DSE Geography | Tropical cyclones and flood risk - tutor prep guide | Four conditions, three layers, four-step answers

DSE Geography | Tropical cyclones and flood risk – tutor prep guide | Four conditions, three layers, four-step answers

2026-11-06

Tutor lesson-prep guides · Secondary Geography

Students can draw the spiral bands, but ask why no cyclone forms at the equator and the answer is that there is no wind. The gap is not memory: the four formation conditions were never treated as a checklist you can tick.

Objectives — Students can: (1) test a sea area against the four formation conditions and name which one fails; (2) label the eye, the eyewall and the spiral bands on a cross-section and describe the weather in each; (3) work out runoff volume as rainfall times area times runoff coefficient and explain the three factors that decide how bad a flood gets.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Pressure and wind	Which way does wind blow?	From high to low pressure, turned right in the northern hemisphere
Sea and land	How warm is the South China Sea in summer?	About 28 to 30 degrees Celsius
Reading maps	What do closely spaced isobars mean?	A steep pressure gradient, so strong wind

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Two satellite images	Show a typhoon beside a temperate cyclone, ask which has an eye	Circle the evidence
8-20 min	Four conditions	Sea temperature, latitude, wind shear, existing disturbance	Mark possible areas on a sea-temperature map
20-32 min	Three layers	Label eye, eyewall, bands with one weather line each	Draw the cross-section once
32-44 min	Runoff equation	Convert rainfall to metres, multiply area and coefficient	Compute 400 mm over 30 km2
44-56 min	Comparing damage	Two districts side by side on four factors	Write three comparisons citing numbers
56-60 min	Exit check	Collect three items, mark at once	Work alone

03 Teaching script (read it out)

Scene 1: Four conditions, all four required

A cyclone forms only when four things hold together: sea surface above 26.5 degrees Celsius, which supplies vapour and convective energy; latitude above 5 degrees, where the Coriolis force is strong enough to make the inflow rotate, because at the equator it is near zero and the inflow simply fills the low; low vertical wind shear, or the rising column is sliced apart at height; and an existing low-pressure disturbance to start the convergence.
Write the four as a vertical checklist with a tick box each, then hand out a real sea-temperature map and have students mark a possible area and explain why the South China Sea qualifies while waters south of Singapore do not. Ticking four boxes produces four mark-earning points; writing the sea is warm produces one.

Ask the student to mark two possible areas and one impossible area, naming the missing condition in each.

Scene 2: Three layers: eye, eyewall, bands

From the centre outwards there are only three parts: the eye (sinking air, clear sky, lowest pressure but weakest wind), the eyewall (deepest convection, strongest wind, heaviest rain) and the spiral bands (intermittent heavy rain further out, weaker wind).
Draw the cross-section before naming anything: leave the centre blank, shade the eyewall darkest, stripe the bands. Then ask for the weather, and the class sees why the passage of the eye is not an improvement but the middle of the worst.
The common error is treating the eye as the windiest part because it looks most dramatic on the image. Lock it with one line: the eye is lowest pressure, weakest wind, no rain; everything strongest sits in the eyewall.

Ask the student to draw the three layers from memory and put one wind, one rain and one pressure fact beside each.

Scene 3: Flooding is not only about rainfall

There is one equation: volume equals rainfall in metres times catchment area in square metres times the runoff coefficient. With 400 mm of rain over 30 square kilometres and a coefficient of 0.7, the runoff is 8,400,000 cubic metres.
The answer, though, needs three factors: rainfall intensity and duration, since short intense bursts do the damage; relief and land use, since urbanisation turns permeable ground into concrete and pushes the coefficient from about 0.3 to 0.7 or higher; and drainage capacity against tide level, since a storm surge holds the water back at the outfall.
Give each factor one real situation so students answer with factors instead of adjectives.

Ask the student to explain why the same storm floods a new town more than farmland, quoting the coefficient.

04 Question types and worked steps

Type	Example	Steps	Answer
Formation conditions	Can a cyclone form in this sea area?	Tick four conditions, name the failing one	Latitude and Coriolis must appear, not just warm sea
Structure labelling	Label eye, eyewall, bands on a cross-section	Centre outwards, then weather for each	Eye: sinking, clear, light wind; eyewall: strongest
Data calculation	Find the runoff volume	Rainfall to metres, times area, times coefficient	Consistent units, answer in cubic metres
Impact evaluation	Compare flood severity in two districts	Rainfall, relief, urbanisation, drainage	Every point cites data, not just more severe

Sanity check (teach this): Sanity check: each of the four conditions must be locatable on a map, or the lesson becomes recitation; the cross-section must be drawn by hand once, or only nouns survive; one equation is taught, but units are written three times, because the marks in a calculation item sit in the middle steps.

05 Independent practice (3 questions)

Question	Answer	What to watch
Four conditions	Two sea areas, say whether and what is missing	Whether the student only writes warm enough
Cross-section	Three layers from memory plus one weather fact each	Whether eye and eyewall are swapped
Runoff	450 mm, 20 km2, coefficient 0.6	Unit conversion and decimal places

06 Common mistakes and what to say

Mistake	Student writes	Say this
Cyclones form at the equator	Singapore is hot, so typhoons form there	The sea is warm enough, but what is the Coriolis force at that latitude? Without spin the low just fills.
Eye equals strongest wind	The eye is the most dangerous part	The eye is sinking air, no cloud, no rain. Where is the heaviest rain? Look at the eyewall.
Rainfall alone means flooding	It rained 400 mm so it must flood	Does 400 mm on a hill behave like 400 mm on a drained reclamation? What are the other two factors?
No unit conversion	Multiplying 400 by 30 directly	Millimetres and square kilometres must become metres and square metres first, or the answer is out by a million.

07 Homework (paper, section and question numbers)

Secondary Geography index — All chapters for this subject
Prep guides index — Matching chapters in other subjects
Redo this chapter — Test three sea areas and compute one runoff volume

08 Exit check (last 5 minutes)

Question	Answer	Decision
Four formation conditions	Sea above 26.5 C, latitude above 5 degrees, low shear, existing disturbance	Missing one means back to act one
Three layers and their weather	Eye clear and calm, eyewall strongest, bands intermittent	Swapping eye and eyewall means repeat act two
Three flood factors	Rainfall intensity, relief and land use, drainage and tide	Rainfall only means back to act three

09 Tutor FAQ

Must students memorise 26.5 degrees?

Yes as a decision threshold, but say it is approximate; the reasoning matters more than the decimal.

What if there is no sea-temperature map?

An annual mean map plus latitude lines is enough; the skill being trained is placing conditions on a map, not reading charts.

Should landslides be taught separately?

Separately, but close the loop: both are triggered by intense rain and differ in slope and soil, so the same equation extends.

Find a tutor — free Tutor Registration →

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.