Deserts and semi-deserts - climate, wildlife and vegetation. Natural zone of semi-deserts: characteristics, geographical location, climate and soils of semi-deserts, photos, pictures Geographical position of subtropical semi-deserts and deserts

Deserts of the world

Most of the world's deserts lie on platforms and occupy very ancient landmasses.

The Asian, African and Australian deserts are located above sea level at an altitude of 200 to 600 m.

The deserts of Central Africa and North America lie at an altitude of 1000 m.

Some deserts are bordered by mountains, while others are surrounded by mountains. Mountains are an obstacle to the passage of cyclones, so precipitation will fall only on one side of the mountains, and on the other there will be little or no precipitation.

The reason for the formation of deserts is the uneven distribution of heat and moisture, as well as geographic zoning planets.

temperature and Atmosphere pressure create special conditions for the circulation of air masses of the atmosphere and the formation of winds. It is the nature of the general atmospheric circulation and the geographical conditions of the area that create a certain climatic situation, due to which a desert zone is formed in both the northern and southern hemispheres.

Exist different types deserts depending on natural zones and surface type.

Deserts are:

• sandy;
• rocky;
• clay;
• solonchak.

Excluding Antarctica, the deserts of the planet occupy 11% of the land surface or more than 16.5 million square meters. km. They are distributed in the temperate zone. northern hemisphere, as well as in the southern hemisphere within the tropical and subtropical zones.

From the point of view of moisture, some deserts do not receive precipitation for decades, and the deserts of extra-arid regions receive less than 50 mm per year.

Aeolian landforms are widespread in deserts, while the erosional type of relief formation is weakened.

Deserts are mostly drainless, but sometimes they can be crossed by transit rivers, for example, the Amu Darya, Nile, Syr Darya, Huang He, etc.

Drying rivers - in Africa it is a wadi, and in Australia - screams and lakes that change their size and shape, for example, Eyre, Chad, Lop Nor.

Desert soils are underdeveloped, and groundwater is often mineralized.

Vegetation cover is very sparse, and in very arid deserts absent altogether.

In those places where there are underground waters, oases with dense vegetation and reservoirs appear in the deserts.

Snowy deserts formed beyond the polar circles.

In deserts, things like this can happen. amazing phenomena not found in other natural areas.

Among these phenomena is "dry fog" that occurs during calm weather, but the air is filled with dust and visibility completely disappears.

At very high temperature the phenomenon of “dry rain” may occur - precipitation evaporates before reaching the surface of the earth.

Remark 2

Tons of moving sand can make high-pitched, melodious sounds with a metallic tinge, they are called "singing sands". One can also hear in the desert both the "sound of the sun" and the "whisper of the stars".

Stones bursting at 40-degree heat are capable of making a special sound, and at a temperature of -70 ... -80 degrees, water vapor turns into ice crystals, which, colliding with each other, begin to rustle.

Definition 1

Thus, the desert is a special natural area that has an almost flat surface with sparse or almost absent flora and specific fauna.

Semi-deserts of the world

Semi-desert or otherwise deserted steppe is formed in a dry climate.

They have specific vegetation and soil cover, and are characterized by the absence of woody vegetation.

As a rule, elements of steppe and desert landscapes are well combined in them.

In the north, the semi-desert is limited to the steppe and the desert in the south.

Semi-deserts of the temperate belt run from the west from the Caspian lowland to the east of Asia to the eastern border of China, which is approximately 10 thousand km.

Subtropical semi-deserts are quite widespread on the slopes of plateaus, plateaus and highlands, for example, the Anatolian Plateau, the Iranian Highlands, the foothills of the Andes, the valleys of the Rocky Mountains, etc.

Tropical semi-deserts occupy large areas, especially in Africa, for example, the Sahel zone in West Africa is located south of the Sahara and looks like a deserted savannah.

Russian semi-deserts occupy a small area. This is the Caspian lowland, which is a transitional strip between steppes and deserts. In addition, it is the most northwestern outskirts of the vast Eurasian deserts.

The Caspian lowland receives during the year the largest amount of total solar radiation in the territory of the Russian Plain.

The semi-desert climate is continental, which distinguishes it from the steppes. High summer temperatures of +22…+25 degrees are pronounced here, and cold winters with little snow.

The January temperature is in the range of -12 ... -16 degrees. The winter period is characterized by strong winds, low snow cover and soil that freezes up to half a meter deep. The short spring has the largest amount of precipitation, the annual amount of which is 300 mm with an evaporation rate of 800 mm.

Desert and semi-desert climate

Deserts and semi-deserts of the world occupy several climatic zones - the temperate zone of the Northern Hemisphere, the subtropical and tropical zone of the Northern and Southern Hemispheres, the polar zone, where ice deserts are formed.

The predominant climate is continental with very hot summers and cold winter.

Precipitation is generally very rare in deserts, ranging from once a month to once every few years.

Small amounts of precipitation do not reach the surface of the earth and evaporate immediately into the air.

In tropical and subtropical deserts, the average temperature during the day ranges from +50 degrees during the day to 0 degrees at night. IN arctic deserts up to -40 degrees.

The maximum temperature, for example, in the Sahara was +58 degrees.

In tropical deserts, daily amplitudes are 30-40 degrees; in temperate deserts, about 20 degrees.

During the day, the air of deserts is also distinguished by dryness - from 5 to 20% during the day, and from 20 to 60% at night.

The driest deserts are the deserts South America. The low humidity of desert air does not protect the surface from solar radiation.

In the deserts of the Atlantic and Pacific coasts, as well as the Persian Gulf, the climate is more favorable, because air humidity increases to 80-90% due to the proximity of water, and daily temperature fluctuations decrease. In such deserts, sometimes there is even dew and fog.

The deserts of the temperate zone are characterized by seasonal fluctuations - warm and even hot summers and harsh winters with frosts down to -50 degrees. Snow cover is small.

A characteristic phenomenon for all deserts are constantly blowing winds. Their speed can reach 15-20 m/s. Their formation leads to a strong warming of the surface and the resulting convective air currents, as well as the terrain, so sand and dust storms are frequent in deserts.

The winds have their own names - in the Sahara it is sirocco, in the deserts of Libya and Arabia - gabli and khamsin, in Australia - brickfielderi, and in Central Asia- Afghan.

The queen of the deserts - the largest among the hot ones - the Sahara, is located in North Africa.

Most of the year, the Sahara is under the influence of the northeast trade wind. The Atlas Mountains are a barrier to the penetration of humid Mediterranean air into the Sahara.

The July temperature is +35 degrees in the central part, but in many places it is also +50 degrees. At night, the thermometer drops to + 10 ... + 15 degrees.

Daily temperatures are high and amount to 30 degrees, and on the soil surface they reach 70 degrees.

According to the precipitation regime, three zones are distinguished - northern, central, southern.

In the north, rainfall is no more than 200 mm per winter period. In the central zone, precipitation falls sporadically, and their average value does not exceed 20 mm. Within 2-3 years, they may not fall out at all. But, in such areas there are sometimes downpours, causing severe floods.

The Sahara changes its aridity from west to east. The Atlantic coast is arid, because the Canarian cold current, which runs along the western coasts, cools the air, and there are often fogs.

Due to the condensation of water vapor, the amount of precipitation increases slightly on the tops of mountain ranges and in the highlands. The Sahara is characterized by a high degree of evaporation.

And very poor wildlife. All this is associated with extremely severe climatic conditions the planets where they are located. Deserts, in principle, can form in almost any. Their formation is primarily associated with low rainfall. That is why deserts are primarily common in the tropics. Tropical deserts occupy the territory of most of tropical Africa and the western coast of the tropical belt, as well as the territory in. Here, their formation is associated with the year-round dominance of the tropical, the influence of which is enhanced by the terrain and cold currents off the coast. Also, a large number of deserts are located in the subtropical and temperate zones of the Earth. This is a territory in South America, where their formation is due to the isolation of the southern tip of the mainland from the penetration of moist air by cold currents, as well as in the interior and Central Asia. Here, the formation of deserts is already associated with a strong continental climate due to the great distance from the coast, as well as mountain systems that prevent the penetration of moisture from the ocean. The formation of deserts can also be associated with extremely low temperatures on the planet, this type of deserts, also called Antarctic deserts, is considered by us separately.

The natural conditions of the deserts are extremely harsh. The amount of precipitation here does not exceed 250 mm per year, and in large areas - less than 100 mm. The driest desert in the world is the Atacama Desert, where precipitation has not been recorded for 400 years. The largest desert in the world is the Sahara, located in the North (pictured. Author: Rosa Cabecinhas and Alcino Cunha). Its name is translated from Arabic as "desert". Here was recorded the highest on the planet + 58 ° C. Under the scorching rays of the sun in the summer months, when it reaches its zenith at noon, the sand underfoot heats up to enormous temperatures, and sometimes you can even fry eggs on the stones. However, with the sunset, the temperature in the desert drops sharply, the drops reach tens of degrees during the day, and frosts even occur here on a winter night. The constantly clear sky is to blame for everything due to the descending flows of dry air from the equator, because of this, clouds are almost not formed here. Huge open spaces deserts do not at all prevent the movement of air along the surface of the earth, which leads to the occurrence of strong winds. Dust storms come unexpectedly, bringing clouds of sand and streams of hot air. In spring and summer, a strong wind rises - simum, which can literally be translated as "poisonous wind". It can last only 10-15 minutes, but the hot dusty air is very dangerous for a person, it burns the skin, the sand does not allow you to breathe freely, many travelers and caravans died in the deserts under this deadly. Also, at the end of winter - the beginning of spring, a seasonal wind begins to blow from the desert almost every year - khamsin, which means "fifty" in Arabic, since on average it blows for fifty days.

Deserts, unlike tropical deserts, are also characterized by strong temperature fluctuations throughout the year. Hot summers give way to cold, harsh winters. Fluctuations in air temperature during the year can be about 100°C. Winter frosts in the deserts of the temperate zone of Eurasia drop to -50 ° C, the climate is sharply continental.

The flora of deserts in especially difficult conditions may be completely absent, where moisture remains sufficient, some plants grow, but the flora is still not very diverse. Desert plants usually have very long roots - more than 10 meters in order to extract moisture from groundwater. In the deserts of Central Asia, a small shrub grows - saxaul. In America, a significant part of the flora is cacti, in Africa - spurges. The fauna of the deserts is also not rich. Reptiles predominate here - snakes, monitor lizards, scorpions also live here, there are few mammals. One of the few who was able to adapt to these difficult conditions was a camel, which was not accidentally called the "ship of the desert." By storing water in the form of fat in their humps, camels are able to travel long distances. For the indigenous nomadic peoples of the deserts, camels are the basis of their economy. Desert soils are not rich in humus, however, they often contain a lot of minerals and are suitable for farming. Agriculture. The main problem for plants is the lack of water.

Semi-deserts of the temperate zone- a natural zone of the temperate zone, which has transitional features from steppes to deserts. A sharply continental climate is characteristic, evaporation is 3-4 times more quantity precipitation. The annual amount of precipitation varies between 150-250 mm.

In semi-deserts, brown semi-desert-steppe soils are formed, as well as light chestnut soils poor in humus. Along with them, salt licks are very widespread.

In the semi-deserts, sparse wormwood-cereal vegetation grows, which is torn in nature.

The fauna of the semi-deserts is not distinguished by its originality; it includes species of the steppe and desert zones. An exceptional role in the animal world is played by rodents.

The deserts of the temperate zone occupy the plains of Eurasia from the Caspian Sea in the west to Central China in the east, the largest of them are the Karakum and Kyzylkum deserts in Central Asia. IN North America- These are the arid regions of the Great Basin, in South America - Patagonia.

The desert climate is characterized by extreme aridity and continentality, with sharp contrasts between very hot summers and cold winters. The amount of precipitation varies from 75 to 150 mm per year.

The soil cover is dominated by brown and gray-brown desert soils, often saline. Takyrs are characteristic - specific formations of clay deserts, which are a cracked dry clay surface.
Vegetation cover is sparse, its composition is dominated by perennial shrubs and ephemera (annual herbaceous plants, flowering during a short rainy period). Of the shrubs, the leading role belongs to various types wormwood and saltwort. In some places there are "forests" of saxaul - a small leafless tree, the roots of which go to a depth of 20 m. At the height of summer, the deserts of the temperate zone differ little from tropical deserts, but they have a short but stormy flowering period - early spring. It happens that the desert is covered with a real flowering carpet.

The fauna is mainly represented by reptiles (snakes, lizards). Many desert animals can go without food and water for a long time, such as a domesticated camel. Of the birds, various larks, plovers, bustard-beauty, desert warbler, etc. are common.

Deserts of the subtropical and tropical zones

Subtropical and tropical deserts are located in the north-west of India, in Pakistan, Iran, Asia Minor. They cover the Arabian Peninsula and the entire north of Africa, the western coast of South America for almost 3500 km and the central part of Australia.

The climate in the deserts is sharply continental. Summer is very dry and hot, during the day the air temperature in the shade rises above 40 0С. At night, the heat subsides, the temperature often drops to 0 0C. Precipitation falls no more than 180 mm per year. Chile's Atacama Desert receives less than 10 mm of precipitation per year.

The soil cover is represented mainly by brown desert soils, but soils are completely absent in vast areas. Salt marshes form in places where groundwater is shallow. Large territories occupy rocky deserts. Clay deserts, located, as a rule, in relief depressions, are almost devoid of vegetation. They are easily flooded during intermittent rains and look like lakes, although the depth of these "lakes" is only a few millimeters. The clay layer does not absorb water - it quickly evaporates in the sun, the dry surface of the earth cracks, and takyrs are formed. Clay areas give way to expanses of moving sand with eolian relief forms - dunes, "crescent" or "sickle" shape, reaching a height of 12 m, and dunes.

Desert plants usually have a well developed root system. Mostly thorny bushes, cacti and some herbs grow here. Other plants - ephemera - survive the drought in the form of seeds, having time to germinate and bloom in a couple of months after a rare rain.

The fauna of the deserts is represented by a wide variety of reptiles (snakes, lizards, turtles), birds (eagles, crows, sparrows, owls, etc.) and mammals (cheetah, kulan, camel, etc.).

Human life in deserts is possible only in oases.

Semi-desert zones of temperate zones

natural land areas in the temperate zones of the Northern and Southern Hemispheres with a predominance of semi-desert landscapes. The largest area is occupied in the inner part of Eurasia, where they extend (approximately 10 thousand km). km) from the Caspian lowland in the north to eastern outskirts the Ordos plateau in the east; the width of the strip of semi-deserts, within which plains predominate, reaches in places 500 km. In North America P. z. y. The settlements are located in the meridionally elongated strip of the foothills of the Rocky Mountains and the basins of the Great Basin, where they mosaically alternate with desert landscapes. In the southern hemisphere, they are distributed in the south of South America (to the east of the Andes, in Patagonia).

Climate P. h. y. The northern hemisphere is arid, continental, with cold winters and long hot and dry summers. The radiation balance is about 5 MJ/m2 or 120 kcal / cm 2 per year, evaporation is several times higher than the annual amount of precipitation (usually 200-300 mm). average temperature July 22-25 °C, January up to -20 °C. Winters are usually snowy with strong winds. In the Southern Hemisphere (in Patagonia) the climate is less continental. In summer, the air temperature is 15-20 °C, in winter - about 1 °C. The Andes retain most of the moisture brought by the dominant west. winds, so precipitation falls only 100-150 mm(in places - up to 250) per year.

Surface runoff is poorly developed, in summer many rivers dry up, they are usually full of water only in spring, during the melting of seasonal snows. Significant areas are generally devoid of surface runoff. There are numerous brackish and salt lakes. Constant deficit of moisture in the soil from the middle of the growing season.

Light chestnut and brown soils predominate, often in combination with solonets soils; saline soils and meadow solonchak soils are common along relief depressions. Soils are characterized by complexity, low humus content (1.5-3°%); Soils are often distinguished by a high content of gypsum, carbonates, and the manifestation of solonetzic processes. They are often suitable for agriculture, but they need irrigation, and in some places, the elimination of solonetsousness and resettlement.

The vegetation is xerophilous, often complex. In the semi-deserts of temperate latitudes of the Northern Hemisphere, grass-wormwood communities with a significant participation of ephemers and ephemeroids predominate. On sandy soils, tree and shrub vegetation is common (loch, birch, pine, dzhuzgun, sand acacia). In the Southern Hemisphere, the vegetation of semi-deserts is sparse, predominantly semi-shrub with the participation of grasses and succulents. Desert and steppe animal species predominate. Semi-deserts of temperate latitudes are usually good pastures for year-round grazing.

M. P. Petrov, Yu. K. Efremov.

Big soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

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To visit the desert, it is not necessary to go to Africa or Australia. Deserts and semi-deserts are also found on the territory of Russia. The lowest part of the Caspian lowland is occupied by deserts, where flat surfaces alternate with sandy deposits. The climate here is sharply continental: very hot and dry summers, cold winters with little snow. Apart from the Volga and Akhtuba, there are no other sources of water here. There are several oases in the deltas of these rivers.

The strip of semi-deserts of Russia is located in the southeast of the European part of the country, starting in the region of the left bank of the Volga and reaching the foothills Caucasus mountains. This West Side The Caspian Sea and the Ergeni Upland. It also has a sharply continental and dry climate. The water arteries of the semi-desert zone are the Volga and Sarpinsky lakes.

On the territory of deserts and semi-deserts, an insignificant amount of precipitation falls - up to 350 millimeters per year. Basically, the soils here are sandy and desert-steppe.

The word "desert" suggests that there is no life here. But it is not so.

The climate of deserts and semi-deserts of Russia

The climatic conditions of deserts and semi-deserts influenced the formation of special flora and fauna. The vegetation in this zone is located in a mosaic manner. Perennial grasses, ephemeroids, spread predominantly in the semi-deserts. Ephemera also grow here, the life cycle of which is two to three months. In general, the plants are small, but have a powerful root system. In the semi-desert region, black wormwood and saltwort, bulbous bluegrass and two-eared conifer, camel thorn and fescue grow. Closer to the Caspian Sea, the semi-desert turns into a desert, where vegetation is less and less common. Sometimes here you can see elmius, wormwood or hair.

Ecological problems of deserts and semi-deserts of Russia

If we talk about environmental issues deserts and semi-deserts of Russia, then the very intervention of man in the nature of this area is a danger. The very process of desertification - the extreme degree of soil erosion - leads to significant changes, especially under the influence of anthropogenic factors. Another problem of the deserts and semi-deserts of Russia is poaching and extermination of animals and plants in in large numbers. And since there are some rare species human activity causes serious damage to nature. Therefore, it is necessary to protect and preserve the landscapes of the country's deserts and semi-deserts, since this is the wealth of our planet.