7.3 What are the causes of desertification?

Desertification is what happens to once productive land that has become a desert and is no longer useful. This is not irreversible but lands in danger are found around the margins of many of the larger deserts
7.3A_desert_map.png

The specification says: The causes of soil erosion and desertification are drought, population pressure, fuel supply, over grazing, war and migration.



As with soil erosion, there are both physical and human causes:
Physical causes
  • Soil erosion – exposed soil is easily removed by wind or water
  • Changing rainfall patterns rainfall has become less predictable and prolonged droughts more common (although whether this is a human and physical cause is a moot point)
  • Intense rainfall when it does happen – hard to store and causes more soil erosion
Main human causes
  • Population growth – more people need more food which puts pressure on the land
  • Overgrazing – too many goats, sheep, cattle can destroy the vegetation
  • Over cultivation- grow too much without replenishing the soil and it becomes exhausted
  • Deforestation – tress are cut down for fuel and building. The loss of roots to hold the soil down gives rise to erosion
  • War – many sub-Saharan countries have suffered for years from civil war, where crops and animals have been destroyed leading to famine
  • It is estimated that 20% of the worlds population, in over 60 countries, have to cope with the threat of desertification.

What are the signs of desertification?
  • Declining groundwater table
  • Salinisation of soil and near-surface-soil water
  • Reduction in areal extent of surface water in streams, ponds, and lakes
  • Unnaturally high rates of soil erosion
  • Damage to native vegetation

This series of YouTube videos follow a discussion which look at the causes of desertification. They range of reasons for migration, population pressure, the issues with trade and the management of scarce resources. 30 minutes well worth a look: