What is desertification?
Desertification means land in dry areas slowly loses its plants and good soil and becomes like a desert.
- It happens in drylands: places where little rain falls and much water evaporates. Drylands cover about 40 % of Earth's land and are home to about 2 billion people.
- It is not sand dunes "marching" out of a desert. It is good land going bad, patch by patch, often far from any desert.
- Land degradation is the general word for land losing its quality. Desertification is land degradation in dry areas.
Causes: people and nature
Human causes
- Overgrazing: too many animals eat grass faster than it grows.
- Deforestation: trees and shrubs are cut for firewood, farms or building.
- Over-cultivation: the same soil is farmed every year with no rest, so it loses nutrients.
- Poor irrigation: too much water without drainage brings salt to the surface (salinisation). Pumping too much groundwater dries the land.
- Population pressure and poverty: people with no other choice must use the land hard.
Natural causes
- Drought: years with very little rain.
- Climate change: higher temperatures dry soils faster and make rain less reliable.
- Wind and water erosion: once plants are gone, wind blows soil away and heavy rain washes it off.
The causes feed each other: fewer plants → more bare soil → less water stored → even fewer plants. This is a vicious circle.
Effects of desertification
- Less food: crops and pasture fail, leading to hunger.
- Dust storms: dry loose soil blows into cities, harming health.
- Water problems: rivers and wells dry up.
- Loss of wildlife: plants and animals lose their home.
- Migration and poverty: families leave the land to find work in towns.
- Climate: bare land stores less carbon, which adds to global warming.
Case study: the Sahel
The Sahel is a long strip of dry grassland across Africa, just south of the Sahara. Long droughts in the 1970s and 1980s, plus fast population growth, overgrazing and firewood cutting, damaged large areas. Herders and farmers suffered famine. Since then, many areas have become greener again through farmer-managed tree regrowth and water harvesting.
Rocky desertification
Some hills are made of limestone (karst land). The soil on them is very thin and forms very slowly. If forests are cleared and steep slopes are farmed, heavy rain washes the soil away. Bare grey rock is left. This is rocky desertification.
It is common in the wet karst hills of south-west China. So rocky desertification can happen even where rain is heavy: the problem is lost soil, not lack of rain.
Fixes: stop farming steep slopes, plant trees and grass, build terraces and small water tanks, and give farmers other income such as fruit trees or tourism.
Solutions and management
- Plant trees and grass: roots hold soil; leaves shade it. Shelterbelts (rows of trees) slow the wind.
- Straw checkerboards: squares of straw pushed into sand stop dunes moving so plants can grow.
- Better grazing: fewer animals, moving them in turns (rotational grazing).
- Save water: drip irrigation, small dams, stone lines and pits that catch rain.
- Better farming: crop rotation, leaving stubble, planting drought-hardy crops.
- Big projects: the Great Green Wall across the Sahel and the Three-North Shelterbelt in China aim to restore millions of hectares.
- Global action: the UN Convention to Combat Desertification (UNCCD) and World Day to Combat Desertification on 17 June.
Try it: the soil-and-roots test
- Fill two trays with soil. Plant grass seeds in one and wait two weeks. Leave the other bare.
- Tilt both trays. Pour the same cup of water on each, slowly.
- Collect the water that runs off. Which is muddier? The bare tray loses much more soil, just like step 3 in the 3D.
- Now blow gently on dry versions of both. Which loses soil to "wind"?
Key formulas and definitions
- Desertification: land in dry areas losing plants and soil until it is desert-like
- Drylands: areas where evaporation is much greater than rainfall
- Overgrazing: more animals than the grass can feed
- Salinisation: salt building up in soil from poor irrigation
- Rocky desertification: soil washed off limestone hills, leaving bare rock
- Shelterbelt: a row of trees planted to slow wind
- Vicious circle: fewer plants → more erosion → less water → fewer plants
Worked examples
1. A village keeps 200 goats on land that can feed 120. What happens over five dry years?
Grass is eaten faster than it grows, roots die, soil becomes bare and blows away. The land can then feed even fewer goats: a vicious circle of overgrazing.
2. Why can rocky desertification happen in a rainy region?
On limestone hills the soil is thin. When trees are cut, heavy rain washes the soil off quickly. The problem is soil loss, not lack of rain.
3. A farmer has fields next to a moving sand dune. Suggest three steps.
Push straw checkerboards into the sand, plant hardy shrubs and grass inside the squares, and plant a shelterbelt of trees on the windward side.
Common mistakes
- Thinking desertification means a desert growing outward. It is good land degrading in place.
- Blaming only drought. Human use (grazing, tree cutting, farming) is usually the main cause; drought speeds it up.
- Thinking only sandy places are affected. Rocky desertification affects rainy limestone hills.
- Thinking it cannot be reversed. Tree planting, grazing control and water harvesting have greened many areas again.