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 Form 2 Geography Lessons on Climate

In this lesson we are going to discuss the definitions and causes of Aridity and Desertification

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Answer Text:
Aridity and Desertification
Aridity - state of land being
deficient of moisture leading
to little or no vegetation.
Desertification - process in
which desert like conditions
slowly and steadily encroach
on formerly productive
agricultural land.
Causes of Aridity and
1. Low and unreliable rainfall
below 250mm per annum
causing little or no vegetation
and absence of animal and
biological life causing soil
forming processes to be
2. High temperatures which
cause high rates of
evaporation which exceeds
precipitation or low
temperatures which reduces
air capacity to hold moisture
causing a place to receive
little or no rain.
3. Where a place is washed by
cold ocean currents causing
moist onshore winds to cool
and then drop moisture over
the sea and reach the land as
dry winds e.g. Kalahari when
onshore westerlies cross the
cold Benguela Current.
4. Where relief barriers such
as hills or mountains cause
some areas to lie on the rain
shadow hence rain winds drop
most of their moisture on the
windward side and when they
reach the leeward side, they
are dry hence causing dry
conditions e.g. Kalahari and
Namib on the rain shadow of
Drakensberg mountains.
5. Location of some places
very far from the sea causing
them not to be washed from
wet onshore winds e.g. Gobi
6. Where hot dry winds blow
over a region causing drying
effect on land e.g. Harmattan
over West Africa.
7. Where cool air descends
causing no rain because cool
air has to rise before
condensation takes place.
Human Activities
8. When people clear forests
which causes runoff to exceed
infiltration which interferes
with the water cycle.
9. Keeping large number of
animals which exceed the
carrying capacity of land.
They eat vegetation leaving
the land bear exposing the
land to soil erosion.
10. Poor agricultural practices
such as over cultivation,
monoculture and slashing and
burning which leads to soil
11. Industrialization which
releases greenhouse gases
such as co2 to the atmosphere
which absorb more heat
making the earth’s
temperature to rise.
12. Reclamation of water
logged areas which lowers the
water table causing arid
conditions to set in when
plants can’t access ground
13. Poor irrigation methods,
when evaporation takes place
and salt from below are
brought to the surface and are
deposited on the top soil
making the soil salty and
hence unable to support