DSE Geography | Hong Kong weather hazards lesson plan (for tutors)

DSE Geography | Hong Kong weather hazards lesson plan (for tutors) — where 70 mm an hour comes from

2026-11-04

Tutor lesson-prep guides · Secondary Geography

Students know the black rainstorm signal and signal eight by name but cannot say where the numbers come from, nor why the same rain hits the city and the New Territories differently.

Objectives — Students can: (1) state the annual rainfall of about 2400 mm and the daily average of 6.6 mm, then show that 70 mm in one hour is about 10.6 times that daily average; (2) give the sustained wind range for signal eight, 63 to 117 km per hour; (3) explain different outcomes in urban and rural areas using surface, slope and drainage; (4) name one limit for each of the three layers of risk management.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Monsoon	Which direction does the winter monsoon blow from?	From the interior, north-east
Water cycle	Where does rain go after landing?	Interception, infiltration, surface runoff
Contours	What do closely spaced lines mean?	A steeper slope

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0–10 min	Two numbers	2400 mm a year and 70 mm an hour	Work out the ratio
10–22 min	Monsoon and typhoons	Winter north-east, summer south-west; tracks and signals	Sketch Hong Kong on a map
22–34 min	Rainstorms and drainage	Impervious city surfaces versus farmland and channels	One consequence per surface
34–44 min	Slopes and landslides	Weathered layer, gradient, vegetation, drainage	Name three human factors
44–56 min	Three layers of management	Warning, engineering, planning, one limit each	Write each limit
56–60 min	Exit check	Mark three items on the spot	All three correct

03 Teaching script (read it out)

Scene 1: Do the arithmetic before naming the signal

Hong Kong receives about 2400 mm a year, so the daily average is 6.6 mm. The black rainstorm signal is issued when rainfall exceeds 70 mm in one hour, which is about 10.6 times the daily average falling in a single hour. Signal eight covers sustained winds of 63 to 117 km per hour, a span of 54. Answers with numbers score higher than answers saying the rain was heavy.

Ask students to divide 2400 by 365, then divide 70 by the result.

Scene 2: The same rain, a different surface

Most urban ground is impervious, so nearly all rain becomes surface runoff and the drains fill far faster. Farmland and channels absorb some water, but channels are narrow and meandering, so they overflow too. Hong Kong is steep and built close to slopes, so fast runoff plus saturated soil produces flooding and landslides together. Three factors are needed: impervious surface, gradient and drainage capacity.

Ask how runoff would change with more greenery, and why not immediately.

Scene 3: Risk management has three layers, not one sentence

Warnings come first, limited by forecast uncertainty measured in hours. Engineering follows: channel upgrades, storage tanks, slope stabilisation, limited by cost and space. Planning comes last: land use zoning, restricting steep slope development, reserving flood storage, limited by a ten-year horizon and existing communities. All three layers belong in the answer; one alone earns a third of the marks.

Ask students to name one measure per layer for an old district beside a steep slope.

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	Rainfall ratio	Annual divided by 365, then by 70	About 10.6 times
Explanation	Why urban flooding is worse	Surface, gradient, drainage	All three named
Comparison	Urban versus rural outcomes	Describe each surface and channel	Not rainfall alone
Application	Three layers of management	One measure and one limit each	All three layers

Sanity check (teach this): Check the figures: 2400 divided by 365 is 6.58 mm a day; 70 divided by 6.58 is 10.65, so about 10.6 times is safe to write. Signal eight spans 63 to 117 km per hour, a difference of 54. Typhoons and rainstorms overlap from May to October but have different triggers: pressure gradient and wind speed in one case, convection and moisture supply in the other.

05 Independent practice (3 questions)

Question	Answer	What to watch
How many times the daily average is 70 mm an hour	About 10.6 times	Was 365 used first
Three causes of worse urban flooding	Impervious surface, gradient, drainage capacity	All three present
One measure and one limit per layer	Signals, storage tanks, zoning	Limits stated

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating black rain as a daily total	Black rain means 70 mm fell all day	It is 70 mm in one hour, not a daily total.
Explaining flooding by rainfall alone	It flooded because rainfall passed 70 mm	Same rain, different ground, different outcome.
Mixing typhoon and rainstorm causes	The rainstorm came from typhoon winds	One is wind speed, the other convection and moisture.
Naming only government action	The government should improve drainage	Split it into warning, engineering and planning, each with a limit.

07 Homework (paper, section and question numbers)

Geography subject index — All chapters
Practice paper — Data response: rainfall graph and slope risk

08 Exit check (last 5 minutes)

Question	Answer	Decision
Ratio of 70 mm an hour to the daily average	About 10.6 times	Recalculate if wrong
Three urban flooding factors	Surface, gradient, drainage	One missing: reteach act two
Three management layers	Warning, engineering, planning	Two wrong: restart act three

09 Tutor FAQ

Must every signal be memorised?

Learn the thresholds for black rain and signal eight; know the rest are graded.

Do rainfall figures change yearly?

They vary, so write about the long-term average and use the word about.

Is engineering enough as an answer?

No. A question about management expects all three layers.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.