Desertification - Earth Geography

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Desertification
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Desertification
Deserts: areas of low rainfall…..
Arid:
less than 10 cm (4 in)
Semi-arid:
less than 25 cm (10 inches)
Desertification: the degradation of land in arid,
semi-arid, and dry sub-humid areas.
Can be caused by human activity or naturally
occurring phenomenon.
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Desertification
Causes of Desertification:
Complex interplay of physical and ecological
processes, and developmental and socioeconomic forces. For example:
a. brief period of excess rainfall “the rain follows the plow”
b. over irrigation (salinization)
c. ground-water depletion
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Desertification
…is the degradation of land in arid, semi-arid,
and dry sub-humid areas.
1. Causes of Desertification: Complex
interplay of physical and ecological
processes, and developmental and socioeconomic forces.
2. Drought: rainfall significantly below normal
for an extended period.
a.several years
b.more than 25% less than normal
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 Drylands cover about 40% of Earth’s land surface
 Home to more than 38% of the total global
population of 6.5 billion (about 2.4 billion)
 Land degradation is present on 10 to 20% of the
global drylands
 Land degradation indirectly affects about 250
million people in the developing world
Dryland regions of the world (yellow)
these are sensitive to desertification
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BIOGEOMORPHIC
 the physical geography of arid lands
 transitional region between savanna and desert
 variability in precipitation
 natural vegetation
Desertification
Excessive forest clearing and overgrazing livestock
reduces vegetation cover.
Two impacts:
1. *Albedo increases: cooling the region in summer
and weakening monsoon circulation.
2. Less vegetation = less evapotranspiration. So less
water vapor in the atmosphere to fuel precipitation
over the region.
Albedo is the fraction of solar energy (shortwave radiation) reflected
from the Earth back into space
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From Lancaster, 2007
Desertification in the US
30% of the land in the U.S. is
affected by desertification.
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Precursers
10-fold increase in population between
1860 and 1920.
Deep plowing and monoculture destroyed
soil structure and increased sensitvity to
erosion.
Additional factors:
Great Depression: no $ for prairie farmers
Out migration “Okies”
True drought.
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Desertification in the US: The Dust Bowl of the 1930s.
Changed farming practices & plowing techniques
1.
2.
3.
4.
Shallow, rather than deep, along contours
Established windbreaks
Crop rotation
Irrigation
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Phoenix, Arizona in the early 1970s
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How have each of these factors
contributed to desertification?
desertification
climate
humans
animals
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