Desertification

Desertification as defined by the U.N. Convention to Combat Desertification is “land degradation in arid, semiarid and dry sub humid areas resulting from various factors, including climatic variations and unsustainable human activities.” Land degradation is in turn defined as the reduction or loss of the biological or economic productivity of dry lands. Desertification is a complex process, involving multiple causes. It takes place at different rates in various climates. It can build up a general climatic trend toward greater aridity, or it may initiate a change in local climate.

Desertification occurs on all continents except Antarctica and affects the livelihoods of millions of people, including a large proportion of the poor in drylands. Desertification takes place worldwide in drylands, and its effects are experienced locally, nationally, regionally, and globally. Drylands occupy 41% of Earth’s land area and are home to more than 2 billion people—a third of the human population in the year 2000. Drylands include all terrestrial regions where water scarcity limits the production of crops, forage, wood, and other ecosystem provisioning services.

Some 10–20% of drylands are already degraded (medium certainty). Based on these rough estimates, about 1–6% of the dryland people live in desertified areas, while a much larger number is under threat from further desertification. Scenarios of future development show that, if unchecked, desertification and degradation of ecosystem services in drylands will threaten future improvements in humanwell- being and possibly reverse gains in some regions. Therefore, desertification ranks among the greatest environmental challenges today and is a major impediment to meeting basic human needs in drylands.

 Desertification

is a historic phenomenon.

 Deserts

have grown and shrunk independent of human activities.

 Paleodeserts

– inactive sand seas stabilized by vegetation (Western Asian Deserts, Sahara)

 Faster

rate of desertification today!

Desertification comes mainly from variations in climate and from human activities. CLIMATIC VARIATIONS High temperatures lasting for months create droughts that prevent the vegetation from growing. HUMAN ACTIVITIES Human activities leading to desertification are mainly related to agriculture.

Overgrazing removes the vegetation cover that protects it from erosion.

The result of overgrazing on the outskirts of Amman city, Jordan.

Overgrazing has made the Rio Puerco Basin of central New Mexico one of the most eroded river basins of the American West and has increased the high sediment content of the river.

Overcultivation exhausts the soil. Deforestation destroys the trees that bind the land to the soil. Wood is the principal source of domestic energy for lighting and cooking in many arid areas. Poor irrigation practices raise salinity, and sometimes dry the rivers that feed large lakes: the Aral Sea and Lake Chad have shrunk dramatically in this way. When these practices coincide with drought, the rate of desertification increases dramatically.

Other root causes, some of which originate outside the drylands, include: • Growing populations that increase pressure on fragile land resources; • Poverty that prevents people from investing in land maintenance and rehabilitation; • Policy and institutional shortcomings, such as ambiguous land tenure, and policies that allow or even encourage frontier expansion and over-mechanized land-clearing; • Inadequate infrastructure such as roads • Limited market access • Inappropriate technologies; and • Insufficient research and development.

Poverty and desertification: the vicious circle Economic pressures can lead to the over-exploitation of land, and usually hit the poorest hardest. Forced to extract as much as they can from the land for food, energy, housing and source of income, they are both the causes and the victims of the desertification. International trade patterns are based on the short-term exploitation of local resources for export, acting against the long-term interests of the local people. Poverty leads to desertification, which in turn leads to poverty.

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Reduced land resilience to natural climate variability

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Less soil productivity

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Damaged vegetation

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Some consequences borne by people living outside immediately affected area

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Undermined food production

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Contribution to famine

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Enormous social cost

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Drain on economic resources

Around a third of the world’s land surface is arid or semi-arid. It has been calculated that global warming will increase the area of desert climates by 17% in the next century. Desertification around the world makes approximately 12 million hectares useless for cultivation every year. During the 1980s, 61% of the 3257 million hectares of all productive drylands were desertified.

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Desertification is associated with biodiversity loss and contributes to global climate change through loss of carbon sequestration capacity and an increase in land-surface albedo.

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Biological diversity is involved in most services provided by dryland ecosystems and is adversely affected by desertification.

Figure 6.1. Linkages and Feedback Loops among Desertification, Global Climate Change, and Biodiversity Loss

 Desertification

affects global climate change through soil and vegetation losses.

 The

effect of global climate change on desertification is complex and not sufficiently understood.

Overgrazing and to a lesser extent drought in the 1930s transformed parts of the Great Plains in the United States into the”Dust Bowl.” During that time, a considerable fraction of the plains population abandoned their homes to escape the unproductive lands. Improved agricultural and water management have prevented a disaster of the earlier magnitude from recurring, but desertification presently affects tens of millions of people with primary occurrence in the lesser developed countries.

Desertification is widespread in many areas of the People’s Republic of China. The populations of rural areas have increased since 1949 for political reasons as more people have settled there. While there has been an increase in livestock, the land available for grazing has decreased. Also the importing of European cattle such as Friesian and Simmental, which have higher food intakes, has made things worse.

Human overpopulation is leading to destruction of tropical wet forests and tropical dry forests, due to widening practices of slash-and-burn and other methods of subsistence farming necessitated by famines in lesser developed countries. A sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total desertification. Examples of this extreme outcome can be seen on Madagascar’s central highland plateau, where about seven percent of the country's total land mass has become barren, sterile land.

Another example of desertification occurring is in the Sahel. The chief cause of desertification in the Sahel is slash-and-burn farming practiced by an expanding human population. The Sahara is expanding south at an average rate of 30 miles per year.

The Sahelian drought that began in 1968 was responsible for the deaths of between 100,000 and 250,000 people, the disruption of millions of lives, and the collapse of the agricultural bases of five countries.

The Desert of Maine is a 40 acre dune of glacial silt near Freeport, Maine. Overgrazing and soil erosion exposed the cap of the dune, revealing the desert as a small patch that continued to grow, overtaking the land. The site is maintained as a tourist attraction. Ghana and Nigeria currently experience desertification; in the latter, desertification overtakes about 1,355 square miles (3,510 km²) of land per year.

The Central Asian countries, Kazakhstan, Kyrgyzstan, Mongolia, Tajikistan, Turkmenistan and Uzbekistan, are also affected. More than 80% of Afghanistan’s and Pakistan’s land could be subject to soil erosion and desertification. In Kazakhstan, nearly half of the cropland has been abandoned since 1980. In Iran, sand storms were said to have buried 124 villages in Sistan and Baluchestan Province in 2002, and they had to be abandoned. In Latin America, Mexico and Brazil are affected by desertification.

Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.

 Restore

and fertilize the land

 Combat

the effects of the wind

Building barriers (fences) to prevent advance of sand dunes at Gour, Niger. Fences are mainly built with the local bush or with dead palm leaves.

 Reforestation  Develop

sustainable agricultural practices

 Traditional

lifestyles

Erosion control by planting grass in rows on steep slopes in India

Milestones: The response of the international community to desertification  1977

– United Nations Desertification Conference, Nairobi  1992 – United Nations Conference on Environment and Development, Rio de Janeiro  1994 – Adoption of the United Nations Convention to Combat Desertification (UNCCD)  2002 – World Summit on Sustainable Development, Johannesburg

References:  Desert

in Iceland: http://www.rala.is/desert/  Deserts and Desertification: http://www. didyouknow.cd/deserts.htm  Desertification: http://www.botany.uwc.ac.za/ envFacts/facts/desertification.htm  Desertification: http://pubs.usgs.gov/gip /deserts/desertification/  Desertification: http://en.wikipedia.org/wiki /Desertification