Desertification, also called desertization, the process by which natural or human causes reduce the biological productivity of drylands (arid and semiarid lands). Declines in productivity may be the result of climate change, deforestation, overgrazing, poverty, political instability, unsustainable irrigation practices, or combinations of these factors. The concept does not refer to the physical expansion of existing deserts but rather to the various processes that threaten all dryland ecosystems, including deserts as well as grasslands and scrublands.
Desertification 1) Trees are being cut down at much larger scale than ever before to be used as fuel, to provide products we use in our daily life, or to simply create more space for agriculture to sustain growing human population. Once the trees and other vegetation in an area are gone, there is nothing left to hold the soil in place. 2) Our planet's ecosystems sustain life only when balanced. They can cope with incremental challenges and adapt but beyond a certain tipping point they collapse. A rapid increase in the number of people demands higher amounts of natural resources and expands more and more over the landscape, leading to increased desertification. 3) Improper irrigation methods used in arid areas, such as canal irrigation, lead to a buildup of salt in the soil and make it difficult for crops and other plants to grow, increasing desertification. Similarly harmful is cultivation of already deteriorated lands. Through inconsiderate farming methods, farmers only speed up the process of desertification in exchange for poor quality crops with low economic value. 4) In arid regions, grass and other vegetation is necessary to keep the soil in place. If such vegetation is used as feed for cattle without sustainable control, there is nothing that remains to prevent soil from blowing or washing away, and if this process occurs long enough, it can lead to desertification.
The increasingly serious issue of land desertification not only leads to environmental degradation, but also reduces the quantity and quality of resources. It disturbs agricultural and industrial production and people’s life, and leaves a dramatic impact on ethnic unity and social stability. Indeed, it has acted as a big drag on economic and social development in western and central China, especially in the northwest.
In China, the consequence of desertification is a growing mismatch between population growth and land loss, along with reduced space of human existence. Every year, the country’s population increases by about 14 million, while an average of 3,436 square kilometers of land is lost to desertification, leading to a progressive decline of arable land. The tug-of-war between humanity and desertification is more prominent than ever before, with around 24,000 villages and towns subjected to strong winds and sandstorms. Residents in some villages and towns even have been forced to relocate many times.
Second, desertification increases the frequency and severity of natural disasters and results in the deterioration of the environment, thus undermining the conditions for human survival. In China, it is also one of the main causes of frequent sandstorms over recent years, sharp decline in biodiversity and wind erosion in affected regions, and recurrent droughts and floods in the middle and lower reaches of the Yellow River. In these affected regions, vegetation cover is drastically reduced, and many species are endangered or on the brink of extinction. Of the 1.6 billion metric tons of sediment loads that the Yellow River carries every year, 1.2 billion come from these regions.
The global reach of desertification
Baobab trees growing in the wooded-grassland area of Senegal in West Africa.Slightly less than half of Earth’s ice-free land surface—approximately 52 million square km (about 20 million square miles)—is drylands, and these drylands cover some of the world’s poorest countries. The United Nations Environment Programme (UNEP) notes that desertification has affected 36 million square km (14 million square miles) of land and is a major international concern. According to the United Nations Convention to Combat Desertification, the lives of 250 million people are affected by desertification, and as many as 135 million people may be displaced by desertification by 2045, making it one of the most severe environmental challenges facing humanity.Africa is the continent most affected by desertification, and one of the most obvious natural borders on the landmass is the southern edge of the Sahara desert. The countries that lie on the edge of the Sahara are among the poorest in the world, and they are subject to periodic droughts that devastate their peoples. African drylands (which include the Sahara, the Kalahari, and the grasslands of East Africa) span 20 million square km (about 7.7 million square miles), some 65 percent of the continent. One-third of Africa’s drylands are largely uninhabited arid deserts, while the remaining two-thirds support two-thirds of the continent’s burgeoning human population. As Africa’s population increases, the productivity of the land supporting this population declines. Some one-fifth of the irrigated cropland, three-fifths of the rain-fed cropland, and three-fourths of the rangeland have been at least moderately harmed by desertification.
Four areas affected by desertification
To better understand how climatic changes and human activities contribute to the process of desertification, the consequences listed above can be grouped into four broad areas:Irrigated croplands, whose soils are often degraded by the accumulation of salts.
Rain-fed croplands, which experience unreliable rainfall and wind-driven soil erosion.
Grazing lands, which are harmed by overgrazing, soil compaction, and erosion.
Dry woodlands, which are plagued by the overconsumption of fuelwood.
Drylands also support rain-fed crops. Before cultivation, such areas were often vast grasslands. They now cover about 5 million square km (about 2 million square miles) and account for roughly one-third of all croplands worldwide. They receive less than 60 cm (about 24 inches) of rain each year, and thus they are at the margin of what farmers can use for crops without at least some irrigation. Rainfall can vary considerably from one year to the next, so those lands may experience droughts that often lead to crop failure. Globally, more than 2,000,000 square km (about 770,000 square miles) of rain-fed croplands are moderately to severely degraded, and each year about 1 percent of those lands is abandoned.
The crops grown on drylands are annuals; each year they emerge from seed, mature, and die. Grains such as wheat and corn (maize) are annuals that account for roughly 85 percent of global food production. After these grains are harvested, the lands are left uncovered until the next planting season. During this time, the soil is vulnerable to erosion by wind and rain. Wind can whip up the unprotected topsoil to create severe dust storms. Such dust storms often transport the soils, along with the nutrients they contain, over long distances. Rainfall is scarce in drylands, but when it does come it can be torrential. Heavy downpours often wash away the soils on bare ground or deplete them of their nutrients. In contrast, native grasslands contain a mix of mainly perennial species that inhibit erosion. Perennials live from year to year, have deeper roots to bind the soil, and do not leave the soils exposed for months on end.
Dry woodlands
The fourth area of desertification is dry woodlands, which are greatly affected by the overconsumption of firewood. Across large areas of Asia and Africa, the principal raw material for cooking and heating is wood. Firewood in these areas is often converted to charcoal in earthen kilns before it is used, because charcoal gives off less smoke than wood. The conversion process is often inefficient, however, with about 75 percent of the wood’s heating potential lost. In Africa and Asia a very rough estimate of the per capita consumption of firewood is about half a ton per year. Across large areas of dryland where total plant production is roughly two tons per hectare per year, a family of four would have to clear a hectare of land or more per year. Very often, such deforested areas are not replanted. As human population densities increase, one can imagine that they might consume more wood than the land could support and create a “fuelwood crisis.”
Solutions to desertification
The struggle against desertification can occur at several levels. Since regional variations in climate are the main causes of the loss of dryland productivity, it is important to understand the influence of global warming in specific dryland regions. According to some models of climate change, many grasslands in western North America, for example, are predicted to be at greater risk of drought due to projected increases in summer temperatures and changes to existing rainfall patterns. Many authorities argue that since desertification and global warming are so closely related, one of the main solutions to the former may be the implementation of effective economic policies (such as carbon trading) and technical measures (such as carbon sequestration) that reduce the production of greenhouse gases.
At local scales, however, desertification is often the result of unsustainable land and soil management. To maintain the biological productivity of the land, soil conservation is often the priority. A number of innovative solutions have been devised that range from relatively simple changes in how people grow crops to labour-intensive landscape engineering projects. Some of the techniques that may help ameliorate the consequences of desertification in irrigated croplands, rain-fed croplands, grazing lands, and dry woodlands include:
Salt traps, which involve the creation of so-called void layers of gravel and sand at certain depths in the soil. Salt traps prevent salts from reaching the surface of the soil and also help to inhibit water loss.
Irrigation improvements, which can inhibit water loss from evaporation and prevent salt accumulation. This technique involves changes in the design of irrigation systems to prevent water from pooling or evaporating easily from the soil.
Cover crops, which prevent soil erosion from wind and water. They can also reduce the local effects of drought. On larger scales, plant cover can help maintain normal rainfall patterns. Cover crops may be perennials or fast-growing annuals.
Crop rotation, which involves the alternation of different crops on the same plot of land over different growing seasons. This technique can help maintain the productivity of the soil by replenishing critical nutrients removed during harvesting.
Rotational grazing, which is the process of limiting the grazing pressure of livestock in a given area. Livestock are frequently moved to new grazing areas before they cause permanent damage to the plants and soil of any one area.
Terracing, which involves the creation of multiple levels of flat ground that appear as long steps cut into hillsides. The technique slows the pace of runoff, which reduces soil erosion and retards overall water loss.
Contour bunding (or contour bundling), which involves the placement of lines of stones along the natural rises of a landscape, and contour farming. These techniques help to capture and hold rainfall before it can become runoff. They also inhibit wind erosion by keeping the soil heavy and moist.
Windbreaks, which involve the establishment of lines of fast-growing trees planted at right angles to the prevailing surface winds. They are primarily used to slow wind-driven soil erosion but may be used to inhibit the encroachment of sand dunes.
Dune stabilization, which involves the conservation of the plant community living along the sides of dunes. The upper parts of plants help protect the soil from surface winds, whereas the root network below keeps the soil together.
Charcoal conversion improvements, which include the use of steel or mud kilns or high-pressure compacting equipment to press the wood and other plant residues into briquettes. Conversion improvements retain a greater fraction of the heating potential of fuelwood.