G17: Desertification
Causes of desertification including climate change, population growth, overgrazing and over-cultivation, and strategies to reduce the risk of desertification.
🌍 What is Desertification?
Definition: Desertification is the process by which fertile land gradually transforms into desert, typically due to drought, deforestation, or inappropriate agriculture. It is land degradation in arid, semi-arid and dry sub-humid areas.
Desertification affects roughly 2 billion people worldwide and threatens around 33% of the Earth's land surface. The Sahel region of Africa is the most severely affected area, where the Sahara Desert is expanding southwards at an estimated rate of 48 km per year.
Key Fact: The UN Convention to Combat Desertification (UNCCD) estimates that 12 million hectares of productive land are lost to desertification each year - an area the size of Bulgaria.
Desertification is not the natural expansion of existing deserts. It is the degradation of land in dry areas caused by human activities and climate variations. When vegetation is removed, the soil loses its structure and is easily eroded by wind and water, making recovery extremely difficult.
🌡️ Causes of Desertification
1. Climate Change
Climate change is a major driver of desertification through several mechanisms:
- Rising global temperatures increase evaporation rates, drying out soil faster
- Changing rainfall patterns lead to more prolonged droughts in already arid regions
- Reduced and more unreliable rainfall makes agriculture increasingly difficult
- Higher temperatures increase the rate of soil moisture loss
- Extreme weather events become more frequent, stripping vegetation cover
Case Study: The Sahel
The Sahel is a semi-arid region south of the Sahara Desert stretching from Senegal to Chad. Since the 1970s, rainfall has declined by 25-40% in some areas. The drought of 1984-85 was particularly devastating, affecting over 20 million people and causing widespread famine. Average temperatures in the Sahel have risen by nearly 1°C since the 1970s, accelerating soil moisture loss.
2. Population Growth
Rapid population growth in dryland regions puts enormous pressure on the land:
- More people require more food, leading to intensive farming on marginal land
- Increased demand for firewood leads to widespread deforestation
- Larger herds of livestock are kept, exceeding the land's carrying capacity
- More water is extracted from aquifers, lowering the water table
- Urban expansion removes productive farmland
Key Fact: The population of the Sahel has grown from around 30 million in 1950 to over 135 million today, putting enormous pressure on fragile ecosystems.
3. Overgrazing
Overgrazing occurs when too many livestock are kept on land that cannot support them:
- Animals eat vegetation faster than it can regenerate
- Protective plant cover is removed, exposing soil to erosion
- Soil becomes compacted by trampling, reducing water infiltration
- Fewer plants means less organic matter returned to the soil
- Wind and water erosion accelerate once vegetation cover falls below 30%
Example: Overgrazing in Mali
In Mali, herds have grown significantly as populations increase. Cattle, goats and sheep strip the land of vegetation, particularly during the dry season. When the rains come, the bare soil cannot absorb water effectively, leading to runoff and further erosion rather than groundwater recharge.
4. Over-cultivation
Over-cultivation exhausts the soil through continuous farming without adequate rest periods:
- Nutrients are removed from the soil faster than they can be replaced
- Soil structure breaks down, making it vulnerable to erosion
- No fallow periods means organic matter is not returned to the soil
- Monoculture depletes specific nutrients, reducing soil fertility
- Inappropriate irrigation can cause soil salinisation, making land unusable
5. Soil Erosion
Soil erosion is both a cause and consequence of desertification:
- Wind erosion removes the most fertile topsoil, reducing productivity
- Water erosion carves gullies into the landscape during intense rainfall
- Once the topsoil is lost, only infertile subsoil remains
- Dust storms transport eroded soil hundreds of kilometres
- Eroded soil silts up rivers and reservoirs downstream
| Cause | Process | Impact |
|---|---|---|
| Climate change | Rising temperatures and reduced rainfall | Soil dries out; droughts become more frequent |
| Population growth | More people need more resources | Land is exploited beyond its carrying capacity |
| Overgrazing | Too many animals eat vegetation | Protective cover removed; soil erodes |
| Over-cultivation | Continuous farming exhausts soil | Nutrients depleted; soil structure collapses |
| Deforestation | Trees cut for fuel and farmland | Roots no longer bind soil; shade is lost |
| Soil erosion | Wind and water remove topsoil | Land becomes infertile and barren |
📉 Impacts of Desertification
- Food insecurity: Crop yields fall by up to 50% in severely degraded areas
- Famine: Loss of agricultural land leads to starvation, especially in the Sahel
- Economic loss: Countries lose billions in agricultural productivity
- Migration: Environmental refugees are forced to move to cities or other countries
- Conflict: Competition for shrinking resources leads to tensions between communities
- Biodiversity loss: Plants and animals adapted to semi-arid conditions die out
- Dust storms: Increased wind erosion causes respiratory problems and damages infrastructure
Key Fact: The UN estimates that desertification costs the global economy around $490 billion per year in lost agricultural production.
🛡️ Strategies to Reduce Desertification
1. Planting and Managing Trees (Afforestation)
Trees help prevent desertification by:
- Binding the soil together with their roots, preventing erosion
- Providing shade that reduces soil evaporation rates
- Adding organic matter (leaf litter) to improve soil fertility
- Acting as windbreaks to reduce wind erosion
- Improving water infiltration into the soil
Case Study: The Great Green Wall
The Great Green Wall is an African-led initiative to restore 100 million hectares of degraded land across the Sahel by 2030. Stretching 8,000 km from Senegal in the west to Djibouti in the east, it aims to plant a belt of trees and vegetation across the continent. By 2020, around 18 million hectares had been restored, mainly in Ethiopia, Nigeria and Senegal. The project also aims to create 10 million jobs and sequester 250 million tonnes of carbon.
2. Appropriate Technology and Farming Methods
Magic Stones (Zai Pits):
Small pits dug into the ground during the dry season. Compost and seeds are placed inside. When rain falls, the pits capture and retain water. Yields can increase by up to 80% compared to conventional planting.
Small pits dug into the ground during the dry season. Compost and seeds are placed inside. When rain falls, the pits capture and retain water. Yields can increase by up to 80% compared to conventional planting.
- Magic stones: Circular stone lines slow runoff and encourage water infiltration
- Zai pits: Small planting pits filled with compost that capture rainfall
- Terracing: Stepped hillsides reduce water runoff and soil erosion on slopes
- Contour ploughing: Ploughing across slopes rather than downhill reduces water erosion
- Crop rotation: Alternating crops maintains soil nutrients and structure
- Wind breaks: Rows of trees or shrubs reduce wind speed and soil erosion
3. Water Management
- Drip irrigation: Delivers water directly to plant roots, reducing waste by up to 70%
- Rainwater harvesting: Collecting and storing rainwater for dry periods
- Check dams: Small dams across gullies slow water flow and trap sediment
- Recharging aquifers: Allowing water to seep back into underground reserves
4. Managing Grazing
- Rotational grazing: Moving livestock between paddocks allows vegetation to recover
- Reducing herd sizes: Keeping animal numbers within the land's carrying capacity
- Enclosing areas: Fencing off degraded land to allow natural regeneration
- Alternative livelihoods: Helping pastoralists diversify into non-farming activities
| Strategy | How It Works | Advantages | Disadvantages |
|---|---|---|---|
| Afforestation | Planting trees to stabilise soil | Long-term solution; provides fuelwood | Slow; needs water for young trees |
| Magic stones | Stone lines slow runoff | Cheap; uses local materials | Labour-intensive to build |
| Zai pits | Pits capture water and compost | Dramatically increases yields | Requires manual labour each season |
| Drip irrigation | Water delivered to roots | Very water-efficient | Expensive; needs maintenance |
| Rotational grazing | Move animals between areas | Allows vegetation recovery | Requires fencing and planning |
🌍 International Responses
- UNCCD (1994): The United Nations Convention to Combat Desertification has 197 member countries and promotes national action programmes
- SDG 15.3: The Sustainable Development Goal target aims to combat desertification and restore degraded land by 2030
- World Bank programmes: Funding for sustainable land management projects in Africa
- NGO initiatives: Organisations like TreeAid and Oxfam support community-based reforestation
Exam Tip: Always link strategies to the specific cause they address. Afforestation tackles deforestation and soil erosion; water management tackles drought; rotational grazing tackles overgrazing. Showing these connections demonstrates higher-level understanding.
❓ Practice Questions
Q1: Define the term desertification. (2 marks)
Q2: Explain how overgrazing contributes to desertification. (4 marks)
Q3: Describe one strategy used to reduce the risk of desertification and explain how it works. (4 marks)
Q4: "Climate change is the most significant cause of desertification." To what extent do you agree? (6 marks)
Q5: Using a named example, assess the effectiveness of strategies to reduce desertification. (9 marks)
✅ Answers
- Desertification is the process by which fertile land gradually becomes desert (1 mark), typically caused by a combination of human activities such as overgrazing and over-cultivation, and climate factors such as drought (1 mark).
- Overgrazing occurs when too many livestock are kept on land, eating vegetation faster than it can regenerate (1 mark). This removes the protective plant cover that would normally shield the soil from wind and rain (1 mark). Trampling by animals compacts the soil, reducing its ability to absorb water (1 mark). Without vegetation to bind it, the topsoil is eroded by wind and water, leaving infertile subsoil (1 mark).
- Afforestation involves planting trees in areas at risk of desertification (1 mark). Tree roots bind the soil together, preventing erosion by wind and water (1 mark). The canopy provides shade, reducing soil evaporation rates and maintaining moisture (1 mark). Leaf litter adds organic matter, improving soil fertility and structure (1 mark). Alternatively: Zai pits are small holes dug during the dry season and filled with compost and seeds (1 mark). When rain falls, the pits capture and retain water that would otherwise run off (1 mark). The compost improves soil fertility and structure (1 mark). Yields can increase by up to 80% compared to conventional methods (1 mark).
- I agree that climate change is significant because rising temperatures increase evaporation and reduce soil moisture (1 mark), and changing rainfall patterns cause prolonged droughts that kill vegetation (1 mark). However, human causes are also very important - overgrazing removes vegetation, over-cultivation exhausts soil, and deforestation removes tree cover (1 mark). Population growth drives many of these human activities as more people need food and fuel (1 mark). In reality, desertification results from the interaction of both climate and human factors (1 mark). Human activities often amplify the effects of climate change, making them the deciding factor in many cases (1 mark).
- The Great Green Wall initiative across the Sahel aims to restore 100 million hectares of degraded land (1 mark). It has been effective in some areas - by 2020, 18 million hectares had been restored, particularly in Ethiopia, Nigeria and Senegal (1 mark). In Senegal, 12 million trees have been planted, helping to stabilise dunes and provide fuelwood (1 mark). However, effectiveness varies - some planted trees have died due to insufficient rainfall and aftercare (1 mark). The project has also created jobs, improving local incomes and reducing pressure on the land (1 mark). Local community involvement is crucial for long-term success, as top-down approaches without local buy-in tend to fail (1 mark). Overall, the Great Green Wall shows promise but needs sustained funding, local participation and complementary strategies like water management to be fully effective (1 mark). It demonstrates that a single strategy alone is insufficient - an integrated approach is needed (1 mark).
🎯 Exam Tips
- Always define desertification before discussing causes or strategies
- Use specific named examples - the Sahel region, the Great Green Wall
- Link each strategy to the cause it addresses (afforestation → deforestation/erosion; zai pits → water scarcity)
- For "to what extent" questions, discuss both climate and human causes, then reach a justified conclusion
- Evaluate strategies by considering effectiveness, cost, sustainability and local acceptance
- Remember that desertification is caused by MULTIPLE factors working together - never give just one cause
⚠️ Common Errors
Watch Out!
Students often confuse desertification with the natural expansion of deserts. Wrong: "Desertification is when deserts get bigger naturally." Correct: "Desertification is land degradation caused by human activities and climate variations in dryland areas."
Students often list causes without explaining the process. Wrong: "Overgrazing causes desertification." Correct: "Overgrazing removes vegetation cover, exposing soil to wind and water erosion, which degrades the land."
Students often forget to evaluate strategies. Wrong: "Planting trees stops desertification." Correct: "Afforestation can reduce desertification by stabilising soil, but young trees need water and protection, which may not be available in arid areas."
📝 Exam Technique
Geography Exam Tips — Desertification:
1. For Desertification questions, always name specific case studies with factual detail
2. Use geographical terminology precisely (e.g. specific processes, not vague descriptions)
3. Consider social, economic and environmental perspectives in your evaluations
4. Support your points about Desertification with data, statistics or named examples
5. For 'assess' or 'evaluate' questions, reach a clear judgement supported by evidence
1. For Desertification questions, always name specific case studies with factual detail
2. Use geographical terminology precisely (e.g. specific processes, not vague descriptions)
3. Consider social, economic and environmental perspectives in your evaluations
4. Support your points about Desertification with data, statistics or named examples
5. For 'assess' or 'evaluate' questions, reach a clear judgement supported by evidence
⚠️ Common Errors
Watch Out!
Students often write vague answers without specific geographical evidence. Wrong: Writing generalised statements like 'it causes problems' Correct: Using specific data and named examples, e.g. 'the 2010 Haiti earthquake killed over 200,000 people due to poor building quality'
Students often confuse causes and effects. Wrong: Mixing up what caused the event with what resulted from it Correct: Clearly separate causes (why it happened) from effects (what happened as a result)
Students often describe rather than evaluate. Wrong: Listing strategies without assessing their effectiveness Correct: Weighing up strengths and weaknesses of each approach and reaching a supported judgement
✍️ Model Answer
Full-Mark Response
6 marks: Explain the key factors affecting desertification.
Desertification involves multiple interconnected factors that geographers must understand. The key concepts include the processes that create and change desertification, the impacts on both people and environment, and the strategies used to manage associated challenges. For a comprehensive answer, specific case study evidence should be used throughout, with named examples and data to support each point. Geographical terminology should be used precisely, and the interrelationship between physical and human factors should be demonstrated. Top-level responses evaluate the relative importance of different factors and consider how the situation varies between locations.
Mark scheme: 2 marks for identifying key factors, 2 marks for explaining processes with detail, 2 marks for using specific evidence
📊 AO Deep Dive
Assessment Objective Analysis
AO1 requires knowledge of the key facts and processes related to desertification. AO2 demands understanding of how and why these processes operate, and their implications. AO3 asks you to analyse, evaluate and make judgements — this is where grade 9 answers stand out by weighing up competing perspectives and reaching supported conclusions. AO4 may involve interpreting maps, graphs or data related to this topic. To move from grade 5 to grade 9: use precise geographical terminology, support every point with specific case study evidence, and always evaluate rather than just describe.
📝 Exam Questions by Topic
🎬 Video Resources
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