Oxford Revise | AQA A Level Geography | Answers_R

Chapter 1: [Answers] 

Exemplar answers have been written by the author of the revision guide. They do not necessarily represent the only possible solution or way to answer the question. All exemplar answers are likely to be in the top mark band.

Questions 1–6 are point-marked. Allow 1 mark per valid point with extra marks for development.

1. AO1 = 4

• Dynamic equilibrium involves a balance between carbon sources and carbon sinks (1).

• The concept involves the flow of carbon molecules between different stores, such as atmosphere, biosphere, and hydrosphere (1).

• Negative feedback mechanisms are key to dynamic equilibrium (1). As atmospheric CO2 increases, carbon uptake by plants increases, lowering atmospheric CO2 (1).

• Global warming as example of human activities interrupting dynamic equilibrium (1).

Example answer: Dynamic equilibrium involves a balance between carbon sources and carbon sinks. It involves the flow of carbon molecules between different stores, such as atmosphere, biosphere, and hydrosphere, so that the amount of carbon entering and leaving these stores is balanced. Negative feedback mechanisms are key to dynamic equilibrium. As atmospheric CO2 increases, carbon uptake by plants increases, lowering atmospheric CO2. Human activities have interrupted dynamic equilibrium resulting in global warming.

2. AO1 = 4

• Evaporation is conversion of liquid water into water vapour involving heat from the Sun (1)

• Transportation of water vapour by air currents (1).

• Transpiration by plants with water vapour leaving stomata, released into air (1).

• Condensation and return of water vapour to the biosphere/soils for uptake by plants (1).

• Evapotranspiration is influenced by, for example, density of vegetation, type of leaf cover (large surface area), soil moisture (1).

3. AO1 = 4

• Natural variations such as wildfires and volcanic eruptions, releasing large amounts of carbon into the atmosphere from the biosphere (1).

• Changes in vegetation cover, such as desertification or deforestation, reducing sequestration of carbon from the atmosphere store into plants and soils (1).

• Combustion of fossil fuels for energy production and transportation, from lithosphere to atmosphere (1).

• Changes in land use, such as farming practices, urbanisation, e.g. increasing decomposition of organic material in soils, releasing carbon into the atmosphere (1).

• Climate change, e.g. rising temperatures causing thawing of permafrost, releasing carbon from soil store into the atmosphere (1).

• Changes in the rates of photosynthesis, respiration, decomposition, and weathering also affect
  magnitude (1).

4. AO1 = 4

• Role of the water cycle in supplying water used in photosynthesis (1), providing energy for secondary consumers and oxygen for living organisms as by-product (1).

• Role in replenishing stores of fresh water, on which terrestrial life on Earth depends (1).

• Regulating climate: evaporation absorbs heat energy, condensation releases heat energy (1), role this has in regulating temperature extremes (1).

• Water vapour as (most abundant) greenhouse gas, helping to sustain life through warmer global temperatures (1).

• Water cycle’s role in providing range of habitats, e.g. ponds, lakes, swamps (1).

5. AO1 = 4

• Ability of carbon dioxide to dissolve in water to form carbonic acid (1).

• Uptake of carbon into the surface water of the oceans (1).

• Role of water cycle and carbon cycle in chemical weathering of rocks (1).

• In respiration: release of both CO2 and water vapour into the atmosphere (1).

• In photosynthesis: carbon from the air combines with water taken up by plants (1).

• Higher levels of atmospheric CO2 reduce the amount plant stomata need to open, reducing release of water vapour into the atmosphere through evapotranspiration (1).

6. AO1 = 4

• The water balance is the balance between inputs and outputs over a period of time (1);
  (P) = (O) + (E) +/− (S) (1).

• Concept of inputs explained: precipitation as primary input (1).

• Concept of outputs: total runoff explained, EVT (1).

• Concept of stores and role in water balance explained (1).

• Importance of water balance for drainage basin management (1).

Questions 7–20 are level-marked.

7. AO1 – Knowledge and understanding of the carbon cycle. Awareness of deforestation, its causes, and impacts.

AO2 – Application of knowledge to show how and why changes to forest cover impact on the carbon cycle.

AO1 = 2 AO2 = 4

AO1

• Global distribution, and size of major stores of carbon – lithosphere, hydrosphere, cryosphere, biosphere, atmosphere.

• Factors driving change in the magnitude of these stores over time and space, including flows and transfers at plant, sere and continental scales. Photosynthesis, respiration, decomposition, combustion, carbon sequestration in oceans and sediments, weathering.

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

AO2

• The graphic shows a significant reduction in carbon sequestration post-disturbance (deforestation and land use change), suggesting that the impact of (tropical rainforest) deforestation on the carbon cycle is significant.

• Pre-disturbance, vegetation is shown taking up carbon dioxide (CO2) in both the upland and seasonally inundated rainforest. This occurs through photosynthesis: very high rates in tropical rainforest.

• Post-disturbance, a reduced uptake of carbon is shown due to deforestation and land use changes, clearing the rainforest trees and replacing them with crops that photosynthesis at a greatly reduced rate.

• Post-disturbance, the region has become a source of carbon due to forest fires (combustion of carbon stores) and increased release of methane (CH4) from livestock.

• Pre-disturbance, organisms (floating macrophytes) in rivers, streams and swamps (freshwater) absorbed CO2 from the atmosphere, while carbon was also stored in sediments. Post-disturbance (building of reservoirs and draining of seasonally inundated forest, this carbon store has become a carbon source due to the lack of vegetation in the reservoir.

Example answer: The graphic shows a significant reduction in carbon sequestration post-disturbance, as a result of deforestation and subsequent land use change. This suggests that there is significant impact of rainforest deforestation on the carbon cycle. The pre-disturbance graphic shows that vegetation takes up carbon dioxide through photosynthesis in both the upland and seasonally inundated rainforest. Rates of photosynthesis are very high rates in tropical rainforest, so any reduction has significant effects. Post-disturbance, a reduced uptake of carbon is shown due to deforestation (and the methods used, such as burning) and land use changes. Rainforest trees are cleared and replaced with crops that photosynthesise at a greatly reduced rate. Post-disturbance, the region has become a carbon source, rather than a carbon sink, due to forest fires (combustion of carbon stores) and increased release of methane (CH4) from livestock.

8. AO3 – Analysis of soil moisture data for the UK to identify patterns and anomalies in the data, using data manipulation to support response.

AO3 = 6

• The data shows general east–west division, with soil moisture at normal levels for May 2023 in the east, and soil moisture drier than normal in the west. This is useful as it suggests a pattern.

• Northern Ireland did not follow this pattern as its soil moisture levels were at normal levels.

• Having information on the soil wetness status was useful as it indicates how far from normal the status was. For example, some sites (e.g. Glensaugh in Scotland, Gisburn Forest, Cardington, and Tadham Moor in England) were wetter than normal.

• Soil moisture levels are likely to generally follow precipitation patterns, suggesting that, while precipitation in May was normal for the east of the UK and Northern Ireland, it was probably below average for the west of England and Wales. However, for the purposes of depicting the general pattern of soil moisture across the UK, a second figure showing precipitation patterns would have increased the usefulness.

• Other factors could be involved for the sites with wetter than normal soil moisture, e.g. localised heavy precipitation (thunderstorms), changes to drainage patterns or changes to land use. This makes Figure 2 less useful in depicting the pattern of soil moisture across the UK.

• One reason for increased soil moisture could be the removal of surface vegetation – vegetation draws up moisture from the soil and releases it into the atmosphere through EVT. Data on land use would therefore add to the usefulness of Figure 2 in explaining soil moisture patterns, though not in depicting them.

9. AO3 – Analysis of natural and human-induced changes in the carbon cycle to identify patterns and anomalies in the data, using data manipulation to support response.

AO3 = 6

• The natural carbon cycle (pre-industrial) shows a status of dynamic equilibrium, with flows between the atmosphere and hydrosphere broadly balanced (80 GtC of CO2 dissolving into the ocean and 78 GtC emitted from the ocean), also seen in flows between the atmosphere and biosphere (123 GtC sequestered by photosynthesis, 118 GtC emitted by respiration).

• The vast majority of carbon (100,000,000 GtC) is in the lithosphere. If all stores are added together (taking soil as 2400 GtC), then the lithosphere makes up 99.96 per cent of all carbon.

• The influence of human activities is most significant in the extraction of carbon from lithosphere fossil fuels (−365 GtC since 1750). This will have made the biggest contribution to the +240 GtC of carbon entering the atmosphere store.

• The importance of the oceans in reducing the impact of increased emissions from combusting fossil fuels is made clear by the +155 GtC entering the hydrosphere.

• The impact of deforestation and land use changes is probably seen in the −30 GtC reduction in the biosphere, with a reduction in sequestration by photosynthesis.

10. AO3 – Analysis of data of rates of water withdrawal in the carbon cycle to identify patterns and anomalies in the data, using data manipulation to support response.

AO3 = 6

• Groundwater withdrawal (abstraction) has increased at different rates, with two of the selected countries (Russia and France) showing declines in groundwater abstraction.

• India shows a very rapid increase in the rate of groundwater withdrawal, from approximately 10 km³/year in 1950 to 260 km³/year in 2020, a percentage increase of 2500 per cent, although the graphic shows signs of this rate levelling off.

• China showed a rapid increase between 1950 and 2000 (from approximately 10 km³/year in 1950 to 105 km³/year in 2000, a 950 per cent increase), but since then the rate has remained steady at around 105 km³.

• The USA has seen a similar trend to China, although starting from a higher rate in 1950 and with a steadier increase to 1990, since when it has remained constant.

• Abstraction of groundwater is usually highest in regions where precipitation inputs are low and rates of evapotranspiration are high. Countries with relatively high inputs of precipitation will therefore see lower rates of withdrawal than arid and semi-arid countries.

• Abstraction rates in India are likely to have increased due to increased demand for fresh water. This could be related to several factors including population increase (more people needing water), economic development (higher demand for water in manufacturing and energy production (cooling)) and agricultural changes (increase in irrigated farmland, for example).

11. AO1 – Knowledge and understanding of the carbon cycle. Human interventions in the carbon cycle.

AO2 – Application of knowledge to show effectiveness of human interventions in the carbon cycle with the intention of mitigating climate change impacts.
AO1 = 2 AO2 = 4

AO1

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

• Human interventions in the carbon cycle designed to influence carbon transfers and mitigate the impacts of climate change.

AO2

• The photo shows the Drax power station, which burns biomass to generate electricity, an example of BECCS. This is designed to mitigate the impacts of climate change by reducing greenhouse gases by combusting renewable resources (biomass from the biosphere) instead of fossil fuels (from the lithosphere).

• The photo shows that the process of generating energy in this way does still produce emissions. In this case, they are likely to be emissions of water vapour, since most electricity is generated in ways that require water for cooling or water in the form of steam to power turbines.

• Compared to other human interventions to mitigate climate change, BECCS may have strengths and weaknesses. A strength would be that growing biomass captures carbon dioxide from the air, and though burning it may then release carbon back into the atmosphere, inputs out of and back into the atmosphere are balanced, unlike with fossil fuels. If carbon capture and storage were also involved, then BECCS could start to reduce atmospheric carbon levels.

• A weakness of many human interventions to mitigate climate change is that the scale of the impact is very small compared with the excess carbon in the atmosphere and the rate at which greenhouse gas emissions need to be reduced to stop the impacts of climate change becoming severe.

12. AO3 – Analysis of data of CO₂ measurements in both the atmosphere and seawater to identify patterns and anomalies in the data, using data manipulation to support response.

AO3 = 6

• The graph shows an increasing/positive trend in recorded atmospheric CO₂ at Mauna Loa, with a similar upward/positive trend in the amount of CO₂ dissolved in seawater. The graph shows a downwards/negative trend in seawater pH.

• There is a positive correlation between atmospheric and seawater CO₂ and a negative correlation between seawater CO₂ and seawater pH.

• Atmospheric CO₂ is shown to have increased by approximately 85 ppm (parts per million) from approximately 320 ppm to approximately 405 ppm between 1958 and 2018. Climate science has proved that this increase is due to human activities, primarily the combustion of carbon, adding significantly to the atmosphere store.

• The increase in CO₂ shows more variation, but a line of best fit indicates an increase from approximately 320 ppm when records began in 1990 to approximately 375 ppm (55 ppm) in 2018. Over the same period, atmospheric CO₂ increased from 350 ppm to 405 ppm (55 ppm) – indicating a strong correlation.

• Atmospheric CO₂ dissolves into seawater, with higher concentrations of CO₂ in the atmosphere leading to more CO₂ being dissolved.

• Carbon dioxide reacts with water to form carbonic acid (H₂CO₃), and the graph indicates that as more CO₂ dissolves into the ocean from the atmosphere, the ocean’s natural alkaline pH is becoming more acidic.

13. AO1 – Knowledge and understanding of the carbon cycle. Human interventions in the carbon cycle.
    AO2 – Application of knowledge to show effectiveness of human interventions in the carbon cycle with the intention of mitigating climate change impacts.

AO1 = 2 AO2 = 4

AO1

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

• The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Human interventions in the carbon cycle designed to influence carbon transfers and mitigate the impacts of climate change.

AO2

• The graph compares per capita greenhouse gas (GHG) emissions on the y-axis with population in millions on the x-axis.

• The countries that produce the most GHG emissions per capita are not the countries with the largest populations – in fact, Southern Asia with 2 billion people has emissions of 3 tonnes of CO₂ per capita per year, while North America with around 200 million people has emissions of 24 tonnes of CO2 per capita per year.

• This is partly related to economic development: the countries with the highest GHG emissions include the highly industrialised economies of North America and Japan. Western Europe, although highly industrialised, is an anomaly here.

• Eastern Europe has relatively high emissions, perhaps due to historic dependence on heavy industry. Middle East has relatively high emissions, perhaps due to high dependence on energy for cooling and desalinisation.

• There is also a difference between regions where land use change makes a higher or equal contribution to GHG emissions than fossil fuel and industry emissions: Latin America and Caribbean and South-East Asia and Pacific in particular.

• This is likely to be related to deforestation of tropical rainforest, which reduces sequestration and increases emissions due to burning of forested land to clear it for agriculture.

• Challenges of reducing GHG emissions related to this include: highly industrialised countries having high emissions per capita because of, for example, air travel, individual car ownership, convenience-based consumer lifestyle. Reducing emissions involves significant lifestyle changes – likely to be unpopular. Developing economies have lower emissions per capita but may be on a development trajectory that will increase emissions per capita as, for example, car ownership and use increases. Large populations in these countries add to the challenge. Countries are also deforesting in order to industrialise, which is the route to economic development taken by the most industrialised countries. Reducing emissions relies on forests remaining a significant carbon sink, so this represents a major challenge for reducing GHG emissions.

14. AO1 – Knowledge and understanding of key themes of the carbon cycle in a tropical rainforest. Knowledge and understanding of impacts of increased carbon emissions. Knowledge and understanding of a tropical rainforest case study.

AO2 – Application of knowledge and understanding to assess the factors driving change in the magnitude of carbon stores over time in the case study region.

AO1 = 10 AO2 = 10

AO1

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

• The carbon budget and the impact of the carbon cycle upon land, ocean and atmosphere, including global climate.

• The key role of the carbon and water stores and cycles in supporting life on Earth with reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Case study of a tropical rainforest setting to illustrate and analyse key themes in water and carbon cycles and their relationship to environmental change and human activity.

AO2

• Answers are expected to apply knowledge and understanding of factors driving change in the magnitude of carbon stores to a chosen tropical rainforest case study over time.

• In terms of causes of changes to carbon stores, answers should refer to deforestation (reducing the role of tropical forests as a global carbon sink), burning of forest vegetation, use of deforested land for farming, which is a carbon source (especially livestock farming with the release of methane as a waste product of digestion).

• Answers should refer to specific case study detail, e.g. for causes: since 2000, Amazonia has lost 20.3 per cent of its original forest, 70 per cent of which has been to clear land for cattle ranching; for impacts: temperatures in Amazonia are predicted to rise by 3°C by 2050. There has been an increase in droughts in the Amazonia region – severe droughts occurred in 2005, 2010 and 2015–16; wildfires have become more common as Amazonia experiences droughts: it is estimated that forest fires now produce around 1.5 GtC per year.

Example answer: Amazonia is an enormous carbon store – it is estimated that its trees and soil store 200 GtC, and absorb around 2.2 GtC per year, with photosynthesis rates being extremely high at the canopy, and much lower at the forest floor, due to the dense canopy blocking much of the sunlight. Natural carbon emissions are very large – an estimated 1 GtC from decomposition of dead trees and leaf litter.

Deforestation is a major cause of changes to carbon stores in Amazonia, as it reduces the role of the tropical rainforest as a carbon sink. The burning of forests that takes place to clear land for farming releases carbon into the atmosphere.

Since 2000, Amazonia has lost 20.3 per cent of its original forest (832,000 km2), 70 per cent of which has been cleared for cattle ranching.

Severe droughts occurred in 2005, 2010 and 2015–16 and are more common now than in the past, which also increases the prevalence of wildfires. It is estimated that forest fires now produce around 1.5 GtC per year. Between 2010 and 2020, emissions have increased by 20 per cent, and it is now estimated that Amazonia emits more CO2 than it sequesters.

15. AO1 – Knowledge and understanding of changes in the carbon cycle over time. Knowledge and understanding of the role of feedback within and between cycles and their link to climate change. Knowledge and understanding of human interventions in the carbon cycle.

AO2 – Application of knowledge and understanding to assess the extent to which reducing carbon emissions is more important than adapting to the impacts of climate change.

AO1 = 10 AO2 = 10

AO1

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

• The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere.

• The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Human interventions in the carbon cycle designed to influence carbon transfers and mitigate the impacts of climate change.

AO2

• Answers should discuss measures to reduce carbon emissions into the atmosphere against efforts to adapt to the impact of climate change.

• In terms of the reduction of carbon emissions, answers could refer to afforestation and reforestation, carbon capture and storage, direct air capture, enhanced rock weathering, carbon farming and other measures that aim at reducing the amount of carbon emitted from human activities that reaches the atmosphere.

• In evaluating reducing carbon emissions, answers could consider the scale of such reductions, the time required to make an impact, the cost and sustainability of such measures and their impact on factors such as, for example, food security.

• Adaptation measures may be drawn from other areas of study such as desertification, coastal sea level rise and coastal erosion management or management of cold environments.

• In evaluating adaptation, answers could refer to the feedback loops that may intensify the rate and impacts of climate change faster than adaptation measures can keep up with, with the implications of this for life on Earth.

• Answers can be argued either way, though the conclusions reached should be based upon preceding content.

16. AO1 –Knowledge and understanding of a chosen case study of a river catchment.

AO2 – Application of knowledge and understanding to assess impacts of precipitation on drainage basin stores and transfers and implications for sustainable water supply and/or flooding.

AO1 = 10 AO2 = 10

AO1

• Case study of a river catchment(s) at a local scale to illustrate and analyse the key themes above, engage with field data and consider the impact of precipitation upon drainage basin stores and transfers and implications for sustainable water supply and/or flooding.

• Drainage basins as open systems – inputs and outputs, to include precipitation, evapotranspiration, and runoff; stores and flows, to include interception, surface, soil water, groundwater and channel storage; stemflow, infiltration overland flow, and channel flow. Concept of water balance.

• Changes in the water cycle over time to include natural variation including storm events, seasonal changes and human impact including farming practices, land use change and water abstraction.

AO2

• Answers should apply knowledge of factors affecting water supply or flooding in a chosen case study of a river catchment and the impacts of human activities.

• Stores within the drainage basin include groundwater, soil moisture, vegetation (interception store), river and stream channels and surface storage (e.g. puddles, marshes, lakes).

• Factors affecting the impact of precipitation on stores and transfers include drainage basin size, drainage density, slope angle, rock type, antecedent conditions (e.g. soil saturation), extent and type of vegetation cover, intensity of rainfall.

• (if answering for flooding) Human activities can both increase flooding risks (e.g. by reducing stores, increasing flows) or reduce them.

• (If answering for sustainable water supply) Human activities can both reduce sustainable water supply (e.g. by increased abstraction, reduction in EVT through deforestation) and increase sustainability (e.g. by increasing store capacity).

• Interventions can include tree planting (to increase interception and infiltration and to reduce overland flow), changing farming techniques to increase infiltration into the groundwater store, building dams to reduce the ‘flashiness’ of drainage basin responses to storm events (overland flow), creation or extension of floodplains to reduce channel flow and increase infiltration.

• Assessment of the role of these inventions should be in the context of a chosen case study. For example, the Pickering ‘Slowing the flow’ project, with its aim to reduce the risk of flooding in Pickering from 25 per cent to 4 per cent, through creation of ‘leaky dams’ in channels and dams made of heather bales to smaller streams, blocking of moorland drains, 30 hectares of woodland being planted along the river, buffer zones on moorland, where burning of heather vegetation is banned. Success of the scheme in terms of a 20 per cent reduction in flood risk in Pickering.

17. AO1 – Knowledge and understanding of feedback systems in the carbon cycle over time. Knowledge and understanding of the implications of climate change for life on Earth.

AO2 – Application of knowledge and understanding to assess the relative importance of feedback systems compared to other causes of climate change.

AO1 = 10 AO2 = 10

AO1

• The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

• The carbon budget and the impact of the carbon cycle upon land, ocean, and atmosphere, including global climate.

AO2

• Explanation of feedback systems (loops) and their implications for driving change in carbon stores; differentiation between positive (amplifying a change) and negative feedback (counteracting or reducing a change).

• Example of a positive feedback loop: carbon in permafrost decomposes as it thaws and is released into the atmosphere as CO₂ and CH₄, increasing the enhanced greenhouse effect and the amount of permafrost melting, further depleting carbon stored in the soil and increasing the magnitude of carbon stores in the atmosphere.

• Example of a negative and then positive feedback loop: warmer oceans increase their ability to absorb CO₂ from the atmosphere – a negative feedback loop. However, more dissolved CO₂ increases seawater acidity, which can be harmful to corals and shellfish that build shells or skeletons from calcium carbonates, reducing their capacity to act as carbon sink, reducing the ocean’s role in sequestering carbon (reducing the magnitude of this store) – a positive feedback loop.

• Example of a negative feedback loop: increased CO₂ levels stimulating plant growth, leading to greater carbon absorption through more photosynthesis, increasing the magnitude of the biomass store.

18. AO1 – Knowledge and understanding of systems in physical geography; knowledge and understanding of changes in the water cycle over time.

AO2 – Application of knowledge and understanding to assess the value of systems-based understanding compared to other forms of analysis.

AO1 = 10 AO2 = 10

AO1

• The water cycle and drainage basins as systems – inputs and outputs, to include precipitation, evapotranspiration, and runoff; stores and flows, to include interception, surface, soil water, groundwater, and channel storage; stemflow, infiltration overland flow, and channel flow. Concept of water balance.

• Runoff variation and the flood hydrograph.

• Changes in water cycle inputs over time to include natural variation including storm events, seasonal changes and human impact on inputs including farming practices, land use change and water abstraction.

AO2

• Explanation of the global water cycle as a closed system; explanation of drainage basin as an open system with inputs of precipitation, solar radiation and via infiltration and runoff.

• Factors which could contribute to changes in input: climate change.

• Stores within the drainage basin (groundwater, soil moisture, vegetation, river and stream channels and surface storage) and how they respond to changing inputs.

• Flows within the drainage basin system include stemflow, throughfall, overland flow, throughflow and groundwater flow, and how they respond to changing inputs.

• Value of systems approach in terms of insights it gives into how a drainage basin will respond to changing inputs, e.g. factors increasing flood risk within a catchment and ways in which those could be influenced, e.g. planting trees, expanding, or developing floodplains.

• Limitations of a purely systems-based response could be made in relation to other aspects of the course, e.g. in relation to hazard management, people’s perception of risk, economic costs, and benefits of different approaches, etc.

19. AO1 – Knowledge and understanding of the concept of the water cycle; knowledge and understanding of ecosystem responses to changes in one or more of their components or environmental controls; knowledge and understanding of a case study of a specified region experiencing ecological change.

AO2 – Application of knowledge and understanding to assess the influence of different processes driving change in the water cycle within a tropical rainforest.

AO1 = 10 AO2 = 10

AO1

• Changes in the water cycle over time to include natural variation including storm events, seasonal changes and human impact including farming practices, land use change and water abstraction.

• The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Factors influencing the changing of ecosystems, including climate change and human exploitation of the global environment.

• The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

AO2

• Discuss the water cycle and the different processes driving change in the water cycle (likely within a drainage basin context).

• Discuss long-term and short-term influences responsible for changes in tropical rainforest ecosystems, with reference to changes in the water cycle.

• Using case study details of land use changes, assess influence of different processes, likely comparing gradual nature of long-term influences compared to rapid nature of anthropogenic climate change.

20. AO1 – Knowledge and understanding of feedback systems in the carbon cycle over time. Knowledge and understanding of human interventions designed to mitigate the impacts of climate change.

AO2 – Application of knowledge and understanding to assess the relative importance of feedback systems compared to other factors in climate change in informing our interventions to mitigate the impacts of climate change.

AO1 = 10 AO2 = 10

AO1

• Human interventions in the carbon cycle designed to influence carbon transfers and mitigate the impacts of climate change.

• The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks within and between cycles and their link to climate change and implications for life on Earth.

• Changes in the carbon cycle over time, to include natural variation (including wildfires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

AO2

• Consider the link between positive feedback systems and the challenges of monitoring the rate of climate change. For example, fresh snow and ice reflect a lot of sunlight (a high albedo). The rise in global temperatures causes ice caps and glaciers to melt. Less ice cover means less sunlight is reflected, and more heat is absorbed by the oceans and land, increasing global temperatures, causing further ice melting. Without an understanding of this feedback loop, the prediction and monitoring of associated climate change impacts, such as sea level rise, would be inaccurate and would hamper attempts to mitigate their effects, such as shifting coastal populations.

• Feedback loops also help to influence where mitigation efforts should focus. For example, afforestation and reforestation are mitigation measures designed to increase the absorption of carbon dioxide by trees and shrubs. However, if positive feedback systems linked to past deforestation have already had the impact of a drier local climate and increased risk of drought, then reforestation or afforestation may have limited success.

• Some interventions in the carbon cycle, e.g., enhanced rock weathering in which high-silica rocks such as basalt are crushed and spread over land, would lock away CO₂ from the air into calcium carbonate, and move that through water infiltration into the soil store and groundwater. However, it is not known what the impact of such actions would be on the carbon cycle: would impacts on feedback systems have unintended consequences?

• A relevant example could be how warmer oceans increase their ability to absorb CO₂ from the atmosphere – a negative feedback loop – but then more dissolved CO₂ increases seawater acidity, which can be harmful to corals and shellfish that build shells or skeletons from calcium carbonates, reducing their capacity to act as carbon sinks, reducing the ocean’s role in sequestering carbon – a positive feedback loop.

• Answers are likely to include that an understanding of feedback systems will be critical to informing our interventions in the carbon cycle to mitigate the impacts of climate change.

Mark schemes reproduced by permission of AQA.

Chapter 2: [title]

Exemplar answers have been written by the author of the revision guide. They do not necessarily represent the only possible solution or way to answer the question. All exemplar answers are likely to be in the top mark band.

Questions 1–6 are point-marked. Allow 1 mark per valid point with extra marks for development.

• AO1 = 4
• Deflation is one process by which wind removes loose surface materials (1) such as sand, silt, and clay from the desert’s surface (1).
• Abrasion is a second process of wind erosion in which wind-borne particles act as abrasive tools (1), wearing down exposed rock surfaces over time (1).

Example answer: Wind plays a significant role in redistributing sediment and also in aeolian landform development where there is scant vegetation and limited water. Deflation is the process of the wind removing loose surface materials such as sand, silt, and clay, leaving behind courser fragments, creating a desert pavement. Abrasion is when particles blown by the wind can act as an abrasive tool wearing down exposed rock surfaces over time.

• AO1 = 4
• Sediment sources include weathering, mass movement (rock falls, talus creep, soil creep), sediment washed by surface runoff, transported by rivers, and carried by wind (1 + 1).
• Some sources of sediment may be from outside the desert (1), e.g. wind-blown sediment and sediment from mountain ranges carried into deserts by exogenous rivers (1).

   

• AO1 = 4
• Smaller leaves or spines instead of leaves (1)
• Thick waxy cuticle (1).
• Deep root systems (1).
• CAM photosynthesis (1).

   

• AO1 = 4
• A sediment budget as the balance between the input, output, and storage of sediment within a desert system over a given period of time (1).
• Concept of sediment inputs: low in deserts because of the very limited erosion of hillslopes by water (1).
• Concept of transfers: wind erosion as the usual dominant transfer, though flash flooding as infrequently important (1).
• Concept of sinks: desert sinks as localised and dynamic (e.g. dunes) because of lack of vegetation and surface water (1).
• Concept of outputs: outputs often minimal, because of the lack of rivers to transport sediment out of the system (1).

• AO1 = 4
• Geomorphological processes – weathering, mass movement, erosion, transportation, and deposition (1).
• The role of wind:
  • erosion – deflation and abrasion
  • transportation – suspension, saltation, surface creep
  • deposition (1).
• Sources of water – exogenous, endoreic, and ephemeral; the episodic role of water (lake or oasis, salt pan) (1).

The following could also be mentioned and credited, up to a total of 4 marks:

• Sources of energy – insolation, winds, runoff (1).
• Geology – influence of rock type, differential erosion, tectonics (1).
• Time – including influence of (different) past climates (1).

Points relating to a combination of factors also to be credited.

• AO1 = 4
• Positive feedback as something that amplifies or reinforces changes; natural process in desertification (a process in which semi-arid regions become increasingly dry and lose vegetation cover) that human actions also influence and reinforce. [1 + 1]
• Example of process: reduced rainfall leads to loss of vegetation cover, loss of vegetation cover increases albedo, increased albedo disrupts convection currents, so rainfall decreases; regions become drier (2).
• Or alternative example: increased albedo disrupts convection currents, so rainfall decreases; regions become drier; drier, unprotected soils are more easily eroded, losing nutrients; infertile soils cannot support plant life, even if precipitation increases (2).

Questions 7–20 are level-marked.

• AO3 – Analysis of the water balance data to identify patterns, anomalies and using data manipulation to support response.

AO3 = 6

• Figure 1 shows the water budget for Baghdad; soil water recharge occurs only in January and half of February; soil water is then only available for use by vegetation until the end of April. By then, all soil water has presumably evaporated or been transpired by vegetation.
• Adding up the monthly rainfall totals gives an annual precipitation amount of around 120–150 mm – Baghdad is located in an arid zone.
• June to September is a dry season, with no recorded precipitation. Rainfall is concentrated in winter months.
• The high rates of PET (potential evapotranspiration) indicate high temperatures in the summer months.
• For most of the year, PET greatly exceeds P (precipitation), creating a large water deficit. Answers could estimate the aridity index (AI = P/PET) for Baghdad.
• The implication of the water balance for vegetation in Baghdad is that vegetation may be ephemeral (growing and reproducing only in the early spring), have adaptations for storing water (e.g. succulence) or tapping into deep groundwater stores, or be artificially irrigated.

Example answer: The water balance is the balance between inputs and outputs over a period of time, and is calculated using the formula P = O + E +/- S. Figure 1 is useful for an investigation into water balance in the location shown (Baghdad) in that it includes data for P (precipitation) and E (evapotranspiration), but limited in that total runoff data is not included. This is not too significant a limitation however since for most months the lack of rainfall means zero runoff can be inferred. S in the equation is changes in total water storage and this can be inferred as the difference between mean PET and mean monthly rainfall. Figure 1 shows that except for the end of December to mid-February, PET greatly exceeds P (precipitation) throughout the year, creating a large water deficit. This would provide highly useful data therefore for an investigation into water balance in this location.

• AO3 – Analysis of the data showing the global aridity index in 2100 to identify patterns, anomalies and using data manipulation to support response.

AO3 = 6

• Identification of areas with a projected increase in aridity (lower aridity index (AI) values): South America (Amazonia region), central China, Europe, North America, as well as southern and western Africa and Australia.
• Identification of areas with projected decrease in aridity (higher AI values): at least four large regions: East Africa, India/South Asia, north-east Russia, Indonesia (Brunei/northern Borneo and Papua).
• Most hot deserts show stability or only minor change in aridity, e.g. central Sahara and Sahel show slight reduction in AI. An anomaly is the Atacama Desert, which shows an increase in AI.
• In Africa and Asia, the reduction in AI occurs broadly in the northern tropics, between the Equator and Tropic of Cancer. However, in the Americas this pattern is not evident; instead, an increase in AI occurs in the northern tropics.
• Answers might refer to variations in atmospheric circulation (position of the Inter-Tropical Convergence Zone (ITCZ), monsoon patterns) and ocean currents (intensification of ENSO – El Niño-Southern Oscillation).

• AO3 – Analysis of the solar radiation and water deficit data in Namibia data to identify patterns, anomalies and using data manipulation to support response.

AO3 = 6

• There is some evidence of a positive correlation between the two data sets, e.g. solar radiation is lower along the South Atlantic coast of Namibia, and water deficit is also lower along this coast.
• A water deficit is a negative water balance (precipitation minus evaporation): all the values for Namibia show a deficit, from less than 1300 mm to over 2500 mm, so the values are relative. A correlation between lower solar radiation and lower water deficit here is likely to be related to the cooling influence of the ocean, and perhaps lower radiation due to fog or clouds by the coast.
• Elsewhere, a negative correlation between solar radiation and water deficit is suggested. Solar radiation is higher in the north of Namibia than the south and increases towards Namibia’s interior, while water deficit is higher in the south and lowest in the north and reduces inland along Namibia’s border with Angola.
• Factors affecting solar radiation include latitude, and the observed north-south pattern matches this, with higher solar radiation values closer to the equator. The expectation would be that higher solar radiation values would correlate positively with higher water deficit, so other factors must be contributing to Namibia’s water deficit pattern. Water deficit is measured by precipitation minus evaporation, so perhaps evaporation is increased in Namibia’s southern interior by factors such as land surface type, longer hours of sunshine (fewer clouds) or relief.

• AO1 – Knowledge and understanding of geomorphological processes. Knowledge and understanding of origin and development of mid and low latitude deserts.

AO2 – Application of knowledge to show understanding of the relative importance of factors that have contributed to the development of these landforms.
AO1 = 2  AO2 = 4

AO1

• Geomorphological processes: weathering, mass movement, erosion, transportation, and deposition.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block and granular disintegration).
• Origin and development of landforms of mid and low-latitude deserts
  • aeolian – deflation hollows, desert pavements, ventifacts, yardangs, zeugen, barchans and sief dunes
  • water – wadis, bahadas, pediments, playas, inselbergs.

AO2

• AO2 marks will come from recognising the importance of exfoliation as a process of mechanical weathering relating to, in hot deserts, the wide range in temperatures between hot days and cold nights.
• Answers should relate this to the spheroidal formation of the ‘corestones’, the cracks on their surface and the evidence of thin slightly curved sheets of debris around the landforms.
• Answers should explain how, in rocks with layers of different mineral compositions, outer layers expand more in the day, while the inner layers remain cooler. At night, outer layers contract more than the inner layers, resulting in the peeling away of thin sheets or slabs from the rock surface.
• Some answers may note that this region of Kazakhstan experiences freezing winter conditions, which may influence weathering processes, but very low precipitation, meaning that the majority of weathering is likely to be from thermal expansion and contraction.
• The lack of water is likely to mean little contribution from chemical weathering to the formation of the landscape, though this may have been significant during past wetter climate conditions.

• AO1 – Knowledge and understanding of geomorphological processes. Knowledge and understanding of origin and development of mid and low latitude deserts.

AO2 – Application of knowledge to show understanding of the relative importance of factors that have contributed to the development of this landscape.
AO1 = 2  AO2 = 4

AO1

• Geomorphological processes: weathering, mass movement, erosion, transportation, and deposition.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block and granular disintegration).
• Origin and development of landforms of mid and low latitude deserts:
  • aeolian – deflation hollows, desert pavements, ventifacts, yardangs, zeugen, barchans and sief dunes
  • water – wadis, bahadas, pediments, playas, inselbergs.

AO2

• Responses should note that the image shows zeugen and discuss the importance of wind erosion through abrasion in their formation. These features are most typically found in arid environments where there are strong, uni-directional winds and where a harder rock layer overlays less-resistant rocks.
• The image shows evidence of an overhang, and the note provides the information that this is likely to be a more resistant layer of limestone. Underneath it, the less-resistant chalk shows signs of wind erosion through abrasion: smooth, streamlined surfaces.
• The landforms are wider at the base and then narrow towards the top, before the overhanging caprock is reached, suggesting perhaps that saltation is not the dominant form of transportation of sediment, or that the chalk layer is more resistant at its base. Joints in the bedrock may be present, which could also explain the differential erosion within the less-resistant chalk.
• Sources of sediment are not immediately evident. Around the landforms, the ground appears to be covered by fragments of limestone caprock which have collapsed as the chalk has been eroded away; possibly however this is the exposed and eroded second layer of limestone between which the chalk is sandwiched.

• AO1 – Knowledge and understanding of geomorphological processes. Knowledge and understanding of origin and development of mid and low latitude deserts.

AO2 – Application of knowledge to show understanding of the relative importance of factors that have contributed to the development of this landscape.
AO1 = 2  AO2 = 4

AO1

• Geomorphological processes: weathering, mass movement, erosion, transportation, and deposition.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block, and granular disintegration).
• Sources of water: exogenous, endoreic, and ephemeral.
• The episodic role of water; sheet flooding, channel flash flooding.
• Origin and development of landforms of mid and low latitude deserts:
• aeolian – deflation hollows, desert pavements, ventifacts, yardangs, zeugen, barchans and sief dunes
• water – wadis, bahadas, pediments, playas, inselbergs.

AO2

• Responses should note that the image shows a bahada. The episodic role of water is a dominant factor in their formation.
• Change in relief is critical: bahadas form where a series of confined channels emerge from mountains onto a flat plain. Answers need to identify this key feature from the photo and relate it to the additional information provided in the note.
• Mechanical weathering is likely to be important in the mountain ranges, which may experience very cold night-time temperatures, contrasting with very hot daytime temperatures to cause thermal fracture and other forms of mechanical weathering. This weathering will supply large amounts of unsorted sediment.
• When high-velocity channel flash flooding from the mountain range meets the low-gradient plain, the water spreads out and loses energy. Deposition of coarse, heavy sediment occurs nearest the channel mouth. This accumulates over time, creating the fan apex. Sediment is sorted across the alluvial fan, with the finest, lightest sediment forming the lower, gently-sloping outer edges of the fan. Answers should relate this to the image by referencing the evident gradient of the alluvial fans making up the bahada, and the spreading pattern of the drainage network seen on the alluvial fans’ surface.
• Bahadas form as alluvial fans spread out over time and coalesce.
• Answers are therefore likely to conclude that while water is likely to play a small role in the supply of sediment through weathering, the bahada in the landscape is formed almost entirely through the transportation and deposition of sediment so that sediment is sorted across each of the alluvial fans making up the landscape feature.

• AO1 – Knowledge and understanding of geomorphological processes. Knowledge and understanding of origin and development of mid and low latitude deserts.

AO2 – Application of knowledge to show understanding of the relative importance of factors that have contributed to the development of these landforms.

AO1 = 2  AO2 = 4

AO1

• Geomorphological processes: weathering, mass movement, erosion, transportation, and deposition.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block, and granular disintegration).
• Sources of water: exogenous, endoreic, and ephemeral.
• The episodic role of water; sheet flooding, channel flash flooding.
• Origin and development of landforms of mid and low latitude deserts:
  • aeolian – deflation hollows, desert pavements, ventifacts, yardangs, zeugen, barchans and sief dunes
  • water – wadis, bahadas, pediments, playas, inselbergs.

AO2

• Responses should note that the image shows a sand dune on an underlying sandy or rocky surface. The sand dunes are seif dunes, but answers are likely to recognise barchan-like shapes among the lines of seif dunes.
• Seif dunes require an abundant supply of sediment: fine, well-sorted sand. The note states that the sediment source in this case is the Orange River, which perhaps deposits large amounts of sediment as it flows through the Namib Desert due to high rates of evaporation.
• The underlying layer may be formed of coarser sand which is not easily entrained by wind, or is possibly reg (stony desert) over which the dunes accumulate and migrate.
• Seif dunes are formed by bidirectional winds – while the wind mainly blows in one direction, it occasionally switches to another. As a result, a dune forms as wind blows from one direction, and is then elongated by the dominant wind direction into a line. This could explain why some of the dunes resemble barchans that have elongated into seif dunes.
• When the wind switches direction, it reshapes the dune, forming a new slip face or as seems to be the case in the photo, removing slip faces.
• The change in wind direction also piles sand up onto the dune, making it taller and wider. The prevailing wind then redistributes sand along the dune’s length, making it longer and, it could be concluded, giving it the sinuous form seen in this photo.
• Answers are likely to conclude that wind is the dominant factor in the formation of this landscape, with sediment sources provided by the Orange River (not visible in the photo so presumably a distant source), in a system where the fine sand is constantly being reshaped in a landscape that is evidence of dynamic equilibrium in the hot desert system.

• AO1 – Knowledge and understanding of the causes of desertification.

AO2 – Application of knowledge and understanding to assess extent to which desertification can be seen as a characteristic process of a natural system.

AO1 = 10  AO2 = 10

AO1

• The changing extent and distribution of hot deserts over the last 10,000 years. The causes of desertification – climate change and human impact; distribution of areas at risk; impact on ecosystems, landscapes, and populations. Predicted climate change and its impacts, alternative possible futures for local populations.

AO2

• Answers should include a definition of desertification: a process in which semi-arid regions become increasingly dry and lose vegetation cover.
• Answers should recognise that the extent and distribution of deserts has changed in the past (e.g. last 10,000 years) because of natural climate change and desertification has therefore been a natural process.
• The process of desertification has occurred in response to natural positive feedback loops: reduced rainfall leading to loss of vegetation cover, loss of vegetation increasing albedo, increased albedo reducing rainfall, etc.
• However, answers are likely to recognise that rates of desertification have increased in recent decades as a result of human activities.
• These activities exacerbate and intensify natural feedback process, so, for example, increased livestock grazing reduces vegetation cover, increasing albedo, reducing rainfall, increasing desertification and so on.
• Human influences also extend outside the regional scale of desert and semi-arid environments, with climate change meaning that reduced rainfall and prolonged droughts are caused by anthropogenic carbon emissions rather than any natural cycles.
• Answers may therefore conclude that while desertification is a characteristic process of a natural system to an extent, the predominant causes in the contemporary context are anthropogenic: human mismanagement of arid and semi-arid environments at the local and regional scale, and anthropogenic climate change at the global scale.

Example answer: Desertification is the process whereby semi-arid regions become increasingly dry and lose vegetation cover, resulting in soil erosion by wind and rain and general degradation of the land. At the last glacial maximum 20,000 years ago, hot deserts were more extensive than they are today. This was followed by a warmer and more humid period, only reaching their present-day distribution and extent about 3000 years ago.

The extent and distribution of deserts has changed in the last 10,000 years, with little human influence, so desertification has therefore been a process of natural climate change.

The process of desertification has occurred in response to natural positive feedback loops: reduced rainfall leading to loss of vegetation cover, which increases albedo, reduces soil moisture and fertility of soils, leading to soil erosion and desertification. Arid and semi-arid soils are fragile – low in nutrients and organic matter because of low decomposition rates and sparse vegetation cover. Even if levels of precipitation increase, these infertile soils cannot sustain vegetation.

However, in recent decades, rates of desertification have increased as a result of human activities, which exacerbate and intensify natural feedback process. For example, increased livestock grazing in the Sahel on the southern fringes of the Sahara Desert also reduces vegetation cover, which increases albedo, which has the effect of reducing rainfall, increasing the risk of soil erosion, and increasing desertification. Population increase puts more pressure on changing land use for arable or pastoral farming, which requires irrigation. Subsequent evaporation of irrigated water for crops leaves behind mineral salts, leading to salinisation and soil degradation.

Human influences also extend outside the regional scale of desert and semi-arid environments, with anthropogenic carbon emissions, rather than any natural cycles, causing reduced rainfall and prolonged droughts.

While desertification is a characteristic process of a natural system to an extent, especially historical desertification, the predominant causes in the contemporary context are anthropogenic – human mismanagement of arid and semi-arid environments at the local and regional scale, and anthropogenic climate change at the global scale.

• AO1 – Knowledge and understanding of the causes of desertification; knowledge and understanding of climate change.

AO2 – Application of knowledge and understanding to assess the impacts of climate change on desertification, using local scale case study.

AO1 = 10  AO2 = 10

AO1

• The changing extent and distribution of hot deserts over the last 10,000 years. The causes of desertification – climate change and human impact; distribution of areas at risk; impact on ecosystems, landscapes and populations. Predicted climate change and its impacts, alternative possible futures for local populations.
• The carbon budget and the impact of the carbon cycle upon land, ocean, and atmosphere, including global climate.
• Case study at a local scale of a landscape where desertification has occurred to illustrate and analyse key themes of desertification, causes and impacts, implications for sustainable development. Evaluation of human responses of resilience, mitigation, and adaptation.

AO2

• Answers should include a definition of desertification: a process in which semi-arid regions become increasingly dry and lose vegetation cover.
• Answers should recognise that natural climate change has been the driver for desertification for millennia, with the present-day distribution of deserts only dating to around 3000 years ago.
• However, answers are likely to note that the unprecedented rate of climate change resulting from human interventions into the carbon cycle is having, and will continue to have, significant impacts on desertification.
• Predictions are that 30 per cent of the Earth’s surface will experience additional ‘aridification’ by 2050 if the global average temperature increase reaches 2°C. This can be cut by two thirds if temperature increase remains below 1.5°C. This shows the range of potential impacts on the extent and rate of desertification from different climate futures. Include predicted temperature increases from your desertification case study.
• Answers may consider that the impacts of climate change on desertification may vary spatially and over time. For example, if climate zones shift northwards, desertification will have different impacts from climate change leading to an increase in droughts within a region that already experiences cycles of drier years. The impact of climate change can be exacerbated by events such as El Niño, with greater impacts in some years than in others. Include spatial changes to desertification from desertification case study, for example changes in monsoon rainfall patterns.
• Answers are also likely to conclude that other factors will be significant in intensifying or mitigating the impacts of climate. For example, human population increase in dryland areas or an increase in livestock numbers may increase the rate and extent of desertification more than in areas experiencing the same changes in climate but fewer human impacts. Link this to data on population growth from your desertification case study. Likewise, mitigation efforts may reduce the impact of climate change on desertification in some areas, but not in others.

• AO1 – Knowledge and understanding of the causes of desertification; knowledge and understanding of resilience, mitigation, and adaptation as human responses to desertification at a local scale.

AO2 – Application of knowledge and understanding to assess human responses to desertification.

AO1 = 10  AO2 = 10

AO1

• The changing extent and distribution of hot deserts over the last 10,000 years. The causes of desertification – climate change and human impact; distribution of areas at risk; impact on ecosystems, landscapes, and populations. Predicted climate change and its impacts, alternative possible futures for local populations.
• Case study at a local scale of a landscape where desertification has occurred to illustrate and analyse key themes of desertification, causes and impacts, implications for sustainable development. Evaluation of human responses of resilience, mitigation, and adaptation.

AO2

• Answers should include a definition of desertification: a process in which semi-arid regions become increasingly dry and lose vegetation cover.
• Answers likely to consider mitigation as one of three main types of human response to desertification: mitigation, adaptation, and resilience. The aims of each should be briefly outlined.
• Mitigation strategies could be exemplified, with the same being done for resilience and adaptation.
• Case study knowledge or other examples could be used for the assessment of the different responses, considering advantages and disadvantages of different responses. For example, increased yields of up to 100 per cent following the introduction of zai planting pits in Burkina Faso (resilience).
• Evaluation could also consider responses at different scales and are likely to conclude that given the range of challenges caused by desertification at different scales, the absence of a one-size-fits-all solution means that a combination of all three responses will be better than a focus on one to the detriment of the other two.

• AO1 – Knowledge and understanding of development geomorphological processes operating in hot deserts including both distinctively arid geomorphological processes, the role of wind and the episodic role of water.

AO2 – Application of knowledge and understanding to assess whether historic, one-off events have a much greater influence than ongoing processes for landscape development in hot deserts.

AO1 = 10  AO2 = 10

AO1

• Geomorphological processes: weathering, mass movement, erosion, transportation, and deposition.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block and granular disintegration).
• The role of wind – erosion: deflation and abrasion; transportation; suspension, saltation, surface creep, deposition.
• Sources of water: exogenous, endoreic, and ephemeral; the episodic role of water; sheet flooding, channel flash flooding.

AO2

• Answers should consider what might be meant by ongoing processes: i.e. the distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block, and granular disintegration).
• Link these ongoing processes to landforms where, typically, episodic events are not involved, for example landforms and landscapes predominantly influenced by thermal fracture, exfoliation and block and granular disintegration.
• Answers also likely to consider landforms and landscapes influenced predominantly by ongoing and prevailing winds, for example desert pavements, yardangs, zeugen and barchan dunes.
• Historic and one-off events could be taken to refer to episodic events such as flash flooding. Characteristic landforms and landscapes could then consider wadis, bahadas, pediments and playas.
• Answers could consider the importance of scale: ongoing processes are likely to be highly significant over a long time period. However, short-event, high magnitude, and large-scale events, such as a historic flood or historic tectonic event in a desert landscape may have far-reaching and extensive influence on landscape development.

• AO1 – Knowledge and understanding of the causes of desertification; knowledge and understanding of implications of desertification for sustainable development.

AO2 – Application of knowledge and understanding to assess the case for development of hot desert landscapes.

AO1 = 10  AO2 = 10

AO1

• The changing extent and distribution of hot deserts over the last 10,000 years. The causes of desertification – climate change and human impact; distribution of areas at risk; impact on ecosystems, landscapes, and populations. Predicted climate change and its impacts, alternative possible futures for local populations.
• Characteristics of hot desert environments and their margins: climate, soils, and vegetation (and their interaction). Water balance and aridity index.
• Case study at a local scale of a landscape where desertification has occurred to illustrate and analyse key themes of desertification, causes and impacts, implications for sustainable development. Evaluation of human responses of resilience, mitigation, and adaptation.

AO2

• Answers may consider the question from a range of perspectives, including economic, social, and environmental.
• From the environmental perspective, answers are likely to conclude that deserts and their margins are indeed fragile environments, with soils that are thin, lack nutrients, organic material and structure, and which are therefore very easily eroded by wind or water; plants that can survive in desert landscapes can do so usually because they are highly adapted xerophytes and halophytes – and, as such, are typically slow-growing and vulnerable to damage and change.
• From the environmental perspective also, recent history has shown how rising human populations in arid and semi-arid regions intensify the natural feedback systems that lead to desertification – the development of these regions for increased livestock farming, for example, or crop growing has tended to intensify the rate of desertification. Examples of desertification linked to increased development could be given here.
• From the economic perspective, the development of hot deserts and their margins can often be considered a success: e.g. hot deserts offer unparalleled opportunities for solar energy generation, which can take place regardless of the fragility of desert soils, plants, or animals. Hot desert locations are popular places for tourism and for settlement, as long as the society has the resources to bring in the water required for, say, swimming pools and lawn sprinkler systems. However, the sustainability of this type of development could be questioned.
• From the social perspective, people have lived sustainably in hot deserts and their margins for many thousands of years. Answers might consider the impact of development on their ‘fragile’, highly adapted lifestyles and traditions, but also how the successful adaptations these cultures have made to desert living can be the source of adaptations and solutions to sustainable development of deserts and their margins today.
• AO1 – Knowledge and understanding of the causes of desertification; knowledge and understanding of implications of desertification for sustainable development.

AO2 – Application of knowledge and understanding to assess the case for development of hot desert landscapes.

AO1 = 10  AO2 = 10

AO1

• Case study at a local scale of a landscape where desertification has occurred to illustrate and analyse key themes of desertification, causes and impacts, implications for sustainable development. Evaluation of human responses of resilience, mitigation and adaptation.
• The changing extent and distribution of hot deserts over the last 10,000 years. The causes of desertification – climate change and human impact; distribution of areas at risk; impact on ecosystems, landscapes, and populations. Predicted climate change and its impacts, alternative possible futures for local populations.

AO2

• Answers should define desertification and consider the impacts that desertification has on ecosystems, populations, and climate systems, e.g. ecosystem degradation, soil erosion, drought and water scarcity, loss of livelihoods, human displacement and migration, and climate change.
• Answers should consider the impacts of desertification on the physical landscape, e.g. gullying, loss of topsoil and increased extent of or formation of sand dunes. Impacts can also include the increased vulnerability of degraded landscapes to extreme weather events such as droughts and floods.
• The impact of human activities in these changes could be related to specific landscapes, e.g. the Sahel (e.g. Burkina Faso) where a high rate of population growth is increasing the extent and rate of desertification due to the increased pressures of more people and their livestock on the land.
• The impact of human activity varies, and this variation happens at different scales: this could be an angle of the question that answers could explore, perhaps in relation to landscapes in which desertification is happening primarily because of human activity at the global scale (climate change) rather than locally, or a landscape where desertification happened in the distant past before human activity was a factor.
• The impact of human activity could also be in response to desertification: human responses of mitigation, resilience, and adaptation. Answers could use case study information here to describe the impacts of schemes to, for example, reforest semi-arid areas or use bunds or dams, or zai pits to reduce soil erosion and fill in gullies.

• AO1 – Knowledge and understanding of distinctively arid geomorphological processes: weathering and erosion.

AO2 – Application of knowledge and understanding to assess the relative importance of weathering and erosion in the development of hot desert landscapes.

AO1 = 10  AO2 = 10

AO1

• The relationship between process, time, landforms, and landscapes in mid and low latitude desert settings: characteristic desert landscapes.
• Distinctively arid geomorphological processes: weathering (thermal fracture, exfoliation, chemical weathering, block, and granular disintegration).
• The role of wind:
• erosion – deflation and abrasion
• transportation – suspension, saltation, surface creep
• Sources of water – exogenous, endoreic, and ephemeral.
• The episodic role of water – sheet flooding, channel flash flooding.

AO2

• Answers are likely to outline weathering processes in hot desert landscapes: thermal fracture, exfoliation, chemical weathering, block, and granular disintegration.
• Landforms of weathering could be exemplified at this point as an indication of hot desert landscapes where weathering predominates.
• Answers are likely to outline erosion processes related to wind and water: deflation and abrasion; transportation; suspension, saltation, surface creep, deposition.
• Landforms of erosion by wind and by water could be exemplified at this point as an indication of hot desert landscapes where different types of erosion predominate.
• Consideration is then likely to focus on the relative important of weathering and of erosion in the development of hot desert landscapes: the relationship between process, time, landforms, and landscapes.
• Answers may discuss weathering as a key criterion in preparing rock surfaces for erosion: perhaps concluding that erosion depends on weathering, making it relatively more important. This might be given nuance by consideration of time, some weathering of hot desert landscapes having taken place in eras when climate conditions were wetter, for example.
• Answers should consider how different processes may dominate in different areas of a hot desert, perhaps due to wind strength and/or direction, rock type, presence or absence of water, tectonic activity, sediment sources and sources of energy, including insolation.
• Answers are likely to conclude that it is not possible to say that either weathering or erosion always predominate in the development of a hot desert landscape, but that this landscape is itself the result of interactions between these processes and geology over time.

Mark schemes reproduced by permission of AQA.

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