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 any 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.

A shepherd guiding his sheep through the high desert outside of Marrakech, Morocco.

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 over cultivation 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 this is 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]

Farmer Managed Natural Regeneration (FMNR) is another technique that has produced successful results for desert reclamation. Since 1980, this method to reforest degraded landscape has been applied with some success in Niger. This simple and low-cost method has enabled farmers to regenerate some 30,000 square kilometers in Niger. The process involves enabling native sprouting tree growth through selective pruning of shrub shoots. The residue from pruned tress can be used to provide mulching for fields thusincreasing soil water retention and reducing evaporation. Additionally, properly spaces and pruned trees can increase crop yields. The Humbo Assisted Regeneration Project which uses FMNR techniques in Ethiopia has received money from The World Bank’s BioCarbon Fund, which supports projects that sequester or conserve carbon in forests or agricultural ecosystems.^[27]

See also

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

• BioGrout; another possible technique for reducing desertification^[28]
• Desert greening
• Arid Lands Information Network
• Aridification
• Deforestation
• Ecological engineering
• Global warming
• Green Wall of China
• Oasification
• Water crisis

References

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

Attribution

•  This article incorporates public domain material from the United States Government document "http://pubs.usgs.gov/gip/deserts/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
• Environmental Issues - Desertification in Africa, The Environmental Blog
• 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