2023 HKDSE Geography Answers & Marking Scheme

At a convergent boundary where an oceanic plate subducts under a continental plate, the bending of the subducting oceanic plate forms a deep ocean trench parallel to the boundary (Statement 1). The compression on the continental plate crumples the crust, forming fold mountains (Statement 2). Earthquakes occur along the Wadati-Benioff zone, where the subducting plate sinks into the mantle. Thus, the depth of earthquake foci increases as you move away from the trench towards the continent (Statement 3). Therefore, all three statements are correct.

Award 1 mark for the correct answer D. No mark for other options.

(1) is correct because downstream discharge increases and friction decreases, leading to an increase in average velocity. (2) is correct because downstream channels are wider and deeper, increasing the cross-sectional area relative to the wetted perimeter (hydraulic radius). (3) is incorrect because channel roughness decreases downstream as the river bed and banks become smoother with finer and more rounded sediments.

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

A groin acts as a barrier to longshore drift. When longshore drift moves from West to East, sediment transport is blocked by the groin on its western (updrift) side, leading to deposition there. Conversely, the eastern (downdrift) side receives no incoming sediment but is still subjected to wave erosion, leading to net coastal erosion.

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

First, calculate the horizontal ground distance: \( 5\text{ cm} \times 20\,000 = 100\,000\text{ cm} = 1000\text{ m} \). Second, calculate the vertical height difference: \( 350\text{ m} - 150\text{ m} = 200\text{ m} \). The gradient is \( \text{Vertical height difference} / \text{Horizontal ground distance} = 200\text{ m} / 1000\text{ m} = 1 / 5 \) or 1 : 5.

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

Statement (1) is correct as high temperature and humidity promote rapid decay and plants absorb the nutrients quickly, so they are stored in biomass rather than the soil. Statement (2) is correct because the excessive rain causes intense leaching of soluble minerals. Statement (3) is incorrect because high temperatures and rainfall promote, rather than limit, physical and chemical weathering, but the minerals are heavily leached out.

Award 1 mark for the correct answer A. No mark for other options.

Drip irrigation delivers water directly to plant roots, reducing excessive evaporation which otherwise draws underground salts to the surface, hence reducing salinisation (1 is correct). It is highly efficient, minimising water loss through evaporation and percolation (2 is correct). It does not raise the water table, as water is applied in precise, small amounts; raising the water table is actually associated with flood irrigation and waterlogging, which are harmful in these contexts (3 is incorrect).

Award 1 mark for the correct answer A. No mark for other options.

Shield volcanoes are formed by basic (basaltic) lava. Basic lava has low silica content, which gives it low viscosity (it is highly fluid). Highly fluid lava allows gases to escape easily, resulting in gentle or effusive eruptions rather than explosive ones.

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

Counter-urbanisation is driven by both push and pull factors. (1) represents a facilitating factor, allowing people to live further away and commute or telecommute. (2) and (3) are push factors from urban areas, as industrial decline reduces inner-city environmental quality, while high land prices and living costs push residents to look for more affordable, spacious housing in rural-urban fringes or small towns.

Award 1 mark for the correct answer D. No mark for other options.

In Stage 4 of the DTM, both birth and death rates are low and stable, resulting in a stable or slowly growing population. In Stage 5, the birth rate declines further and falls below the death rate, resulting in a natural population decrease (e.g., negative natural growth rate), which is the key distinguishing feature.

Award 1 mark for the correct answer A. No mark for other options.

Statement (1) is correct as headquarters cluster in global cities for proximity to advanced producer services, stock markets, and information flow. Statement (2) is incorrect because R&D centres require highly-skilled scientific labour and proximity to universities, not cheap manual labor. Statement (3) is correct as assembly is labor-intensive and low-skilled, seeking lower land/labor costs and preferential policies in developing countries.

Award 1 mark for the correct answer A. No mark for other options.

Systematic sampling (2) avoids subjective selection bias. A larger sample size of at least 30 pebbles (3) provides statistical validity. Option (1) introduces bias towards specific shapes. Option (4) is incorrect because measuring only the long axis (a-axis) is insufficient; the intermediate axis (b-axis) is typically measured to represent pebble size in standard geographic analysis.

1 mark for the correct option (B). No marks for other options.

At an oceanic-continental convergent boundary, the denser oceanic plate subducts, forming a deep ocean trench. The continental plate is crumpled to form a volcanic arc (mountain range with volcanoes). The subducting plate generates shallow to deep-focus earthquakes along the Benioff zone.

1 mark for option (C).

As waves approach an irregular coastline, they touch the shallow sea bottom around headlands first, causing them to slow down and bend. This focuses wave energy onto headlands, leading to intense erosion, while wave energy diverges in bays, promoting deposition.

1 mark for option (B).

Although clay particles are much smaller than sand particles, they require a higher velocity to be eroded because clay particles are highly cohesive and stick together due to electrostatic forces.

1 mark for option (B).

Slope gradient (1), bedrock geology/fault lines (2), and rainfall distribution (3) are critical physical factors that determine slope stability and trigger landslides. The distribution of shopping malls (4) has no relevance to the physical risk of landslide occurrence.

1 mark for option (C).

Statements (1) and (3) are correct human factors explaining LDCs' higher vulnerability. Statements (2) and (4) are scientifically incorrect because plate tectonics operate independently of human economic development; MDCs can also be located directly on plate boundaries (e.g., Japan, USA).

1 mark for option (A).

Soft engineering acts to blend in with natural coastal environments, preserving the visual landscape and maintaining dynamic equilibrium. Hard engineering constructs (like seawalls) often reflect wave energy, worsening erosion elsewhere, and disrupt natural ecological habitats.

1 mark for option (C).

The ice-albedo positive feedback loop is a self-reinforcing process: warming causes ice melt, exposing darker land/ocean (lower albedo), which absorbs more solar radiation, warming the Earth further and causing more ice to melt.

1 mark for option (A).

1. Actual horizontal distance (run) = \(5\text{ cm} \times 20\,000 = 100\,000\text{ cm} = 1000\text{ m}\). 2. Vertical height difference (rise) = \(450\text{ m} - 150\text{ m} = 300\text{ m}\). 3. Gradient = Rise / Run = \(300 / 1000 = 3 / 10 = 1 : 3.33\).

1 mark for option (B).

Statement (1) is incorrect because a tsunami-triggering earthquake must occur beneath the ocean (submarine) to displace water. Statements (2), (3), and (4) are correct as high magnitude, shallow focus, and vertical seafloor displacement (dip-slip faulting) are critical physical requirements to generate massive waves.

1 mark for option (C).

(a) Comparison:
- Both Event A and Event B are strong earthquakes with magnitude near 7.0 Mw (Event A: 7.1; Event B: 6.9).
- Both are shallow-focus earthquakes (Event A: 8 km depth; Event B: 10 km depth), which typically cause severe shaking at the surface.
- Both occurred very close to densely populated city centres (Event A: 12 km; Event B: 15 km).
- Overall, Event A released slightly more energy and shook the ground slightly more intensely than Event B due to its higher magnitude and shallower focus.

(b) Explanation of casualty discrepancy:
- Building standards & technology: Event A occurred in a developed region where buildings are designed with strict seismic codes (e.g., steel reinforcement, cross-bracing, dampers), preventing structures from collapsing. In contrast, Event B occurred in a developing region with poor building quality and non-seismic structures (e.g., mud-brick, unreinforced masonry), causing widespread building collapse, which is the primary cause of death.
- Emergency response & medical care: Event A has highly trained, professional search-and-rescue teams equipped with heavy machinery, and high-capacity hospital networks. Event B lacks advanced rescue equipment and medical infrastructure, leading to slow rescue and higher post-earthquake fatalities.
- Public awareness & warning systems: Event A has a comprehensive disaster education system, regular earthquake drills, and an early warning network. Event B lacks public awareness, disaster education, and warning systems, leading to panic and slow evacuation.
- Economic factor contrast: Event A has much higher economic losses because of the high concentration of high-value infrastructure, expensive properties, and business interruption, whereas Event B has lower-value assets despite massive physical damage.

(c) Evaluation:
- Community preparedness (drills & education):
- Strengths: Highly cost-effective and affordable for developing countries with limited financial budgets; saves lives immediately by teaching people to 'drop, cover, and hold on'; requires minimal advanced technology.
- Limitations: Cannot prevent the physical collapse of buildings. If buildings are structurally unsound, survival rates remain low even with drills.
- Structural engineering measures (seismic design):
- Strengths: Physically prevents building collapse, which is the root cause of both deaths and economic losses.
- Limitations: Extremely expensive to construct or retrofit; requires high technological capacity and capital, which developing countries often lack.
- Conclusion: In developing nations, community preparedness is a highly effective and immediate life-saving strategy due to its low cost, but it must be paired with low-cost, localized structural building regulations to be truly effective.

(a) Max 4 marks:
- Both are strong earthquakes (above 6.0 Mw) / Event A is slightly stronger than Event B (1 mark)
- Both are shallow earthquakes (less than 70 km focal depth) / Event A is shallower than Event B (1 mark)
- Both have small epicentral distances to city centres / Event A is closer than Event B (1 mark)
- Event A has a higher hazard potential / intensity of shaking due to combined higher magnitude and shallower depth (1 mark)

(b) Max 8 marks:
- Building collapse as primary cause of death (1 mark); contrast developed country's strict earthquake-resistant codes (e.g., steel frames, dampers) in Event A with poor, unreinforced masonry structures in Event B (2 marks)
- Search and rescue efficiency: high-tech equipment and trained teams in Event A vs. lack of heavy machinery in Event B (2 marks)
- Medical infrastructure: rapid treatment in Event A vs. overwhelmed healthcare in Event B (1 mark)
- Disaster awareness: early warning and regular drills in Event A vs. lack of education and panic in Event B (2 marks)
- Economic loss explanation: Event A has higher-value properties and economic exposure, leading to higher financial loss despite fewer deaths (1 mark)

(c) Max 6 marks:
- Evaluates community preparedness (max 3 marks): cost-effective, easy to implement in developing countries, reduces panic and immediate casualties (2 marks); but cannot prevent building collapse (1 mark)
- Evaluates engineering measures (max 2 marks): prevents building collapse, provides ultimate safety (1 mark); but too expensive and technologically demanding for developing nations (1 mark)
- Concluding decision/judgment on balanced strategy (1 mark)

(a) Comparison and Explanation:
- Comparison: After urbanisation, peak discharge increased significantly (from 42 to 118 m³/s), lag time shortened drastically (from 4.2 to 1.1 hours), infiltration rate dropped (from 16 to 1.5 mm/hour), and surface runoff increased (from 18% to 72%).
- Explanation: Urban development replaces natural vegetation and soil with impermeable surfaces (e.g., concrete, asphalt). This reduces infiltration and percolation, causing a larger proportion of rainfall to become surface runoff rather than groundwater recharge. Artificial drains and smooth concrete channels speed up the transport of surface runoff into the main river channel, reducing the lag time and concentrating water quickly, which leads to a higher and earlier peak discharge.

(b) Comparison of Strategy X and Strategy Y:
- Strategy X (Hard Engineering):
- Strengths: Highly effective in the short term at the local section by increasing hydraulic efficiency (concrete reduces friction, speeding up water flow) and discharge capacity.
- Weaknesses: Increases flood risk downstream due to high-velocity water delivery; destroys natural river habitats, blocks ecological connectivity, and reduces river aesthetics.
- Strategy Y (Soft Engineering & SuDS):
- Strengths: High environmental sustainability; restores river biodiversity and ecosystems; re-meandering slows flow velocity, reducing downstream flood peaks; permeable pavements and retention ponds promote infiltration and store runoff at source.
- Weaknesses: Requires a large amount of land; less effective during extreme, high-magnitude storm events compared to concrete channels; takes a longer time to establish and manage.

(c) Challenges of implementation in built-up urban areas:
- Land constraints: High-density cities have extremely limited space and high land values. Finding land for retention ponds, wetlands, or re-meandering has immense opportunity costs (competing with housing/commercial developments).
- High retrofitting costs and disruption: Replacing existing conventional drainage and concrete roads with permeable pavements and sustainable drainage systems is very expensive and causes massive disruption to urban traffic and daily life.
- Planning and institutional barriers: Traditional urban planning focuses on rapid water removal. Shifting to soft engineering requires inter-departmental collaboration (e.g., drainage, highways, planning departments) and specialized engineering expertise, which may face bureaucratic resistance.

(a) Max 6 marks:
- Compares data correctly: peak discharge increased, lag time shortened, infiltration decreased, runoff increased (2 marks, must mention specific values to get full marks)
- Explains physical mechanisms: impermeable surface reducing infiltration (1 mark), decrease in groundwater recharge (1 mark), smooth artificial surfaces/channels reducing friction and increasing runoff speed (1 mark), leading to rapid concentration of water and earlier/higher peak (1 mark)

(b) Max 6 marks:
- Strategy X (max 3 marks): increases local water flow speed and capacity (1 mark), but increases downstream flooding risk (1 mark) and causes severe ecological damage/habitat loss (1 mark)
- Strategy Y (max 3 marks): promotes infiltration and source reduction (1 mark), slows water speed and restores biodiversity/aesthetic value (1 mark), but requires extensive land space and has limited capacity during extreme events (1 mark)

(c) Max 6 marks:
- Land scarcity and high land premium in built-up cities limits availability of space for soft engineering (2 marks)
- High financial cost of retrofitting existing concrete infrastructure and disruption to public transit (2 marks)
- Co-ordination issues between government departments and potential resistance to non-traditional engineering practices (2 marks)

Part 1: Urbanisation and Flood Risk. Urbanisation replaces natural vegetation with impermeable surfaces like concrete and asphalt. This significantly reduces infiltration and increases surface runoff. Urban drainage systems, such as storm drains, speed up the delivery of water to the river channel. Consequently, the lag time of the river basin is shortened, and the peak discharge increases, dramatically elevating the risk of flooding in the lower course. Additionally, the clearance of vegetation reduces interception and evapotranspiration, allowing more rainfall to directly enter the drainage basin. Part 2: Evaluation of Soft vs. Hard Engineering. Soft engineering strategies, such as afforestation and floodplain zoning, aim to work with natural processes. They are highly sustainable as they preserve local ecosystems, enhance biodiversity, and have lower capital and maintenance costs. However, they require extensive land area and take a long time to become effective (e.g., trees taking decades to grow). In contrast, hard engineering strategies, such as channelisation and concrete dykes, provide immediate and highly reliable flood protection, which is crucial for densely populated urban centers. However, they are expensive to build and maintain, disrupt aquatic ecosystems, and may worsen flood risks further downstream. Therefore, while soft engineering is environmentally superior, an integrated approach combining both methods is often the most practical and sustainable solution for urbanized river basins.

Part 1: Urbanisation and flood risk (Maximum 6 marks). - Award 1 mark for identifying impermeable surfaces reducing infiltration. - Award 1 mark for explaining increased surface runoff. - Award up to 2 marks for explaining shortened lag time and higher peak discharge. - Award 1 mark for discussing how storm drains accelerate water transport. - Award 1 mark for explaining how vegetation clearance reduces interception and evapotranspiration. Part 2: Evaluation of Soft vs Hard Engineering (Maximum 6 marks). - Award 1 mark for clear definition or examples of both engineering types. - Award up to 2 marks for explaining the strengths of soft engineering (e.g., ecological harmony, lower costs, long-term sustainability). - Award up to 2 marks for explaining the limitations of soft engineering or advantages of hard engineering in urban areas (e.g., large land requirement, slow onset of benefits, necessity of hard engineering for high-density assets). - Award 1 mark for a balanced conclusion or recommending an integrated basin management approach.