Why are deserts expanding?
Student activity:
Causes of desertification card sort for the Venn diagram
Changes in seasonal rain due
to global warming, reduces
rainfall in already dry areas.
Over-grazing of pasture land.
Too many livestock eat the
plants at a faster rate than
regrowth.
Over-cultivation. Farmers
plant crops year after year on
the same land, reducing its
nutrients and fertility.
Long droughts dry out
temporary surface water
storage bodies like oases,
seasonal rivers and lakes.
Reduced rainfall decreases
water available for plant
growth. When the roots die
the soil is easily eroded.
Excessive use of irrigation
water causes salinization,
where water brings salt to the
surface.
Large herds of cattle can
compact the top soil layer,
making it hard for water to
penetrate/infiltrate.
Deforestation. Logging to
provide fuel wood for local
communities and their
growing populations.
Excessive water consumption
in tourist areas means
groundwater and surface
water stores become
depleted.
Logging leaves top soil at risk
of erosion from natural
rainfall events, surface run
off can carry away the fertile
layer.
Destruction of the soil by poor
farming methods (ploughing
too deeply and over use of
pesticides and fertilisers).
Population growth puts
pressure on scarce farmland
leading to overgrazing and
cultivation.
People in rural desert
communities rely on fuel
wood for cooking due to the
remoteness of settlements.
Urbanisation and building of
roads and infrastructure
increases surface run off and
soil erosion.
Global temperatures are
expected to rise, which
results in more water
evaporating from plants and
surface water (lakes and
rivers).
Reduction in nomadic
lifestyles in the Sahel has
meant cattle and goat herds
stay in one place, resulting in
overgrazing.
Incorrect irrigation is
commonly used in poorer
areas. Farmers are using canal
irrigation which causes a
build-up of salt in the soil.
Desertification is occurring in
the Sahel region because
farmers are using the slash
and burn method to clear
land for crops. This degrades
the quality of soil.
Keywords:

Nomads/Nomadic: Traditional farmers who move around the land with their herd from place
to place to find a constant source of vegetation for their animals.

Slash and burn: Vegetated land is cleared by burning trees and shrubs to clear the way to
grow crops creating arable land.

Surface run-off: Where water from rainfall flows over the surface of the land, rather than
sinking in/infiltrating.

Drought: Prolonged periods of below average rainfall.
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Why are deserts expanding?
Climate change
Population Pressure
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Agriculture
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Why are deserts expanding?
Teaching notes: Why are Deserts Expanding?
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All students will be able to describe desertification.
Most will be able to classify reasons as human or physical.
Some may be able to explain how desertification has led to negative long term
consequences.
Starter:
Numeracy is an important skill at GCSE level Geography as it is being tested formally in the new
examinations. The task introduces numeracy within the context of the high rates of
desertification.
Answers:
1. Write out this number using words.
Thirty thousand
2. What is 30000 hectares in acres (1 hectare = 2.5 acres of land).
30000 x 2.5 = 75000 acres
3. Industrial logging removes more trees and this weakens the top layer of soil, so the rates of
desertification increase 10% each year (year on year). How many hectares of land are lost in
total over three years starting from 2016?
year 1 (2016) 30000
year 2 (2017) 30000 + 10% (3000) = 33000
year 3 (2018) 33000 + 10% (3300) = 36300
Total 99300 hectares
The teacher should talk through the process of desertification in detail and refer to the image to
show how they might identify it in a particular place. For example, in the image shown there has
been a layer of sandy soil blown onto the road due to the lack of vegetation dotted around the
landscape.
Main Task:
Classifying causes of desertification.
A Venn diagram is a useful tool to classifying actions, effects or causes into two to three
categories. They are a form of graphic organiser used to promote higher order thinking skills and
help to understand complex ideas. For information on Venn diagrams and their usefulness see:
www.learnnc.org/lp/pages/2646
Instead of students writing out their own statements onto a blank diagram, they should use a
large A3 laminated copy to place pre-cut cards onto. In this way they can have dialogue and
move cards round to a new position. There may be cards which fall between 2 categories, for
example “Reduction in nomadic lifestyles in the Sahel has meant cattle and goat herds stay in
one place, resulting in overgrazing.” This statement can be linked to BOTH population pressure
and agriculture, therefore it should be placed in the overlapping between the yellow and green
circles.
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Why are deserts expanding?
Extension:
Mind mapping.
Once the group is happy with their card arrangements on the Venn diagram and discussion has
been generated, students should write concise notes on each of the three main causes (climate
change, agriculture and population pressure). The writing on a mind map should be concise and
include visual elements to help explain the processes behind desertification. Depending on the
time available and ability of the students you may wish to get them to include causes and
consequences. A good example of a ‘free to download’ desertification mind map can be found at
the following link:
quicksmartrevision.weebly.com/desertification.html
You could use free mind-mapping tools like mindmapfree.com/# to provide a starter structure
for the mind-map. These could be printed out to improve task completion for lower ability
students, simply displayed on the classroom whiteboard or students could use computers to
complete their own.
Depending on the learning styles of the class you may wish to offer other options for note
making: paragraphs, bullet points, flow diagram etc.
Discussion.
Lesson could finish with a discussion of the consequences of desertification. This could be used
as the basis of a ranking homework task, where students consider the four main consequences of
desertification and justify which they think is the most concerning and which they consider the
least.
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