S1 Geography | Natural Hazards and Response: landslides, flooding and warning signals

S1 Geography | Natural Hazards and Response: landslides, flooding and warning signals – tutor prep guide

2026-11-14

Tutor lesson-prep guides · Secondary Geography

Students can recite black rainstorm and signal eight, but cannot say why Hong Kong suffers so many landslides or why the black threshold is 70 mm an hour. This lesson links causes to thresholds, then sorts every measure into mitigation, preparation or response.

Objectives — Students can: (1) explain landslides by two causes, a steep slope plus intense rain raising soil water content, and flooding by three, intense rain, low-lying land and inadequate drainage; (2) state the amber, red and black rainstorm thresholds of 30, 50 and 70 mm per hour and the wind bands of signals 1, 3, 8 and 10; (3) classify measures as mitigation (slope strengthening, flood storage), preparation (drills, supplies) or response (staying indoors, following broadcasts) with examples.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Contours and gradient	What do closely spaced contours mean?	A steep slope, because height changes a lot over a short horizontal distance
Rainfall units	What does 70 mm per hour mean?	70 mm of rain accumulates in one hour, the black rainstorm level
Hong Kong relief	What landform covers most of Hong Kong?	Hills and uplands, with flat land mainly along the coast and on reclamation

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Three real scenes	Write “crack in a slope”, “water pouring into a station” and “signal eight” and ask which hazard each is	Name landslide, flooding and typhoon
5-16 min	Landslides	Explain steep slope plus intense rain: the soil gains weight and loses cohesion along a slip surface	State both the slope and the rainfall condition
16-28 min	Rainstorms and flooding	Use 30, 50 and 70 mm per hour for amber, red and black, then add low land and drainage	Order the three levels with their thresholds
28-39 min	Typhoon signals	Signals 1 (below 41 km per hour), 3 (41 to 62), 8 (63 to 117) and 10 (above 118)	Match each signal to its wind band
39-43 min	Sorting measures	Place slope works, flood storage, drills and staying home into mitigation, preparation and response	Classify four measures and justify each
43-45 min	Exit check	Collect three items: causes, thresholds, measure classification	Answer and hand in

03 Teaching script (read it out)

Scene 1: Landslides: a steep slope meets intense rain

Two conditions must coincide: a steep slope, where contours are close together so much of the weight acts downslope, and intense rain that raises soil water content. Once the soil soaks up water its weight rises while the cohesion between particles falls, and beyond the critical point it slides along a slip surface. That is why Hong Kong records cluster in the heavy rain days of May to September, and why engineered slopes on natural hillsides can still fail. Three checks: (1) rain alone is not a cause, intense rain saturating the soil is; (2) slope angle must appear, since flat land cannot produce a landslide; (3) human factors such as slope cutting for buildings and blocked drains count too.

Ask for one sentence on why Hong Kong has landslides every rainy season, containing both the steep slope and the intense rain ideas

Scene 2: Rainstorms and flooding: thresholds are numbers

The rainstorm scale uses rainfall per hour, not accumulation: amber at 30 mm, red at 50 mm and black at 70 mm. Seventy millimetres in one hour means a whole mornings rain arrives inside sixty minutes and the drains simply cannot keep up. Flooding still needs low-lying ground, which is why one storm produces landslides on the hills and flooding in coastal and reclaimed districts. Teach the two variables, threshold plus relief, and answers stop saying only that the rain was heavy.

Ask students to order 30, 50 and 70 and state the minimum hourly rainfall for black

Scene 3: Typhoon signals: wind speed sets the number

The numbers are not arbitrary, they are wind bands: signal 1 when a tropical cyclone is within 800 km but winds stay at or below 41 km per hour, signal 3 at 41 to 62, signal 8 at 63 to 117, signal 9 as winds keep strengthening, and signal 10 above 118. Writing that signal eight means 63 to 117 km per hour scores far better than writing strong wind. Measures must match the signal: before eight, secure loose objects near windows and stay indoors, and in low-lying coastal areas watch for storm surge arriving on top of a high astronomical tide.

Ask for the wind band of signal eight and one correct action under that signal

04 Question types and worked steps

Type	Example	Steps	Answer
Explaining causes	Why do landslides occur on natural hillsides in Hong Kong?	(1) Name the steep slope (2) Name saturation by intense rain (3) Weigh gain and cohesion loss (4) Cite the rainy season	Steep slope plus intense rain; the saturated soil fails
Threshold recall	What is the rainfall threshold for the black rainstorm warning?	(1) Recall 30, 50 and 70 (2) Match amber, red and black (3) Attach per hour units	70 mm per hour or more
Signal matching	What sustained wind speed does signal eight represent?	(1) Recall the 41, 63 and 118 divides (2) Attach signals 3, 8 and 10 (3) Give the band	63 to 117 km per hour
Sorting measures	Classify slope strengthening works and explain their purpose.	(1) Identify it as reducing risk before an event (2) Call it mitigation (3) Explain it lowers failure chance	A mitigation measure that lowers risk in advance

Sanity check (teach this): Three checks. First, the number of conditions: a cause question needs at least two, a steep slope with intense rain, or low land with poor drainage, and one alone usually earns half marks. Second, the numbers: 30, 50 and 70 belong to rainfall in millimetres per hour while 41, 63 and 118 belong to wind in kilometres per hour, so never mix the two systems. Third, timing: slope works happen before an event (mitigation), drills happen before (preparation), staying home happens on the day (response), and wrong timing means a wrong category.

05 Independent practice (3 questions)

Question	Answer	What to watch
What two conditions are needed for a landslide?	A steep slope and intense rain saturating the soil	Check both conditions are named
What are the amber, red and black thresholds?	30, 50 and 70 mm per hour	Check the per hour unit
What should you do under signal eight?	Stay indoors, keep away from windows and follow observatory broadcasts	Check it is an action on the day, not preparation

06 Common mistakes and what to say

Mistake	Student writes	Say this
Blaming the rain alone	Hong Kong floods because the rain is too heavy.	Heavy rain is only half the story. Add low-lying relief and drainage that cannot cope, and you have a full answer.
Using accumulated rainfall	Black rainstorm means 70 mm in a day.	It means 70 mm in one hour. The unit is per hour and mixing it up loses marks.
Mixing wind and rain units	Signal eight is 70 kilometres of rain per hour.	Typhoon signals use wind speed in kilometres per hour, rainstorm warnings use rainfall in millimetres per hour.
Wrong timing for a measure	Slope strengthening is a response measure on the day of a typhoon.	Slope works are mitigation done in normal weather. Doing them on the day is far too late, and the category follows the timing.

07 Homework (paper, section and question numbers)

Hong Kong land use and urban development, questions 1 to 3 — Both landslides and flooding relate to land use, so start from hillside and reclamation patterns
Mass movement and slope safety, questions 2 to 4 — Take the S1 causes further into slip surfaces and water content
Secondary Geography index, two timed hazard papers — Twenty minutes timed, with every answer quoting thresholds

08 Exit check (last 5 minutes)

Question	Answer	Decision
What two conditions make a landslide?	A steep slope and intense rain saturating the soil	One condition alone means the causes are incomplete
What is the black rainstorm threshold?	70 mm per hour or more	The unit must be included
Which category covers slope strengthening?	Mitigation, risk is lowered in advance	Answering response means the timing is wrong

09 Tutor FAQ

Should global warming be linked to extreme rainfall here?

One sentence on a rising trend in extreme rainfall is enough. The S1 assessment focus is causes and response, not the mechanics of climate change.

Students confuse signals eight and ten. How do I help?

Build a three-step ladder with 41 for signal 3, 63 for signal 8 and 118 for signal 10. Drawing the ladder once beats memorising prose.

Do all the warning signals need memorising?

At S1 only the three rainstorm levels and signals 1, 3, 8 and 10 are needed. Signal 9 can be described as winds still strengthening.

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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.