1. Desertification
environment.nationalgeographic.com

2. 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.

3. Desertification Causes of Desertification:
Complex interplay of physical and ecological processes, and developmental and socio-economic forces. For example:
brief period of excess rainfall “the rain follows the plow”
over irrigation (salinization)
ground-water depletion

4. Desertification
…is the degradation of land in arid, semi-arid, and dry sub-humid areas.
Causes of Desertification: Complex interplay of physical and ecological processes, and developmental and socio-economic forces.
Drought: rainfall significantly below normal for an extended period.
several years
more than 25% less than normal

5. 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

6.
Dryland regions of the world (yellow) these are sensitive to desertification

7. koeppen-geiger.vu-wien.ac.at

8. BIOGEOMORPHIC the physical geography of arid lands
transitional region between savanna and desert
variability in precipitation
natural vegetation

9. Desertification
Excessive forest clearing and overgrazing livestock reduces vegetation cover.
Two impacts:
*Albedo increases: cooling the region in summer and weakening monsoon circulation.
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

10. Desert Formation
From Lancaster, 2007
mrborden.wordpress.com

11. 30% of the land in the U.S. is affected by desertification.
Desertification in the US
30% of the land in the U.S. is affected by desertification.

16. 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.

18. Shallow, rather than deep, along contours Established windbreaks
Desertification in the US: The Dust Bowl of the 1930s.
Changed farming practices & plowing techniques
Shallow, rather than deep, along contours
Established windbreaks
Crop rotation
Irrigation

19. Phoenix, Arizona in the early 1970s

21. How have each of these factors contributed to desertification?