PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26X. DesertificationA. Deserts: areas of low rainfall….. Arid: less than 10 cm (4 in)Semi-arid: less than 25 cm (10 inches)X. DesertificationA. DesertsB. Drylands: What life cares about.Effective Moisture: the ratio of precipitation(PPT) to potential evapo-transpiration (PET).Hyperarid: PPT/PET <0.05Arid: PPT/PET 0.05 to 0.20Semi-arid: PPT/PET 0.20 to 0.5Dry sub-humid: 0.5 to 0.65Humid: PPT/PET >1X. DesertificationA. DesertsB. DrylandsC. Distribution1. Sunbelt2. Rainshadow3. Continental interior4. Coastal Adjacent to these real deserts are the sensitive drylands.X. DesertificationA. DesertsB. DrylandsC. DistributionD. Desertification:the degradation of land in arid, semi-arid, and dry sub-humid areas. Can be caused by human activity or climate change.X. DesertificationD. 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:a. brief period of excess rainfall “the rain follows the plow”b. over irrigation (salanization)c. ground-water depletionX. DesertificationD. 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 yearsmore than 25% less than normalDryland regions of the world (yellow)These are sensitive to desertificationD. Desertification:4. The Sahel as an exampleclimateclimate changeagricultural practicespolitical processpopulationD. Desertification:3. The Sahel as an examplea. Sub-saharan rainfall index shows drought from 1970 to 2000. b. Impact on human activity in the Sahel.D. Desertification:3. The Sahel as an examplea. Sub-saharan rainfall index shows drought from 1970 to 2000. b. Impact on human activity in the Sahel.c. Possible explanations for the SahelRemember what drives the 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.D. Desertification:c. Possible explanations 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 feedbacksD. Desertification:c. Possible explanations for the Saheld. Positive feedbacksFuel 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.D. Desertification:4. The Sahel as an example5. Desertification in the USPrecursers10-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 farmersOut migration “Okies”True drought.D. Desertification:5. Desertification in the US: The Dust Bowl of the 1930s.PrecursersCausesConsequences: Changed farming practicesPlowing techniques Shallow, along contoursEstablished windbreaksCrop rotationIrrigationD. Desertification:5. Desertification in the US: The Dust Bowl of the 1930s.PrecursersCausesConsequences: Changed farming practicesBetter? Yes, but….Phoenix, Arizona in the early