Magazine article UNESCO Courier

Erosion, Drought and Deserts; When Man Is Careless, Water Can Be a Destroyer

Magazine article UNESCO Courier

Erosion, Drought and Deserts; When Man Is Careless, Water Can Be a Destroyer

Article excerpt

Erosion, drought and deserts

When man is careless, water can be a destroyer

SOIL is a country's most precious natural resource, aptly described as "the bridge between the inanimate and the living'. It consists of weathered and decomposed bedrock, water, air, organic material formed from plant and animal decay, and thousands of different life forms, mainly micro-organisms and insects. All play their part in maintaining the complex ecology of a healthy soil.

Although soil erosion does occur naturally, the process is slow. Man has increased the rate of natural erosion by at least 2.5 times and, over the centuries, has destroyed an estimated 2,000 million hectares of land. There is good evidence that past civilizations, in the Mediterranean and in Central America, collapsed as a result of soil erosion following the cutting of forests on steep slopes and other destructive practices.

Soil erosion occurs primarily when land is exposed to the action of wind and rain. Unprotected by a cover of vegetation, and the binding action of roots, each raindrop hits the naked soil with the impact of a bullet. Soil particles are loosened, washed down the slope of the land, and either end up in the valley below or are washed out to sea by streams and rivers.

Water erosion is the commonest form of erosion. It is causing massive damage in nearly all developing countries. It is found where steep land is being unwisely farmed and where gently sloping land is left exposed to the effects of heavy rain for any length of time.

Worldwide, about 25,000 million tonnes of soil are being washed away each year, ending up in the rivers and finally the oceans. According to a study carried out by the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Environment Programme (UNEP) an estimated 11.6 per cent of Africa north of the equator and 17.1 per cent of the Near East are subject to water erosion. So are 90 million of India's 297 million hectares.

Water erosion causes two sets of problems: an "on-site' loss of agricultural productivity; and a downstream movement of sediment, causing flooding, a loss of river navigability and the silting up of reservoirs.

While heavy rainfall, prolonged drought or high winds may be the direct cause of soil erosion, they are not the real problem. A landscape can remain stable under all these conditions, whether it is in a natural state or being sensibly farmed. Erosion occurs when farming practices are used which fail to take account of the ease with which soils can be washed or blown away.

For example, over-stocking and over-grazing have caused untold damage in much of Africa and Asia in the past few decades. In arid areas, soil is compacted around water holes, the vegetation is stripped and dies, and erosion sets in. Too often the land ends up as desert, the intimate result of soil erosion and degradation. If erosion is the sickness of a land, desertification is its death.

Today, desertification is threatening about 3,200 million hectares of land; the livelihoods of the 700 million people who depend on that land are at stake. …

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