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 fallen away.
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 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
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
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 Nackoney (2003)
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.
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.
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.
From Doctors Without Borders
- 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
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 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
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
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
- 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.
- 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
- 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
- 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
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 plant stress.
- 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 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.
Reynolds, J. F., D. M. S. Smith, et al. (2007). "Global Desertification:
Building a Science for Dryland Development." Science 316(5826):
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
World Meteorological Organization (2005). Climate and Land Degradation. Geneva,
World Meteorological Organization. Report WMO-No. 989.
5 January, 2009