Causes & Impacts of Soil Erosion (Cambridge (CIE) IGCSE Environmental Management): Revision Note

What are the causes of soil erosion?

• Soil erosion refers to the removal of the top layer of soil (usually by wind or water)

  • Topsoil contains most of the soil’s nutrients and organic matter, so losing it reduces crop growth

• Soil erosion happens when the soil is unprotected, disturbed, or exposed to strong forces like rain, rivers or wind

Unsustainable agricultural practices

• Some farming methods damage soil health

  • Includes overcultivation, overgrazing and poor irrigation

• Overcultivation (growing crops repeatedly on the same land) removes nutrients quickly

  • Soil becomes dry and loose, making it easier for wind or water to carry it away

• Overgrazing (too many animals feeding in one area) exposes soil by removing vegetation

  • Roots that hold soil together are lost

  • Exposed soil becomes loose and easier to wash or blow away

• Mismanaged irrigation (too much or too little water) weakens soil structure

  • Runoff can wash soil downhill

  • Excessive irrigation can cause soil salinisation (build-up of salts)

    • Salty soil becomes dry and crumbly, increasing erosion risk

Deforestation

• Cutting down trees and natural vegetation removes protective cover

  • Leaves and branches normally slow down rainfall, reducing soil loss

• Tree roots help bind soil together

  • Without roots, soil becomes loose and more likely to be eroded

• Land cleared for farming or development becomes exposed to wind and rain

Farming on steep slopes

• Gravity pulls water and soil downhill, especially after heavy rain

• Rainwater runs quickly down slopes

  • Fast-moving water removes soil in layers or can create deep gullies

• Machinery use on slopes can make this worse

  • Tractors and equipment disturb soil

  • This creates loose soil that can wash downhill quickly

Bare soil

• Soil without plant cover is easily eroded

  • Plants protect soil from rain impact and help hold it in place

• Bare soil dries out faster

  • No roots to hold soil together

  • Soil becomes dry and light

  • Dry soil breaks into small particles that are easily blown away by wind

• No wind barrier from trees or other plants means wind can lift and transport loose, dry soil particles

• Leaving fields bare between harvesting and the next planting increases erosion risk

Wind and water erosion

• Wind erosion—strong winds blow away dry, loose soil

  • Common in dry climates or during droughts

• Water erosion—rain, rivers or runoff remove soil

  • Heavy rain can splash soil particles loose or wash them downhill

  • Rivers can cut into banks, removing soil from the edges of fields

  • Storm events (intense rainfall over a short time) greatly increase the rate of soil erosion on exposed land

What are the impacts of soil erosion?

• Soil erosion reduces soil productivity and affects both the environment and human communities

  • Impacts can be local, such as reduced crop yield, or wide-reaching, such as desertification or even displacement of communities

Silting of rivers

• Eroded soil is carried by water into rivers and lakes

  • This causes silt to build up on the riverbed

• Silt reduces the depth of rivers

  • This increases the risk of rivers flooding during heavy rain

• Silting also reduces water quality

  • Muddy water blocks sunlight, reducing plant growth in the river

  • Suspended particles clog fish gills, making it harder for them to breathe

  • Silt can smother fish eggs and aquatic plants, reducing survival rates

Desertification

• Loss of soil creates dry, infertile land that cannot support crops

• Vegetation dies, leaving the ground exposed

• Over time, the land turns into desert-like conditions

  • This is common in areas with drought, overgrazing or deforestation

Mass movement: landslides, rockslides and mudslides

• Removing vegetation weakens soil structure on hillsides

  • This is mainly because plant roots normally hold soil in place

• Heavy rain can trigger landslides or mudslides

  • Loose soil becomes saturated and slides downhill

• Rockslides occur when exposed rock breaks away

  • These events can destroy homes, roads and farmland

Loss of habitats and biodiversity

• Soil erosion destroys habitats for plants, insects and animals

  • Many species cannot survive once their habitat is gone

• Loss of vegetation reduces biodiversity

  • Fewer plant species mean fewer food sources for wildlife

• Rivers filled with silt may lose aquatic species

  • Ecosystems become less stable

Reduction in crop yield

• With less topsoil, crops have fewer nutrients and poorer growing conditions

  • Roots cannot spread deeply or absorb enough water

• Reduced yields affect farm income and food availability

• Farmers may need more fertiliser, increasing costs and pollution

Malnutrition and famine

• Lower crop yields reduce the amount of food available

  • Communities may not have enough to eat

• Malnutrition occurs when people lack essential nutrients in their diets

• Severe or long-term soil erosion can contribute to famine

  • Especially in areas already facing poverty and drought

Displacement of people

• When land becomes unproductive and crops fail, families may be forced to move elsewhere

  • This can lead to rural-to-urban migration

• Loss of farmland reduces income

  • People leave to find work or food

• Displacement can cause overcrowding in towns or cities

  • This can put pressure on housing, water and healthcare