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Desertification Lecture 4 presentation.ppt
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- 2. X. Desertification A. Deserts:areas of low rainfall….. Arid: less than 10 cm (4 in) Semi-arid: less than 25 cm (10 inches) 2
- 3. X. Desertification A. Deserts B.Drylands: What life cares about. Effective Moisture: the ratio of precipitation (PPT) to potential evapo-transpiration (PET). Hyperarid: PPT/PET <0.05 Arid: PPT/PET 0.05 to 0.20 Semi-arid: PPT/PET 0.20 to 0.5 Dry sub-humid: 0.5 to 0.65 Humid: PPT/PET >1 3
- 4. X. Desertification A. Deserts B.Drylands C. Distribution 1. Sunbelt 2. Rainshadow 3. Continental interior 4. Coastal Adjacent to these real deserts are the sensitive drylands. 4
- 5. X. Desertification A. Deserts B.Drylands C. Distribution D. Desertification:the degradation of land in arid, semi-arid, and dry sub-humid areas. Can be caused by human activity or climate change. 5
- 6. X. Desertification D. Desertification:thedegradation 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 socio- economic forces. For example: a. brief period of excess rainfall “the rain follows the plow” b. over irrigation (salanization) c. ground-water depletion 6
- 7. X. Desertification D. Desertification: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 socio- economic forces. For example: 2. Drought: rainfall significantly below normal for an extended period. several years more than 25% less than normal 7
- 8. Dryland regions ofthe world (yellow) These are sensitive to desertification 8
- 9. D. Desertification: 4. TheSahel as an example climate climate change agricultural practices political process population 9
- 10. D. Desertification: 3. TheSahel as an example a. Sub-saharan rainfall index shows drought from 1970 to 2000. b. Impact on human activity in the Sahel. 10
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- 12. D. Desertification: 3. TheSahel as an example a. Sub-saharan rainfall index shows drought from 1970 to 2000. b. Impact on human activity in the Sahel. c. Possible explanations for the Sahel 12
- 13. Remember what drivesthe monsoon circulation. • Strong seasonal pressure gradient between land and sea (hot land mass) • Warm oceans to supply moisture. • Sufficient recycling of rainfall by plants (evapotranspiration) to allow moisture to reach deep into the interior. 13
- 14. D. Desertification: c. Possibleexplanations for the Sahel • Natural climate variability: Monsoon activity controled by sea surface temperatures, related to ENSO variability. • Inappropriate technology/misguided foreign aid. • Aerosols produced by industrialization in Europe cool Sahel, reducing strength of the African Monsoon. d. Positive feedbacks 14
- 15. D. Desertification: c. Possibleexplanations for the Sahel d. Positive feedbacks Fuel wood gathering and stock overgrazing 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 the monsoon and deliver precipitation over the Sahel region. 15
- 16. D. Desertification: 4. TheSahel as an example 5. Desertification in the US 16
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- 22. Precursers 10-fold increase inpopulation 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. 22
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- 24. D. Desertification: 5. Desertificationin the US: The Dust Bowl of the 1930s. Precursers Causes Consequences: Changed farming practices Plowing techniques Shallow, along contours Established windbreaks Crop rotation Irrigation 24
- 25. D. Desertification: 5. Desertificationin the US: The Dust Bowl of the 1930s. Precursers Causes Consequences: Changed farming practices Better? Yes, but…. 25
- 26. Phoenix, Arizona inthe early 1970s 26
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