There is a desert right behind the village,” explained a local resident. - When the wind blows, close all the windows. It was so difficult to get used to this... I remember that where the sands are now, there was waist-deep grass.

The car had to be pushed: the road was blocked by a sandy “snowdrift” - a dune - that had been swept up overnight.

The hot wind hurts your face with tiny grains of sand. It doesn’t let you forget for a minute: the desert is coming. Where is all this happening? In the south of our country, in the so-called Black Lands.

Black... Did the people who long ago gave such a name to this region foresee misfortune? No, that's not the point. In winter there is usually no snow here, and the area appears black without it. And now the Black Lands have become a victim of a terrible disaster - desertification.

What is desertification? This is the gradual transformation of dry lands into deserts. Like rust on the surface of metal, the desert is growing, expanding its borders, capturing more and more new areas. Over the past 50 years, an area equal to half of South America has become barren deserts around the world. Part of the entire landmass of the Earth in more than 100 countries of the world is now on the verge of desertification. The African Sahara Desert, for example, moves southward by up to 10 km every year!

Why does desertification occur? To answer this question, let's return to the Black Lands.

The local pastures have fed flocks of sheep for centuries. People knew: the layer of fertile soil here is very thin, underneath there is sand. Therefore, the land cannot be plowed here. And there shouldn’t be too many livestock. In addition, you can’t graze it in the same places all year round so that the grasses that hold the soil together are not eaten and trampled by domestic animals. If you violate these conditions, the sand will break free from centuries-old captivity.

In these parts, to this day, no trouble would have happened if people had not decided to ignore the laws of nature. Let's start plowing the land! And they bred so many sheep that, willy-nilly, they had to graze them all year round on the same pastures.

Yes, watermelons, corn, wheat, and barley were obtained from the plowed lands. But the thin layer of soil quickly collapsed. The sand became the master here. And people plowed up a new plot.

Yes, they got meat and wool from sheep. But there were fewer and fewer places where they could still graze. People increased the number of sheep from year to year! The unfortunate emaciated animals ate everything that was still growing, and hundreds of thousands died of hunger...

So why does desertification occur? The example of the Black Lands and observations of scientists in other areas of the world show that most often people themselves are to blame for this. Plowing of land and excessive grazing of livestock play a major role in this.

By understanding the causes of desertification, we can decide how to stop it, or at least slow it down.

1. It is necessary to stop plowing land in areas experiencing desertification.
2. We need to bring order to livestock farming. Keep as many sheep as the remaining pastures can support. Move the animals around so that the pastures rest for part of the year.
3. It is necessary to sow grass and plant forests to create a vegetation cover that protects the soil.

Of course, becoming a true desert does not threaten the entire Earth. This is a problem in areas with arid climates. But this environmental disaster can be considered a symbol of what is happening to the Earth now. People are devastating their planet. Doesn't air and water pollution bring disease and death to the living? Doesn't deforestation and extermination of plants and animals make the planet lifeless? Doesn’t any of us, by mindlessly knocking over mushrooms or swatting innocent insects, impoverish the environment? In ruined, destroyed natural home people can't survive. There are 8 dead planets orbiting the Sun, and only one still bears life. We urge you to save this life by doing everything you can for this.

Test your knowledge

1. What is desertification?
2. In which area of ​​our country is desertification occurring particularly rapidly?
3. What human actions open the way to the desert?
4. How can we stop desertification?

Think!

1. In the early 70s. XX century in one of the regions of the Black Lands there were 850 thousand hectares of pastures. After 15 years, 170 thousand hectares remained. It was no longer possible to farm on the remaining lands. Calculate how many hectares of land have been lost over the years.
2. According to scientists, the pastures of the Black Lands in the mid-80s. XX century could feed no more than 750 thousand sheep. But in fact, more than 1 million 500 thousand sheep were kept here. Give a rough estimate: how many times were the pastures overloaded?

In many areas of the world, desertification is occurring - the gradual transformation of dry lands into deserts. Among the main causes of desertification are plowing of land and excessive grazing by livestock, which eats up and tramples down vegetation. To stop desertification, it is necessary to stop plowing, bring order to livestock farming, sow grass and plant forests.

Areas called “deserts” range from salty to sandy. Wherever you find yourself, know that deserts are places of extremes: intense heat during the day, extreme cold at night, very few plants, trees, lakes and rivers. Deserts can be found throughout the world, covering about one fifth of the Earth's surface. Among the most famous are the Sahara, Gobi, Arabian Desert and the flat plains of the southwestern United States.

Movement

Water is the main factor for survival in the desert. Carry it with you as much as you can, even if you have to leave something else behind. If you decide to move:

- move only in the evening, at night or early in the morning; - go along the coast, to a known route, to a water source or to a populated area. Sweating can be reduced by wetting your clothes.

- choose the easiest route possible, avoiding quick sand, difficult terrain, paths along road tracks.

In sand dunes, walk on the hard sand in the valley between the dunes or along the ridges of the dunes:

- Avoid following streams to access the sea, except in coastal deserts or areas where large rivers cross them. In most deserts, valleys lead to an enclosed body of water or temporary lake;

- Dress appropriately to protect yourself from direct sunlight and excessive sweating. If you don't have sunglasses, make yourself glasses with slits. Clothing is necessary in the desert to keep warm, since cold nights are very common there;

- watch your feet. Boots are the best footwear for walking in the desert. Only cross the dunes barefoot in cool weather, otherwise the sand will burn your feet. Follow caravan tracks to avoid quicksand or rocky areas;

— check the map if possible. Maps of desert areas are usually imprecise;

- find shelter during sandstorms. Do not attempt to travel in poor visibility. Mark the direction by drawing deep arrows on the ground, laying them out with stones or whatever is at hand. Lie on your side with your back to the wind and lie there until the end of the storm. Cover your face with a cloth. Don't be afraid of being buried under sand. Even in dune areas, it takes years to bury a dead camel.

If possible, find shelter on the leeward side of the hill;

- multiply distance calculations by 3, since the lack of landmarks often leads to incorrect calculations;

- In summer, mirages can often appear when you are facing the sun, although it is difficult to generalize under what conditions they appear and what forms they take.

Shelter

Shelter from the sun, heat and possible sandstorms is essential to survival in the desert. Since there is basically no material for constructing a shelter, use the following methods.

1. Provide yourself with some protection from the sun by covering your body with sand.
Burying in sand also reduces moisture loss.
2. If you have a parachute or other suitable material, dig a hole and cover its edges. In rocky deserts or deserts where there are bushes, thorns or mounds of tall grass, throw a parachute or blanket over the rocks or bushes.
3. To create shade or shelter, use both natural and man-made features of the terrain - a tree, a rock, a pile of stones or a cave. The wall of a dry riverbed can provide shelter, but if clouds roll in, your shelter may suddenly become flooded. The banks along dry river beds, valleys and ravines are especially good places to find caves.
4. If possible, use native shelters.

Water

General provisions. The importance of water cannot be overstated. It is significant no matter how well your food supplies are selected.

In hot deserts, at least 3.5 liters per day is needed. If sweating is moderate and movement in the desert occurs on a cold night, this reserve will be enough for 30 km of travel. In the heat of the day you can only walk 15 km.

Save water.
1) Stay dressed at all times. Clothes help you control
Sweating prevents sweat from evaporating as quickly, causing it to lose its cooling properties. You will feel cooler without a shirt, but you will sweat more and may also get sunburned.
2) Don't rush. By using less water and sweating less, you will last longer.
3) Do not use water for washing until you have a reliable source of it.
4) Do not swallow water in one gulp. Drink it in small sips.
If you're running low on water, use it only to wet your lips.
5) As a means of relieving heat, keep small pebbles in your mouth or chew grass. You can reduce water loss by breathing through your nose. Do not speak.
6) Use salt only with water and only if there is enough water.
Salt increases thirst.
7) Limiting water consumption to 1-2 liters per day leads to disaster (at high temperatures), since such an amount of water does not prevent dehydration. In such cases, limit sweating rather than water.

Local wells. A minimum of four quarts of water per day may be difficult to find unless there is a well or oasis nearby. Since wells are the main source of water in the desert, The best way to find them, drive along the local road. There are other ways to find water in the desert.

Be guided by the following:

1) Along sandy shores or desert lakes, dig a hole in the first hole behind the first sand dune. Water from local rains will be collected in this place. Once you find damp sand, stop digging and let the water seep out. Further digging may expose salt water;
2) wherever you find raw sand, dig a well;
3) dried up streams have water just below the surface. If the stream
dries out, the water descends to the lowest point on the surface at the place where the channel turns. Dig along these bends to find water;
4) dew can be a source of water, especially in some areas. Cooled stones or any metal surface will work as a dew condenser. Remove the dew with a piece of cloth and squeeze it out. Dew evaporates immediately after sunrise and must be collected before that;
5) look natural places, which can be under the roots in ravines and side canyons, under the tops of rocks. Often there is a strong stone or compaction of earth near them. In the absence of such landmarks, look for sources based on animal droppings;
6) watch the flight of birds, especially at sunset and dawn. In real desert areas, birds fly over wells. Wild sand gourd can be considered as a source of water in the Sahara. A large cactus that looks like a gun barrel in the American desert contains a large number of moisture that can be squeezed out of its pulp. Sometimes this can be difficult to do. An alternative to this may be a well or other source;
7) ignore romantic stories about poisoned wells. These stories mainly assume that water contains salt, is alkaline, and has a bad taste;
8) disinfect any water. This is especially important in native villages and where there is civilization.

It's hard to find food in the desert. But it still ranks second in importance compared to water. And you can do without it for several days without any health consequences. Distribute the food from the beginning. Do not eat anything for the first 24 hours and do not eat until you have no water.

Natural springs.

1) Animals are rarely seen in the desert. Rats and lizards can be found near water sources and may be your only food. Even-toed ungulates can be found in the desert, but they are difficult to approach. The most common animals are rodents (rats), rabbits, jackals, snakes and lizards, which are usually found near bushes or water. Look for sand snails on rocks and bushes.
2) Some birds can also be found in the desert. Try to kiss back side your palm, making a sucking sound to attract them. Sand grouse, bustards, pelicans and even gulls have been spotted on some desert lakes. Use traps or a hook and try hard to catch them.
3) Usually, where there is water, there are plants. Many desert plants look dried out and unappetizing. Look for the soft part on them that is edible. Try all the soft parts growing on the surface of the earth - flowers, fruits, seeds, young shoots and bark. At some times of the year you can find grass seeds or pods. These pods grow on acacia trees, which are often thorny and similar to the mosquito tree or cat claw found in the southwestern United States. There is a prickly pear (a type of cactus), which is native to the Northern and South America, it is often found in North Africa, in the Middle East and Australian deserts.
4) All grass is edible, but some of its species, growing in the Sahara or Gobi, are tasteless and non-nutritious. Try any plant you find, it's not lethal. Dates may be found in northern Africa, southwest Asia and parts of India and China.

Native food.

1) The food of the natives in the Sahara is both tasty and nutritious. In the Gobi, the Mongols are not very careful about cleanliness, so the food is unhygienic. Take advantage of the natural hospitality of the natives, do not steal food.
2) The daily food of the natives is extremely dangerous, as are the fruits and other prepared foods offered local residents. If possible, barter or buy raw food and cook it yourself.

Starting a fire

Palm leaves and similar fuels are found everywhere near oases. In the depths of the desert, however, use any piece of dry plant you can find. Dry camel dung can be used when wood is not available.
Probably the most effective way to start a fire without matches is to shine the sun's rays through a magnifying glass. Other simple ways lighting a fire may not be possible.

Cloth

Protect yourself from direct sunlight, excessive sweating, and the many irritating desert insects.

1) Cover your body and head well during the day. Wear long pants and a long sleeve shirt.
2) Wear a cloth around your neck that protects the back from the sun.
3) If any part of the clothing must be left behind to lighten the load, keep that part of the clothing that is necessary to protect against the cold of the night in the desert.
4) Wear loose clothing.
5) Only unbutton your clothes in thick shade. Reflected sunlight may cause sunburn.

Protecting your feet can be a matter of life and death. It is useful to know the following.

1) Avoid sand and insects getting into your shoes and socks, even if you need to stop frequently to clean your shoes.
2) If you don't have boots, make some kind of windings from any material you have on hand. To do this, cut two strips, each 3-4 inches wide and 4 feet long. Wrap them around your legs in a spiral, starting from the foot, from the bottom up to the shin. This will prevent you from getting sand.
3) Make a pair of sandals from the wall of an old car tire, if there are cars nearby. However, it is better to reinforce the soles of your boots with durable material if worn soles are causing problems.
4) When relaxing in the shade, take off your shoes and socks. Do this carefully as your feet may become swollen and it can be very difficult to put your socks back on.
5) Don't try to walk barefoot. Sand can cause burns on your feet. In addition, walking barefoot on salty hard or swampy surfaces can lead to alkaline burns.
6) Make shoes with wooden soles to protect your feet while moving. Nail the strap to pieces of wood and tie it to your leg. Protect top part feet from the sun.

Dehydration

General provisions.
1) In the desert heat, thirst alone is an inaccurate indicator of how much water you need. If you only consume enough water to quench your thirst, dehydration may still slowly progress. Drink more water whenever possible, especially during meals. If you drink water only with meals, you will tend to become dehydrated between meals, but will return to normal after eating and drinking water; however, you will often feel tired due to the loss of energy along with the loss of water.
2) Strength lost due to dehydration is quickly restored if you drink water.
3) Losing water does not cause any permanent complications, even if you lose up to 10 percent of your weight. At 70kg - 7kg can be lost through sweating, provided you drink enough water afterwards to replace it. Cold water Causes stomach pain if swallowed quickly.
4) At 25 percent fluid loss, you can survive if the air temperature is 30 degrees or cooler. At temperatures of 32 degrees and above, a 15% loss of fluid is dangerous.

Signs of fluid loss. Thirst and general malaise appear first, followed by a desire to slow down any movement and loss of appetite. As you continue to lose water, you become drowsy. Your temperature rises and by the time you lose 5 percent of your weight, you begin to feel nauseous. As you lose 6 to 10 percent of your body weight, the symptoms will increase in the following order: dizziness, headache, difficulty breathing, trembling legs and arms, dry mouth, bluish discoloration of the body, speech impairment, loss of ability to walk.

How to prevent water loss. There is no substitute for water. Alcohol, salt water, and gasoline only increase dehydration. In emergency cases, you can drink salt water(containing half the amount of salt present in sea water) and obtain a net increase in body fluids. Any liquid containing a higher percentage of unusable elements can only disrupt the body's cooling system. Chewing gum or rocks in the mouth can be a pleasant way to stave off the pangs of thirst, but they are not a substitute for water and do not help maintain normal temperature bodies.

Vegetation. Desert vegetation, represented by xerophytes and halophytes, does not form a closed cover and usually occupies less than 50% of the surface, characterized by a great variety of life forms (for example, tumbleweeds). Important place in plant communities they occupy ephemerals and ephemeroids. Many endemics. In Asia, leafless shrubs and semi-shrubs (white saxaul, sand acacia, cherkes, ephedra) are common on the sands; In America, as well as in Africa, succulents (cacti, yucca, prickly pear, etc.) are common. Clay deserts are dominated by a variety of wormwood, solyanka and black saxaul.

Animal world. Animals that have adapted to life in the open spaces of the desert can run quickly and remain without water for a long time. For example, the long-domesticated camel, which is called the “ship of the desert” for its endurance and reliability. Many of the animals are marked with a yellow or gray-brown “desert” coloration. Most animals are nocturnal in summer, some hibernate. Rodents (jerboas, gerbils, gophers) and reptiles (lizards, snakes, etc.) are numerous and ubiquitous. Among the ungulates, goitered gazelles and antelopes, including gazelles, are often found; Carnivores include the wolf, fennec fox, hyenas, jackals, coyote, caracal, etc. Insects and arachnids (phalanxes, scorpions, etc.) are numerous.

Impact on business activities

As already noted, deserts are distinguished by natural contrasts. Many natural processes occur in them under extreme conditions or on the verge of them. For this reason, they are characterized by violent reactions when the balance in ecosystems is disturbed. Each of the desert phenomena has its own impact on the topography, soil, vegetation, wildlife, on humans and their economic activities. Like any extreme phenomenon, desert phenomena are unfavorable for people, sometimes dangerous. They cause crop failure of forage plants; they cover buildings, roads, wells, etc. with sand. Dust storms work in the fields is stopped for several days in a row; dry winds have a depressing effect on living organisms, including humans, causing them to feel depressed. Even gentle winds set the sand in motion.

Extreme events in winter manifest themselves in severe frosts, followed by thaws and ice. The peculiarity of extreme events is that they are irregular and always unexpected, which makes them even more dangerous in their consequences. For example, stable snow cover with a height of more than 0.5 meters does not occur every year, but in unfavorable times

In rare years, it stays in certain lowland regions of Central Asia for 40 - 70 days, which is dangerous for sheep.

Human influence

Sharp changes in existing natural desert complexes occur under the influence of natural processes and anthropogenic factors. In the first case, the natural environment changes temporarily and not radically. The human influence is manifested differently: in the conditions of hunting, it is slower than in nomadic livestock farming, and in the latter it is less noticeable than in the development of irrigated agriculture over large areas in certain areas.

The largest and most noticeable transformations in deserts occurred in the twentieth century, when the mining industry, and in cities, manufacturing, the construction of railways, and then roads, and the mechanization of agriculture brought modern machinery to the desert. This significantly increased the intensity of its transformation, requiring the identification of a special category of impact on the territory - the technogenic factor. Being part of the influence of the anthropogenic factor, technogenic forces also have their own distinctive characteristics. In desert conditions, this is very noticeable, since the action of technogenic forces sharply worsens the appearance of the area and, moreover, changes the natural processes that form ecosystems.

The construction of roads crossing the desert, the digging of large main canals, the laying of gas and oil pipelines - all this is possible only with the use of modern equipment: tractors, bulldozers, excavators, hydraulic monitors, vehicles and other technical means. While performing a great deal of useful work, they simultaneously cause significant and not easily repairable damage: during their movement, vegetation is destroyed, fixed sands become mobile and are blown over. At the same time, wind and dry hot air dry them out, and the sands lose their water-physical properties, level groundwater decreases beneath them. In this case, phytomelioration does not give the desired result. Bare sands fall out of the pasture stock. They generate dusty winds, sand tornadoes, create drifts on roads, and expand the area of ​​loose, moving sand. But not only technogenic forces, but also any excessively intensive environmental management in the desert can lead to similar results. Thus, a pasture, when overloaded with sheep or very long continuous grazing of livestock, or with heavy cutting of bushes, turns into a hotbed of sand blowing.

Equally, an irrigated area with excessive watering turns into a salt marsh or, at a minimum, into an array of saline soils, unsuitable for cultivation without complex reclamation.

As we see, natural processes and the anthropogenic factor can, each in their own way, significantly modify and transform the desert, and the more intense the use of natural resources, the more intense it is. Undoubtedly, in this regard, technogenic forces take first place, but other factors cannot be discounted. Therefore, economic activity in the desert, more than in any other landscape, must be closely linked with nature conservation, with measures to compensate for the damage caused.

The problem of desertification. As a result of long-term and intense anthropogenic impacts (system of shifting cultivation, overgrazing

cattle, etc.) the onset of the desert and the expansion of its areas are noted. This process is called desertification, or desertification. This is a real threat to many peoples of Northern and Eastern Africa, South Asia and tropical America. For the first time, the problem of desertification attracted special attention after the tragic events of 1968-73, when a catastrophic drought engulfed the southern regions of the Sahara, the Sahel zone, where thousands of local residents died of starvation. In such extreme natural conditions, the problems of food, feed, water and fuel become extremely acute. Pastures and agricultural lands cannot withstand overload. The territories adjacent to the desert become deserts themselves. This is how the process of desertification begins or intensifies. The Sahara, moving south, annually takes away 100 thousand hectares of arable land and pastures. The Atacama moves at a speed of 2.5 km per year, the Thar - 1 km per year. Through the joint efforts of scientists from many countries, a comprehensive approach to studying the problem of desertification has been developed within the framework of the UNESCO Man and the Biosphere program.

The expansion of desert boundaries and desertification problems are characteristic of areas immediately adjacent to deserts, where human activity is active.

Table 4 of potential desertification by continent shows that the largest areas of highly degraded landscapes are located in Asia, Africa and Australia, where the largest

deserts. The smallest areas are located in Europe, North and South America.

Table 4 Potential desertification territories by continent (thousand sq. km)

The factors leading to desertification in arid regions of the globe are quite diverse. The following play a special role in intensifying desertification processes:

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

2) 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;

intensification of takyr and solonchak formation in foothill plains and drainless depressions;

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

There are many natural processes leading to desertification. But among them 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 (weathering of salts, water erosion, deflation, formation of shifting sands, etc.);

soil – drying out of soils and their salinization;

phytogenic – degradation of vegetation cover;

zoogenic - reduction in the population and number of animals.

Desert Conservation. To protect and study the typical and unique natural landscapes of the deserts of the world, a number of nature reserves and national parks have been created, including Etosha, Joshua Tree (in Death Valley - one of the hottest places on the globe), Repetek, Namib, etc.