HKDSE · Answers & Marking Scheme

2021 HKDSE Geography Answers & Marking Scheme

Thinka 2021 DSE-Style Mock — Geography

98 marks225 mins2021
An original Thinka practice paper modelled on the structure and difficulty of that year's HKDSE paper. Not affiliated with or reproduced from the HKEAA.

Section A

Answer all 20 multiple-choice questions. All questions carry equal marks.
20 Question · 20 marks
Question 1 · MCQ
1 marks
Which of the following are reasons why the Pacific coast of Japan is more vulnerable to tsunamis than the Pacific coast of Canada? (1) Japan is closer to active subduction zones where megathrust earthquakes occur. (2) Japan has a higher proportion of low-lying, indented ria coasts that amplify tsunami waves. (3) Japan lacks a tsunami warning system.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

A

Worked solution

Statement (1) is correct because Japan is located along the Pacific Ring of Fire with highly active subduction zones (e.g., Japan Trench), whereas western Canada has different tectonic settings with lower frequency of megathrust events. Statement (2) is correct because ria coasts (indented bays) funnel tsunami waves, increasing their height and destructiveness. Statement (3) is incorrect because Japan has one of the world's most advanced tsunami warning systems.

Marking scheme

Award 1 mark for the correct answer A. Reject other options.
Question 2 · MCQ
1 marks
Which of the following is/are example(s) of a positive feedback loop associated with global warming? (1) Melting of permafrost -> Release of methane -> Enhanced greenhouse effect -> Further temperature rise. (2) Increase in global temperature -> Increase in evaporation -> More low-level clouds -> Increased reflection of solar radiation -> Decrease in temperature. (3) Shrinking of Arctic sea ice -> Decreased planetary albedo -> Increased absorption of solar radiation -> Further ice melt.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

B

Worked solution

Statements (1) and (3) are positive feedback loops because the initial change (warming) triggers a sequence of events that amplifies the initial change, leading to more warming. Statement (2) is a negative feedback loop because the increase in low-level clouds reflects more solar radiation, which cools the Earth, counteracting the initial warming.

Marking scheme

Award 1 mark for the correct answer B. Reject other options.
Question 3 · MCQ
1 marks
Compared to traditional flood irrigation, which of the following are the environmental benefits of adopting drip irrigation in arid farming regions? (1) Minimising soil salinisation. (2) Reducing water loss through evaporation. (3) Raising the groundwater table.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

A

Worked solution

Drip irrigation delivers water directly to the plant roots, which significantly reduces evaporation loss (Statement 2) and prevents waterlogging. This avoids raising the groundwater table, which would otherwise bring dissolved salts to the surface and cause soil salinisation (Statement 1). Raising the groundwater table (Statement 3) is not a benefit and indeed causes salinisation in arid regions.

Marking scheme

Award 1 mark for the correct answer A. Reject other options.
Question 4 · MCQ
1 marks
Which of the following descriptions about wave refraction at a headland and bay coast are correct? (1) Wave energy is concentrated at the headland, leading to active erosion. (2) Wave energy is dispersed in the adjacent bays, promoting deposition. (3) Wave crests bend and become parallel to the offshore submarine contours.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

D

Worked solution

As waves approach an irregular coastline, they touch the shallow sea floor around headlands first, causing them to slow down. This causes wave crests to bend and tend to parallel the submarine contours (Statement 3). Consequently, wave energy is concentrated on the headlands (Statement 1) and dispersed in the bays (Statement 2).

Marking scheme

Award 1 mark for the correct answer D. Reject other options.
Question 5 · MCQ
1 marks
Why is the soil in tropical rainforests generally nutrient-poor despite the extremely high plant biomass? (1) Rapid decomposition of organic litter under hot and wet conditions. (2) Intense leaching of soil nutrients by heavy, frequent rainfall. (3) Rapid absorption of nutrients by the dense root networks of vegetation.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

D

Worked solution

In a tropical rainforest, the high temperature and humidity lead to rapid decomposition of litter (Statement 1). The released nutrients are quickly absorbed by the extensive root systems of the plants (Statement 3), leaving very little in the soil. Any remaining nutrients are easily washed away deep into the soil profile by heavy rain through leaching (Statement 2). Thus, the soil nutrient store remains very small.

Marking scheme

Award 1 mark for the correct answer D. Reject other options.
Question 6 · MCQ
1 marks
Which of the following factors best explains the spatial shift of major iron and steel plants in China from inland cities (such as Anshan) to coastal locations (such as Shanghai) since the late 20th century?
  1. A.Depletion of local energy resources in inland provinces
  2. B.Increased reliance on imported high-grade iron ore and proximity to large coastal markets
  3. C.Cheaper land rent and abundant labor supply in coastal megacities
  4. D.Lower transport costs of shipping finished steel products to inland provinces

Answer

B

Worked solution

Modern coastal steel plants (like Baosteel in Shanghai) rely heavily on high-grade iron ore imported from countries like Australia and Brazil via cheap ocean transport. They are also located close to the major domestic manufacturing and construction markets concentrated in the coastal economic zones.

Marking scheme

Award 1 mark for the correct answer B. Reject other options.
Question 7 · MCQ
1 marks
In the urban renewal process of Hong Kong, which of the following approaches is most effective in preserving existing social networks and the local community character of old districts?
  1. A.Redevelopment
  2. B.Rehabilitation
  3. C.Clearance and resettlement
  4. D.Land reclamation

Answer

B

Worked solution

Rehabilitation involves repairing and upgrading existing buildings rather than demolishing them. This allows residents and shopkeepers to remain in their original neighborhood, thereby preserving long-established social networks and community character, unlike redevelopment which displaces residents.

Marking scheme

Award 1 mark for the correct answer B. Reject other options.
Question 8 · MCQ
1 marks
In the rock cycle, which of the following pairs correctly matches a parent rock with its metamorphic equivalent under high temperature and pressure?
  1. A.Granite -> Gneiss
  2. B.Limestone -> Slate
  3. C.Sandstone -> Marble
  4. D.Shale -> Quartzite

Answer

A

Worked solution

Granite (igneous) undergoes regional metamorphism to become gneiss. Limestone becomes marble, sandstone becomes quartzite, and shale becomes slate.

Marking scheme

Award 1 mark for the correct answer A. Reject other options.
Question 9 · MCQ
1 marks
Which of the following atmospheric conditions are characteristic of the Subtropical High Pressure Belt? (1) Sinking air mass leading to dry and stable weather. (2) Strong convection currents producing heavy afternoon thundershowers. (3) Prevailing wind divergence at the surface.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

B

Worked solution

The Subtropical High Pressure Belt is characterized by descending (sinking) air from the Hadley cell, which inhibits cloud formation and results in dry, stable climates (Statement 1). Convective showers are characteristic of the Equatorial Low, not the Subtropical High. Since it is a high-pressure zone, air diverges at the surface towards lower pressure zones (Statement 3).

Marking scheme

Award 1 mark for the correct answer B. Reject other options.
Question 10 · MCQ
1 marks
A geography student wants to conduct a questionnaire survey on the shopping habits of visitors in a shopping mall. She stands at the main entrance and interviews every 10th visitor who enters the mall. What sampling method is the student using?
  1. A.Random sampling
  2. B.Systematic sampling
  3. C.Stratified sampling
  4. D.Convenience sampling

Answer

B

Worked solution

Selecting interviewees at a regular, predetermined interval (in this case, every 10th person) is the definition of systematic sampling.

Marking scheme

Award 1 mark for the correct answer B. Reject other options.
Question 11 · MCQ
1 marks
Which of the following coastal conditions is most favorable for the formation of a spit?
  1. A.Strong longshore drift and a sudden change in the direction of the coastline.
  2. B.High wave energy and a steep offshore gradient.
  3. C.Intense hydraulic action and a lack of sediment supply.
  4. D.Dominance of destructive waves along a straight rocky shoreline.

Answer

A

Worked solution

A spit is a depositional landform. It forms when longshore drift carries sediment along the coast, and when there is a sudden change in the coastline's direction (e.g., at an estuary or bay), the sediment continues to be deposited in the original direction, forming a spit. Destructive waves and high wave energy lead to erosion rather than deposition.

Marking scheme

Award 1 mark for the correct answer A. No marks for other options.
Question 12 · MCQ
1 marks
Which of the following factors explain why a deep-focus earthquake generally causes less ground shaking and destruction at the epicentre than a shallow-focus earthquake of the same magnitude? (1) Seismic waves lose energy as they travel a longer distance to the surface. (2) Deep-focus earthquakes only produce primary (P) waves. (3) The surface waves produced by deep-focus earthquakes are much weaker when they reach the surface.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

B

Worked solution

Statement (1) is correct because seismic waves attenuate (lose energy) as they travel through a greater thickness of rock from a deep focus to the surface. Statement (2) is incorrect because deep-focus earthquakes produce both body waves (P and S waves) and surface waves. Statement (3) is correct because surface waves (which cause the most destruction) are strongest near the source and weaken significantly or are poorly developed at the surface when the focus is deep.

Marking scheme

Award 1 mark for the correct answer B. No marks for other options.
Question 13 · MCQ
1 marks
In the study of climate change, which of the following is an example of a positive feedback loop?
  1. A.Rising temperatures -> Increased evaporation -> More low-level clouds -> Increased reflection of solar radiation -> Decreased temperatures.
  2. B.Rising temperatures -> Melting of permafrost -> Release of methane gas -> Enhanced greenhouse effect -> Rising temperatures.
  3. C.Increased atmospheric carbon dioxide -> Enhanced plant photosynthesis -> Increased absorption of carbon dioxide -> Decreased atmospheric carbon dioxide.
  4. D.Rising temperatures -> Increased forest growth in high latitudes -> Carbon sequestration by trees -> Decreased greenhouse effect -> Decreased temperatures.

Answer

B

Worked solution

A positive feedback loop is a process where the initial change triggers a sequence of events that amplifies or reinforces the initial change. In option B, the initial warming leads to permafrost melting, releasing methane (a greenhouse gas), which causes further warming. Options A, C, and D are negative feedback loops because the final outcome counteracts the initial change.

Marking scheme

Award 1 mark for the correct answer B. No marks for other options.
Question 14 · MCQ
1 marks
Which of the following factors explain why the iron and steel industry in China has increasingly relocated from inland regions (e.g. Anshan) to coastal regions (e.g. Zhanjiang) in recent decades? (1) Depletion of local high-grade iron ore and coal reserves in northern inland regions. (2) Increasing reliance on imported high-grade iron ore from Australia and Brazil. (3) Shift of the major steel market towards the prosperous southern and coastal economic zones.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

D

Worked solution

All three factors are correct. Inland iron and steel bases face resource depletion. Coastal locations offer excellent port facilities to import high-grade raw materials directly by bulk carriers, reducing transport costs. Additionally, coastal and southern regions have become major markets due to rapid urbanisation, infrastructure development, car manufacturing, and shipbuilding.

Marking scheme

Award 1 mark for the correct answer D. No marks for other options.
Question 15 · MCQ
1 marks
Which of the following descriptions about the nutrient cycle in a tropical rainforest ecosystem is correct?
  1. A.The soil nutrient pool is the largest among the three pools due to rapid rock weathering.
  2. B.The litter pool is exceptionally large because of the continuous and heavy leaf fall throughout the year.
  3. C.Nutrients are rapidly absorbed by the dense, shallow root systems of trees, keeping the biomass pool the largest.
  4. D.Heavy rainfall enhances leaching, which increases the concentration of soluble nutrients in the topsoil.

Answer

C

Worked solution

In a tropical rainforest, the biomass pool is the largest because vegetation is abundant and grows rapidly. The soil pool is very small because heavy rainfall causes intense leaching, washing away nutrients, and roots absorb nutrients almost immediately. The litter pool is also small because the hot and wet climate promotes rapid decomposition by decomposers.

Marking scheme

Award 1 mark for the correct answer C. No marks for other options.
Question 16 · MCQ
1 marks
In a sustainable city, which of the following transport planning strategies is most effective in achieving BOTH carbon reduction and social equity?
  1. A.Implementing high electronic road pricing in all residential districts to discourage private car ownership.
  2. B.Developing a transit-oriented development model centered on subsidized, high-accessibility public transit.
  3. C.Providing generous tax incentives for middle-income households to replace diesel cars with electric vehicles.
  4. D.Restricting pedestrian zones in busy commercial areas to speed up the flow of private vehicular traffic.

Answer

B

Worked solution

A Transit-Oriented Development (TOD) model encourages the use of public transport, reducing carbon emissions. Subsidizing public transit and ensuring high accessibility promote social equity by making affordable transport available to lower-income groups. High road pricing without alternatives (A) or tax incentives for private electric vehicles (C) do not promote social equity.

Marking scheme

Award 1 mark for the correct answer B. No marks for other options.
Question 17 · MCQ
1 marks
Compared to traditional flood irrigation, which of the following are the advantages of using drip irrigation in arid agricultural regions? (1) It minimizes water loss through evaporation and deep percolation. (2) It reduces the risk of soil salinisation. (3) It requires a much lower initial capital investment.
  1. A.(1) and (2) only
  2. B.(1) and (3) only
  3. C.(2) and (3) only
  4. D.(1), (2) and (3)

Answer

A

Worked solution

Statements (1) and (2) are correct because drip irrigation delivers water directly to the plant roots in controlled amounts, minimizing evaporation and preventing waterlogging that leads to salinisation. Statement (3) is incorrect because drip irrigation systems require a high initial investment for pipes, emitters, pumps, and filtration systems, which is often a major barrier for poor farmers.

Marking scheme

Award 1 mark for the correct answer A. No marks for other options.
Question 18 · MCQ
1 marks
A group of geography students wants to study the microclimate of a high-density urban residential area. Which of the following sampling methods and data collection strategies is the most appropriate?
  1. A.Measuring air temperature at a single fixed station for 24 hours to represent the spatial variation of the entire district.
  2. B.Selecting multiple measuring points at regular intervals along a transect from an urban park to a concrete commercial core, using systematic sampling.
  3. C.Distributing questionnaires to 100 local residents to collect subjective perceptions of daily wind speed as primary scientific data.
  4. D.Using opportunistic sampling to measure wind speed only in open plazas during rainy days to study the urban heat island effect.

Answer

B

Worked solution

To study microclimate spatial variation (such as the urban heat island effect), setting up a transect across different land use types (e.g., from green space to concrete core) using systematic sampling is the standard scientific geographical method. A single station (A) cannot show spatial variation. Questionnaire data (C) is subjective and not suitable as primary climatic measurements. Rainy days (D) are unsuitable for studying the heat island effect, and opportunistic sampling is highly biased.

Marking scheme

Award 1 mark for the correct answer B. No marks for other options.
Question 19 · MCQ
1 marks
In the rock cycle, which of the following geological processes directly transforms sedimentary rocks into metamorphic rocks?
  1. A.High temperature and pressure causing mineral recrystallisation without complete melting.
  2. B.Intense weathering and erosion followed by deep compaction and cementation.
  3. C.Complete melting into magma followed by slow cooling and solidifying underground.
  4. D.Subduction of plates carrying rocks into the mantle to be completely recycled.

Answer

A

Worked solution

Metamorphic rocks are formed when pre-existing rocks (sedimentary or igneous) are subjected to high temperature and pressure, causing physical or chemical changes (recrystallisation) in the solid state (without melting). Complete melting (C) would form magma which cools to become igneous rocks. Compaction and cementation (B) form sedimentary rocks.

Marking scheme

Award 1 mark for the correct answer A. No marks for other options.
Question 20 · MCQ
1 marks
During the winter monsoon in East Asia, which of the following atmospheric conditions typically develops over the Eurasian continent and brings cold, dry weather to Hong Kong?
  1. A.A strong low-pressure centre over Siberia, driving warm maritime air masses southward.
  2. B.A powerful high-pressure system (Siberian High), driving cold, dry continental airstreams southward.
  3. C.A tropical depression in the South China Sea, drawing humid southeasterly winds into southern China.
  4. D.The development of the Subtropical High over the Pacific Ocean, causing stagnant, hot air over the region.

Answer

B

Worked solution

In winter, the Eurasian continent cools down rapidly, forming a huge thermal high-pressure system known as the Siberian High. The air blows outwards from this high-pressure centre, creating cold and dry northwesterly to northeasterly continental monsoonal winds that reach South China and Hong Kong.

Marking scheme

Award 1 mark for the correct answer B. No marks for other options.

Section B

Consists of 5 data / skill-based structured questions. Attempt any TWO questions in this section.
2 Question · 36 marks
Question 1 · Structured
18 marks
Refer to the data below concerning "Silver Bay", a coastal resort town:\n\nTable 1a: Annual rate of coastal retreat (metres/year) at Silver Bay:\n- 2010 to 2014 (Before engineering works): Sector A = 1.2 m/yr; Sector B = 1.1 m/yr\n- 2015 to 2018 (After seawall built at Sector A only): Sector A = 0.1 m/yr; Sector B = 2.8 m/yr\n- 2019 to 2022 (After beach nourishment introduced at Sector B): Sector A = 0.1 m/yr; Sector B = 0.4 m/yr\n\nQuestions:\n(a) (i) Describe the change in the rate of coastal retreat at Sector B from 2010 to 2018. (2 marks)\n(a) (ii) Explain how the construction of the seawall at Sector A led to the change at Sector B during 2015-2018. (4 marks)\n(b) (i) Identify the soft engineering measure introduced in 2019 and explain how it helps reduce coastal erosion at Sector B. (4 marks)\n(b) (ii) Suggest TWO environmental impacts of this soft engineering measure on the coastal ecosystem. (3 marks)\n(c) "Soft coastal engineering is always more sustainable than hard coastal engineering." Evaluate this statement with reference to the economic and social conditions of a developing coastal community. (5 marks)

Answer

Detailed solution provided below.

Worked solution

(a) (i) From 2010 to 2018, the annual rate of coastal retreat at Sector B increased significantly, rising from 1.1 m/yr to 2.8 m/yr (more than doubling). (a) (ii) The construction of the seawall at Sector A protected Sector A by reflecting wave energy and trapping sediment. However, it blocked the sediment transport pathway along the coast (longshore drift). As a result, Sector B (downdrift side) was deprived of its sediment supply. Without replenishment, waves at Sector B eroded the coastline more intensively, a phenomenon known as terminal groyne or seawall downdrift erosion. (b) (i) The soft engineering measure is beach nourishment. It involves importing large quantities of sand or gravel from external sources to replenish the eroded beach. This increases the width and volume of the beach, creating a larger buffer zone. The wide beach dissipates wave energy through friction, protecting the cliffs or hinterland from direct wave attack. (b) (ii) 1. Smothering of benthic (seabed) marine organisms during the dumping of imported sand. 2. Habitat destruction at the marine dredging site where sand was originally harvested. 3. Increased turbidity of water, blocking sunlight and disrupting photosynthesis of marine plants or damaging coral reefs. (c) While soft engineering is ecologically friendlier, it is not always more sustainable. In developing coastal communities, financial resources are limited. Soft engineering (like beach nourishment) requires periodic, high-cost maintenance to replenish washed-away sand, which may be economically unviable. Hard engineering (like seawalls) offers long-term, highly reliable protection for critical infrastructure (e.g., ports, schools, housing) after high initial costs. Socially, communities may prefer the immediate safety assurance of hard engineering over the temporary nature of soft engineering. Thus, sustainability depends heavily on local financial capability and protection priorities.

Marking scheme

(a) (i) [Max 2 marks] \n- Identify increasing trend (1 mark) \n- Use figures correctly (1.1 m/yr to 2.8 m/yr) (1 mark) \n\n(a) (ii) [Max 4 marks] \n- Seawall reflects wave energy at Sector A / traps sediment (1 mark) \n- Interrupts longshore drift (1 mark) \n- Deprives Sector B (downdrift) of sediment supply (1 mark) \n- Stronger wave attack / higher erosion rate at Sector B (1 mark) \n\n(b) (i) [Max 4 marks] \n- Identify 'beach nourishment' (1 mark) \n- Explain adding sediment to beach (1 mark) \n- Explain increased beach width/volume (1 mark) \n- Explain wave energy dissipation through friction (1 mark) \n\n(b) (ii) [Max 3 marks] \n- Suggest any TWO valid environmental impacts (1 mark each, 1 extra mark for elaboration of mechanism up to 3): e.g., smothering benthic life, dredging site damage, water turbidity. \n\n(c) [Max 5 marks] \n- Discuss benefits of soft engineering (ecological, natural landscape) (1 mark) \n- Discuss limitations in developing context (high maintenance costs, need for technical equipment) (1 mark) \n- Discuss role of hard engineering (immediate safety, protects high-value assets) (1 mark) \n- Apply to developing country context (poverty, lack of long-term funds) (1 mark) \n- Provide a balanced conclusion (sustainability depends on context, not 'always' soft) (1 mark)
Question 2 · Structured
18 marks
Refer to the information below about "Mount Maru", an active volcano in Southeast Asia:\n\nTable 2a: Characteristics of risk zones around Mount Maru:\n- Zone A (Proximal zone, 0-5 km from crater): Population density = 450 people/km²; Hazard type = Pyroclastic flows; Soil fertility = Exceptionally high (rich in minerals)\n- Zone B (River valleys, 5-20 km from crater): Population density = 800 people/km²; Hazard type = Lahars (mudflows); Soil fertility = Very high (alluvial volcanic soil)\n- Zone C (Distal plains, 20-50 km from crater): Population density = 250 people/km²; Hazard type = Heavy ash fall; Soil fertility = Moderate to high\n\nQuestions:\n(a) Based on the given information, explain the physical and human factors that attract high population density to areas near active volcanoes. (4 marks)\n(b) (i) Distinguish between "pyroclastic flows" and "lahars" in terms of their physical characteristics and formation. (4 marks)\n(b) (ii) Explain why lahars pose a severe, long-term hazard to local communities even years after a volcanic eruption has ceased. (4 marks)\n(c) Evaluate the effectiveness of land-use zoning versus early warning systems in reducing volcanic disaster risks in a less developed country. (6 marks)

Answer

Detailed solution provided below.

Worked solution

(a) Physical factors: Weathering of volcanic materials releases rich minerals (phosphorus, potassium) into the soil, generating exceptionally fertile soil. River valleys (Zone B) accumulate alluvial volcanic sediments, ideal for farming. Human factors: Fertile volcanic soils support intensive farming and high crop yields, sustaining large populations. Furthermore, in less developed regions, farmers are highly dependent on agriculture for livelihood, forcing them to tolerate hazards for economic survival. (b) (i) Pyroclastic flows are superheated, fast-moving avalanches of hot gas, ash, and rock fragments (temp up to 1000°C) formed directly during explosive eruptions. Lahars are hot or cold mudflows/landslides of wet volcanic debris, formed when loose volcanic ash and rocks mix with water (from heavy rain, melted snow, or crater lakes). (b) (ii) Huge volumes of loose volcanic ash and debris remain deposited on steep slopes long after an eruption. Heavy rain (e.g., monsoon rains) can easily remobilise this loose material, triggering secondary lahars. These flow down river channels (Zone B) at high speeds, burying downstream villages, choking rivers, causing floods, and ruining agricultural lands years later. (c) Land-use zoning is highly effective in theory as it restricts developments in high-risk zones (Zones A and B), completely separating populations from hazards. However, in less developed countries (LDCs), high population pressure, lack of alternative land, and weak government enforcement make zoning difficult to implement. Early warning systems (EWS) monitor volcanic tremors, gases, and ground swelling, giving populations time to evacuate. This is highly flexible and cost-effective, saving thousands of lives without relocating entire communities. However, LDCs may lack funds for high-tech monitoring, and communication networks might be weak. In conclusion, while land-use zoning is a great long-term ideal, EWS is often a more practical and effective immediate tool for LDCs, although integrating both yields the best resilience.

Marking scheme

(a) [Max 4 marks] \n- Explain soil fertility (volcanic ash/minerals) (1 mark) \n- Explain high agricultural yields / intensive farming (1 mark) \n- Explain river valleys collecting nutrients (1 mark) \n- Explain human factors: poverty, lack of alternative land, economic livelihood (1 mark) \n\n(b) (i) [Max 4 marks] \n- Pyroclastic flows: hot gas/ash mixture, dry, high temperature, formed during eruption (2 marks) \n- Lahars: water-debris mixture (mudflow), wet, hot/cold, formed by rain/melted ice mixing with debris (2 marks) \n\n(b) (ii) [Max 4 marks] \n- Loose material remains on steep slopes (1 mark) \n- Remobilised by heavy rainfall/monsoons (1 mark) \n- Flows rapidly along river channels (Zone B) (1 mark) \n- Causes long-term physical damage: burials of infrastructure, river siltation, flooding (1 mark) \n\n(c) [Max 6 marks] \n- Land-use zoning: Explain benefits (separates hazard & vulnerability, long-term safety) (1 mark) \n- Land-use zoning: Explain limitations in LDCs (poor enforcement, high population density, resettlement issues) (1 mark) \n- EWS: Explain benefits (saves lives, cost-effective, flexible) (1 mark) \n- EWS: Explain limitations in LDCs (high-tech cost, false alarms, poor communication infrastructure) (1 mark) \n- Comparison & evaluation (e.g., EWS is more feasible in LDCs for immediate life-saving, zoning is an ideal but hard to implement) (2 marks)

Section C

Consists of 3 short essay questions. Attempt any ONE question in this section.
1 Question · 12 marks
Question 1 · Essay
12 marks
Explain how the melting of Arctic permafrost and glaciers under global warming can trigger positive feedback loops that further accelerate global temperature rise. Evaluate the effectiveness of international agreements in mitigating global warming.

Answer

Model essay outline: 1. Positive feedback loops: - Albedo feedback: Global warming -> melting of ice/snow -> decreases surface albedo -> increases absorption of solar radiation -> further warming -> more melting. - Permafrost feedback: Global warming -> melting of permafrost -> decomposition of organic matter -> release of methane and carbon dioxide -> enhances greenhouse effect -> further warming -> more melting. 2. Evaluation of international agreements (e.g., Kyoto Protocol, Paris Agreement): - Strengths: Broad global consensus, sets clear temperature limits (e.g., \(1.5^\circ\text{C}\)), provides frameworks for climate finance and technology transfer, encourages transition to renewable energy. - Limitations: Voluntary nature with no legal penalties for missing targets (NDCs), conflicts between economic growth and emission cuts (especially in developing countries), political instability affecting long-term commitments, current commitments still insufficient to limit warming to \(1.5^\circ\text{C}\).

Worked solution

This essay requires students to demonstrate their understanding of atmospheric processes and global warming feedback mechanisms, as well as to critically evaluate international efforts.

Part 1: Feedback Mechanisms (6 marks)
Students should clearly explain the mechanisms of the ice-albedo feedback and the permafrost-carbon feedback.
- Ice-Albedo Feedback: As greenhouse gases trap heat, global temperatures rise, causing Arctic glaciers, sea ice, and snow cover to melt. This exposes dark ocean and soil surfaces. Since ice has a high albedo (reflecting up to 90% of sunlight) and dark water/soil has a low albedo (absorbing over 90%), this transition reduces the Earth's reflectivity. More solar radiation is absorbed, heating the surface and the air above, which leads to further melting of ice and snow. This is a self-reinforcing positive feedback loop.
- Permafrost-Carbon Feedback: Permafrost contains vast amounts of ancient organic matter frozen for thousands of years. As temperatures rise, the permafrost melts, allowing microbes to decompose this organic matter. Under anaerobic conditions (such as in waterlogged thermokarst lakes), methane (\(\text{CH}_4\)) is produced; under aerobic conditions, carbon dioxide (\(\text{CO}_2\)) is produced. Since methane is a highly potent greenhouse gas (with a global warming potential much higher than \(\text{CO}_2\)), the release of these gases significantly enhances the greenhouse effect, trapping more outgoing longwave radiation. This further raises global temperatures, accelerating permafrost thawing.

Part 2: Evaluation of International Agreements (6 marks)
Students need to offer a balanced evaluation of international climate agreements (such as the Paris Agreement).
- Positive Aspects:
1. Setting concrete goals: The Paris Agreement established a clear global threshold of keeping temperature rise well below \(2^\circ\text{C}\), aiming for \(1.5^\circ\text{C}\).
2. National commitments: It requires countries to submit Nationally Determined Contributions (NDCs), promoting accountability and long-term domestic green policy-making.
3. Support mechanisms: It facilitates financial aid (e.g., Green Climate Fund) and technology transfer to help developing nations adapt and mitigate emissions.
- Limitations:
1. Lack of enforcement: The agreements are largely non-binding without legal sanctions or fines for countries failing to meet their NDCs.
2. Free-rider and withdrawal problems: Countries can withdraw due to shifting domestic political landscapes (e.g., the United States' fluctuating participation).
3. Development conflicts: Developing countries face a trade-off between rapid industrialization/poverty alleviation and emission reduction.
4. Emission gap: Current pledges under NDCs are still mathematically insufficient to limit global warming to \(1.5^\circ\text{C}\), indicating a gap between political will and environmental necessity.

Marking scheme

Marking Scheme:
Max Marks: 12.

Part 1: Positive feedback loops (Max 6 marks)
- Award 1 mark for each clear, logically explained step of the feedback loops (up to 3 marks per feedback loop):
- Albedo feedback loop:
- Warming -> melting of ice and snow [1 mark]
- Exposing darker underlying land/sea surfaces, lowering albedo / decreasing reflectivity [1 mark]
- More solar radiation absorbed, leading to higher temperatures and more melting [1 mark]
- Permafrost carbon feedback loop:
- Warming -> thawing of Arctic permafrost [1 mark]
- Decomposition of organic matter under aerobic/anaerobic conditions [1 mark]
- Release of greenhouse gases (carbon dioxide / methane), enhancing the greenhouse effect and amplifying warming [1 mark]
- Accept other valid feedback loops (e.g., water vapor feedback, forest dieback/wildfires) but focus should be on the requested Arctic context (glaciers and permafrost).

Part 2: Evaluation of effectiveness of international agreements (Max 6 marks)
- Assess candidates' ability to offer a balanced and critical evaluation of international climate agreements:
- High performance (5-6 marks): Comprehensive discussion of both effectiveness (e.g., sets clear common targets like \(1.5^\circ\text{C}\), enhances international clean tech transfer, promotes green transformation) and limitations (e.g., non-binding nature, lack of penalty, economic development priority in developing countries, political withdrawals). Provides a balanced conclusion.
- Medium performance (3-4 marks): Explains some strengths and limitations of international agreements, but the evaluation may be slightly one-sided or lack specific detail/geographical terms.
- Low performance (1-2 marks): Brief or superficial points, merely listing some agreements without analyzing their actual effectiveness or weaknesses.
- Note: No marks should be given for just naming agreements without evaluation.

Section D (Elective Data)

Consists of 4 elective data-based questions. Attempt any ONE question in this section.
1 Question · 18 marks
Question 1 · Structured
18 marks
Table 1 shows the meteorological data of Tropical Cyclone 'X' at 24-hour intervals. Figure 1 represents its idealized atmospheric cross-section during its peak intensity on Day 3.\n\nTable 1: Meteorological Data of Tropical Cyclone 'X'\n- Day 1: Position 18.2 N, 122.5 E | Central Pressure: 992 hPa | Max Sustained Wind Speed: 85 km/h\n- Day 2: Position 19.8 N, 119.2 E | Central Pressure: 970 hPa | Max Sustained Wind Speed: 130 km/h\n- Day 3: Position 21.5 N, 115.8 E | Central Pressure: 935 hPa | Max Sustained Wind Speed: 195 km/h\n- Day 4 (Landfall): Position 22.4 N, 113.8 E | Central Pressure: 955 hPa | Max Sustained Wind Speed: 150 km/h\n\nFigure 1: Atmospheric Cross-Section of Tropical Cyclone 'X' (Day 3)\n[Description: A mature, symmetrical tropical cyclone structure. The center features a cloud-free eye with weak descending air. The eye is surrounded by a towering wall of cumulonimbus clouds (eyewall) featuring violent updrafts. Beyond the eyewall are spiral rainbands with alternating updrafts and downdrafts.]\n\nQuestions:\n(a) Describe the changes in the intensity and movement of Tropical Cyclone 'X' from Day 1 to Day 4 based on Table 1. (4 marks)\n(b) With reference to Table 1 and Figure 1:\n(i) Explain the physical factors that led to the rapid intensification of Tropical Cyclone 'X' from Day 1 to Day 3 over the ocean. (5 marks)\n(ii) Explain why the intensity of Tropical Cyclone 'X' decreased on Day 4 after landfall. (4 marks)\n(c) Climate change is projected to increase the frequency of super typhoons. Evaluate the effectiveness of using hard engineering vs. soft engineering measures to protect coastal communities in South China from storm surges. (5 marks)

Answer

Please refer to the solution and marking scheme for detailed structured sub-question answers.

Worked solution

(a) Movement: The tropical cyclone moved consistently northwestward, shifting from lower latitude (18.2 N) to higher latitude (22.4 N) and westward (from 122.5 E to 113.8 E). Intensity: It intensified rapidly from Day 1 to Day 3, with central pressure dropping from 992 hPa to 935 hPa, and maximum wind speeds increasing from 85 km/h to 195 km/h. On Day 4, the intensity weakened as central pressure rose to 955 hPa and wind speed dropped to 150 km/h.\n\n(b) (i) 1. High sea surface temperature (> 26.5 deg C) in the Western Pacific/South China Sea provided abundant heat and moisture. 2. Strong evaporation and condensation of water vapor released massive latent heat, fueling the eyewall updrafts shown in Figure 1. 3. Low vertical wind shear allowed the vertical convective structure of the eyewall to remain intact. 4. Strong Coriolis force at these latitudes (18 N to 21 N) initiated and maintained the cyclonic rotation.\n\n(b) (ii) 1. Loss of moisture and latent heat supply: Once the cyclone moved over land, the source of warm moisture from the ocean surface was cut off. 2. Increased surface friction: Terrestrial landscapes (buildings, vegetation, rugged topography) increased friction, rapidly dissipating the kinetic energy of the winds.\n\n(c) Hard engineering (e.g., seawalls, breakwaters): Highly effective at blocking immediate wave energy and protecting densely populated urban centers (e.g., Hong Kong, Shenzhen). However, they are costly to construct/maintain and may disrupt coastal ecosystems. Soft engineering (e.g., mangrove restoration, wetland conservation): Environmentally friendly, cheaper to maintain, and absorbs wave energy naturally. However, they require vast coastal spaces (which are limited in urban South China) and are less effective against extreme, high-magnitude storm surges. A combined approach is optimal.

Marking scheme

(a) [Max 4 marks]\n- Award 1 mark for describing the northwestward direction of movement (with reference to coordinates).\n- Award 1 mark for identifying the overall speed/consistent movement.\n- Award 1 mark for describing the intensification from Day 1 to Day 3 (quoting pressure/wind speed figures).\n- Award 1 mark for describing the weakening of intensity on Day 4 (quoting pressure/wind speed figures).\n\n(b) (i) [Max 5 marks]\n- High sea surface temperatures (> 26.5 deg C) [1]\n- Intense evaporation and latent heat release during condensation [1]\n- Updrafts in the eyewall as depicted in Figure 1 [1]\n- Low vertical wind shear [1]\n- Sufficient Coriolis force to sustain rotation [1]\n\n(b) (ii) [Max 4 marks]\n- Landfall cuts off the primary energy source (warm ocean/latent heat) [2]\n- Friction from land surface is much higher than ocean [1], which dissipates wind energy and slows down wind speed [1]\n\n(c) [Max 5 marks]\n- Hard engineering: clear evaluation of benefits (physical barrier, immediate protection) and limitations (high cost, ecological damage) [2]\n- Soft engineering: clear evaluation of benefits (ecological, sustainable) and limitations (space-consuming, limited capacity during extreme events) [2]\n- Concluding decision/synthesis: advocating for integrated coastal zone management (combining both) in South China [1]

Section E (Elective Essay)

Consists of 4 elective short essay questions. Attempt any ONE question in this section.
1 Question · 12 marks
Question 1 · Essay
12 marks
Explain how the implementation of green infrastructure can mitigate the urban heat island (UHI) effect in high-density cities. Evaluate the constraints of retrofitting green infrastructure in older, established urban districts.

Answer

Refer to the marking scheme and solution for detailed breakdown.

Worked solution

Part 1: Mitigation of UHI by Green Infrastructure (6 marks)
- Shading effect: Vegetation (e.g., street trees, green roofs) blocks solar radiation from reaching artificial concrete and asphalt surfaces, reducing sensible heat storage.
- Evapotranspiration: Transpiration from plants and evaporation from soil absorb latent heat, which directly lowers the surrounding air temperature.
- Increasing Albedo: Green roofs and vertical greening have a higher albedo than dark building materials, reflecting more solar radiation back to space.
- Air ventilation: Well-designed green corridors and parks can serve as wind paths, facilitating air circulation to disperse trapped anthropogenic heat.
- Feed-back reduction: Lower ambient air temperatures reduce the energy demand for air conditioning, leading to a reduction in anthropogenic heat emissions.

Part 2: Constraints of Retrofitting in Older Districts (6 marks)
- Spatial and land constraints: High building density and narrow streets in old districts leave extremely limited ground-level space for parks or roadside planting.
- Structural limitations: Older buildings are often not engineered to support the heavy loads of green roofs (soil and water), posing safety hazards.
- Socio-economic and maintenance issues: Retrofitting is expensive. Fragmented property ownership in old buildings (e.g., lack of owners' corporations) makes it difficult to coordinate and finance long-term maintenance (e.g., irrigation, pest control).
- Underground infrastructure: The high density of underground utilities (water pipes, electricity cables) in old districts restricts the space for deep-root planting.
- Policy and institutional constraints: Lack of unified planning guidelines and incentives for retrofitting private old residential buildings.

Marking scheme

Part 1: Mitigation mechanisms (Max 6 marks; 2 marks for each well-elaborated point):
- Explain shading and albedo effects with geographic terms (sensible heat, solar radiation) (Up to 2 marks)
- Explain evapotranspiration and latent heat absorption (Up to 2 marks)
- Explain how green corridors improve wind flow to disperse heat (Up to 2 marks)
- Explain the reduction of anthropogenic heat loop (Up to 1 mark)

Part 2: Constraints of retrofitting (Max 6 marks; 2 marks for each well-evaluated point):
- Spatial/land constraints (narrow streets, lack of open space) (Up to 2 marks)
- Structural constraints (load-bearing capacity of old buildings) (Up to 2 marks)
- Management/financial constraints (fragmented ownership, high maintenance costs) (Up to 2 marks)
- Technical/underground constraints (existing utility pipelines blocking tree roots) (Up to 2 marks)