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Land Degradation in Arid Regions

Introduction

Population increases in semi-arid and arid regions and changes in regional climate often lead to land degradation and sometimes to the collapse of societies in these regions. The problem is as old as civilization. Societies living in the western areas of what is now the Saharan desert of Egypt collapsed when the region dried out around 5,000 to 3,000 BC. The Anasazi society collapsed due to over population and land abuse between 1130 AD and 1300 AD. Now Mongolia and China, parts of the middle east and the US Southwest face similar problems. For example: see Trends of Desertification and its Rehabilitation in China.

Plato: Attica (Athens) was no longer cultivated by true herdsmen, who made husbandry their business, and were lovers of honor, and of a noble nature. As a result Attica had become deforested, the soils depleted, and there are remaining only the bones of the wasted body –all the richer and softer parts of the soil having fallen away.
From US Department of Agriculture web page on Land Degradation and Desertification.

Some Definitions

Land Degradation

Land degradation means the reduction, or loss, in arid, semi-arid and dry sub-humid areas, of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland or range, pasture, forest and woodlands, resulting from land uses or from a process or combination of processes, including processes arising from human activities and habitation patterns, such as: (i) soil erosion caused by wind and/or water; (ii) deterioration of the physical, chemical, and biological or economic properties of soil; and (iii) long-term loss of natural vegetation.
From United Nations Convention to Combat Desertification Item (f).

Others point out that land degradation in not limited to drylands. Cutting down rainforests, such as deforestation of the Amazon, also leads to land degradation. More broadly, it can be defined as:

Any form of deterioration of the natural potential of land that affects ecosystem integrity either in terms of reducing its sustainable
ecological productivity or in terms of its native biological richness and maintenance of resilience.

From Global Environmental Facility.

Desertification

Desertification is the degradation of land in arid, semi-arid, and dry sub-humid areas. It is caused primarily by human activities and climatic variations. Desertification does not refer to the expansion of existing deserts. It occurs because dryland ecosystems, which cover over one third of the world's land area, are extremely vulnerable to over-exploitation and inappropriate land use. Poverty, political instability, deforestation, overgrazing, and bad irrigation practices can all undermine the land's fertility.
From Food and Agricultural Organization web page on Desertification.

Thus desertification is a type of land degradation. The degradation converts useful but arid lands to less useful desert. It is characterized by:

  1. Declining groundwater,
  2. Increased erosion,
  3. Disappearance of native vegetation,

Areas Vulnerable to Desertification

Drylands cover about 41% of Earth’s land surface and are home to more than 38% of the total global population of 6.5 billion. Some form of severe land degradation is present on 10 to 20% of these lands, the consequences of which are estimated to affect directly some 250 million people in the developing world, an estimate likely to expand substantially in the face of climate change and population growth.
From Reynolds et al, 2007.


Extent of Drylands
      Semi   Dry Sub-  
All
   
Region
Arid
%
Arid
%
Humid
%
Drylands
%
Population
Asia (Incl. Russia) 6,164 13 7,649 16 4,588 9 18,401 39 1,444,906
Africa 5,204 17 5,073 17 2,808 9 12,933 43 267,563
Oceania 3,488 39 3,532 39 996 11 8,016 89 140,586
North America 379 2 3,436 16 2,081 10 5,896 28 86,990
South America 401 2 2,980 17 2,233 13 5,614 32 59,323
C. America & Caribbean 421 18 696 30 242 10 1,359 58 31,719
Europe 5 0 373 7 961 17 1,339 24 6,960
15,910
12
23,739
18
13,909

10

53,558
41
2,038,047

Land area: millions of square kilometers. Population: thousands. From White and Nackoney (2003)


The vulnerable areas are mostly in mid-latitudes near 30 degrees of latitude.

global map of dryland areas
Global map of dryland areas. Click on the map for a zoom.
From Millennium Ecosystem Assessment (2005): Appendix A.

Causes of Degradation

Land degradation involves two interlocking, complex systems: the natural ecosystem and the human social system. Natural forces, through periodic stresses of extreme and persistent climatic events, and human use and abuse of sensitive and vulnerable dry land ecosystems, often act in unison, creating feedback processes, which are not fully understood. Interactions between the two systems determine the success or failure of resource management programmes. Causes of land degradation are not only biophysical, but also socioeconomic (e.g. land tenure, marketing, institutional support, income and human health) and political (e.g. incentives, political stability).
From Climate and Land Degradation.

A. Human Systems

Degradation is due to a complex mix of many types of human activity, including many interlocking threads of the human societal system.

human factors influencing land degradation and renewal
Schematic graphic showing how drylands can be developed in response to changes in key human factors.
Left: Developments that lead to a downward spiral of desertification.
Right: Developments that can help avoid or reduce desertification. In this development, land users respond to stresses by improving their agricultural practices on currently used land. This leads to increased livestock and crop productivity, improved human well-being, and political and economic stability. Both development pathways occur today in various dryland areas.
From Millennium Ecosystem Assessment (2005): Ecosystems and Human Well-Being. Desertification Synthesis.

  1. Population Increases.
    Nomadic peoples lived in harmony with drylands for thousands of years. Land degradation begins when populations increase to the point that the land can no longer sustain the people.

    For example, the population of Maradi Province, Niger in the west African sahel increased from 0.56 million in 1960 to 1.39 million in 1998 accompanied by migration of farmers into northern areas where farmland was free (Reynolds and Smith, 2007). As a result—

    Niger is a country with chronic food shortages. Every year, during the "hunger season," there is a significant increase in the number of children aged five years and under who will face acute malnutrition. The intake of food, both in terms of quality and quantity, is insufficient to meet the nutritional needs of young children. This, combined with diseases such as malaria, diarrhea, and acute respiratory infections, causes high levels of death among children in the country.
    From Doctors Without Borders

  2. Unsustainable Agricultural Practices
    Large populations relative to what the land can support leads to attempts to grow too many crops. Cropland in drylands needs time to recover from growing crops when no fertilizer is used. if the land is replanted to soon, fertility declines, loss of soil humus, and poorer soils. If the crops are irrigated without good management practices, the soil becomes too salty, and crops can no longer be grown.

  3. Overgrazing
    Too many people trying to raise too many animals leads to overgrazing. This removes grass cover and vegetation, causes soil compaction, and leads to high rates of wind and water erosion. Overgrazing is made worse by the conversion of traditional rangelands to crop lands, cities, roads, and industrial sites. All reduce the acreage available for grazing.

  4. Deforestation
    People use wood for cooking and heating. When the population is too large, forests are destroyed to obtain wood. Forests are also cut or burned to make way for crops (slash-and-burn agriculture),or to obtain wood for export.

  5. Bad Government
    Unsustainable agriculture, overgrazing, and deforestation are the result of poor planning, laws, and regulations by governments. Wise governments recognize the importance of the land and plan appropriately. Poor governments do not. Laws, economic policy, land rights, and the wisdom of government officials are all inter-related. The type of government is much less important. Strong central governments have led to wise use of the land (Japan under the Tokugawa rule in the 17th century) or to disaster (the Soviet Union in the 20th century).

    For example, the Soviet Union's policy to expand agriculture into drylands, by diverting water from the Amu Darya and Syr Darya rivers into the desert for irrigation, led to widespread land degradation and drying up of the Aral Sea.

    Indeed, the only large-scale ecosystem collapse of modern times – the case of the Aral Sea – is intimately tied to a chain of decisions emanating from the former Soviet State, translated into large, inefficient irrigation systems on the two rivers feeding the sea. From IGBP Global Land Project.

  6. Poverty
    Poverty reduces the options for improving land use, and aggravates degradation. Poor nations seek income by exporting crops or minerals to developed countries. The push to increase cropland leads to unsustainable agricultural practices.

  7. Globalization
    It removes barriers to the trade in commodities such as crops or minerals. Developments in one part of the world influence developments in other parts. As a result, European demand for crops leads to increased farming in African drylands, leading to degradation.

  8. Inappropriate Technology and Advice,
    For example, the Soviet Union paid for the Aswan High Dam, which reduced the flooding of the Nile valley in Egypt, reducing the fertility of the land, and leading to the encroachment of the Mediterranean Sea into the Nile delta.

  9. Colonial Legacy.
    Country boundaries set up during colonial times sometimes separated areas used by nomadic, pastoral people. Governments then prohibited the free movement across the boundaries, forcing the nomads to live in one area. Nomads followed rain, moving to new grasslands as needed. Once movement was restricted, and they were forced to remain in an area after grass was gone, land degradation resulted. National boundaries left from colonial times can also disrupt rational use of water. An upstream country may overuse water rights, leaving little for downstream countries, leading to land degradation downstream.

  10. Lack of Tenure (private ownership of land).
    Nomadic societies that traditionally lived in drylands held land in common, leading to the tragedy of the commons as populations increased.

  11. War and Civil Unrest
    It is hard to care for the land during war. High population densities leading to a lack of resources leads to civil strife and war. Today it is Darfur in the Sudan and many regions in the middle east. In the past it was in Rwanda and the Congo. When resources are scarce, one region may try to steal from another through war, or to kill local competitors for the resource, especially if the scarce resource is food necessary to live.

B. Natural Systems

Land degradation is also due to extended periods of drought or climate change leading to a permanent reduction of rainfall or timing of rains. Before large populations moved into arid lands, the natural variability of rainfall and climate change caused deserts to grow and shrink. Of the two primary causes of degradation, human activity, especially political ineptitude dominates. Drought mainly amplifies the human influence.

Drought

Drought is a normal, recurrent feature of climate, although many erroneously consider it a rare and random event. It occurs in virtually all climatic zones, but its characteristics vary significantly from one region to another. Drought is a temporary aberration; it differs from aridity, which is restricted to low rainfall regions and is a permanent feature of climate.
From National Drought Mitigation Center's web page on What is Drought?

There are several important types of drought, each of which depends on the duration of the reduction of precipitation:

  1. Meteorological drought, which is determined by the rainfall, temperature, and evaporation, including evapotranspiration. The Palmer Drought Severity Index and the Standardized Precipitation Index are both widely used indices in this category.
    1. Rainfall is usually very irregular in semi-arid regions. Rain tends to fall in some seasons, but not in others. There are large variations in rainfall from year to year.
    2. Higher temperatures cause rapid evaporation of water from the surface and from lakes.

  2. Agricultural drought, which is determined by soil water availability and plant stress.

  3. Hydrological drought, which is determined by stream flow, storage in reservoirs, groundwater levels, soil moisture, and snow pack.

climate types

From National Drought Mitigation Center's web page on What is Drought?

Semi-arid and arid lands are especially susceptible to drought because rainfall in these regions is much more variable than in wetter areas.

References

Reynolds, J. F., D. M. S. Smith, et al. (2007). "Global Desertification: Building a Science for Dryland Development." Science 316(5826): 847-851.

Abstract: In this millennium, global drylands face a myriad of problems that present tough research, management, and policy challenges. Recent advances in dryland development, however, together with the integrative approaches of global change and sustainability science, suggest that concerns about land degradation, poverty, safeguarding biodiversity, and protecting the culture of 2.5 billion people can be confronted with renewed optimism. We review recent lessons about the functioning of dryland ecosystems and the livelihood systems of their human residents and introduce a new synthetic framework, the Drylands Development Paradigm (DDP). The DDP, supported by a growing and well-documented set of tools for policy and management action, helps navigate the inherent complexity of desertification and dryland development, identifying and synthesizing those factors important to research, management, and policy communities.

White, Robin P, and Janet Nackoney (2003) Drylands, People, and Ecosystem Goods and Services: A Web-Based Geospatial Analysis. World Resources Institute Report.

Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-being: Desertification Synthesis. Washington, DC, World Resources Institute.

World Meteorological Organization (2005). Climate and Land Degradation. Geneva, World Meteorological Organization. Report WMO-No. 989.

Revised on: 5 January, 2009

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