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Desertification is the degradation of drylands. It involves
the loss of biological or economic productivity and complexity
in croplands, pastures, and woodlands. It is due mainly to climate
variability and unsustainable human activities. The most commonly
cited forms of unsustainable land use are overcultivation, overgrazing,
deforestation, and poor irrigation practices. Seventy percent
of the world's drylands (excluding hyper-arid deserts), or some
3,600 million hectares, are degraded. While drought is often associated
with land degradation, it is a natural phenomenon that occurs
when rainfall is significantly below normal recorded levels for
a long time.
Drylands respond quickly to climatic fluctuations. By definition,
drylands have limited freshwater supplies. Precipitation can vary
greatly during the year. In addition to this seasonal variability,
wide fluctuations occur over years and decades, frequently leading
to drought. Over the ages, dryland ecology has become attuned
to this variability in moisture; plants and animals can respond
to it rapidly. For example, satellite imagery has shown that the
vegetation boundary south of the Sahara can move by up to 200
km when a wet year is followed by a dry one, and vice versa.
People must also adjust to these natural fluctuations.
The biological and economic resources of drylands, notably soil
quality, freshwater supplies, vegetation, and crops, are easily
damaged. People have learned to protect these resources with age-old
strategies such as shifting agriculture and nomadic herding. However,
in recent decades these strategies have become less practical
due to changing economic and political circumstances, population
growth, and a trend towards more settled communities. When land
managers cannot or do not respond flexibly to climate variations,
desertification is the result.
The relatively low priority given to environmental protection
often leads to poor land management decisions. The overuse
of land may result from specific economic conditions or from inappropriate
land laws or customs. In many cases, unregulated access to land
resources may lead some individuals to maximize their own gains
by overexploiting the land at the expense of the community as
a whole. Poor people, particularly poor women, often lack access
to the best land, depending instead on the most fragile areas
and resources. Their poverty may give them little alternative
but to extract what they can from the scarce resources available
to them, even though this degrades the land.
International economic forces can encourage people to overexploit
their land. International trade patterns can lead to the short-term
exploitation of local resources for export, leaving little profit
at the community level for managing or restoring the land. Similarly,
the development of an economy based on cash crops, or the imposition
of taxes, can distort local markets and promote overexploitation
of the land.
Ignorance, errors, and natural and man-made disasters can also
contribute to land degradation. Ignorance of the natural environment
played an important role in the US during the infamous Dust Bowl
of the 1930s; among other errors, during a time of drought Midwestern
farmers used ploughs better suited for the more temperate latitudes
of Western Europe. In recent decades, similar mistakes in the
choice of policies or technologies have led to land degradation
in many countries, both developed and developing. Disasters such
as wars and national emergencies also destroy productive land
by displacing its managers or causing heavy concentrations of
migrants to overburden an area. Natural disasters such as floods
and droughts can have a similar effect.
What role do increasing populations and population densities
play? It is tempting to conclude that an expanding human population
is the ultimate driving force behind desertification. More people
in an area inevitably exert a greater pressure on that area's
resources; sometimes this pressure is indirect, as when growing
urban populations place demands on food production in uncrowded
rural areas. But the causes of desertification are complex, and
the relationship between two variables such as population and
desertification is not clear-cut. For example, a decline in population
can result in desertification since there may no longer be enough
people to manage the land adequately. Many hillside terraces in
Yemen have fallen into disrepair with the exodus of labour to
neighbouring oil-rich countries. Examples can also be cited of
areas that support large concentrations of people without much
degradation, such as around the city of Kano in Nigeria.
Desertification reduces the land's resilience to natural climate
variability. Soil, vegetation, freshwater supplies, and other
dryland resources tend to be resilient. They can eventually recover
from climatic disturbances, such as drought, and even from human-induced
impacts, such as overgrazing. When land is degraded, however,
this resilience is greatly weakened. This has both physical and
socio-economic consequences.
Soil becomes less productive. Exposed and eroded topsoil
can be blown away by the wind or washed away by rainstorms. The
soil's physical structure and bio-chemical composition can change
for the worse. Gullies and cracks may appear and vital nutrients
can be removed by wind or water. If the water table rises due
to inadequate drainage and poor irrigation practices, the soil
can become waterlogged, and salts may build up. When soil is trampled
and compacted by cattle, it can lose its ability to support plant
growth and to hold moisture, resulting in increased evaporation
and surface run-off.
Vegetation becomes damaged. The loss of vegetation cover
is both a consequence and a cause of land degradation. Loose soil
can sandblast plants, bury them, or leave their roots dangerously
exposed. When pastures are overgrazed by too many animals, or
by inappropriate types, edible plant species may be lost, allowing
inedible species to invade.
Some of the consequences are borne by people living outside
the immediately affected area. Degraded land may cause downstream
flooding, reduced water quality, sedimentation in rivers and lakes,
and siltation of reservoirs and navigation channels. It can also
cause dust storms and air pollution, resulting in damaged machinery,
reduced visibility, unwanted sediment deposits, and mental stress.
Wind-blown dust can also worsen health problems, including eye
infections, respiratory illnesses, and allergies. Dramatic increases
in the frequency of dust storms were recorded during the Dust
Bowl years in the US, in the Virgin Lands scheme area in the former
USSR in the 1950s, and in the African Sahel during the 1970s and
1980s.
Food production is undermined. Desertification is considered
a major global environmental issue largely because of the link
between dryland degradation and food production. A nutritionally
adequate diet for the world's growing population implies tripling
food production over the next 50 years. This will be difficult
to achieve even under favourable circumstances. If desertification
is not stopped and reversed, food yields in many affected areas
will decline. Malnutrition, starvation, and ultimately famine
may result. The relationship between soil degradation and crop
yields, however, is seldom straightforward. Productivity is affected
by many different factors, such as the weather, disease and pests,
farming methods, and external markets and other economic forces.
Desertification contributes to famine. Famine typically
occurs in areas that also suffer from poverty, civil unrest, or
war. Drought and land degradation often help to trigger a crisis,
which is then made worse by poor food distribution and the inability
to buy what is available.
Desertification has enormous social costs. There is now
increased awareness of the relationship between desertification,
movements of people, and conflicts. In Africa, many people have
become internally displaced or forced to migrate to other countries
due to war, drought, and dryland degradation. The environmental
resources in and around the cities and camps where these people
settle come under severe pressure. Difficult living conditions
and the loss of cultural identity further undermine social stability.
Desertification is a huge drain on economic resources.
There is little detailed data on the economic losses resulting
from desertification, although an unpublished World Bank study
suggested that the depletion of natural resources in one Sahelian
country was equivalent to 20% of its annual Gross Domestic Product
(GDP). At the global level, it is estimated that the annual income
foregone in the areas immediately affected by desertification
amounts to approximately US$ 42 billion each year. The indirect
economic and social costs suffered outside the affected areas,
including the influx of "environmental refugees" and
losses to national food production, may be much greater.
Source: Fact Sheets of the UNCCD.
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