Geoscience Reference
In-Depth Information
countries of the world occupy this zone; most of them are
experiencing rapid population growth, which puts
additional pressure on the national resources. As a result
the future of the dry lands is giving cause for concern.
Even potential solutions may differ, depending upon such
factors as the wealth of the nation, its political system and
the relative importance of the dry areas in the overall
economy. These days we must not forget the attitudes of
international organizations and the media. The sight of
starvation on television screens brings a vivid perspective
to the problems of marginal agriculture in ways which
were impossible when communication was achieved on
foot or by animal. Unfortunately the response to such
problems is more likely to be short-term food aid with no
consideration of the long-term problems which allowed
the famine to develop in the first place.
We must not consider all dry lands as areas of great
hardship and stress. Many economies survive adequately
with the resources available, supplemented where possible
by additional water for irrigation. With care and
understanding dryland areas can make an effective
contribution to the national economy. A good example
would be Australia, but it does help if there is financial
and technological support.
KEY POINTS
1
The dry lands are characterized by a moisture deficit caused by relatively low precipitation and high inputs
of solar energy which lead to high levels of evaporation. Natural levels of vegetation are controlled by
moisture availability. There is a strong seasonal cycle of growth associated with the wet season and
generally a low density of vegetation. Where water is available crop growth can be good, but it requires
the supply of adequate volumes of good-quality water.
2
Supplying water to dry land can cause a wide range of problems. The most frequent method is dam
construction, but the resulting lake has many harmful effects and incorrect use of the water can produce
major problems of salinization. Under these conditions the land can become sterile, as in parts of the
Indus valley.
3
Soil erosion can be another major problem in dryland areas, where bare ground is easily eroded by heavy
rainstorms. It is made worse by deep ploughing and attempts at intensive commercial agriculture.
4
Desertification has been threatening the drier margins of the dryland areas, though a strict definition of
the problem is difficult. As a result of overgrazing, coupled with fluctuating rainfall levels, the vegetation
of the drier margins may experience stress and degrade in quality. This does not mean that the desert is
advancing; it is a reflection of recent pressures on the vegetation.
FURTHER READING
Agnew, C., and Anderson, E. (1992) Water Resources in the Arid Realm, London: Routledge. A modern text concerned
with the availability and use of water resources in a dryland environment. Emphasis on the Middle East and Africa.
Beaumont, P. (1993) Drylands: environmental management and development, London: Routledge. A full discussion of
environmental management in dryland areas. Emphasis on regional examples.
Thomas, D. S. G., and Middleton, N. J. (1994) Desertification: exploding the myth, Chichester: Wiley. This topic sets out
to analyse the range of scientific, social and political issues surrounding desertification. Puts forward various interesting
ideas about the factors, especially political ones, involved in desertification and their validity.
WEB RESOURCES
http://ag.arizona.edu/OALS/IALC/Home.html A
n extensive website with useful links to research and information about
drylands.
