Desertification

Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.^[1]

Desertification is the degradation of land in drylands.^[2] Caused by a variety of factors, such as climate change and human activities, desertification is one of the most significant global environmental problems.^[3]

Definitions

Considerable controversy exists over the proper definition of the term "desertification" for which Helmut Geist (2005) has identified more than 100 formal definitions.^[2] The most widely accepted^[2] of these is that of the United Nations Convention to Combat Desertification which defines it as "land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities"^[4]

The earliest known discussion of the topic arose soon after the French colonization of West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore the prehistoric expansion of the Sahara Desert.^[5]

History

The world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara, the largest desert.^[6]

Desertification has played a significant role in human history, contributing to the collapse of several large empires, such as Carthage, Greece, and the Roman Empire, as well as causing displacement of local populations.^[3][7]

Areas affected

Global Desertification Vulnerability Map

Drylands occupy approximately 40-41% of Earth’s land area^[8][9] and are home to more than 2 billion people.^[9] It has been estimated that some 10–20% of drylands are already degraded, the total area affected by desertification being between 6 and 12 million square kilometres, that about 1–6% of the inhabitants of drylands live in desertified areas, and that a billion people are under threat from further desertification.^[10][11]

The Sahara is currently expanding south at a rate of up to 48 kilometres per year.^[12]

Causes

A herd of goats in Norte Chico, Chile. Overgrazing of drylands is one of the primary causes of desertification.

Dryland ecosystems are already very fragile, and can rarely sustain the increased pressures that result from intense population growth. Many of these areas are inappropriately opened to development, when they cannot sustain human settlements.^[13]

The most common cause of desertification is the overcultivation of desert lands.^[14] Over-cultivation causes the nutrients in the soil to be depleted faster than they are restored. Improper irrigation practices result in salinated soils, and depletion of aquifers.^[13]

Vegetation plays a major role in determining the biological composition of the soil. Studies have shown that, in many environments, the rate of erosion and runoff decreases exponentially with increased vegetation cover.^[15] Overgrazing removes this vegetation causing erosion and loss of topsoil.^[13]

Desertification and poverty

At least 90% of the inhabitants of drylands live in developing nations, where they also suffer from poor economic and social conditions.^[10] This situation is exacerbated by land degradation because of the reduction in productivity, the precariousness of living conditions and the difficulty of access to resources and opportunities.^[16]

A downward spiral is created in many underdeveloped countries by overgrazing, land exhaustion and overdrafting of groundwater in many of the marginally productive world regions due to overpopulation pressures to exploit marginal drylands for farming. Decision-makers are understandably averse to invest in arid zones with low potential. This absence of investment contributes to the marginalisation of these zones.When unfavourable agro-climatic conditions are combined with an absence of infrastructure and access to markets, as well as poorly adapted production techniques and an underfed and undereducated population, most such zones are excluded from development.^[17]

Desertification often causes rural lands to become unable to support the same sized populations that previously lived there. This results in mass migrations out of rural areas and into urban areas, particularly in Africa. Because of these migrations into the cities, there are often large numbers of unemployed people who end up living in slums.^[18][19]

Countermeasures and prevention

Anti-sand shields in north Sahara, Tunisia.

Jojoba plantations, such as those shown, have played a role in combating edge effects of desertification in the Thar Desert, India.

Techniques exist for mitigating or reversing the effects of desertification, however there are numerous barriers to their implementation. One of these is that the costs of adopting sustainable agricultural practices sometimes exceed the benefits for individual farmers, even while they are socially and environmentally beneficial. Another issue is a lack of political will, and lack of funding to support land reclamation and anti-desertification programs.^[20]

Desertification is recognized as a major threat to biodiversity. Some countries have developed Biodiversity Action Plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.^[21][22]

Reforestation gets at one of the root causes of desertification and isn't just a treatment of the symptoms. Environmental organizations^[23] work in places where deforestation and desertification are contributing to extreme poverty. There they focus primarily on educating the local population about the dangers of deforestation and sometimes employ them to grow seedlings, which they transfer to severely deforested areas during the rainy season.^{[citation needed]}

Techniques focus on two aspects: provisioning of water, and fixation and hyper-fertilizing soil.

Fixating the soil is often done through the use of shelter belts, woodlots and windbreaks. Windbreaks are made from trees and bushes and are used to reduce soil erosion and evapotranspiration. They were widely encouraged by development agencies from the middle of the 1980s in the Sahel area of Africa.

Some soils (for example, clay), due to lack of water can become consolidated rather than porous (as in the case of sandy soils). Some techniques as zaï or tillage are then used to still allow the planting of crops.^[24]

Enriching of the soil and restoration of its fertility is often done by plants. Of these, the Leguminous plants which extract nitrogen from the air and fixes it in the soil, and food crops/trees as grains, barley, beans and dates are the most important. Sand fences can also be used to control drifting of soil and sand erosion.^[25]

As there are many different types of deserts, there are also different types of desert reclamation methodologies. An example for a that are the salt-flats in the Rub`Al Khali desert in Saudi-Arabia. These salt-flats are one of the most promising desert areas for seawater agriculture and could be revitalized without the use of freshwater or much energy.^[26]

See also

	Environment portal
	Ecology portal
	Earth sciences portal
	Biology portal
	Global warming portal
	Sustainable development portal

• Desert greening
• Arid Lands Information Network
• Aridification
• Deforestation
• Ecological engineering
• Global warming
• Green Wall of China
• Oasification
• Water crisis

References

1. ^ Mayell, Hillary (April 26, 2001). "Shrinking African Lake Offers Lesson on Finite Resources". National Geographic News. http://news.nationalgeographic.com/news/2001/04/0426_lakechadshrinks.html. Retrieved 20 June 2011. 
2. ^ ^{a b c} Geist (2005), p. 2
3. ^ ^{a b} Geist (2005), p. 4
4. ^ UNCCD (1994), Part I - Article 1
5. ^ Mortimore, Michael (1989). Adapting to drought: farmers, famines, and desertification in west Africa. Cambridge University Press. p. 12. ISBN 9780521323123. http://books.google.com/books?id=Dx89AAAAIAAJ&pg=PA12. 
6. ^ United States Geological Survey, "Desertification", 1997
7. ^ Whitford, Walter G. (2002). Ecology of desert systems. Academic Press. p. 277. ISBN 9780127472614. http://books.google.com/books?id=OZ4hZbXS8IcC&pg=PA277. 
8. ^ Bauer (2007), p. 78
9. ^ ^{a b} Johnson et al (2006), p. 1
10. ^ ^{a b} Holtz (2007)
11. ^ World Bank (2009). Gender in agriculture sourcebook. World Bank Publications. p. 454. ISBN 9780821375877. http://books.google.com/books?id=XxBrq6hTs_UC&pg=PA454. 
12. ^ Hunger is spreading in Africa
13. ^ ^{a b c} Ci, Longjun & Yang, Xiaohui (2010). Desertification and Its Control in China. Springer. p. 10. ISBN 9787040257977. http://books.google.com/books?id=agd8MFDYLXEC&pg=PA10. 
14. ^ Mares, Michael S., ed (1999). "Middle East, deserts of". Encyclopedia of deserts. University of Oklahoma Press. pp. 362. ISBN 9780806131467. http://books.google.com/books?id=g3CbqZtaF4oC&pg=PA362. 
15. ^ Geeson, Nichola et al (2002). Mediterranean desertification: a mosaic of processes and responses. John Wiley & Sons. p. 58. ISBN 9780470844489. http://books.google.com/books?id=G_0qg0f49GQC&pg=PA58. 
16. ^ Dobie, Ph. 2001.“Poverty and the drylands,” in Global Drylands Imperative, Challenge paper, Undp, Nairobi (Kenya) 16 p.
17. ^ Cornet A., 2002. Desertification and its relationship to the environment and development: a problem that affects us all. In: Ministère des Affaires étrangères/adpf, Johannesburg. World Summit on Sustainable Development. 2002. What is at stake? The contribution of scientists to the debate: 91-125..
18. ^ Pasternak, Dov & Schlissel, Arnold (2001). Combating desertification with plants. Springer. p. 20. ISBN 9780306466328. http://books.google.com/books?id=B-i8-DPf6xgC&pg=PA20. 
19. ^ Briassoulis, Helen (2005). Policy integration for complex environmental problems: the example of Mediterranean desertification. Ashgate Publishing. p. 161. ISBN 9780754642435. http://books.google.com/books?id=CpYnV45hVRsC&pg=PA161. 
20. ^ Briassoulis, Helen (2005). Policy integration for complex environmental problems: the example of Mediterranean desertification. Ashgate Publishing. p. 237. ISBN 9780754642435. http://books.google.com/books?id=CpYnV45hVRsC&pg=PA237. 
21. ^ Techniques for Desert Reclamation by Andrew S. Goudie
22. ^ Desert reclamation projects
23. ^ For example, Eden Reforestation Projects.
24. ^ Arid sandy soils becoming consolidated; zai-system
25. ^ List of plants to halt desertification; some of which may be soil-fixating
26. ^ Rethinking landscapes, Nicol-André Berdellé July 2011 H2O magazine

Bibliography

• Arnalds, Ólafur & Archer, Steve (2000). Rangeland Desertification. Springer. ISBN 9780792360711. http://books.google.com/books?id=E7kaBkPlJfAC. 
• Barbault R., Cornet A., Jouzel J., Mégie G., Sachs I., Weber J. (2002). Johannesburg. World Summit on Sustainable Development. 2002. What is at stake? The contribution of scientists to the debate. Ministère des Affaires étrangères/adpf.
• Bauer, Steffan (2007). "Desertification". In Thai, Khi V. et al. Handbook of globalization and the environment. CRC Press. ISBN 9781574445534. http://books.google.com/books?id=mR3E4xJFNw0C&pg=PA77. 
• Batterbury, S.P.J. & A.Warren (2001) Desertification. in N. Smelser & P. Baltes (eds.) International Encyclopædia of the Social and Behavioral Sciences. Elsevier Press. pp. 3526–3529
• Geist, Helmut (2005). The causes and progression of desertification. Ashgate Publishing. ISBN 9780754643234. http://books.google.com/books?id=acbWdynlU3cC. 
• Hartman, Ingrid (2008). "Desertification". In Philander, S. George. Encyclopedia of global warming and climate change, Volume 1. SAGE. ISBN 9781412958783. http://books.google.com/books?id=mNoW858izZcC&pg=PA312. 
• Hinman, C. Wiley & Hinman, Jack W. (1992). The plight and promise of arid land agriculture. Colombia University Press. ISBN 9780231066129. http://books.google.com/books?id=dMmEjsySvrUC. 
• Holtz, Uwe (2007) Implementing the United Nations Convention to Combat Desertification from a parliamentary point of view - Critical assessment and challenges ahead
• Johnson, Pierre Marc et al., ed (2006). Governing global desertification: linking environmental degradation, poverty and participation. Ashgate Publishing. ISBN 9780754643593. http://books.google.com/books?id=da6vhzHEpf0C. 
• Lucke, Bernhard (2007): Demise of the Decapolis. Past and Present Desertification in the Context of Soil Development, Land Use, and Climate. Online at [1]
• Mensah, Joseph (2006). "Desertification". In Leonard, Thomas M.. Encyclopedia of the developing world, Volume 1. Taylor & Francis. ISBN 9780415976626. http://books.google.com/books?id=3mE04D9PMpAC&pg=PA452. 
• Millennium Ecosystem Assessment (2005) Desertification Synthesis Report
• Moseley, W.G. and E. Jerme 2010. “Desertification.” In: Warf, B. (ed). Encyclopedia of Geography. Sage Publications. Volume 2, pp. 715–719.
• Oliver, John E., ed (2005). "Desertification". Encyclopedia of world climatology. Springer. ISBN 9781402032646. http://books.google.com/books?id=-mwbAsxpRr0C&pg=PA319. 
• Parrillo, Vincent N., ed (2008). "Desertification". Encyclopedia of social problems, Volume 2. SAGE. ISBN 9781412941655. http://books.google.com/books?id=mRGr_B4Y1CEC&pg=PT271. 
• Reynolds, James F., and D. Mark Stafford Smith (ed.) (2002) Global Desertification – Do Humans Cause Deserts? Dahlem Workshop Report 88, Berlin: Dahlem University Press
• UNCCD (1994) United Nations Convention to Combat Desertification

External links

• Beyerlin, Ulrich. Desertification, Max Planck Encyclopedia of Public International Law
• Taming The Yellow Dragon
• Bell, Trudy; Phillips, Tony, Dr. (December 6, 2002). "City-swallowing Sand Dunes". NASA. http://exploration.nasa.gov/articles/06dec_dunes.html. Retrieved 2006-04-28. 
• Desert Research Institute in Nevada, United States
• Desertification.Info - IOSD/CED^R Center on Ecological Desertification and Reforestation
• Eden Foundation article on desertification
• FAO Information Portal - Properties and Management of Drylands
• UNEP (2006): Global Deserts Outlook
• UNEP Programme on Success Stories in Land Degradation/ Desertification Control
• United Nations Convention to Combat Desertification - Secretariat
• A guide for desert and dryland restoration by David A. Bainbridge
• French Scientific Committee on Desertification (CSFD)

News

• Fighting Desertification Through Conservation Report on a project to stop the advance of the Sahara in Algeria - IPS, 27 February 2007

 This article incorporates public domain material from the United States Government document "http://pubs.usgs.gov/gip/deserts/desertification/".