Soil Erosion & Desertification (CIE IGCSE Geography)

Soil Erosion

• Soil erosion is the wearing away of the topsoil by the action of wind or water
• It is a natural process which is made worse by human activities which leave the soil exposed to wind and water

Cause	How it leads to soil erosion
Deforestation	Removes the trees reducing interception so the soil is more exposed to the rainfall. Reduces the amount of roots which reduces infiltration and increases surface run off The bare soil is more exposed to the wind which would have been reduced by tree cover
Overgrazing	Removes vegetation cover which acts to protect the soil from both wind and water More animals trampling the land leads to compaction and increased surface run off This happens more in LEDCs where farmers have less and less land to graze
Overcultivation	Land is not left to rest (fallow) between crops and so the fertility of the soil is reduced
Population Increase	More people increase the settlement sizes reducing the areas which can be farmed - increasing overcultivation and overgrazing Increases the demand for food which leads to overcultivation and overgrazing
Over abstraction of groundwater	Leads to the soil moisture content decreasing. This leads to drier soil which is more easily eroded by wind or water
Human induced climate change	Changes in climate patterns, increasing floods and increasing droughts all lead to an increase in soil erosion

• Salinisation is also an increasing issue in many semi-arid areas
  • Occurs when high rates of evaporation lead to groundwater being drawn to the surface
  • When the groundwater evaporates salts are left in or on the topsoil
  • These salts make the land toxic to many crops and so the land can no longer be used
• Soil erosion may over time lead to desertification

Desertification

• Desertification is caused by both natural factors and human activities
• Many of the natural causes may be made worse by climate change 

Natural causes	Human causes
Soil erosion leads to the loss of nutrients. Plants are unable to establish and grow	Overgrazing means the vegetation has all gone due to the numbers of animals or the land does not have chance to recover
Rainfall patterns have become less predictable leading to drought and any vegetation dying due to lack of water	Over-cultivation leads to all the nutrients being taken up by crops leaving none for future vegetation to grow
Reduced vegetation means that nutrients are not added to the soil through the decomposition of dead organic matter	Deforestation removes shade for the soil and means there are no roots which bind the soil together. This increases soil erosion, whilst decreasing infiltration and interception
Any rain that does fall is often in short, intense bursts, leading to increased surface run off and soil erosion	Population growth puts increased pressure on the land as people raise more animals and grow more crops

Causes of Desertification

Sustainable Management of Soil Erosion and Desertification

• Halting and reversing soil erosion and desertification means tackling the causes
• There are a variety of political and social responses 

Education

• Education including:
  • Sustainable farming methods including agroforestry and crop rotation, which help to keep the soil healthy
  • Family planning to reduce population growth

Agroforestry 

• This combines agriculture with forestry, which means some trees remain, which:
  • Decreases deforestation
  • Provides shade as well as increasing infiltration and interception, which reduces soil erosion
  • Provides organic matter from the trees and adds nutrients to the soil

Afforestation

• Tree planting, such as the Great Green Wall across the Sahel, helps to reverse desertification in several ways:
  • The roots help to bind the soil together reducing soil erosion
  • The canopy offers shade helping to prevent the soil from drying out and also reducing soil erosion from rainfall landing directly on the soil
  • Nutrients in the soil are replaced by falling leaves and branches
  • The trees increase animal and insect activity which helps improve soil quality

Contour Stones and Terraces

• These help to reduce soil erosion by:
  • Preventing the soil from being blown or washed away
  • Increasing infiltration of water and reducing overland flow
  • Ensuring that dead organic matter stays in one place and can decompose adding nutrients to the soil

Contour Stones