NASA study predicts devastating droughts during the last half of the century

http://www.gizmag.com/nasa-drought-s...-states/36128/



WHAT CAUSES DESERTIFICATION?
* Overgrazing is the major cause of desertification worldwide. Plants of semi-arid areas are adapted to being eaten by sparsely scattered, large, grazing mammals which move in response to the patchy rainfall common to these regions. Early human pastoralists living in semi-arid areas copied this natural system. They moved their small groups of domestic animals in response to food and water availability. Such regular stock movement prevented overgrazing of the fragile plant cover.

In modern times, the use of fences has prevented domestic and wild animals from moving in response to food availability, and overgrazing has often resulted. However, when used correctly, fencing is a valuable tool of good veld management.
The use of boreholes and windmills also allows livestock to stay all-year round in areas formerly grazed only during the rains when seasonal pans held water. Where not correctly planned and managed, provision of drinking water has contributed to the massive advance of deserts in recent years as animals gather around waterholes and overgraze the area.
* Cultivation of marginal lands, i.e lands on which there is a high risk of crop failure and a very low economic return, for example, some parts of South Africa where maize is grown.
* Destruction of vegetation in arid regions, often for fuelwood.
* Poor grazing management after accidental burning of semi-arid vegetation.
* Incorrect irrigation practices in arid areas can cause salinization, (the build up of salts in the soil) which can prevent plant growth.
When the practices described above coincide with drought, the rate of desertification increases dramatically.
Increasing human population and poverty contribute to desertification as poor people may be forced to overuse their environment in the short term, without the ability to plan for the long term effects of their actions. Where livestock has a social importance beyond food, people might be reluctant to reduce their stock numbers.

http://www.botany.uwc.ac.za/envfacts/facts/desertification.htm


Increased population and livestock pressure on marginal lands has accelerated desertification. In some areas, nomads moving to less arid areas disrupt the local ecosystem and increase the rate of erosion of the land. Nomads are trying to escape the desert, but because of their land-use practices, they are bringing the desert with them.
It is a misconception that droughts cause desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. By 1973, the drought that began in 1968 in the Sahel of West Africa and the land-use practices there had caused the deaths of more than 100,000 people and 12 million cattle, as well as the disruption of social organizations from villages to the national level.

Camels and other animals trample the soil in the semiarid Sahel of Africa as they move to water holes such as this one in Chad (photograph courtesy of the U.S. Agency for International Development).
While desertification has received tremendous publicity by the political and news media, there are still many things that we don't know about the degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out in an important scientific paper that the desertification problem and processes are not clearly defined. There is no consensus among researchers as to the specific causes, extent, or degree of desertification. Contrary to many popular reports, desertification is actually a subtle and complex process of deterioration that may often be reversible.

http://pubs.usgs.gov/gip/deserts/desertification/

Human activities: in countries where major economic resources are dependent on agricultural activities, there are few or no alternative sources of income. Soils become damaged through excessive use when farmers neglect or reduce fallow periods, necessary to sufficiently produce enough food to feed the population. This in turn causes soil to lose organic matter, limiting plant growth and reducing vegetation cover as a consequence. The bare soils are thus more vulnerable to the effects of erosion.

In the Bible it was mentioned to leave the land fallow in the seventh year if I remember correctly.

http://www.unesco.org/mab/doc/ekocd/chapter1.html


What Causes Desertification

Desertification occurs when:

  • the tree and plant cover that binds the soil is removed. It occurs when trees and bushes are stripped away for fuelwood and timber, or to clear land for cultivation.
  • animals eat away grasses and erode topsoil with their hooves.
  • intensive farming depletes the nutrients in the soil.

Wind and water erosion aggravate the damage, carrying away topsoil and leaving behind a highly infertile mix of dust and sand. It is the combination of these factors that transforms degraded land into desert.


What can be done?

  • Reforestation and tree regeneration
  • Water management — saving, reuse of treated water, rainwater harvesting, desalination, or direct use of seawater for salt-loving plants
  • Fixating the soil through the use of sand fences, shelter belts, woodlots and windbreaks
  • Enrichment and hyper-fertilizing of soil through planting
  • Farmer Managed Natural Regeneration (FMNR), enabling native sprouting tree growth through selective pruning of shrub shoots. The residue from pruned tress can be used to provide mulching for fields thus increasing soil water retention and reducing evaporation.


http://www.un.org/en/events/desertificationday/background.shtml


What are the major causes of desertification?

  • 4.1 What social, economic, and policy factors can contribute to desertification?
  • 4.2 Does globalization play a role in desertification?
  • 4.3 How can land use affect desertification?

The source document for this Digest states:
Desertification is caused by a combination of factors that change over time and vary by location. These include indirect factors such as population pressure, socioeconomic and policy factors, and international trade as well as direct factors such as land use patterns and practices and climate-related processes.
Desertification is taking place due to indirect factors driving unsustainable use of scarce natural resources by local land users. This situation may be further exacerbated by global climate change. Desertification is considered to be the result of management approaches adopted by land users, who are unable to respond adequately to indirect factors like population pressure and globalization and who increase the pressure on the land in unsustainable ways. This leads to decreased land productivity and a downward spiral of worsening degradation and poverty (as illustrated in Figure 1.1). Where conditions permit, dryland populations can avoid degradation by improving their agricultural practices and enhancing pastoral mobility in a sustainable way. On the whole, the interaction between climatic factors and human responses can create a range of different outcomes. (See the discussion of MA scenarios in Key Question [How will different future development paths affect desertification?]) To counter the problems effectively, it is important—but difficult— to distinguish between those resulting from the natural conditions of dryland ecosystems and those caused by unsustainable management practices as well as broader economic and policy factors (C22.3.1).

Source & ©: MA Desertification Synthesis Report (2005),
Chapter 3, p.9



4.1 What social, economic, and policy factors can contribute to desertification?

The source document for this Digest states:
Social, Economic, and Policy Factors
Policies leading to unsustainable resource use and lack of supportive infrastructure are major contributors to land degradation. Conversely, this makes public policies and physical infrastructure useful intervention points. Thus agriculture can play either a positive or a negative role, depending on how it is managed. This in turn depends on the socioeconomic resources available, the policies adopted, and the quality of governance. Local institutions, such as community-based land-use decision-making bodies and social networks, can contribute to preventing desertification by allowing land users to manage and use ecosystem services more effectively through enhanced access to land, capital, labor, and technology (C22.6.4).
Policies to replace pastoralism with sedentary cultivation in rangelands can contribute to desertification.Policies and infrastructure that promote farming in rangelands that cannot sustain viable cropping systems contribute to desertification. The majority of dryland areas (65%) are rangelands that are more suited to sustainable pastoralism than crop production. For example, nomadic pastoralism is a rangeland management practice that over the centuries has proved to be sustainable and suited to the ecosystem carrying capacity. Sedentarization of nomads in marginal drylands and other limitations to their transboundary movement lead to desertification because they reduce people’s ability to adjust their economic activities in the face of stresses such as droughts (R6.2.2, C22.3.2).
Land tenure practices and policies that encourage land users to overexploit land resources can be important contributors to desertification. When farmers and herders lose control or long-term security over the land they use, the incentives for maintaining environmentally sustainable practices are lost. Problems of water scarcity, groundwater depletion, soil erosion, and salinization have all been recognized as outcomes of deeper policy and institutional failures. Security of tenure does not necessarily imply private property rights; many long-established collective and community-based management practices have operated quite effectively. In successful communal systems, greater transparency and fairness in the allocation of resources to all stakeholders is essential. Private land tenure systems in drylands have been less successful in ensuring that pastoralists have access to various ecosystem services such as provisioning of water and pasture (C22.3.2, R17.3).

http://www.greenfacts.org/en/deserti...cation.htm#1p0

http://www.millenniumassessment.org/...t.355.aspx.pdf

http://en.wikipedia.org/wiki/Desertification