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What is desertification? The Earth is covered by a fragile layer of soil which forms very slowly, but can be blown and washed away in a few seasons. This is what is now happening in many areas. Nowhere is the problem more acute than in arid, semi-arid and dry sub-humid areas, which cover more than one third of the Earth's surface. "Desertification" is a process by which susceptible areas lose their productive capacity. Land degradation is often linked with food security and poverty, in a cause-effect relationship. The United Nations Convention to Combat Desertification (UNCCD) attempts to reverse this trend. Land Degradation "desertification" means land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities. While land degradation occurs everywhere, it is only defined as "desertification" when it occurs in drylands. Seventy percent of the 5,200 million hectares of drylands used for agriculture around the world are already degraded (Down to Earth, UNCCD Secretariat). Susceptible Drylands The main characteristic of aridity or dryness is the lack of available moisture in average climatic conditions: arid or dry lands are those that experience a negative balance between moisture inputs (annual precipitation levels) and moisture losses (evapo-transpiration). An Aridity Index, or moisture input/losses ratio, is used to delimit different climatic zones with respect to dryness (World Atlas of Desertification, UNEP). In this schema, "arid, semi-arid and dry sub-humid areas", refers to areas, other than polar and sub-polar regions, in which the ratio of annual precipitation to potential evapo-transpiration is between 0.05 and 0.65 units (Article 1, UNCCD). These areas are also referred to as "drylands". Drylands cover forty percent of the world's land surface (about 5.1 billion ha), and are the habitat and source of livelihood of more than 1 billion people (World Atlas of Desertification, UNEP). Desertification affects seventy percent of the world's drylands, amounting to 3.6 billion ha or one fourth of the world's land surface (Down to Earth, UNCCD Secretariat). Soil Degradation Severity Source: UNEP, World Atlas of Desertification Hyper-arid lands, those with an Aridity Index below 0.05 units, are deserts and are therefore not considered susceptible drylands as indicated above, because they have naturally very low biological productivity. Dryness varies both in time and space due to variation in moisture inputs and losses. The inherent natural dynamism of dryland ecosystems is very largely governed by climatic fluctuations. Changes in storage (rivers, groundwater, lakes and soil moisture) and in resource uses (food production, cash crops, range farming, trees and woodlands) also affect dryland boundaries. Land includes soil and local water resources, land surface and vegetation, including crops. Degradation implies reduction of resource productivity by one or a combination of processes acting on the land. Desertification As indicated in the desertification Convention, "land degradation" means reduction or loss, in arid, semi-arid and dry sub-humid areas, of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from land uses or from a process or combination of processes, including processes arising from human activities and habitation patterns, such as: soil erosion caused by wind and/or water; deterioration of the physical, chemical and biological or economic properties of soil; long-term loss of natural vegetation. Soil is an integral part of most terrestrial ecosystems and serves a fundamental function in supporting human communities. Soil degradation is therefore an environmental issue of crucial concern to all societies. Soil degradation, in particular, is defined as human-induced phenomena which lower the current and/or future capacity of the soil to support human life (GLASOD). In drylands, soils are especially vulnerable to degradation due to the slowness of their recovery from a disturbance. It is recorded that almost twenty percent of susceptible drylands experience soil degradation (World Atlas of Desertification, UNEP). Asia possesses the largest land area affected by desertification, seventy-one percent of which is moderately to severely degraded. For Latin America, this proportion is seventy-five percent. In Africa, two thirds of which is desert or drylands, seventy-three percent of the agricultural drylands are moderately to severely degraded (Down to Earth, UNCCD Secretariat). Africa, with a rate of disappearance of forest cover of 3.7 to 5 million ha per year bearing down on both surface and groundwater resources and with half the continent's farmland suffering from soil degradation and erosion, is under the greatest desertification threat. |
| More information about: Northern Mediterranean |
| More information about: Asia |
| More information about: Latin America and the Caribbean |
| More information about: Central and Eastern Europe |
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