4))Desert fringes and desertification

• Names for desert fringe areas

  • semi-deserts
  • semi-arid areas
  • drylands
• In some places, rain falls in a fairly predictable pattern, making settled agriculture possible
• Savanna


  • Mixed woodland-grassland ecosystem
  • Trees sufficiently widely spaced so that the canopy does not close
• There are different types of savannas because there is less rain the further you are away from the equator
• The cold air cool down and starts to sink because it is getting heavier
• When air sinks down from higher places it warms up and clouds disappear
• Wind always blows from a high-pressure area (H) to a low-pressure area (L)
• The difference between high-pressure areas and the low-pressure areas at the equator leads to winds near the ground
• Trade winds blow to dry areas to try to equalise the difference between H and L
• The sun moves over the course of the year, which means that the ITCZ and the trade winds follow the zenith of the sun
• Most rainfall is in areas where the sun is in the zenith
• Different types of savana 


  Thorn savana (200-500mm)

  Dry savana (500-1000mm)

  Wet savana (1000-2000mm)
• Desert fringes classified alongside hot deserts as fragile environements

  Catastrophic ecological and environmental consequences cause by climate change or poor Land management : desertification is the risk
• Zaï or tassa farming technique

  1. Digging pits in less permeable soil

  2. Catching water

  3. Concentrating compost

  4. Pits 15-50 cm across, 5-15 cm deep, 80 cm apart

  5. Traditionally used in western Sahel to restore degraded drylands and increase soil fertility
• Desertification is the land degradation and loss of its biological capacities, process in which vegetation in semi arid landscape disapears : causes : human and natural
• In sahel areas people used to be nomad not using all areas for farming and housing

  Settlement and growing population lead to soil over use, erosion and desertification