Desertification in Sahel Desert

  • Describe the global distribution of arid and semi-arid areas.
  •  What is meant by the diurnal temperature range? Why is it so large in hot desert areas?
  •  Outline how the cold ocean current and the mountains are responsible for aridity in the Atacama Desert.
  •  Outline how the atmospheric circulation is responsible for the Sahara.
  •  Desert Plant – Barrel Cactus (Mojave Desert)
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  • Created on: 03-03-13 12:16
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Desert Locations, Characteristics and Causes of Aridity
Exam Question Hw.
Describe the global distribution of arid and semi-arid areas. (5 marks)
Arid areas are located along the Tropic of Cancer and the Tropic of Capricorn, i.e. LOW LATITUDES. The
semi-arid areas lie along the margins of these arid areas, for example the Sahara desert is an arid area and
the Sahel would be classified as a semi-arid area. Some of these areas also located adjacent to mountain
ranges, like the Atacama Desert which is alongside the Andes. Other patterns for the distribution of these
arid and semi-arid areas are the way they are on the western margins of their relative land masses.
What is meant by the diurnal temperature range? Why is it so large in hot desert areas? (3 marks)
Diurnal temperature range is the variation in temperatures recorded between the highs of the day and the
cool of the night. In hot deserts this range is much higher because of the absence of cloud cover. Clouds
reflect the solar radiation and only a small amount is absorbed by them. Therefore during the day when
there is little/low cloud cover the earth's surface heats up very quickly but at night this heat escapes;
resulting in significantly lower temperatures during the night.
Outline how the cold ocean current and the mountains are responsible for aridity in the Atacama
Desert. (4 marks)
The Atacama Desert is located along the west coast of South America. Due to the action of cold ocean
wind currents circulating, there is an upwelling of cold sea water. These winds travel over the cold Humboldt
/ Peruvian current and cool. Cool winds are unable to pick up the moisture needed, so limiting the amount
of precipitation which can be held. The lack of precipitation results in less than 100-250mm of rainfall
annually and therefore results in the aridity of the Atacama Desert.
Outline how the atmospheric circulation is responsible for the Sahara.
The Hadley Cell is an atmospheric circulation pattern in the tropics. The air in the Hadley cell rises at the
equator and sinks at the medium latitudes. The Sahara Desert lies along the Tropic of Cancer and under the
falling limb of the Hadley Cell, carrying warm dry air from the equator and high pressure which means that
there is little chance of rainfall. The air around the Sahara Desert has very low amounts of water vapour due
to very high evaporation rates. Therefore little precipitation reaches these areas.
Desert Plant ­ Barrel Cactus (Mojave Desert)
5 ­ 11 feet tall
Swollen trunk which stores water
Shallow root system to catch water when it rains
Round shape and no leaves to minimise water loss
Spines which directs water to the ground to be absorbed by
roots
Special metabolism which allows the stomata to stay closed
during the day and open at night to release oxygen and absorb CO2
which is stored as malate which is then used in photosynthesis

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