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Deserts

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Formation of a Desert

  • Dry areas created by global circulation patterns of wind and water.

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  • Independent of latitude, longitude or elevation.
  • Exist on Venus and Mars as well as Earth.

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What is a desert?

An area that has…

… at least 12 consecutive months without rainfall and less that 500 millimeters (20 inches) of precipitation per year.

Compared to Raleigh…

… which has 46.55 inches of rainfall in an average year.

Compared to a rainforest…

… which has 80 inches of rainfall in an average year.

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Types of Deserts

Trade Winds Deserts

  • Caused by hot, dry winds near the equator.
  • Most of the world’s major deserts.
  • EX: Sahara (Africa)

Mid-latitude Deserts

  • Occur north or south of the subtropical high pressure zones.
  • Form far from oceans.
  • EX: Sonoran (N. America)

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Types of Deserts

Rain Shadow

  • As air rises over the mountains the precipitation falls on the “windward”/ shadow side.
  • EX: Great Basin (N.A.)

Coastal

  • Found on the western edges of continents near the tropics.
  • Created by cold currents running parallel to the coast.
  • EX: Namib and Atacama

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Types of Deserts

Monsoon

  • Seasonal deserts due to variations in temperature between the oceans and the continents.
  • EX: Thar (Pakistan)

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Polar

  • Temperatures of less than 10*C and precipitation less than 250mm.
  • Some have snow dunes.
  • EX: Dry Valleys of Antarctica

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Desertification

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Desertification

  • The gradual transformation of habitable land into desert; is usually caused by climate change or by destructive use of the land.

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  • The rate is increasing due to human activity.

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Sahel

The Sahel is in Africa between the Sahara to the north and the Sudanian savanna to the south.

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Dessertification of the Sahel

The Sahel was increasingly afflicted by soil erosion and desertification resulting from growing human populations that made more demands upon the land than previously. Town dwellers and farmers stripped the tree and scrub cover to obtain firewood and grow crops, after which excessive numbers of livestock devoured the remaining grass cover. Rainfall runoff and the wind then carried off the fertile topsoils, leaving arid and barren wastelands. (Britannica)

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The Causes

  • Drought
  • Overgrazing
  • overuse of groundwater
  • Overpopulation
  • Deforestation
  • Global climate change

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Possible Solutions

  • Change to human activities (required by national and international laws) including…
  • Water conservation,
  • Improved farming practices ,
  • Modification of water use,
  • Smart planting to prevent erosion and increase soil fertility.