Knox Academy
Higher Geography
Land Degradation in
North Africa
Case Study:
The Sahel
Introduction
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When soil is bare, it can be easily blown away
by the wind or washed away by rain.
This is called soil erosion.
If a lot of soil is eroded the land cannot be
farmed and it becomes a desert.
This is called desertification.
http://www.bbc.co.uk/learningzone/clips/e
xpansion-of-the-sahara-desert/1500.html
Location
The Sahel runs parallel to
the southern edge of the
Sahara Desert from the
west coast to the east
coast of Africa.
The average width of the
Sahel is 500km.
Its proximity to the
Sahara is one of the
principal reasons it is
prone to desertification.
Climate
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Total annual rainfall is low,
ranging between 200mm in
the northern Sahel to 500
mm in southern Sahel.
Rainfall is unreliable and
highly variable.
Rainfall occurs in a very
intense tropical downpour,
creating high potential
erosivity.
ITCZ
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The rainfall pattern in the Sahel region
is a result of the Intertropical
Convergence Zone (ITCZ) which
migrates across the region each year.
During the dry season, Tropical
Continental air is dominant along with
dry Harmattan winds blowing across
the Sahara.
Natural Environment
Range of species and vegetation decreases
Soil depth decreases and soil erodibility increases
Total rainfall decreases and rainfall reliability decreases
Soil moisture decreases due to increase in sand content
Traditional way of life
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Most people are herders of sheep,
camels or goats. They move from area to
area to find enough water and grazing
land.
They are called nomadic herders.
Causes of rural land degradation
in the Sahel
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The causes of rural land degradation in
the Sahel cannot be attributed to any
one factor, but an interaction of a wide
range of both physical and human
variables.
Unpredictable Climate
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Burkina Faso’s cotton crop destroyed by
flash floods in 1994, 1996 & 1997.
67, 000 tonnes of emergency food aid
were required by Burkina Faso to deal
with food shortages caused by drought.
http://ww
w.youtub
e.com/wa
tch?v=6X
AxIKHebE
http://www.irinnews.org/report/96313/WEST-AFRICA-After-thedrought-floods-and-harvest-worries
http://www.bbc.co.uk/learningzone/clips/desertification
-and-climate-change/1501.html
Desertification
Some years are
wetter than average
and some are much
dryer.
Although the Sahel
should get 100500mm of rain each
year, the rainfall is
very unreliable.
Physical
The soil is eroded
until some of the land
is turned to desert.
With very little rain,
few crops can grow so
there were few roots to
hold the soil together.
At the same time, the
soil dries out and is
easily blown or washed
away.
Human Factors
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Improved medical care resulting in a reduced
death rate, coupled with high birth rates
means that rapid population growth is
occurring in the Sahel.
In countries such as Burkina Faso and Mali
populations are increasing by at a rate of
2.5% per year (while at the same time food
production increases by only 1% year)
Overcultivation
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Rising populations have also forced farmers to
increase the amount of land utilised for
arable farming.
This has led to the cultivation of marginal
areas (edge of the Sahara).
These are not a viable option in terms of
sustained crop production and as a result
cultivating them accelerates the process of
desertification.
Overgrazing
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Places pressure on certain grazing areas
particularly around wells, lakes and rivers.
The concentration of herds in these areas
results in vegetation being stripped down to
its roots, leaving soil exposed.
Compaction of the soil by trampling reduces
the infiltration capacity of the soil and
increases run off.
Deforestation (1)
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Since 1990, 90% of forests have been cleared
in the Ethiopian Highlands.
Deforestation removes the binding effect of
tree roots and prevents the trees from
reducing wind speed.
The shortage of fire wood means that more
and more families are having to resort to
animal dung and crop residues for their
domestic energy requirements.
Deforestation (2)
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The dung and crop residues would
normally be used as fertiliser so the soil
is further degraded as it is deprived of
essential nutrients.
In the long term this will affect crop
yields.
Urbanisation
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Urbanisation has led to an increased demand
for firewood.
Large areas of forest are cut down and the
wood is often turned into charcoal for ease of
transport.
This process is extremely inefficient and half
of the energy of the wood is lost during
conversion.
Growth of cash crops
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During the 20th C some farmers in the Sahel
moved away from traditional techniques and
began growing cash crops such as cotton and
rice.
This monoculture often combined with
inappropriate farming techniques has
rendered the soil infertile in many areas.
Physical consequences of land
degradation
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The increasing frequency of drought
periods the farming of marginal areas
along the northern boundary of the
Sahel and deforestation have led to the
southwards expansion of the Sahara
desert.
In the last 50 years, 65
million hectares of the
Sahel have turned to
desert.
In Sudan the Sahara
has advanced by
100km in 17years.
Desertification is now
estimated to be spreading
at a rate of 1.5 million
hectares per year in the
Sahel.
Physical Consequences
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Rills and gullies
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Loss of topsoil
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Salinisation
Social and economic
consequences of land
degradation
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P.102 – 103
Make notes on the 3 impacts.
Social and economic consequences
of land degradation
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Malnutrition and starvation – The
failure of crops year after year leads to
starvation and death eg: Sudan and
Ethiopia (mid 1980’s).
Cash crop farming can also lead to
malnutrition.
http://www.bbc.co.uk/learningzone/clips/b
ob-geldof-and-the-ethiopiancrisis/3883.html
Migration
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Many people have now migrated away
from the Sahel.
This has led to the loss of traditional
farming techniques and in some cases
(eg: northern Niger) a demographically
imbalanced rural population.
Dependence on external support
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Where the effects of land degradation
and drought have been the most acute,
people have come to rely on food and
other aid sent from other countries, eg:
the band aid campaigns of 1985 and
2005.
This can lead to over dependency on
external help.
Access to education and
healthcare
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In many Saheian countries such as
Burkina Faso, education and health care
must be paid for and therefore the loss
of income brought about by the failure
of crops and herds may mean that
individuals have their schooling
interrupted and individuals go untreated
when ill.
Solutions to RLD
?
Solution 1 : Irrigation
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There have been several expensive
irrigation schemes where rivers have
been dammed and reservoirs formed.
The water from the reservoirs is then
taken by canals to irrigate large areas
of farmland.
The Gezira Scheme
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In Sudan the Gezira scheme allows one
million hectares of land to be irrigated
using water from the White Nile and
Blue Nile.
The Gezira
Scheme
The Gezira Scheme
Farmer
income has
increased
considerably
Farmers can
have two
harvests a year
Wheat is
grown for
food
Cotton is
grown for
export
Advantages
Crops grow even
though there is little
rain
150 000 people
are now
employed there.
The Gezira Scheme
The reservoir
flooded land
which had
previously been
used by local
farmers
Only helped people
in one small area
of the country
Disadvantages
Very expensive
Solution 2 - Terraces
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There are over 200 000 kilometres of
terraces in Ethiopia.
They help trap water, stopping it from
washing the soil away.
Solution 3 – Afforestation
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Planting new trees helps to bind the soil, and
also provides shade, windbreaks, nutrients
and fuel for families.
Depending on the species planted the trees
may also provide nuts and fruit for humans
and animals.
Tree planting needs to be sustainable if it is
to be successful in the Sahel.
Solution 4 – Stone lines
(Magic stones) p.104
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In Burkina Faso and other Sahel countries local
people have built lines of stones along contours on
their sloping farmland.
These stone lines trap run-off after heavy rain so
that the soil is not washed away.
Crops also grow much better in the deeper soil behind
the stones.
This method requires a lot of labour but is cheap and
simple to work.
STONE
LINES
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Organisations such as Oxfam and Tear
Fund, have used this method very
effectively. In some cases crop yield
has increased by as much as 50%.
Other methods (1)
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Managed grazing areas
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Reduced herd sizes
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Education
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Fuel efficient stoves
ADD NOTES
ON THE
FOLLOWING
Other methods (2)
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http://www.youtube.com/watch?v=tDWS6AzEkE0
http://www.youtube.com/watch?v=UKKo0dHmplk
(ethiopia learning from other farmers) excellent
Micro dams
http://www.thewaterchannel.tv/en/videos/categories
/viewvideo/1288/soil-conservation/micro-dams
Micro basins
http://www.thewaterchannel.tv/en/videos/categories/vi
ewvideo/1305/soil-conservation/micro-basins
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Past Paper 2006
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In pairs Answer Q2 part (a) (i) (ii).
Part (i) 6 marks
Part (ii) 8 marks
Past Paper 2006
(a) (i)
Description could include the following points:
 the pattern shows constant fluctuations
 from 1950 until about 1970 rainfall is above average
 after 1970 rainfall is consistently below average.
6 marks
(a)(i)
Past Paper 2006
Answers might include:
1. During drier periods – soil will dry out – plants die – hence no
root systems to protect the soil. The soil can easily be blown
away
2. It is often the most fertile topsoil which is affected
3. If a heavy rain storm falls unprotected soil is easily washed
away
4. Reference might also be made to human responses – eg during
periods of above average rain, cropping and animal husbandry
boundaries can be extended into previously dry areas – when a
climatic reverse occurs the resulting overcropping/
overcultivation can lead to considerable degradation.
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Award up to 2 marks for detail regarding erosion processes by
wind or rain.
Assess out of 4
4 marks
Past Paper 2006
(b)