Temps de lecture :4 minutes
These fragile zones have to sustain the habitats, crops and livestock of over a third of mankind, 90% of who live in developing countries. This is also the case of a third of the Mediterranean Sea’s European bank and 85% of pasture in the United States.
It is estimated that about 48 billion Euros are lost every year due to soil degradation.
Desertification is now threatening about a billion people. A third of the world’s population could be affected in the future. By 2025, two thirds of farmable land in Africa, a third in Asia and a fifth in South America could disappear. In the United States and in Spain, a third of the country is headed for desertification.
The United Nations Convention to Combat Desertification (UNCCD) defines desertification as « land degradation in arid, semi-humid areas resulting from various factors, including climatic variations and human activities » which causes the gradual loss of soil productivity and the erosion of vegetation cover. It is the result of environmental and human factors and leads to a drop in the environment’s fertility and therefore, to a decrease in income and increased poverty. Scarce and highly variable of water resources, the thin layer of arable land and the low productivity of the biomass make land in arid areas very vulnerable to harmful exploitation practices such as overgrazing, intensive deforestation as well as poorly-managed or poorly-controlled rain cultures or irrigated cultures.
Because of desertification, more rainwater drips on the ground instead of seeping into it and refilling the water stocks necessary to plants. Soil subjected to the influence of wind and runoff waters is stripped and loses its most fertile elements. The level of the organic matter is decreases significantly. Every year, 6 million hectares of land loses its biological potential. If the degradation is moderate, the phenomenon is reversible. The restoration of desertificated environments often means better water seepage, an increased vegetation cover rate and larger biodiversity. However, if the degradation can be considered severe or extremely severe, the trend can become irreversible unless very expensive work is undertaken.
Desertification appears differently depending on the geographical setting. In pastoral areas, one can see the degradation of vegetation and soil and a decrease in aquifer regeneration; in rain crop areas, the main concern is the physical, chemical and biological degradation of soils; and in irrigated crop areas the gradual sterilisation of soil through salination is also an issue. (desertification indicator link)
Climate changes that can be seen through changes in rainfall, he sharp increase in the world population leading to an increase in cultivated spaces, pressure on pastures and forest exploitation have multiple consequences:
– Soil erosion, encouraged by extensive deforestation which damages soil consistency. This is as much because of clearing activities and the extension of agricultural perimeters as energy needs being satisfied. In Senegal, wood covers 40% of domestic energy needs and over 90% in Chad. The disappearance of vegetation cover – forests in particular – causes the loss of water from vegetation. As the atmosphere contains less water vapour, there is less rain.
– The destruction and alteration of vegetation cover through overgrazing; this causes more dust to be released into the atmosphere, the degradation of soil and water loss through runoff. Desertification affects 73% of rangelands.
– Soil salination as a result of ill-adapted irrigation practices. Desertification affects 30% of irrigated land – and 47% of non-irrigated farmland.
– Watercourses and lakes drying up due to dams being built and rivers being diverted for irrigation on a large scale. The destruction of the Aral Sea is an example; it is now made up of large stretches of salt where the wind carries away 15 to 75 million tons of sand and dust polluted by pesticides a year.
– Wildlife becoming extinct or endangered due to the decrease of their food resources or the conversion of natural ecosystems into cultivated areas.
The observations from numerous studies show that there has been an amplification of these trends.
Poverty and desertification
« Desertification is both the cause and consequence of poverty […] It is poverty that forces the people of the drylands to extract as much as they can from the land, and produces the imperative for short-term survival...» (UNCCD). There is an acute threat, particularly for the 250 million poor people in arid areas who directly depend on their production and combustible wood to survive.
Scarce resources fuel competition and cause numerous crises: famines, conflicts, etc. The destruction of soil’s biological potential in particular leads to a decrease in food production; as populations cannot feed themselves correctly, many choose migration as a means of survival. 70% of people suffering from hunger live in the countryside. And half of the 50 million environmental refugees forecast by 2010 will be from Sub-Saharan African.
In China, since the 1950s, 100.000 km2 of land has stopped being productive. Sandstorms, loaded with toxic pollutants are five times more common than 50 years ago. In 2002, the cloud affected 70 million people in the north of the country. In 2006, the worst of 8 storms spread 330.000 tons of particles over Peking. They affect crops and cause respiratory disorders. The desert and sand dunes are advancing at about 2000 km2/year. They are engulfing towns and productive soil and threatening the incomes of 400 million people.
La Revue durable n°23: dossier «histoires de désertification»