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 of the world's arid areas are located in the 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 is a characteristic feature of the 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 zone located in the temperate zone, reaching 50° N. w. The largest deserts in the 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 the Pacific Ocean with its 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)
- Arid - a zonal type, characteristic of the tropical and subtropical zones. The climate in this area is dry and hot.
- Anthropogenic - occurs as a result of direct or indirect human impact on nature. There is a theory that explains that it is a desert whose environmental problems are associated with its expansion. And all this is caused by the activities of the population.
- Populated - a territory in which there are permanent residents. There are transit rivers and oases that form where groundwater emerges.
- Industrial - areas with extremely poor plant cover and fauna, which is caused by industrial activities and disturbance of the natural environment.
- 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, and by the 21st century it had shifted 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 improper agricultural practices, 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 of natural factors can occur on the border of already existing arid territories, but less often 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)
- Lack of water is the main factor that increases the vulnerability of desert landscapes. Heavy evaporation and dust storms lead to erosion and further degradation of marginal soils.
- Salinization is an increase in the content of easily soluble salts, the formation of solonetzes and solonchaks, which are practically unsuitable for plants.
- 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.
- “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.
- Dust bowls are areas where catastrophic erosion occurs as a result of drought and uncontrolled plowing of the land.
- Clogging, accumulation of waste - objects foreign to the natural environment that do not decompose for a long time or emit toxic substances.
- Human exploitation and pollution from mining, livestock development, transport and tourism.
- Reduction of the area occupied by desert plants, impoverishment of the fauna. Loss of biodiversity.
Desert life. Plants and animals
The harsh conditions, limited water resources and barren desert landscapes change after the rains fall. Many succulents, such as cacti and crassulas, are able to absorb and store bound water in their 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 a nocturnal lifestyle 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.
I think that due to human activity in recent decades, several anthropogenic deserts could have formed, that is, deserts that owe their appearance to inept and careless land development and agriculture. But the most famous example of such a desert is ARALKUM - a desert that appeared on the site of a once deep salt lake in Central Asia called the Aral Sea. This sea-lake completely dried up when man disturbed its water balance, using the lake's waters to irrigate vast agricultural areas. The area of this anthropogenic desert is 38 thousand square kilometers and continues to increase, although people are trying to return the Aral Sea.
Anthropogenic deserts are understood as those deserts that were formed as a result of one or another (usually harmful) human impact on a certain (extensive) area of the earth's surface.
In addition to the desert formed on the site of the Aral Sea, one can name a desert called the Black Lands, formed in Kalmykia.
The problem of environmental management at this moment in time is one of the most acute and pressing - the prospect of being left in the future not only without fertile soils, but also without fresh water is not at all as far away as it might seem, and these periods are constantly decreasing...
Desert landscapes do not always appear through natural processes on the planet; sometimes they arise as a result of human actions. Such young deserts that appear on the sites of water bodies are called anthropogenic. For example, in this way the water balance was disturbed Aral Sea, as a result of irrational use of water resources.
Today the Aral Sea is a depressing sight: the sea is turning into a desert and this dried-up area has already received the appropriate name: Aralkum. Today the desert covers an area 5 million hectares, which is an environmental disaster on a planetary scale. Scientists have calculated that by 2020 the Aral Sea maybe finally disappear, and in its place a man-made new desert will appear, which has already acquired its name - Aralkum.
First, let's figure out what anthropogenic origin means.
As we see, a person leaves traces of his presence everywhere and these traces do not always have a beneficial effect on the world around us.
Now about a specific desert, it will be ARALKUM.
And more can be added.
Man actively interferes with nature, disrupting the ecosystem. Such interference can have a negative impact, for example, once fertile lands turn into deserts and animals die.
Anthropogenic deserts occupy 7% of the landmass, and in a broad sense, all deserts are of anthropogenic origin.
For example, the desert, which was formed due to the plowing of sandy lands and active grazing of livestock - Black Lands, in the south of the European part of Russia, is located between the Ergeni upland and the lower reaches of the Volga River. It is located in the Republic of Kalmykia and occupies almost half of its territory. Also, on the site of the Aral Sea, a desert is formed, on which the remains of the Aralkum ships stand. The increase in the area of the Sahara is also associated with human activity, its active development of land and its improper use.
There is an opinion that almost all deserts are of anthropogenic origin. Thus, as a result of improper use of natural resources since ancient times, the once fertile lands of Mesopotamia turned into a desert. Already before our eyes, part of the former Aral Sea has turned into a desert. This desert is called ARALKUM.
Most of the world's deserts were formed on geological platforms and occupy the oldest land areas. Deserts in Asia, Africa and Australia are usually located at altitudes from 200 to 600 m above sea level, in Central Africa and North America - at an altitude of 1 thousand m above sea level.
The “mechanism” of the formation and development of deserts is subject, first of all, to the uneven distribution of heat and moisture on Earth, the zonality of the geographical envelope of our planet. The zonal distribution of temperatures and atmospheric pressure (baric relief) determines the specificity of the winds and the general circulation of the atmosphere.
Above the equator, where the greatest heating of land and water occurs, ascending air movements dominate. An area of calms and weak variable winds forms here. Warm air rising above the equator, cooling somewhat, loses a large amount of moisture, which falls in the form of tropical showers. Then, in the upper atmosphere, air flows north and south, towards the poles. These air currents are called anti-trade winds. Under the influence of the Earth's rotation, antitrade winds are deflected to the right in the northern hemisphere, and to the left in the southern hemisphere. At approximately latitudes 30° - 40° (near the subtropics), their deviation angle is about 90°, and they begin to move along parallels. At these latitudes air
the masses descend to the heated surface, where they heat up even more, and move away from the critical saturation point.
Due to the fact that in the subtropics there is high atmospheric pressure all year round, and at the equator, on the contrary, it is low, a constant movement of air masses (trade winds) occurs at the surface of the earth from the subtropics to the equator. Under the influence of the same deflecting influence of the Earth's rotation, trade winds move from northeast to southwest in the northern hemisphere, and from southeast to northwest in the southern hemisphere. Trade winds cover only the lower thickness of the troposphere - 1.5 - 2.5 km.
The trade winds prevailing in subtropical and tropical latitudes determine the stable stratification of the atmosphere and prevent vertical movements and the associated development of clouds and precipitation. Therefore, cloudiness in these belts (especially subtropical) is very insignificant, and the influx of solar radiation is the greatest. As a result, the air here is extremely dry (relative humidity in the summer months averages around 30%) and extremely high summer temperatures. The average air temperature on continents in the tropical zone in summer exceeds 30 o - 35 o; The air temperature here is the highest on the globe - plus 50 o. The average annual amplitude of air temperature is about 20 o, the soil surface sometimes exceeds 80 o. Precipitation occurs rarely, in the form of showers.
In subtropical latitudes (between 30° and 45° northern and southern latitudes), the amount of total radiation decreases, and cyclonic activity contributes to moistening and precipitation, confined mainly to the cold period of the year. However, sedentary depressions of thermal origin develop on the continents, causing severe aridity. Here, the average temperature in the summer months is 30°C or more, and the maximum can reach 50°C. In subtropical latitudes, intermountain depressions are the driest, where annual precipitation does not exceed 100–200 mm.
In the temperate zone, conditions for the formation of deserts occur in inland regions, such as Central Asia, where precipitation falls no more than 200 mm. Due to the fact that Central Asia is fenced off from cyclones and monsoons by mountain uplifts, a pressure depression forms here in the summer. The air is very dry, high temperature (up to 40 o or more) and very dusty. Rarely penetrating here with cyclones, air masses from the oceans and the Arctic quickly warm up and dry out.
The nature of the general circulation of the atmosphere, determined by planetary features, and local geographical conditions create a unique climatic situation that forms a desert zone to the north and south of the equator, between 15° and 45° latitude.
Thus, the emergence, development and geographical distribution of deserts on the globe are determined by the following factors: high values of radiation and radiation, low amounts of precipitation or their complete absence. The latter, in turn, is determined by the latitude of the area, the conditions of the general circulation of the atmosphere, the peculiarities of the orographic structure of the land, and the continental and oceanic position of the area.
And the degradation of all forms of organic life in a specific area is called desertification.
The main reason for the current increase in desertification in various countries of the world is the environmental crisis caused by the discrepancy between the existing structure of economic use of natural resources and the potential natural capabilities of a given landscape, population growth, increasing anthropogenic loads, and the imperfection of the socio-economic structure of a number of countries. The acid rain discussed above also contributes to the increase in desertification of territories.
Desertification occurs in all natural areas of the world. Currently, more than 9 million km are occupied by deserts of anthropogenic origin, and up to 7 million hectares are lost from productive land use every year. An example of modern desertification of territories of anthropogenic origin is the saline plain of the drained part of the Aral Sea bottom.
Desertification problem
Desertification processes currently threaten a vast territory, covering some regions in southern Russia and the Asian CIS countries.
In Russia, an area of 50 million hectares is subject to this process. Irrational use of land, in particular uncontrolled grazing, led to the emergence of the only desert in Europe, “Black Lands” in Kalmykia. With a grazing rate of no more than 750 thousand sheep, 1 million 650 thousand were constantly grazing here. In addition, over 200 thousand saigas constantly lived in this territory. Overload of pastures exceeded the norm by 2.5-3 times. As a result, more than a third of the pasture area (650 thousand hectares) has been converted into moving sand. Gradually, the Kalmyk steppe becomes a barren desert.
Experts have calculated that if the process continues at the same pace, then in 15-20 years the area of desertified lands in this republic will reach 1 million hectares.
Cleared lands in the Komi Republic are also subject to desertification.
Every year in the southern region of Russia, sands occupy 40-50 thousand hectares. In the Caspian region alone, about 800 thousand hectares are occupied by sand. There is an increase in the area of harvested pastures. Over the five years since 1985 in Dagestan, Saratov and Astrakhan regions, these areas increased by 14,260 and 394.2 thousand hectares, respectively.
Desertification process- an important problem for Uzbekistan. According to the latest data, deserts and semi-deserts occupy about 4/5 of the territory of the republic. As a result of the drying of the Aral Sea, an additional 33,400 km 2 of dry seabed and secondary deserts (Aral-Kum) were formed. About 70% of the deserts of the Aral Sea region arose as a result of degradation of the vegetation cover, so a scientifically based selection of drought-resistant plants and their zoning is necessary. It is important to identify promising heat-, drought-, salt- and gas-resistant species adapted to the conditions of the arid zone. It must be taken into account that Central Asia is characterized by a warm climate and low rainfall; long periods of drought are common here, causing a high risk of desertification.
Soil degradation and desertification
The annual global loss of fertile soils on cultivated lands is currently estimated at 24 million tons. For comparison, the same area is sown with grain throughout Australia.
One of the main reasons for the destruction of the fertile layer is soil erosion. It occurs mainly due to the so-called “agro-industrial” farming: soils are plowed over large areas, and then the fertile layer is blown away by the wind or washed away by water. As a result, to date there has been a partial loss of soil fertility on an area of 152 million hectares, or 2/3 of the total area of arable land. It has been established that a 20-centimeter layer of soil on gentle slopes is destroyed by erosion under a cotton crop in 21 years, under a corn crop in 50 years, under meadow grasses in 25 thousand years, under a forest canopy in 170 thousand years.
Soil erosion has now become widespread. In the United States, for example, about 44% of cultivated land is susceptible to erosion. In Russia, unique rich chernozems with a humus content of 14-16%, which were called “the citadel of Russian agriculture,” have disappeared, and the areas of the most fertile lands with a humus content of 10-13% have decreased by almost 5 times.
Soil erosion is especially severe in the largest and most populous countries. The Yellow River in China annually carries about 2 billion tons of soil into the World Ocean. Soil erosion not only reduces fertility and reduces crop yields. As a result of erosion, artificially constructed water reservoirs become silted much faster than is usually envisaged in projects, reducing the possibility of irrigation and obtaining electricity from hydroelectric power plants.
Processes associated with desertification cause great damage to the condition of the Earth's soil cover. This is one of the most significant global problems of humanity.
The United Nations Convention to Combat Desertification was signed and entered into force in December 1996. It emphasizes the need for a new participatory approach to addressing desertification. Desertification affects the condition of topsoil, which is of great importance for agriculture and food production.
Desertification can be caused by deforestation, irrational land use and irrigation (waterlogging and salinization), drought, overgrazing, soil degradation and other reasons.
As a result of irrational land use, soil productivity decreases, its surface layer dries out, yields decrease, the erosion of the fertile layer increases, sand dunes encroach on irrigated lands and destroy crops with sandstorms.
Deforestation and slash-and-burn agriculture also contribute to soil destruction. Deforestation of mountain forests is especially dangerous. From mountain slopes devoid of greenery, rains wash away the soil, making the changes irreversible. New forest plantations will no longer take root here. Soil erosion occurs on the plains, their fertility decreases, and the local population is deprived of their main bread - rice. Rivers carry soil washed away from fields into the sea. If there are coral reefs rich in animal and plant life nearby, then the smallest soil particles settle on coastal corals. This means that at the same time another forest is being destroyed - the underwater one. The silted water does not allow the sun's rays to pass through, and the unique coral world dies, and the local population is deprived of fish.
One of the reasons leading to desertification is overgrazing. As the population increases, the load on pastures increases, and at the same time their productivity decreases.
The destruction of forest and grassy vegetation, overgrazing, water and wind erosion have turned the territories of the once “green” countries of the Middle East and North Africa into deserts and semi-deserts. There is an opinion that all the deserts of the Middle East are the work of man. Historians believe that it was the desertification of the Sahara and Arabia that gave impetus to the development of modern civilization, displacing people from lands that had lost fertility into the disastrous swampy valleys of the Nile, Tigris and Euphrates, where they were forced, willy-nilly, to improve technology and social relations.
Over the 100 years from 1882 to 1982, the proportion of areas defined as deserts increased from 9.4% to 23.3%. The deserts keep coming.
Great damage to the Earth's soil layer is caused by salinization as a result of improper reclamation. Irrational irrigation leads to flooding and waterlogging of the soil. Salts come to the surface or are washed with water if drainage systems do not remove this water. Deforestation causes floods, which also contribute to the salinization process, as salt is washed out along with the water.
Anthropogenic salinization of the territory occurs due to the enrichment of soil and other substrates with various salts - waste products of animals and humans or man-made impacts (domestic wastewater, industrial wastewater, runoff from roads where salt is used together with sand to prevent ice).
Compaction of soil and other substrates causes disruption of the air-gas regime and other physical properties. As a result, the density and porosity of the substrate and the oxygen content in the root layer change, which leads to disruption of root nutrition and other physiological processes in plants, and ultimately to the disappearance from ecosystems of species that are not resistant to this influence.
Chemical methods of weed control in agriculture and forestry also damage soils. They cause such negative phenomena as a violation of biological balance, a decrease in the species diversity of communities of soil organisms, a decrease in biochemical processes, changes in the physical and chemical properties of the soil, and a decrease in the resistance of the soil ecosystem to unfavorable environmental factors. With the current level of chemicalization in agriculture, the issue of protecting soils, especially those with a low level of biogenicity, is of particular relevance.
Some experts believe that desertification is just one phase of a natural climate process that occurs very slowly. Others believe that droughts only provoke the process of desertification, but are not its cause. In their opinion, it is irrational land use and overgrazing, which significantly deplete the land and reduce its productivity, that is the true cause of desertification.
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