IGCSE Geography / Fragile environments and climate change

What causes desertification revision notes

Edexcel International GCSE Geography (4GE1), chapter 7: Fragile environments and climate change, specification point 7.1b, 7.S2. Free lesson.

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Desertification is the degradation of land in dry areas until it loses its vegetation and fertile soil. It is caused by climate and human activity, which remove plant cover and allow erosion to damage the land.

What desertification means

Desertification is land in dry areas being degraded, or damaged, until it becomes like desert. The land loses its vegetation and its fertile soil. It is not simply the desert getting bigger. Both climate and human activity can cause desertification.

The five causes of desertification

Each cause removes vegetation that protects the soil. There is one physical cause and four human causes. Check which type a question asks you to describe. Drought, the physical cause: a long period with too little rain, so plants die. Population pressure: more people need food, so land is farmed repeatedly without resting and the soil becomes worn out. Fuel supply: trees and shrubs are cut for firewood and charcoal. Overgrazing: too many animals eat plants faster than they can grow back. Migration: people and their herds move into one area, concentrating pressure…

How to read population pressure from a graph

A line graph can show whether population is growing faster than the land's food supply. The example uses invented data for a made-up dryland country. Values after 2020 are predictions, so they are less certain. Population rises from 4 million in 1960 to 22 million in 2020, and the line gets steeper. The predicted population reaches 44 million by 2050. The number of people the land can feed rises more slowly, from 9 million to 16 million. The population and food-supply lines cross in 2000 at 12 million. After this, there are more people than the land can feed, and the gap widens.

How the causes combine to damage land

Physical and human causes link together. When plants die, are cut or are eaten, the soil is left bare. Without roots to hold it or leaves to shade it, dry topsoil can blow away, and rain can wash more soil off. This is soil erosion, the removal of soil by wind and water. Because topsoil is fertile, losing it means crops and grass grow poorly or fail. The land becomes desert-like and loses its fertility. The process can feed itself: people and herds crowd onto the land that remains, so pressure and vegetation loss begin again.

Explain causes precisely

A vague statement such as “a change in rainfall” is not enough. Rainfall could increase, so name drought and explain what it does to the land. For two human causes, explain how each one removes plants and leaves soil exposed. For example, overgrazing removes plants faster than they regrow, while cutting trees and shrubs for firewood removes roots that hold the soil.