S5 Geography Paper: Weather, Climate And Tropical Cyclones (100 Marks)

S5 Geography Paper: Weather, Climate and Tropical Cyclones (100 marks)

2026-11-11

S5 Geography – weather and climate

S5 Geography paper on lapse rate, humidity, tropical cyclone winds and surge, runoff and climate change, with answers and marking notes.

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Paper details　S5 Geography practice paper with six questions on lapse rate calculations, relative humidity and dew point, tropical cyclone wind and pressure gradients, storm surge, rainfall types and runoff, the urban heat island and climate change trends. Full answers with working and marking notes are included.

Section A: Air Temperature and the Lapse Rate (18 marks)

The lapse rate is the rate at which air temperature falls with height, usually expressed as degrees Celsius per 1000 metres. Stations at different heights allow the observed value to be compared with the standard figure.

#	Question	Answer and marking notes
1	Define the lapse rate and state the value of the standard environmental lapse rate.	Answer: the lapse rate is the rate at which temperature falls as height increases; the standard environmental lapse rate is 6.5 degrees Celsius per 1000 m. (Marking: 2 marks definition, 2 marks value.)
2	A sea level station records 24.0 degrees Celsius and a hillside station at 700 m records 18.4 degrees Celsius. Calculate the observed lapse rate in degrees Celsius per 1000 m.	Answer: the difference is 24.0 minus 18.4, that is 5.6 degrees; the lapse rate is 5.6 divided by 700 and multiplied by 1000, which is 8.0 degrees per 1000 m. (Marking: 1 mark difference, 2 marks conversion, 1 mark answer with unit.)
3	Assuming the standard environmental lapse rate applies, estimate the temperature at 1000 m above sea level.	Answer: 24.0 minus 6.5 gives 17.5 degrees Celsius. (Marking: 2 marks working, 1 mark answer.)
4	Explain two reasons why the observed lapse rate is higher than the standard environmental lapse rate.	Answer: first, the hillside air is drier, so less latent heat is released on condensation and cooling is faster; second, strong daytime heating generates convection and rising air expands and cools quickly. (Marking: 2 marks per reason with mechanism.)
5	Calculate the temperature difference as a percentage of the sea level temperature and explain what this means for how the hillside feels.	Answer: the percentage is 5.6 divided by 24.0 and multiplied by 100, which is 23.33 per cent, so the hillside is about a quarter cooler than sea level. (Marking: 2 marks working, 1 mark percentage.)

Section B: Humidity, Dew Point and Condensation (17 marks)

Relative humidity shows how close the air is to saturation. As temperature falls the saturation capacity drops, and once the air is saturated the excess vapour condenses as cloud, fog or dew.

#	Question	Answer and marking notes
6	Define relative humidity and state its formula.	Answer: relative humidity is the actual water vapour content expressed as a percentage of the saturation capacity at the same temperature; formula is actual vapour divided by saturation capacity times 100 per cent. (Marking: 2 marks definition, 2 marks formula.)
7	At 30 degrees Celsius the saturation capacity is 30.4 grams per cubic metre and the air actually holds 18.2 grams per cubic metre. Calculate the relative humidity to one decimal place.	Answer: relative humidity is 18.2 divided by 30.4 and multiplied by 100, giving 59.9 per cent. (Marking: 3 marks working, 2 marks answer.)
8	If the air cools to 22 degrees Celsius, where the saturation capacity is 19.4 grams per cubic metre, decide whether condensation occurs and state the dew point using the table values of 17.3 at 20 degrees and 18.3 at 21 degrees.	Answer: no condensation, because the actual content of 18.2 grams per cubic metre is below the saturation capacity of 19.4 at 22 degrees; the dew point is about 21 degrees Celsius. (Marking: 1 mark decision, 1 mark reason, 2 marks dew point.)
9	Calculate the dew point depression, the gap between air temperature and dew point, and explain why a small depression favours fog in the city.	Answer: the depression is 30 minus 21, that is 9 degrees. A small depression means the air is near saturation, so slight further cooling reaches the dew point and vapour condenses into tiny droplets that hang in the air as fog. (Marking: 1 mark calculation, 3 marks explanation.)

Section C: Structure and Impacts of Tropical Cyclones (20 marks)

Tropical cyclones form over warm oceans with a low central pressure, and surrounding air spirals inwards and rises. Wind speed, pressure gradient and storm surge are the main measures of their destructive power.

#	Question	Answer and marking notes
10	List four conditions required for tropical cyclone formation.	Answer: sea surface temperature above about 26.5 degrees Celsius with a deep warm layer; an abundant supply of water vapour; the Coriolis force to set up rotation; low level convergence with upper level divergence and weak vertical wind shear. (Marking: 1 mark each, 1 mark for complete explanation.)
11	A tropical cyclone has a ten minute mean wind speed of 150.0 kilometres per hour, and peak gusts reach about 1.4 times the mean. Calculate the gust speed in kilometres per hour and convert it to metres per second to one decimal place.	Answer: the gust is 150.0 times 1.4, that is 210.0 kilometres per hour, and 210.0 divided by 3.6 gives 58.3 metres per second. (Marking: 2 marks gust, 2 marks conversion.)
12	The central pressure is 950.0 hectopascals and the pressure 300.0 kilometres from the centre is 1010.0 hectopascals. Calculate the pressure gradient per 100 kilometres and explain what a large gradient means for wind strength.	Answer: the difference is 1010.0 minus 950.0, that is 60.0 hectopascals, so the gradient is 60.0 divided by 300.0 and multiplied by 100, giving 20.0 hectopascals per 100 kilometres. A larger gradient means a stronger pressure gradient force and higher wind speed. (Marking: 1 mark difference, 2 marks gradient, 1 mark explanation.)
13	On the day the astronomical tide is 2.1 metres, the storm surge adds 1.6 metres and the pressure effect adds 0.5 metres. Calculate the peak water level and how far it exceeds the 3.5 metre alert level.	Answer: the level is 2.1 plus 1.6 plus 0.5, that is 4.2 metres, and it exceeds the alert level by 4.2 minus 3.5, which is 0.7 metres. (Marking: 2 marks level, 2 marks exceedance.)
14	State two measures the public should take when the number eight gale or storm signal is in force.	Answer: stay indoors away from windows and secure them, and stop water sports, move vessels into typhoon shelters and keep away from the shore and low lying areas. (Marking: 1.5 marks each, must be practical.)

Section D: Rainfall Types and Runoff (15 marks)

Rainfall in Hong Kong is concentrated in summer, when convective, relief and frontal rain all occur. Part of the rain infiltrates the catchment and part becomes surface runoff, and the runoff coefficient expresses that share.

#	Question	Answer and marking notes
15	Name three types of rainfall and identify the main type responsible for summer rainstorms in Hong Kong, with its cause.	Answer: convective, relief and frontal rainfall. Convective rain dominates in summer: strong heating makes surface air rise, vapour condenses into cumulonimbus and short intense rain falls, often with thunderstorms. (Marking: 3 marks for the three types, 2 marks for cause and mechanism.)
16	A station records 2398.0 millimetres of rain in a year, of which 1940.0 millimetres fall from May to September. Calculate the share of the annual total that falls in the wet season.	Answer: the share is 1940.0 divided by 2398.0 and multiplied by 100, which is 80.9 per cent. (Marking: 3 marks working, 1 mark answer.)
17	A catchment covers 12.0 square kilometres, monthly rainfall is 320.0 millimetres and the runoff coefficient is 0.55. Calculate the volume of surface runoff in millions of cubic metres to three decimal places.	Answer: the volume is 12.0 times one million times 320.0 divided by 1000 times 0.55, giving 2112000 cubic metres, or 2.112 million cubic metres. (Marking: 1 mark conversion, 1 mark coefficient, 1 mark answer.)
18	Explain how urbanisation changes the runoff coefficient and raises peak discharge.	Answer: concrete surfaces and buildings reduce infiltration, so the coefficient rises from about 0.3 to above 0.7, and drains deliver water to streams quickly, shortening the lag time so the peak arrives sooner and higher. (Marking: 1 mark infiltration, 1 mark coefficient, 1 mark peak response.)

Section E: Urban Heat Island and Microclimate (16 marks)

The urban heat island is the tendency for city temperatures to exceed those of the surrounding countryside. Building density, surface materials and waste heat make the city absorb more heat by day and release it slowly at night.

#	Question	Answer and marking notes
19	Define the urban heat island effect and state the time of day when it is usually most pronounced.	Answer: it is the tendency for urban temperatures to be higher than the surrounding countryside, and it is clearest at night and early morning because buildings and roads store heat by day and release it slowly after dark. (Marking: 2 marks definition, 2 marks timing with reason.)
20	On the same day the urban maximum is 31.8 degrees Celsius and the rural maximum is 27.4 degrees. Calculate the heat island intensity and express it as a percentage of the rural temperature to one decimal place.	Answer: the intensity is 31.8 minus 27.4, that is 4.4 degrees, and as a percentage of the rural value it is 4.4 divided by 27.4 and multiplied by 100, giving 16.1 per cent. (Marking: 2 marks intensity, 2 marks percentage.)
21	List three causes of the urban heat island effect.	Answer: concrete and asphalt absorb much heat and have a low albedo; dense buildings trap outgoing longwave radiation in street canyons; and air conditioning, traffic and industry release waste heat. (Marking: 1 mark each, 1 mark for quantified detail.)
22	Suggest two measures to relieve urban heat and explain how each works.	Answer: first, add roof gardens and street trees so transpiration cools the air and shade increases; second, use pale high albedo roof materials to cut daytime heat gain and therefore the heat released at night. (Marking: 1 mark per measure, 1 mark per explanation.)

Section F: Climate Change Trends and Impacts (14 marks)

Long records show rising annual mean temperature and sea level in Hong Kong. Trend analysis compares averages over equal periods and distinguishes mitigation from adaptation.

#	Question	Answer and marking notes
23	The 1991 to 2020 mean temperature in Hong Kong is 23.5 degrees Celsius and the 2011 to 2020 mean is 24.1 degrees. Calculate the difference between the two period means.	Answer: the difference is 24.1 minus 23.5, that is 0.6 degrees, so the recent decade is 0.6 degrees warmer than the thirty year mean. (Marking: 2 marks working, 2 marks answer with interpretation.)
24	If sea level rises by 3.2 millimetres a year, calculate the cumulative rise over 30 years in millimetres and in centimetres to one decimal place.	Answer: 3.2 multiplied by 30 gives 96.0 millimetres, which is 9.6 centimetres. (Marking: 2 marks millimetres, 2 marks centimetres.)
25	Explain two impacts of rising temperature and sea level on low lying coastal areas of Hong Kong.	Answer: first, higher water levels when storm surges coincide with spring tides increase flooding in low lying districts; second, salt water intrusion raises salinity in groundwater and soil, affecting farmland and foundations. (Marking: 1.5 marks each with mechanism.)
26	Give one mitigation measure and one adaptation measure, and explain how the two differ in responding to climate change.	Answer: mitigation means cutting greenhouse gas emissions, for example by raising building energy efficiency, and it addresses causes; adaptation means adjusting to impacts already under way, for example raising seawalls and upgrading drainage. Mitigation treats the cause while adaptation treats the symptom, and both are needed. (Marking: 1 mark per example, 1 mark for the distinction.)

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