Download Wind, Dust and Deserts (video)

Wind, Dust and Deserts (video)
Global Geography 12
Definition of a Desert:
Dry most of the year, total rainfall less than 25cm each year.
Where and why deserts form:
Global Weather Patterns Convection cells of air from the equator lose most of their
moisture through heavy rains. When air in the cells descend at the subtropics (30ºN and
S latitude), they are warm and very dry.
Local Landforms A rain shadow desert forms when prevailing winds force air up over
mountains, where condensation and precipitation remove moisture. Air descending on
the other side is dry, creating a desert.
Distance from Ocean The interior of large continents are far from oceans, so air masses
lose moisture before reaching these areas. The Gobi desert in China
Desertification (human activity) Vegetation absorbs suns energy, resulting in cooler air,
while increasing humidity. Both conditions make rain more likely.
Removal of vegetation allows soil to dry out and erode, so new plants cannot take root.
If the climate is semi-arid or near a desert, desertification results.
Desertification is nearly irreversible, due to difficulty in re-establishing plants.
The Sahel
Rainy years (1960’s) encouraged farmers to increase herds and grazing lands, while
population increased as people moved in to farm.
Drought (early 1970’s) caused a loss of herds.
Continuing drought (1980’s) complete exposure of soil, dust storms and moving dunes
20 million people affected, Over 100 000 starved, especially in Ethiopia and Sudan
Problem partly created by technology – deep drilled wells allowed population increase
beyond the capacity of the environment to sustain their other activities, especially when
lower rainfall returned.
Prevention
Water conservation techniques to save groundwater reserves
Farming techniques (saving trees, shallow or minimal ploughing) that minimize erosion
and water loss
Eden Foundation Website
http://www.edenfoundation.org/project/slideshow15.html