DESERTIFICATION AND THE SAHEL
THE HUMAN – BIOSPHERE LINK
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Desertification Web Poster - Brook Hill & Michael Jordan Climate & Society Fall 2009
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WHAT IS DESERTIFICATION? DEFEATING THE MYTH OF “THE MARCHING DESERT”
THE MYTH
The myth of the “marching desert" (Forse 1989).
 Desertification is not the movement of an
“advancing desert.” As stated by in the Bulletin of
the American Meteorological Society: The image of
a “living environment becoming sterile and
barren…is not an accurate picture (Nicholson
1994a).” While this image is not wholly incorrect,
it is an oversimplification for a phenomenon
affecting ecosystems in semi-arid regions across
the world.

WHAT IS DESERTIFICATION?
DEFINING THE TERM

Desertification is a process of severe land
degradation. There are several main factors that
can cause this degradation, but they all work
together in a reinforcing system ultimately turning
many productive drylands into expanses incapable
of supporting a lively ecosystem. The effect is
often localized and can occur over long periods of
time as well as relatively small spans in light of
other natural occurring phenomena.
WHERE AND WHO? THE SAHEL BELT: DESERTIFICATION MADE
SIGNIFICANT

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Desertification is perhaps
one of the greatest life and
biosphere altering
phenomena in
contemporary history,
particularly affecting the
Sahel belt. The Sahel belt
runs through 10 countries:
Senegal, Mauritania, Mali,
Burkina Faso, Niger, Nigeria,
Chad, Sudan, Eritrea and
Cape Verde Islands. This
belt was historically a region
of agricultural prosperity
and economic
dependability, however, this
situation has changed.
WHY SHOULD WE CARE?


Population of Sahel belt:
over 50 million…and
growing!
In the Sahel “…production
in severely eroded plots
averaged 21 percent less
than production in normal
or slightly eroded soils.”
Soil is critical to life in the
Sahel belt, yet a quarter
of soil degradation comes
from agricultural
activities” (Warren 1996).
In the Sahel “…production in severely
eroded plots averaged 21 percent
less than production in normal or
slightly eroded soils.” Soil is critical to
life in the Sahel belt, yet a quarter of
soil degradation comes from
agricultural activities.
(Warren 1996). Its roots lie in societal
changes like increasing population,
sedentarization of indigenous
nomadic peoples, breakdown of
traditional market and livelihood
systems, introduction of new and
inappropriate technology in the
affected regions, and, in general, bad
strategies of land management.”
FERTILE SOIL: THE CRITICAL RESOURCE IN THE SAHEL BELT
SO WHAT… ABOUT DESERTIFICATION ?

Through collected data and conclusions of
reputable experts, this paper makes the claim that
human-induced components of desertification
significantly reinforce biophysical phenomena
causing desertification in the Sahel. This paper
argues that there are severe impacts to the
biosphere and is ability to sustain human life due
to desertification and proposes possible solutions
to this significant and impending threat to life
sustainability in the Sahel belt.
THE BIOPHYSICAL FACTORS:
Key in causing desertification in the Sahel:
 Climate change: SST’s and warming
 Rain variability: As a result of prolonged drought,
fertile top soil became exposed and vulnerable to
periods of intense rainfall variability and
deteriorated from lack of organic matter and water
resources; causing desertification.
 Soil erosion: degradation of productivity which
threatens sustainability.

SEA SURFACE TEMPERATURES AND DESERTIFICATION

In Dr. Held’s, et. al Simulation of Sahel drought in the
20th and 21st centuries (2005) his climate models
suggest that there has been an “anthropogenic drying
trend in this region, due partly to increased aerosol
loading and partly to increased greenhouse gases, and
that the observed 20th century record is a superposition
of this drying trend and large internal variability” (Held,
et al. 2005). In addition, Dr. Held’s, et al. models provide
evidence that Sea Surface Temperature warming,
through increase in global warming due to greenhouse
gases, affects rainfall variability in the Sahel thus
making it a biophysical factor for desertification
reinforced and accelerated through human activity.
THE HUMAN FACTOR:

At issue is direct human reinforcement through
acceleration or deceleration of biophysical
phenomena such as soil erosion, land degradation,
and agricultural practices.

Over-cultivation is a significant cause of
desertification for it reduces soil fertility (a quickly
changing variable) and reinforces a cyclic decline in
crop yield (a slowly changing variable).

As detailed by The Center for International Earth
Science Information Network (CIESIN) at Columbia
University, The most commonly cited forms of
unsustainable land use are over-cultivation,
overgrazing, deforestation, and poor irrigation
practices. Let us examine each of these significant
causes individually.

Additionally, the variables used to judge
desertification need to be addressed individually as
they indicate desertification at different rates and
are effects of the human-biosphere link in different
proportions depending on the micro-ecosystem.
EFFECT OF DESERTIFICATION ON ALBEDO
THE LINK BETWEEN ALBEDO AND
DESERTIFICATION

Land surface albedo products for land surface
and climate modeling (Löw et al.) support the
claim that “progressive removal of vegetation
cover changes the surface albedo (the degree
to which the land surface reflects the sun's
energy) and can also reduce atmospheric
humidity, which in turn affects cloud formation
and precipitation” (SEDAC/CIEN 2009).
MOVE FROM CAUSES TO IMPACT

We as humans are interdependent on the biosphere and its many micro-ecosystems. We
support, rely upon, and are affected by the
biosphere as much as we affect it. This type of
interdependency can have positive outcomes,
such as environmental sustainability and
development, but it can also have potentially
life and biosphere altering results. This is no
truer than in the Sahel belt.
THE IMPACTS OF DESERTIFICATION
Continued degradation of soil negatively affects the ability
of Sahelian farmers to grow crops, results in less grazing
land for livestock, and can have considerable impacts for
people that live not only, but near, the degraded areas.
Decreased soil productivity


Less grazing land for livestock cause livestock
populations to decrease

Negative economic growth

Environmental side effects
SOIL DEGRADATION AND LOST PRODUCTIVITY

Soil degradation decreases the productivity of soil which
is a serious threat to food security in the Sahel.

productivity loss past 6.6% 21st century will be
approximately 14.5% (Lal, 2001).

Population growing 3% annualy

Degraded land has decreased livestocks food supply
lowering population in Gourma regoin of Mali by 80%
between 1971-1988.
.
EFFECTS OF LOST PRODUCTIVITY ON THE
ECONOMY OF AFFECTED COUNTRIES
Decreased agricultural and livestock production threatens to
shrink already fragile economies of Sahelian nations.

Over 50% of Sahelian populations work in agriculture or livestock
herding.

40 per cent of the GDP for those countries (qtd in Kandji).

One Sahelian country could loose 20% of its GDP in future.
IMPACTS ON THE ENVIROMENT OF
SURROUNDING AREAS
Desertification and it’s the decreased production that comes
with it has many non-economic effects on people living outside
the affected areas.

flooding, reduced water quality, sedimentation in rivers and lakes.
increased numbers of dust storms,. (UNCCD, fact sheet 3).

forced mass exodus of people from effected areas to urban areas.
overcrowding, increased unemployment, and stress on
social services
RAINWATER USE EFFICENCY
Using rainfall more efficiently could be an
effective way to mitigate the effects of and land
degradation its self
 20
to 40% rainfall lost as run largest contributor to
dryness (Kandji et all, 25)
 sub- Saharan Africa water use efficiencies 5%15%. East Africa is 20% > United States similar
climate, efficiency 50% - soil management (2003).
METHODS OF INCREASING EFFICENCY

Hedgerow systems and stone lines are promising ways to limit run off in fields
because they provide a barrier to run off.

greater the number of stone lines increases water infiltration improving
yields (Kandji et all).

Stroosnidjer wrote that in Kenya where hedgerow systems were used
infiltration increased and run off decreased (2003).

Another way to mitigate the effects of desertification is through planting
trees in and around fields where crops are being grown. agroforestry.
promotes diversified and sustainable crop production, additional source
of income for Sahelian farmers (Kandji et all). Agro forestry is a practical
and simple way to improve productivity in the Sahel.