Desertification is the degradation of land in arid, semi-arid, and dry sub-humid areas. It is a gradual process of the loss of soil productivity and the thinning out of the vegetative cover resulting from human activities and climatic variations such as prolonged droughts and floods. What is alarming is that the land's topsoil, which takes centuries to build up, can, if mistreated, be blown and washed away in a few seasons. Among human causal factors are overcultivation, overgrazing, deforestation and poor irrigation practices. Such overexploitation is generally caused by economic and social pressure, ignorance, war and drought. Desertification is a worldwide problem directly affecting 250 million people and more than 4 billion hectares of land one third of the Earth's surface area.In addition, desertification threatens the livelihoods of some one billion people who depend on land for most of their needs and are usually the world's poorest, in more than 100 countries. Although the region most affected by desertification is Africa, where two thirds of the land is desert or drylands, the problem is not confined to this continent. More than 30 per cent of the land in the United States is affected by desertification. One quarter of Latin America and the Caribbean is deserts and drylands. In Spain, one fifth of the land is at risk of turning into deserts. The growing severity of the threat in the northern hemisphere is also illustrated by severe droughts in the United States and water scarcity in southern Europe. In China, since the 1950s, sand drifts and expanding deserts have taken a toll of nearly 700,000 hectares of cultivated land, 2.35 million hectares of rangeland, and 6.4 million hectares of forests, woodlands and shrub lands. Worldwide, some 70 per cent of the 5.2 billion hectares of drylands used for agriculture are already degraded and threatened by desertification.
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