Desertification


Nature Gallery (Global Trends)
Desertification
Desertification is the encroachment of desert conditions into areas that were not previously dry and barren. It is an environmental problem affecting nearly half of all countries. Worldwide, an estimated 6 million to 27 million hectares (15 million to 67 million acres) of land are lost each year to desertification. Of the one-third of the world's land mass that is dry land, 70 per cent is damaged enough to be vulnerable to such losses. More than simply the advance of sand dunes, desertification implies degradation of soil so extreme that the land loses the capacity to support growth. The most notable cause of desertification is lack of rain, but overgrazing, deforestation, excessive irrigation, and unsound agricultural practices also contribute to the problem. Once vegetation is stripped from the land by any of these causes, wind and water erosion carry off thin, dryland soils, which will not regenerate for centuries.

Aral Sea
A pre-eminent example of human-caused desertification occurred in Kazakhstan and Uzbekistan in the middle of the 20th century. To meet the demand for agricultural irrigation and industry in the two states, the former Union of Soviet Socialist Republics (USSR) diverted water from rivers that flowed into the Aral Sea. Without water from feeder rivers to replenish it, the level of the inland sea dropped by one-third. As a result, fisheries along the Aral Sea shoreline have been destroyed and nearby farm land ruined by salinization and wind-blown sand. Moreover, without the moderating influence of the huge body of water, the regional climate has grown more harsh. Vast areas in Africa, Australia, and the western United States have also experienced declines in biological productivity due to desertification, and the problem could become more severe in the United States. As recently as 1,000 years ago, the Great Plains were strewn with sand dunes, a situation that could be repeated in the near geological future. In 1990 alone, dry eastern Colorado lost more than 400,000 hectares (1 million acres) of topsoil. Desertification is sometimes attributed to the pressures caused by a growing human population, but the link is not clear-cut. Even without the stresses of overpopulation, deserts regularly expand and contract in response to rainfall patterns. And although overgrazing cattle are often blamed for compacting fragile soil, which leads to desertification, the cattle may actually help arid regions by pushing seeds underground where water can reach them. Using proper land-management techniques, even people in densely populated areas may be able to save vulnerable terrain from desertification, through intensive cultivation and stewardship. Many nations have taken steps to counteract conditions such as soil erosion that sometimes lead to desertification. For example, after losing hundreds of towns and millions of hectares of farm land to deserts along its northern border, China launched a campaign in 1978 to plant trees and other vegetation in exposed areas. The resulting tree buffer, called the “Great Green Wall,” now encompasses 22 million hectares (54 million acres).