AQA A-level Geography · 3.1.2

Desertification and desert case studies

50 exam-style questions with answers for 3.1.2 Desertification and desert case studies in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.1.2.4 · Definition and extent
Define desertification. [2 marks]
Answer:
The degradation of land in arid, semi-arid and dry sub-humid areas (1); caused by climatic variation and human activities, reducing its productivity (1).
Question 2 · Spec 3.1.2.4 · Definition and extent
Explain why desertification mainly affects desert margins rather than core deserts. [2 marks]
Answer:
Core deserts are already extremely dry and have little to degrade (1); semi-arid margins have marginal, variable rainfall and fragile vegetation, so human pressure and drought easily degrade them (1).
Question 3 · Spec 3.1.2.4 · Definition and extent
Describe how the extent of hot deserts has changed over the last 10,000 years. [3 marks]
Answer:
The Sahara was much wetter, with lakes and grassland, until about 5,000 to 6,000 years ago (1); the climate then became drier and the desert expanded (1); desert extent has expanded and contracted with climatic fluctuations, and may be expanding at its margins today (1).
Question 4 · Spec 3.1.2.4 · Definition and extent
Give three pieces of evidence that the Sahara was wetter in the past. [3 marks]
Answer:
Ancient rock art showing cattle, giraffes and swimmers (1); fossil lake sediments and animal remains such as hippos (1); buried river channels revealed by satellite radar and pollen records of grassland vegetation (1).
Question 5 · Spec 3.1.2.4 · Definition and extent
Suggest why North Africa was wetter around 10,000 years ago. [2 marks]
Answer:
Changes in the Earth's orbit and tilt increased summer insolation in the northern hemisphere (1); this strengthened the African monsoon, which pushed rain much further north (1).
Question 6 · Spec 3.1.2.4 · Definition and extent
What proportion of the Earth's land is dryland? [1 mark]
Answer:
About 40%.
Question 7 · Spec 3.1.2.4 · Definition and extent
Describe the distribution of areas most at risk of desertification. [3 marks]
Answer:
Semi-arid and dry sub-humid margins around the world (1); for example the Sahel, southern Africa and Central Asia (1); also northern China, the interior of Australia and parts of South America and the Mediterranean (1).
Question 8 · Spec 3.1.2.4 · Causes
Explain how climate change can cause desertification. [3 marks]
Answer:
Rising temperatures increase evaporation and the aridity of the soil (1); changes in rainfall patterns and more frequent droughts reduce plant growth (1); vegetation loss leaves soil exposed to erosion (1).
Question 9 · Spec 3.1.2.4 · Causes
Explain the role of natural climate variability in the Sahel droughts of the late twentieth century. [2 marks]
Answer:
Changes in sea surface temperatures in the Atlantic and other oceans altered the West African monsoon (1); this caused years of reduced rainfall, particularly from the late 1960s to the mid-1980s (1).
Question 10 · Spec 3.1.2.4 · Causes
Explain how overgrazing causes desertification. [3 marks]
Answer:
Too many livestock eat vegetation faster than it can regrow (1); hooves compact and break the soil surface (1); loss of plant cover exposes soil to wind and water erosion (1).
Question 11 · Spec 3.1.2.4 · Causes
Explain how overcultivation causes desertification. [3 marks]
Answer:
Repeated cropping without fallow removes nutrients from the soil (1); reduced fertility and organic matter make soils structureless and easy to erode (1); farmers then extend farming onto marginal land, spreading the problem (1).
Question 12 · Spec 3.1.2.4 · Causes
Explain how deforestation for fuelwood contributes to desertification. [3 marks]
Answer:
Where wood is the main fuel, people cut trees and shrubs for cooking and heating (1); roots no longer bind soil and canopies no longer protect it (1); wind and water erosion increase, and local rainfall recycling is reduced (1).
Question 13 · Spec 3.1.2.4 · Causes
Explain how poor irrigation can cause desertification. [3 marks]
Answer:
Over-irrigation raises the water table (1); evaporation then leaves salts in the topsoil, causing salinisation (1); salty soils cannot support crops, and the land is abandoned (1).
Question 14 · Spec 3.1.2.4 · Causes
Explain how population growth increases the risk of desertification. [3 marks]
Answer:
More people need more food, fuel and water (1); this increases grazing, cultivation and tree cutting beyond the carrying capacity of marginal land (1); there is less time for land to recover, so degradation accelerates (1).
Question 15 · Spec 3.1.2.4 · Causes
Explain how soil erosion contributes to desertification. [3 marks]
Answer:
With vegetation removed, wind blows away fine topsoil and water carries it off in gullies (1); topsoil holds most nutrients and organic matter, so fertility falls (1); the remaining soil holds less water, so plants struggle to recover (1).
Question 16 · Spec 3.1.2.4 · Causes
Explain how positive feedback can intensify desertification. [3 marks]
Answer:
Loss of vegetation reduces evapotranspiration, so local rainfall falls (1); bare soil is eroded and reflects more heat, which makes the area drier (1); drier conditions kill more plants, so the cycle continues (1).
Question 17 · Spec 3.1.2.4 · Causes
Explain how poverty and weak land management can contribute to desertification. [2 marks]
Answer:
People with few resources cannot afford fertiliser, irrigation or fuel alternatives and rely on exploiting land (1); insecure land tenure and lack of education discourage long-term conservation (1).
Question 18 · Spec 3.1.2.4 · Causes
Suggest why it is difficult to separate the human and climatic causes of desertification. [2 marks]
Answer:
Drought and human pressure usually occur together and reinforce each other (1); long-term data are limited and vegetation recovers after rain, which can hide degradation (1).
Question 19 · Spec 3.1.2.4 · Impacts
Describe the impacts of desertification on ecosystems. [3 marks]
Answer:
Loss of vegetation cover and soil fertility (1); decline in biodiversity as habitats shrink and species die or migrate (1); loss of ecosystem services such as soil protection and water regulation (1).
Question 20 · Spec 3.1.2.4 · Impacts
Describe the impacts of desertification on landscapes. [3 marks]
Answer:
Bare, eroded ground with gullies and exposed rock (1); sand dunes advancing on farmland and settlements (1); more dust storms and salt crusts on irrigated land (1).
Question 21 · Spec 3.1.2.4 · Impacts
Describe the impacts of desertification on local populations. [4 marks]
Answer:
Reduced crop yields and loss of grazing land (1); food insecurity, malnutrition and famine (1); loss of livelihoods and increased poverty (1); out-migration and conflict over scarce land and water (1).
Question 22 · Spec 3.1.2.4 · Impacts
Explain how desertification can lead to migration. [3 marks]
Answer:
Falling crop and livestock production removes income (1); people move to cities or other regions to find work (1); this can increase pressure on urban services and may cause tension between groups (1).
Question 23 · Spec 3.1.2.4 · Impacts
Explain how desertification can lead to conflict. [2 marks]
Answer:
Reduced land and water resources increase competition (1); disputes can arise between farmers and herders or between neighbouring communities and states (1).
Question 24 · Spec 3.1.2.4 · Impacts
Explain the impacts of increased dust storms. [2 marks]
Answer:
Dust reduces visibility, damages crops and causes respiratory illness (1); dust can be carried over long distances, affecting air quality and ecosystems in other regions (1).
Question 25 · Spec 3.1.2.4 · Impacts
Explain how desertification can affect economic development. [2 marks]
Answer:
Falling agricultural output reduces incomes and exports and increases dependence on aid (1); money is diverted to emergency relief and land restoration rather than development (1).
Question 26 · Spec 3.1.2.4 · Futures
Describe how predicted climate change may affect dryland areas. [3 marks]
Answer:
Higher temperatures will increase evaporation and drought risk (1); rainfall is predicted to fall in places such as the Mediterranean and southern Africa (1); rainfall is likely to become more variable, with heavy storms raising erosion risk (1).
Question 27 · Spec 3.1.2.4 · Futures
Outline alternative possible futures for local populations in areas threatened by desertification. [3 marks]
Answer:
Adapt in place using sustainable farming and water management (1); leave the land through managed migration to cities or other regions (1); remain without adapting, risking worsening poverty, famine and conflict (1).
Question 28 · Spec 3.1.2.6 · Responses
Distinguish between resilience, mitigation and adaptation in responding to desertification. [3 marks]
Answer:
Resilience is the ability of people and ecosystems to cope with and recover from stress (1); mitigation is action to reduce the causes or severity of the problem (1); adaptation is adjusting to the changing conditions to reduce harm (1).
Question 29 · Spec 3.1.2.6 · Responses
Explain how zai pits help to combat desertification. [3 marks]
Answer:
Planting pits are dug into hard, crusted soil and filled with manure or compost (1); they trap rainwater and nutrients near the seeds (1); this increases crop yields and helps restore degraded land (1).
Question 30 · Spec 3.1.2.6 · Responses
Explain how stone lines (diguettes) help to conserve soil and water. [2 marks]
Answer:
Lines of stones are laid along the contours of slopes (1); they slow runoff, trap soil and give water time to infiltrate (1).
Question 31 · Spec 3.1.2.6 · Responses
Explain how farmer-managed natural regeneration restores land. [3 marks]
Answer:
Farmers protect and prune shoots that regrow from tree stumps and roots instead of clearing them (1); trees fix nutrients, give shade, fodder and fuelwood, and reduce wind erosion (1); in Niger this has re-greened millions of hectares at very low cost (1).
Question 32 · Spec 3.1.2.6 · Responses
Explain how agroforestry can reduce the risk of desertification. [2 marks]
Answer:
Trees grown among crops protect soil from wind and rain and add organic matter (1); they provide fuel, fodder and food, reducing pressure on natural woodland (1).
Question 33 · Spec 3.1.2.6 · Responses
Outline the aims of the Great Green Wall initiative in Africa. [3 marks]
Answer:
An African-led initiative launched in 2007 across the Sahel (1); aims to restore degraded land and create a mosaic of green land by planting trees and improving land use (1); intends to improve food security, jobs and resilience, though progress has been slower than planned because of funding and security issues (1).
Question 34 · Spec 3.1.2.6 · Responses
Explain how better grazing management can reduce desertification. [2 marks]
Answer:
Limiting livestock numbers and rotating herds between pastures lets vegetation recover (1); plant cover protects soil and maintains productivity (1).
Question 35 · Spec 3.1.2.6 · Responses
Explain how drip irrigation reduces the risk of salinisation. [2 marks]
Answer:
Small amounts of water are delivered directly to plant roots (1); this reduces waterlogging and evaporation, so fewer salts build up in the soil (1).
Question 36 · Spec 3.1.2.6 · Responses
Explain how sand dunes can be stabilised to protect settlements and farmland. [2 marks]
Answer:
Planting drought-tolerant grasses and shrubs binds the sand with roots (1); fences made of brushwood reduce wind speed near the surface and trap sand (1).
Question 37 · Spec 3.1.2.6 · Responses
Describe the role of the UN Convention to Combat Desertification (UNCCD). [2 marks]
Answer:
An international agreement of 1994 that coordinates action against land degradation and drought (1); countries prepare national action programmes and share knowledge and funding (1).
Question 38 · Spec 3.1.2.6 · Responses
Compare top-down and bottom-up approaches to combating desertification. [3 marks]
Answer:
Top-down projects, such as large government or international schemes, can operate at a large scale with substantial funding (1); bottom-up projects led by communities use local knowledge and low-cost methods, so are more likely to be sustained (1); top-down schemes may ignore local needs, while bottom-up projects may be limited in scale (1).
Question 39 · Spec 3.1.2.6 · Case studies
Describe the physical characteristics of the Sahel. [3 marks]
Answer:
A semi-arid belt south of the Sahara, stretching from Senegal to Sudan (1); rainfall of roughly 200 to 600 mm falling in a short summer wet season brought by the ITCZ (1); sparse grassland, acacia and scrub vegetation (1).
Question 40 · Spec 3.1.2.6 · Case studies
Describe the impacts of the Sahel drought of the early 1970s and 1980s. [3 marks]
Answer:
Crop failure and widespread famine (1); death of large numbers of livestock and loss of livelihoods (1); migration of people to cities and refugee camps, and a need for international aid (1).
Question 41 · Spec 3.1.2.6 · Case studies
Explain how the Dust Bowl of the 1930s illustrates desertification. [3 marks]
Answer:
Settlers ploughed up the grasslands of the Great Plains for wheat (1); severe drought killed the crops, leaving bare soil that wind eroded in huge dust storms (1); farms were abandoned and thousands migrated west, and soil conservation measures were later introduced (1).
Question 42 · Spec 3.1.2.6 · Case studies
Explain why Lake Chad has shrunk dramatically since the 1960s. [2 marks]
Answer:
Prolonged drought reduced rainfall and river inflow (1); increased water abstraction for irrigation and a growing population further reduced the lake, by about 90% by the early 2000s (1).
Question 43 · Spec 3.1.2.6 · Case studies
Describe the main physical features of the Namib Desert. [3 marks]
Answer:
A coastal desert with very low rainfall, often under 50 mm a year (1); frequent fog from the cold Benguela Current (1); a huge sand sea with some of the highest dunes in the world, over 200 m tall (1).
Question 44 · Spec 3.1.2.6 · Case studies
Approximately how large is the Sahara? [1 mark]
Answer:
About 9 million km², the largest hot desert in the world.
Question 45 · Spec 3.1.2.6 · Field data
Describe how vegetation cover could be sampled to investigate land degradation. [3 marks]
Answer:
Lay a transect from a degraded area to a healthy area (1); use quadrats at regular intervals to record the percentage cover and number of species (1); compare with soil measurements such as moisture, compaction and organic matter (1).
Question 46 · Spec 3.1.2.6 · Field data
Suggest how sustainability of a land management scheme could be evaluated. [3 marks]
Answer:
Compare crop yields, vegetation cover and soil quality before and after the scheme (1); survey local farmers about costs, labour and benefits (1); consider whether the scheme can continue without outside funding (1).
Question 47 · Spec 3.1.2.6 · Responses
Explain why the success of anti-desertification schemes depends on local people. [2 marks]
Answer:
Local people use and manage the land every day, so their cooperation is needed to maintain schemes (1); methods that fit local culture, skills and resources are more likely to be adopted and continued (1).
Question 48 · Spec 3.1.2.6 · Impacts
Explain how the Sahara dust travelling across the Atlantic can have both positive and negative impacts. [2 marks]
Answer:
Dust carries nutrients such as phosphorus that fertilise rainforests and oceans (1); it can also reduce air quality and affect human health far from its source (1).
Question 49 · Spec 3.1.2.4 · Causes
Explain why areas with a high proportion of subsistence farmers are especially vulnerable to desertification. [2 marks]
Answer:
Subsistence farmers depend directly on local land and rainfall for food and income (1); they have few savings or alternatives, so drought or soil loss quickly causes hunger and forces more intensive use of land (1).
Question 50 · Spec 3.1.2.4 · Impacts
Suggest why desertification is described as a threat to sustainable development. [2 marks]
Answer:
It reduces the productive capacity of land and the water available for people (1); this undermines food security, health and incomes, making long-term development harder (1).

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