[학생] 자유게시판

Characteristics of the drylands

The world’s drylands are particularly affected by desertification.
On an environmental basis, these regions are defined by:

1. low precipitation that is infrequent, irregular and unpredictable.
2. large variations between day and night temperatures.
3. soil that is poor in organic matter.
4. lack of water for consumption.
5. plants and animals adapted to climatic variables (heat resistance, lack of water).

The drylands are comprised of arid, semi-arid and sub-humid areas, the difference being in their degree of aridity. Aridity is the result of the interaction between various climatic factors (rain, temperature, wind) and evapo-transpiration. These elements combine together to determine the growth of plants and the capacities of animals or humans to live fittingly in a harsh natural environment.

5. World map of aridity zones
© CRU / UEA, UNEP / DEWA

Different categories of drylands

There are four main categories that are distinguished by their temperatures and rain cycles:

Hyper-arid regions:
rainfall is less than 100 mm/year. Drought periods can last longer than a year. Biological productivity is low and the sole viable activity is nomadic pastoralism.
Arid regions:
generally rainfall does not exceed 200 mm/year. These regions are characterized by farming (sedentary or nomadic) and irrigated agriculture.

Semi-arid regions:
rainfall does not exceed 500 mm/year in areas of winter rains or 800 mm/year in areas of summer rains. These regions are characterized by cattle-rearing and sedentary agriculture.
Dry sub-humid regions:
rainfall cycles are highly seasonal. These regions are characterized by rain-fed agriculture. As with semi-arid regions, they are particularly vulnerable to the phenomenon of desertification due to pressure from the rising population.

These regions undergo the same processes of degradation as a result of natural resource over-exploitation and are all characterized by water shortages.

Desertification in the drylands

In all, more than 110 countries have drylands that are potentially at risk. In Africa, a billion hectares or 73% of its drylands are affected by desertification with another 1.4 billion hectares affected in Asia. But it is not just a problem for developing countries, in fact the continent that has the highest proportion of drylands subject to desertification is North America with 74% affected. Five countries of the European Union are also affected while many of the most affected areas are in the former Soviet Union.