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Where does deser-
tification occur?
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Surface area of the world’s drylands

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4. Nevada in the USA: golf in the middle of the desert,
north of Las Vegas.
© Yann Arthus-Bertrand / Earth from Above / UNESCO

Almost half of the terrestrial land surface, equal to 6.45 billion hectares, is made up of drylands (47% according to the World Atlas of Desertification, UNEP 1997).
They are distributed among all the great regions of the planet.
One billion hectares is hyper-arid: these are real deserts such as the Sahara. 5.45 billion hectares are made up of arid, semi-arid and sub-humid areas. Desertification occurs in this part of the planet. These areas are inhabited by one fifth of the world’s population or 1.2 billion inhabitants in the year 2000. It is here— where the soils are especially fragile, vegetation is sparse and the climate particularly unforgiving— that desertification takes place. (Land degradation occurs everywhere, but can only be defined as ‘desertification’ when it occurs in the drylands). Some 70% of the 5.2 billion hectares of drylands used for agriculture around the world are already degraded.
Thus desertification now damages practically one quarter of the total land surface area of the world.

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.

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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:

puntHyper-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.
puntArid regions:
generally rainfall does not exceed 200 mm/year. These regions are characterized by farming (sedentary or nomadic) and irrigated agriculture.

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6. Ayers Rock Uluru in Australia: sand dunes.
© Yann Arthus-Bertrand Earth from Above / UNESCO

puntSemi-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.
puntDry 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.

activities

question

Locate your country and your region on the world map (See the poster).

Is your country located in a desertification zone?

Locate those countries that have arid zones and those that do not.

pencil

On the world map, colour the arid regions in yellow and write the names of the corresponding countries (or make and stick country flags on the map) in the desertification areas.

Colour the oceans in blue and the temperate zones
in green.

What do you notice?

pencil

On a ball or a sphere made of paper maché, draw the continents and their deserts with a felt tip pen while respecting their dimensions.

Decorate the colourful globe by painting the ball and glue sand for the desert areas.

You could also use an orange or any round fruit to achieve the same effect.

pencil

Select 10 words that symbolize the desert.

Write a poem using these 10 words.


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