☀️ Drought
This is the natural cause. When rain fails for several years in a row, plants die. Bare soil is baked hard by the Sun or blown away by the wind. When the rain finally returns, it runs off the hard ground instead of soaking in.
Fragile Environments Under Threat » Causes of Desertification
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 7.1 Fragile environments are under threat from desertification, deforestation and global climate change (b)
- The five main causes of desertification: drought, population pressure, fuel supply, overgrazing and migration
- How these causes link together in a cycle
- How to read line graphs of past and predicted population growth and of population compared with resources
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Unlock This CourseWhy does land turn into desert?
Desertification does not happen overnight, and it is not caused by one thing. It usually starts with a dry-land area that is already fragile. Then a natural cause, a human cause, or both together, strip away the plants that hold the soil in place. Without plants, the soil dries out, blows away and cannot grow crops. The spec names five causes you must know.
Key terms:
- Drought: a long period with much less rain than normal.
- Population pressure: when more people live in an area than its land and resources can support.
- Overgrazing: too many animals eating the plants in one area, so the plants cannot grow back.
- Fuel supply: the wood and other materials people collect to burn for cooking and heating.
- Migration: the movement of people from one place to live in another.
The five causes
👪 Population pressure
As the number of people grows, more food, water and land are needed. Farmers grow crops on the same fields year after year, so the soil loses its nutrients. Poor soil blows away easily.
🔥 Fuel supply
In many dry regions, families rely on wood for cooking. Trees and shrubs are cut down faster than they can regrow. Without roots to hold it, the soil is easily eroded.
🐐 Overgrazing
Goats, sheep and cattle eat grass and young shrubs. If herds are too big, the plants are eaten right down. Animals also trample the soil, which makes it hard and dusty.
🚶 Migration
When people move into a dry area, or move from one part of it to another, they put extra pressure on the land that is already there. Herders who move their animals onto land that is already grazed make the problem worse. Migration spreads the damage to new places.
Putting the causes together
The causes work together. A drought kills plants, so farmers and herders have less food for their animals. The animals are then crowded onto a smaller area and overgraze it. People cut more wood and move on to new land. Each step leaves less vegetation, and less vegetation makes the next drought even more harmful. This is a vicious cycle.
Natural or human?
Drought is a natural cause. Population pressure, fuel supply, overgrazing and migration are human causes. Exam answers that link a natural cause to a human cause, for example drought making overgrazing worse, usually score higher than a list.
Skill: reading line graphs
The spec asks you to use and interpret line graphs of past and predicted population growth, and of population in relation to resources. Here is an imaginary example. It is not real data and is only used to show the skill.
📈 Graph 1: population
An imaginary dry region has 100,000 people in 1980, 160,000 in 2000 and 230,000 in 2020. The line is predicted to reach 320,000 by 2040. The line is going up and getting steeper, so the population is growing faster over time.
🌾 Graph 2: people and food
On the same graph, a second line shows how much food the land can produce. It rises slowly and then flattens. Where the population line crosses above the food line, there are more people than the land can feed. That is population pressure.
Worked example
Question: How much did the imaginary population grow between 1980 and 2000?
Read the value at 1980 (100,000) and at 2000 (160,000). Subtract: 160,000 - 100,000 = 60,000.
To describe the trend, say it rises, say how fast, and quote two numbers: "The population rises steadily from 100,000 in 1980 to 160,000 in 2000, then more quickly to 230,000 in 2020."
For a prediction, say it is a forecast and may not happen: "It is predicted to reach 320,000 by 2040."
Common mistakes
- Writing only "drought" or "too many people" with no explanation. Say how it damages the land, for example "plants die, so the soil is blown away".
- Saying people cause all desertification. Drought is a natural cause.
- On a graph, giving a trend with no numbers. Always quote the years and values.
- Treating a predicted line as certain. It is an estimate.
Exam-style question
(a) Describe how overgrazing can lead to desertification. [3 marks]
(b) Explain why population pressure can make desertification worse. [3 marks]
Model answer
(a) Too many animals eat the plants faster than they can regrow (1). The animals trample the soil, which makes it hard and dusty (1). With no plant roots to hold it, the soil is blown or washed away (1).
(b) More people need more food, so farmers grow crops on the same land again and again (1). This uses up the nutrients in the soil (1). More people also cut more wood for fuel, so fewer plants hold the soil and it is eroded (1).
Exam tip
"Describe" and "Explain" questions need links. Use the word "so" or "because" to show how each step leads to the next.