desertification

Spread of deserts by changes in climate, or by human-aided processes. Desertification can sometimes be reversed by special planting (marram grass, trees) and by the use of water-absorbent plastic grains, which, added to the soil, enable crops to be grown. About 30% of land worldwide is affected by desertification (1998), including 1 million hectares in Africa and 1.4 million hectares in Asia. The most rapid desertification is in developed countries such as the USA, Australia, and Spain.

Natural causes of desertification include decreased rainfall, increased temperatures, lowering of the water table, and soil erosion.

The human-aided processes leading to desertification include overgrazing, destruction of forest belts, and exhaustion of the soil by intensive cultivation without restoration of fertility - all of which may be prompted by the pressures of an expanding population or by concentration in land ownership. About 135 million people are directly affected by desertification, mainly in Africa, the Indian subcontinent, and South America. The Sahel region in Africa is one example.