Land Degradation in Arid Regions
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
From US Department of Agriculture web page on Land
Degradation and Desertification.
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 rain fed 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 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
- Declining groundwater,
- Increased erosion,
- 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.
|Asia (Incl. Russia)
|C. America & Caribbean
Land area: millions of square kilometers. Population: thousands. From White and
The vulnerable areas are mostly in mid-latitudes near 30 degrees of latitude.
Global map of dryland areas. Click on the map
for a zoom.
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.
Schematic graphic showing how drylands can be
developed in response to changes in key human factors.
that lead to a downward spiral of desertification.
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.
Ecosystem Assessment (2005): Ecosystems and Human Well-Being. Desertification
- 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.
- 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.
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.
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.
- 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
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
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.
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.
- 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
- 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
- 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
- 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 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
There are several important types of drought, each of which depends
on the duration of the reduction of precipitation:
- 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.
- 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.
- Higher temperatures cause rapid evaporation of water from the surface
and from lakes.
- Agricultural drought, which is determined by soil water availability and
- Hydrological drought, which is determined by stream flow, storage in reservoirs,
groundwater levels, soil moisture, and snow pack.
From National Drought Mitigation Center's web page on What
Semi-arid and arid lands are especially susceptible to drought because rainfall
in these regions is much more variable than in wetter areas.
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.
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.
5 January, 2009