3.1.2.4 desertification

• Desertification


  The persistent degradation of dryland ecosystems, arid, semi-arid and dry sub-humid areas, by human activities + climate change, resulting in desert like conditions
• Desertification


  • It is an example of positive feedback
  • Leaves land unproductive
• Regions worst affected by desertification

  • Africa
  • Asia
  • Latin America
• 1/3 of land worldwide is at risk from desertification
• 250 million people are already affected by desertification
• 46% of Africa is at risk of desertification
• 25% of Africa is already desertified according to the UN
• 12 million hectares of land lost to desertification annually according to the UN
• Desertification reduces the wellbeing of at least 1 billion people in 100 countries
• Hot deserts


  Since the last glacial period ended 11,500 years ago, the climate became more wet, reducing the amount of land covered by deserts
• Hot deserts


  9,000 years ago, only deserts were on the west coast of South America and South Africa
• The extent of deserts have increased over the past few thousand years
• Late Holocene (approximately 4,000 years ago to present)


  • Desert landscapes have continued to evolve in response to climate fluctuations, human activities, and other factors
  • Some regions have experienced desertification due to factors such as deforestation, overgrazing, soil erosion, and changes in land use practices
  • Human civilization has also influenced desert distribution through activities such as irrigation, agriculture, urbanization, and infrastructure development
• The Sahara desert


  • 5,000-9,000 years ago, it was a 'green Sahara' with lakes, vegetation, and animals like antelope, giraffes, and cattle
  • Ancient cypress trees up to 2,000/3,000 years old survived due to long taproots and the water table
  • The Sahara's precipitation decreased as the belt of rains moved northwards across Europe
• Most deserts were formed during the last glacial period, around 6,000-4,000 years ago
• Climate change as a physical cause of desertification

  • Less and more unpredictable rainfall, especially in the Sahel region
  • Reduced water supply as rivers dry up and water tables are lowered
  • Increased evapotranspiration and vegetation loss due to higher temperatures
• Human activities increasing the rate of desertification/land degradation

  • Population growth and increased pressure on the land
  • Over-cultivation reducing soil productivity and fertility
  • Deforestation for agriculture, fuel, and building materials
  • Over-grazing leading to soil depletion and erosion
  • Unsustainable irrigation practices depleting surface water and groundwater, and causing salinization
• Irrigation can cause desertification

  • River channels can be diverted to irrigate crops, depleting water sources like the Aral Sea
  • Irrigation depletes surface water and/or fossil aquifer systems, lowering water levels and availability
• The Nubian Sandstone Aquifer System in North Africa is the world's largest known fossil water aquifer system, spanning four countries, and is an important but contested water source
• Impacts of desertification on ecosystems, landscapes, and populations

  • Loss of topsoil through exposure to wind and rain
  • Over-exploitation of biodiversity through agricultural practices
  • Vegetation destruction leading to animal migration
  • Water source depletion and increased soil salinity
  • Landscape changes like reduced sand dune formation, increased erosion, and soil/sand encroachment
  • Dust clouds affecting air quality and health
  • Reduction in clean water supplies and increased water-borne diseases
  • Forced migration and disputes over land
  • Food shortages leading to malnutrition and famine
  • Reduced farm income and agricultural productivity, leading to poverty and increased reliance on aid
• Climate change and desertification

  • Temperatures in drylands could rise by 2-5°C by 2050, accelerating desertification
  • Precipitation rates will decrease, moving semi-arid areas into arid regions
  • Extreme weather events are likely to become more frequent
  • Increased migration to overcrowded cities
  • Less productive soils will force more people to migrate, adding pressure on other countries