7.3+Causes+of+desertification?

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

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:==

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