Transcript causes-of-land-degradation-sahel

STARTER – Describe 2
solutions and say how
effective they are at solving
land degradation in a
developed country.
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Learning Intensions:
1. Location and climate of the Sahel.
2. Causes of land degradation in Prairies – Human and Physical.
Sahara Desert
Sahel
Shade in the Sahel
and Sahara Desert
in your booklet
(page 11) and
name the
countries of the
Sahel using an
atlas.
Inter Tropical Convergence
Zone (ITCZ)
This is covered in the
Atmosphere section of the
course and explains how
the 2 air masses (from the
north and south of the
Sahel) bring about the
short wet and long dry
season.
To see the climate of the Sahel complete the
climate graph in your booklet (page 11) and
describe the climate of the area. To help with
the description write about:
• What is the highest temperature and when
• Lowest temperature and when.
• Range of temperatures (difference between
highest and lowest).
• When is the highest and lowest rainfall and
when.
• What is the total rainfall.
• Sahel has a long dry season – when the area is affected by
the tropical continental air mass form the Sahara.
• Area has become drier since the 1970s
• Drought is more common
• Rainfall variability is increasing, especially further from the
sea – the Tropical Maritime air mass is not penetrating far
enough inland.
The Human causes of land degradation relate to the land being
overused. This is due to one main reason…
POPULATION INCREASE
An increase in population means that more demands are put on the
land for resources – food and fuel. The land is then put under stress
causing the plants to fail, the soil to lose its structure and therefore
blown or washed away. Complete page 12 in your booklet.
There are 4 human reasons for desertification to occur.
1. Overgrazing
2. Overcultivation
3. Vegetation clearance – forests
4. Salinization and waterlogging.
Use the information on the following slides to complete the boxes, in your
booklet (page 13), with your own notes
OVERGRAZING
What does the term ‘carrying capacity’ of the land mean?
Maximum number of animals (or
crops) that the ground can support
before degradation occurs
Overgrazing means that there are too many animals being kept in an
area, removing all the vegetation and trampling the ground. This is made
worse if many animals are kept in one area. In times of drought people
move their animals around waterholes/ wells where the animals
overgraze the soil.
How cattle trample an area around a waterhole.
Removing the vegetation means that the soil is left exposed to the wind
and the heavy rain. Animals also trample and compact the soil reducing
infiltration rates and increasing surface run-off. This causes 2 problems,
firstly, increasing soil erosion by water. Secondly, reducing the amount
of water in the soil (eg lower water table) and therefore less water for
future use.
As vegetation
removed herders
must move further
afield, thus the
overgrazed area
gets bigger.
Waterhole
Land directly
around the
waterhole
overused
DEFORESTATION
Cutting down the trees for fuel. Draw a simple diagram of a tree and label
it to explain how trees help to reduce soil erosion.
Leaves help
protect the soil
below from rain
splash
Leaves add
some nutrients
to the ground
when they
decompose
When all trees
removed people
use dried animal
dung as fuel. This
also causes a
problem as it is no
longer being added
to the soil.
Roots help bind soil
together
Leaves help provide
shade from sun
reducing
evaporation from
soil
Trees/
vegetation
lifts the wind
and reduces
soil erosion
POOR IRRIGATION TECHNIQUES – SALINIZATION/
WATERLOGGING.
When farmers irrigate their crops salinization can occur. This is due to
the high evaporation rates which brings salt to the surface as water is
drawn up through the layers of soil.
Also if farmers flood the fields, due to poor techniques, then crops can
not grow and the land will be left bare.
In this region of the world the process of land
degradation is often called DESERTIFICATION – this
is the process of the land turning into desert.
Collect a homework sheet ‘Physical Causes of Land
Degradation’ and complete the question.