One of the most serious environmental problems today is the global problem of desertification. Human agricultural activities are becoming the main cause of desertification. When plowing fields, a huge amount of particles of the fertile soil layer rises into the air, dissipates, is carried away from the fields by streams of water and is deposited in other places in huge quantities. The destruction of the upper fertile soil layer under the influence of wind and water is a natural process, however, it is accelerated and intensified many times over when plowing large areas and in those cases when farmers do not leave the field "fallow", that is, do not allow the land to "rest".
In the surface layers of the soil, under the influence of microorganisms, air and water, a fertile layer is gradually formed. One handful of good fertile soil contains millions of soil-friendly microorganisms. For the formation of a fertile layer one centimeter thick, nature needs at least 100 years, and it can be lost literally in one field season.
Geologists believe that before the beginning of intensive agricultural activities of people - plowing of land, active grazing of livestock by rivers, about 9 billion tons of soil were transported into the ocean annually, today this amount is estimated at about 25 billion tons.
Soil erosion has become universal in our time. For example, in the United States, approximately 44% of arable agricultural land is subject to erosion. Due to erosion, fertile chernozems containing 14-16% of humus have disappeared in Russia, and the areas of the most fertile lands with a humus content of 11-13% have decreased by 5 times. Soil erosion is especially high in countries with a large territory and high population density. The Yellow River, a river in China, annually carries about 2 billion tons of soil into the oceans. Soil erosion not only reduces fertility and productivity; under the influence of soil erosion, artificial water canals and reservoirs are silted up much faster, and, consequently, the possibility of irrigating agricultural land is reduced. Particularly serious consequences occur when, after the fertile layer, the parent rock, on which this layer develops, is demolished. Then irreversible destruction occurs and an anthropogenic desert is formed.
The Shillong Plateau, located in the north-east of India in the Cherrapunji region, is the wettest place in the world, with more than 12 m of precipitation per year. However, during the dry season, when the monsoon showers stop pouring (from October to May), the area resembles a semi-desert. The soil on the slopes of the plateau was practically washed away, and barren sandstones were exposed.
The expansion of desertification is one of the most rapidly developing global processes in our time, while there is a decrease and sometimes complete destruction of the biological potential in the territories subject to desertification, thus, these territories are turning into deserts and semi-deserts.
Natural deserts and semi-deserts occupy about one third of the entire surface of the earth. These territories are home to up to 15% of the total population of the planet.
The deserts have an extremely arid continental climate, usually there are no more than 150-175 mm of precipitation per year, and evaporation is much higher than natural moisture.
The most extensive deserts are located on both sides of the equator, as well as in Central Asia and Kazakhstan. Deserts are natural formations that have a certain value for the overall ecological balance of the planet. However, as a result of intensive anthropogenic activity in the last quarter of the 20th century, more than 9 million 2 km of land appeared. deserts, their territories covered about 43% of the total land surface of the earth.
In the 1990s, 3.6 million hectares of drylands were threatened by desertification, accounting for 70% of all potentially productive drylands.
Lands in different climatic zones are subject to desertification, but the desertification process is especially intense in the hot and arid regions of the planet. One third of all arid regions of the world are located on the African continent, they are widespread in Asia, Australia and Latin America.
On average, 6 million hectares of arable land are subjected to desertification per year until complete destruction, and yield decreases on more than 20 million hectares of agricultural land under the influence of desertification.
According to UN experts, while maintaining the current rate of desertification by the end of this century, humanity may lose 1/3 of all arable land. Combined with the rapid population growth and the constant increase in food demand, the loss of such a large amount of agricultural land could be disastrous for humanity.
Desertification of territories leads to degradation of the entire natural life support system. People living in these territories need either external help or resettlement to other more prosperous areas to survive. For this reason, the number of environmental refugees is increasing every year in the world.
The desertification process is usually caused by the combined actions of man and nature. Desertification is especially destructive in arid regions, because the ecosystem of these regions is already quite fragile and easily destroyed. The already scarce vegetation is destroyed due to the massive grazing of livestock, intensive felling of trees, shrubs, plowing of soils unsuitable for agriculture and other economic activities that violate the precarious natural balance. All this enhances the effect of wind erosion. At the same time, the water balance is significantly disturbed, the level of groundwater goes down, wells dry up. In the process of desertification, the structure of the soil is destroyed, and the saturation of the soil with mineral salts increases.
Desertification and land depletion can occur in any climatic zone as a result of the destruction of the natural system. In arid regions, an additional cause of desertification is drought.
Desertification arising from irrational and excessive human economic activity has more than once become the cause of the death of ancient civilizations. Is humanity able to learn from its past history? However, there are significant differences between the desertification process taking place now and the process that took place in those distant times. In those ancient times, the scale and rate of desertification was completely different, that is, much smaller.
If in ancient times the negative consequences of excessive economic activity took shape for centuries, then in the modern world the consequences of inept irrational human activity are already being felt during the current decade.
If in ancient times individual civilizations perished under the onslaught of the sands, then the process of desertification in the modern world, originating in different places and manifesting itself in different regions, takes on a global scale in different ways.
An increase in the concentration of carbon dioxide in the atmosphere, with an increase in its dustiness and smoke, accelerates the process of auridization of the land. Moreover, not only arid regions are subject to this phenomenon.
The increase in the area of deserts contributes to the formation of dry climatic conditions favorable for the occurrence of perennial droughts. Thus, in the transition zone of the Sahel, 400 km wide, located between the Sahara Desert and the savannahs of West Africa, an unprecedented multi-year drought broke out in the late sixties, the apogee of which came in 1973. As a result, more than 250,000 people died in the countries of the Sahel zone - Gambia, Senegal, Mali, Mauritania and others. There was a massive death of livestock. Meanwhile, animal husbandry is the main activity and source of livelihood for the majority of the local population. Not only most of the wells were dry, but also such large rivers as Senegal and Niger, and the water surface of Lake Chad was reduced to one third of its former size.
In the 1980s, the ecological disaster in Africa resulting from drought and desertification became continental-wide. The consequences of these phenomena are being felt by 35 African states and 150 million people. In 1985, more than one million people died in Africa and 10 million became "environmental refugees". The expansion of the boundaries of deserts in Africa occurs at a rapid pace, in some places reaching 10 km per year.
The history of human civilization is closely related to forests. For primitive people living by gathering and hunting, forests served as the main source of food. Much later, they became a source of fuel and material for the construction of dwellings. Forests have always been a refuge for man, and also were the basis of his economic activity.
Approximately 10 thousand years ago, even before the beginning of active agricultural activities of man, the forest-covered spaces occupied about 6 billion hectares of the earth's land. By the end of the 20th century, the area of forest territories had decreased by 1/3; at present, forests occupy just over 4 billion hectares. For example, in France, where forests initially covered up to 80% of the country's territory, by the end of the 20th century, no more than 14% remained. In the United States at the beginning of the 17th century, there were about 400 million hectares of forests, and by 1920 the forest cover in this country had been destroyed by 2/3.
Forests are a deterrent to desertification, and accordingly, their destruction leads to acceleration of the processes of auridization of the land, therefore, forest conservation is a priority in the fight against desertification. By conserving forests, we not only preserve the planet's lungs and curb the growth of deserts, we also ensure the well-being of our descendants.
Can you imagine that the Sahara Desert in North Africa is 9.4 million square kilometers? This is exactly the case, because the Sahara is the largest desert in the world.
What else is remarkable about the Sahara Desert?
- The Sahara occupies 30% of the entire African continent;
- The Sahara is the hottest and hottest place in the world with summer temperatures often exceeding 57 ° C;
- The Sahara has an annual downpour and very powerful sandstorms that raise sand 1 kilometer in height and move the dunes. This year ;
- There is an amazing plateau in the Sahara called Tassilig-Ajer. Here's what the book says about him AllatRa by Anastasia Novykh:
« Yes, such kind of "stone books", applied on rocks, each the size of a football field, scientists find to this day. For example, rock carvings (petroglyphs) on the White Sea (Zalavruga, Republic of Karelia, Russia), or Swedish Nemforsen (in the province of Ongermanland) and Tanuma (in Bohuslain), or in the foothills of the central Alps in the Val Camonica valley (Italy), or the inscriptions of the African Bushmen in the Drakensberg mountains, or the drawings of the Tassilin-Ajer plateau in the Sahara, and so on. "
Recently, scientists have been worried about the changing size of the Sahara. Indeed, at the beginning of the XXI century, its area was just over 7 million square kilometers. Experts have studied and analyzed historical records collected throughout Africa, as well as climate models over the past 100 years. Thanks to these historical data, the researchers concluded that between 1920 and 2013, the area of the Sahara grew by at least 10%. Why has the Sahara increased so much? Researchers at the University of Maryland have suggested that one of the factors may be a link to climate change. Scientists have been able to trace the relationship between the decrease in rainfall along the southern border of the Sahara and the desertification of the ecosystem of pastures in Nigeria, Chad and Sudan. The result of the research showed that the rainfall in the Sahara decreased by a third. This gave scientists reason that the decrease in precipitation provoked an increase in the area of the desert. Also, when analyzing seasonal precipitation, it turned out that the number of summer rains fell sharply, in contrast to precipitation during other seasons. Given that the border regions of the desert are temporarily expanding based on seasonal rainfall, the Sahara desert borders are 16 percent larger in summer. First of all, Chad suffers from the increase in the area of the Sahara - it is experiencing a real climate crisis.
Scientists note that if no action is taken, the area of the Sahara Desert will continue to grow. But the growth of the Sahara can dramatically affect the wildlife and the people living along its borders. Areas where food is grown are becoming drier, and drought can lead to complete loss of crops and hunger.
“Only early preparation and unity of the peoples of the world in front of the threatening natural danger gives mankind great chances for survival and joint overcoming of difficulties in the era associated with global climate change on the planet”, -.
Why are climate changes happening? And can you prepare for them?
Deserts and semi-deserts occupy at least 22-23% of the land area, g. at least 31.5 million sq. km. According to some estimates, the area of deserts and semi-deserts exceeds a third of the earth's surface. As a result of ecologically illiterate farming, the area of deserts on the planet is constantly increasing, capturing an average of 50-70 thousand square meters. km of productive land annually (UN Conference on Desertification..., 1978). Only in the last quarter of the XX century. more than 9 million sq. km of deserts, and another 30 million sq. km is under the threat of desertification (these territories are home to more than 15% of the world's population).
Generally The territory is defined as arid (zasuiiioaya) in the event that the evaporation of moisture from it exceeds the amount of precipitation (moisture). There are various variants of arid biotas - tropical and extratropical deserts, semi-deserts and steppes, arid savannas. Each of them is characterized by a specific amount of precipitation, the ratio of dry and wet seasons, biomass, etc.
Of the main climatic and environmental factors affecting humans in the arid zone of tropical latitudes, one should first of all call high temperatures. In deserts, the average summer temperatures in the shade exceed + 25 ° C. Due to low cloudiness and high transparency of the air, insolation is very high: the annual amount of solar radiation in the deserts of North Africa reaches 200-220 kcal / sq. cm, which is 2.5 times higher than in the middle lane.
Physiologically, the problem of adaptation to an arid climate is complicated by heme, that at air temperatures above +33 ° C, heat transfer through the skin (convection) is sharply reduced and is provided practically only by evaporation. The vital activity of the human body when the body temperature rises above 44 ° C is impossible (upper legal temperature).
Morphological adaptation to reduced heat transfer in representatives of semi-desert and desert populations is provided either due to general gracilization (reduction in body size, as in the Kalahari Bushmen), or due to a combination of high growth and low weight (Tuareg of the Sahara, Gurcan, and the south of the East African arid savanna ). Both options lead to an increase in the ratio of body area (heat transfer) to muscle mass (heat production), g. reduce the risk of overheating.
Daily temperature drops in deserts are quite significant. Although the average daily temperature in a tropical desert is only 8 ° C higher than in a rainforest, the difference between daytime and nighttime temperatures in a desert is almost double that of a rainforest. In the area of Gurkana (Kenya, semi-desert savanna), the average pre-morning temperature is +24 ° С with an average daytime temperature of +37 ° С. In the early morning hours, the air temperature in the Central Asian deserts drops to 18-23 ° C, and in the Kalahari and the deserts of southern Australia, night temperatures are even lower.
Seasonal temperature drops insignificant in tropical deserts, but very large in non-Stropichs (Karakum, Kyzylkum, Gobi). Winter in the Gobi lasts about 6 months, without thaws, with frosts down to -40 ° C. The absolute maximums of summer daytime temperatures reach + 50 ° С in the shade. The steppes of the temperate climate are also characterized by long hot summers and rather cold winters. Thus, the environmental pressure of the continental climate factors is added to the influence of the factors of the arid zone in the non-Stropic regions.
Typical for deserts dry air leads to rapid dehydration of the body. The average relative humidity in deserts is about 30% (in the tropical rainforest it reaches 80-100%). The effect on the body of dry air is aggravated by constant winds. At the same time, desert winds are often combined with a significant increase in air temperature and therefore lead not only to additional loss of moisture, but also to overheating of the body (the well-known expression - "the wind in the desert does not bring coolness").
Chapter 11. Deserts
Deserts on the planet occupy vast territories. They cover the largest areas in Africa (75% of the total area of deserts), Asia and Australia.
There are also many deserts in North and South America. In total, deserts on earth occupy 20 million km2. But in Europe there are no deserts.
There are deserts of the temperate zone, subtropical and tropical. In the temperate zone, they spread across the plains of Asia from the Caspian Sea in the west to Central China in the east. In North America, some areas of intermontane depressions in the western part of the mainland are also deserts.
Deserts of subtropical and tropical zones are located in the northwest of India, Iran, Pakistan and Asia Minor, on the Arabian Peninsula, in the northern part of the African continent, on the west coast of South America and in the heart of Australia.
Most deserts are characterized by a sharply continental climate. In summer, it is hot and dry, during the day the air temperature in the shade in temperate and subtropical deserts exceeds 40 ° C, and in tropical deserts it sometimes reaches 58 ° C. It becomes cold at night, the temperature often drops to 0 ° C. In winter, in deserts it is very cold, and even in the unusually hot Sahara, frosts are not uncommon at this time.
There is very little rainfall in the deserts, on average - no more than 180-200 mm per year, and in some places even less, as, for example, in the Atacama Desert in Chile (about 10 mm). In tropical deserts, even the smallest rain may not fall for several years.
In the spring, vegetation appears in the deserts, while in the summer it almost completely burns out. That is why the soil of deserts takes on a light yellow, light gray or almost white color.
In many deserts, rocky and clayey areas pass into spaces occupied by sand alone. Here you can see huge waves - dunes, the height of which sometimes exceeds 10–12 m. They have a crescent shape. Sometimes the ends of the dunes converge, and long chains appear. The dunes move under the influence of the wind. Some overcome only 10 cm in a year, others - several hundred meters.
There are no forests and very few mountain ranges in the deserts, so the wind has a place to roam. Not meeting any obstacles on its way, it gains tremendous strength, lifts up the sand and sometimes turns into a dusty sandstorm.
Clay deserts are devoid of even the most sparse vegetation. They usually occupy lowlands, which are filled with water during rain. Moisture does not penetrate the clay and evaporates when exposed to sunlight. Soon the dry soil is covered with cracks. Such areas of the desert are called takyrs.
Often, various salts come to the surface and salt marshes are formed. Not a single blade of grass grows on them.
Clay deserts are completely unsuitable for animal life, but living creatures live in the sands. Here you can find plants that have adapted to a waterless environment. The sand allows moisture to pass through, and in summer it accumulates in its lower layers.
The representative of the desert flora is saxaul. Some of its species can grow up to 5 meters in height. Saxaul has tiny leaves, which allows it to conserve moisture, and therefore seems completely naked from a distance. By winter, its leaves fall off. Despite this, black saxaul is able to create a shadow in which animals and people can hide from the incinerating sun.
In the desert, many plants change their large spring leaves to smaller ones with the onset of summer. In some representatives of the desert flora, the leaves are covered with a shiny waxy layer, and the sun's rays are reflected from them.
Thorny sandy acacia and black wormwood grow in deserts, which have no leaves at all for most of the year. Only in early spring does it become covered with delicate leaves, but very soon they fly around, giving the plant the opportunity to survive in the difficult conditions of a waterless desert.
Various types of cacti can be found in the deserts of the Western Hemisphere. They are able to collect huge reserves of moisture in their stems and leaves, and often more than 90% of the weight of the entire plant is in water. Almost 3 thousand liters of water are stored in a huge North American cactus carnegia giant, growing up to 15 meters in height. Most desert plants have a well-developed root system, which allows them to receive water from the depths of the soil.
For many centuries living in the desert, animals have also perfectly adapted to life in difficult conditions. Most of them are yellowish-gray in color, which allows you to hide from enemies or sneak up on a victim.
From the heat, representatives of the desert fauna hide in a wide variety of places. Sparrows, pigeons, owls rest in the holes on the walls of the wells. They also make their nests there. Feathered predators, for example, eagles, ravens, falcons, find the remains of buildings or hillocks for nesting, choosing the shady side on them.
Cactus
Many animals hide from the heat in cool burrows. At night, this shelter saves them from the cold. Some desert dwellers can do without water at all. So, the fine-toed gopher uses the moisture obtained from the plants it eats. A number of desert animals have the ability to run fast, covering long distances in search of food and water. For example, kulans (wild donkeys) run at a speed of 70 km per hour. One of the most amazing inhabitants of the sands, the camel, drinks very little and can quench its thirst with water from salt lakes. And he eats those plants that other animals will never eat. Huge reserves of fat (up to 100 kg) are collected in its humps, so the camel goes without food for a long time. In addition, he is able to lie on hot sand, calluses on his body and legs protect him from the heat.
One of the inhabitants of the deserts and semi-deserts of North Africa, similar to the fennec fox, moves very quickly and dexterously along the sands. Its huge ears easily catch the slightest rustle of the night desert, thanks to which Fenech successfully hunts lizards, small rodents and beetles.
A variety of amphibians live in deserts: snakes, lizards, turtles. From heat, as well as in danger, they hide in the sand. The horned viper, which lives in the deserts of North Africa, has many sawtooth scales on its body, allowing it to instantly burrow into the ground.
If most reptiles take refuge from the heat in the soil, then the agama lizard, on the contrary, climbs the bushes and trees, where the hot sand no longer frightens it.
The jerboas, found in the Central Asian deserts, spend the whole day in small burrows, from which they get out only at nightfall to feast on seeds and underground parts of plants. With small front legs and unusually long hind legs, they are able to make 3-meter jumps, while balancing with a long tail with a tassel. A typical desert dweller is a scorpion that sleeps in an underground shelter at night and goes hunting in the evening. It feeds on spiders and other insects, as well as small lizards. At night, a predatory tarantula spider is looking for its prey.
Scientists and travelers often find ruins of ancient cities and irrigation canals in the desert sands. Many of these settlements were destroyed during the wars. People left their habitable places forever, and soon the once flourishing city was at the mercy of the sands.
The desert continues to advance into neighboring territories at the present time. This happens most often where people ruthlessly cut down trees, destroy bushes and do not change their grazing places for a long time. Plants, the roots of which held the sands, are disappearing, and the desert invades more and more new lands. Scientists estimate that each year the area of deserts increases by 60,000 km2, which corresponds to half the area of Belgium.
This text is an introductory fragment.
In the surface layers of the soil, under the influence of microorganisms, air and water, a fertile layer is gradually formed. One handful of good fertile soil contains millions of soil-friendly microorganisms. For the formation of a fertile layer one centimeter thick, nature needs at least 100 years, and it can be lost literally in one field season. Soil erosion has become universal in our time.
Soil erosion not only reduces fertility and productivity; under the influence of soil erosion, artificial water canals and reservoirs are silted up much faster, and, consequently, the possibility of irrigating agricultural land is reduced. Particularly serious consequences occur when, after the fertile layer, the parent rock, on which this layer develops, is demolished. Then irreversible destruction occurs and a desert is formed.
The expansion of desertification is one of the most rapidly developing global processes in our time, while there is a decrease and sometimes complete destruction of the biological potential in the territories subject to desertification, thus, these territories are turning into deserts and semi-deserts. Natural deserts and semi-deserts occupy about one third of the entire surface of the earth. These territories are home to up to 15% of the total population of the planet.
Lands in different climatic zones are subject to desertification, but the desertification process is especially intense in the hot and arid regions of the planet. One third of all arid regions of the world are located on the African continent, they are widespread in Asia, Australia and Latin America. On average, 6 million hectares of arable land are subjected to desertification per year until complete destruction, and yield decreases on more than 20 million hectares of agricultural land under the influence of desertification.
The desertification process is usually caused by the combined actions of man and nature. Desertification is especially destructive in arid regions, because the ecosystem of these regions is already quite fragile and easily destroyed. The already scarce vegetation is destroyed due to the massive grazing of livestock, intensive felling of trees, shrubs, plowing of soils unsuitable for agriculture and other economic activities that violate the precarious natural balance. All this enhances the effect of wind erosion. At the same time, the water balance is significantly disturbed, the level of groundwater decreases,
Unfortunately, the areas of many deserts are increasing every year. The Gobi Desert in Mongolia, the Kalahari in South Africa, and the Karakum Desert in Central Asia also grow. Every year, the deserts reclaim an area comparable in area to Belgium. But the record holder is the African Sahara, the largest desert on our planet. At the beginning of the XXI century, its area was more than 7 million square kilometers. Its sands are advancing south and southeast at a speed of 50 kilometers per year. The reasons for this movement are still unclear to scientists. There is no way to stop this relentless gritty advance.
Did you know that. ... ... The Sahara stretches across most of North Africa, covering 9 million square kilometers. The Sahara Desert occupies 30% of the entire African continent. The Sahara is the hottest and hottest place in the world with summer temperatures often exceeding 57 degrees Celsius. The Sahara has an annual downpour and very powerful sandstorms that raise sand 1 kilometer in height and move the dunes.
Conclusion: Currently, there is a tendency to expand the territories of some of the largest deserts. Thus, the southern border of the Sahara in recent years has been moved southward by an average of 15 kilometers annually. Agricultural lands are often subjected to desertification, which causes significant damage to the economies of countries whose territory is directly adjacent to deserts. The reasons for this phenomenon are poor irrigation, irrational use of pastures, and too intensive farming. Deserts are the source of dust storms. A huge amount of dust and sand is carried by powerful air currents over considerable distances, and then thrown onto the ground, covering the soil layer with sand and contributing to land desertification. The problem has taken on a global character, as evidenced by the fact that, at the initiative of the UN, a special commission was created to study the problem and develop a targeted program of ways to solve it. The targeted program for the prevention of desertification includes a comprehensive economic study of deserts, their protection, as well as a system of measures to prevent their expansion.