IGCSE Environmental Management Topic 6: Natural Hazards

6.1 Earthquakes and Volcanoes 6.2 Tropical Cyclones 6.3 Flooding 6.4 Drought

Hi Tara. Topic 6 looks like four separate topics — earthquakes and volcanoes, cyclones, floods, drought — and it is really one topic taught four times. Put the four sub-topics side by side and you find that 6.1, 6.2 and 6.3 share almost the same list of impacts and almost the same list of management strategies. Eight impacts appear in all three. Seven management strategies appear in all three. That is not padding on Cambridge’s part; it is a framework, and once you have it you can answer a question about a hazard you have never studied.

So this guide teaches the framework once, properly, in 6.1. Then 6.2 and 6.3 only tell you what is different about that hazard — what it adds to the list, what it drops, and which strategy matters most for it. Drought is genuinely different and gets its own treatment in 6.4. Doing it this way means less to learn and more that transfers, which is what the exam actually rewards, because Paper 2 will hand you an unfamiliar event.

Three details are worth flagging before you start. Focus and epicentre get confused every single year: the focus is underground where the rock breaks, the epicentre is the point on the surface directly above it. Land use zoning appears for earthquakes and for flooding but is not on the cyclone list — check each list rather than assuming they are identical. And the objectives most students skip, 6.1.10 the opportunities volcanoes give people and 6.3.5 the opportunities flooding gives people, are exactly where the balanced-evaluation marks are hiding. Nobody who only knows the damage can write a good “discuss” answer.

One note on how this is written. Natural hazards invite dramatic language, and dramatic language scores nothing. Cambridge marks mechanisms and magnitudes: how the harm happens, to what, and how much. So you will find “buildings collapse because the shaking makes the ground move sideways faster than the walls can flex” rather than adjectives. Write it the same way.

6.1 Earthquakes and Volcanoes ▼

▶ Watch: 6.1 Earthquakes and Volcanoes

Opens on YouTube in a new tab. The IGCSE 0680 videos follow the OLD chapter numbering, where this topic was Chapter 6, Managing Natural Hazards — the content matches this topic. The last two are general geography, not 0680 lessons, chosen for one diagram each. Nothing here teaches 6.3 Flooding or 6.4 Drought directly — those sub-topics are on the page above and nowhere in this list.

The structure of the Earth (6.1.1)

Three layers, and the syllabus says limited to those three, so three is all you need. What matters is not the list but the chain that runs from the bottom layer to the hazards at the top: the core is hot, that heat drives convection currents in the mantle, those currents move the plates of the crust, and moving plates cause earthquakes and volcanoes. Every “explain” question in 6.1 is a piece of that chain.

Layer	What it is like	Why it matters here
crust	the thin outer layer of solid rock, on which everything lives; broken into tectonic plates	The plates are pieces of it, so all the movement you can feel happens here.
mantle	the thick layer beneath the crust, made of very hot rock that can flow slowly	Convection currents in the mantle are what drag the plates about.
core	the innermost part, the hottest of the three	Its heat is the energy source that keeps the mantle convecting.

Learn the right-hand chain as four sentences. It is the answer to most “explain why” questions in this sub-topic.

The continents and where the hazards are (6.1.2, 6.1.3)

6.1.2 asks you to identify seven continents: Africa, Antarctica, Asia, Europe, North America, Oceania and South America. Learn those seven names and be able to point at them on a map, because a source in Paper 2 may simply name one and expect you to know where it is.

6.1.3 then asks you to describe and explain the distribution of earthquakes and volcanoes. The answer is short and it earns marks for being precise: they are not spread evenly — they occur in narrow lines and belts, and those belts follow the boundaries of the tectonic plates. Name real ones if you can: the belt round the edge of the Pacific Ocean, the line down the middle of the Atlantic, and the belt running from the Mediterranean eastwards through Asia.

The exception is a hotspot: a place where unusually hot magma rises through the middle of a plate, far from any boundary, producing volcanoes in the interior of an ocean or a continent. Because the plate keeps moving over the fixed hotspot, a chain of volcanoes is built, with the oldest at one end. Hotspots are the reason you should never write “all volcanoes are at plate boundaries”.

Four belts and one hotspot. Notice that the belts run along lines, which is the whole of the answer to “describe the distribution”.

Plate boundaries (6.1.4) — the diagram that carries the sub-topic

Convection currents in the mantle move the plates, and what happens where two plates meet depends entirely on which way they are moving relative to each other. There are three cases and each produces a different hazard. This is the highest-value thing in Topic 6: get the three straight and a large part of 6.1 answers itself.

Boundary	Movement	What happens	Hazards produced
divergent (also called constructive)	the two plates move apart	Magma rises into the gap and cools to form new crust, building a ridge of volcanoes along the line.	volcanic activity and earthquakes. The earthquakes are generally shallow.
convergent (also called destructive)	the two plates move towards each other	Subduction: one plate is forced down beneath the other into the mantle, where it melts. The molten rock rises through the plate above.	earthquakes and a line of volcanoes running parallel to the boundary.
conservative	the two plates slide past each other	The plates lock together, stress builds, and eventually they jerk past one another. No crust is made and none is destroyed.	earthquakes only. No volcanoes, because no plate is being melted and no gap opens for magma.

Two words that decide the answer

Apart, towards, past. Apart makes new crust (constructive). Towards destroys crust by subduction (destructive). Past conserves crust — nothing made, nothing lost — which is where the word conservative comes from. And if the question mentions volcanoes at all, the boundary is not conservative.

Panels 1 and 2 are cross-sections through the crust. Panel 3 is drawn looking down from above, which is the only way to show sliding.

Features of earthquakes (6.1.5)

Four items, and the middle two are the pair that costs marks every year.

Feature	What it means
release of energy	Plates lock against each other and stress builds in the rock. When the rock finally fractures and moves, the stored energy is released as seismic waves that travel out in all directions and shake the ground.
focus	The point underground where the rock breaks and the energy is released. Sometimes called the hypocentre.
epicentre	The point on the ground surface directly above the focus. It is where the shaking is usually strongest, because the waves have the shortest distance to travel.
magnitude	How much energy the earthquake released, measured on the Moment Magnitude Scale. The scale is not linear: each whole step up represents a much larger release of energy, so a magnitude 7 event is far more than one seventh more powerful than a magnitude 1.

Focus, epicentre

Focus is deep, epicentre is on the surface. Think of the “epi” in epicentre as meaning on top of — the epicentre sits on top of the focus. If a diagram asks you to label them, the focus is the dot inside the rock and the epicentre is the dot on the ground vertically above it. Getting them the wrong way round is the single most common error in 6.1.

One point underground, one point on the surface immediately above it.

Features of volcanic eruptions (6.1.6)

Feature	What it is, and why it matters
magma rising to form lava	Molten rock below the surface is called magma; once it reaches the surface it is called lava. Same material, different name either side of the ground. Lava flows destroy what is in their path but move slowly enough that people can usually walk away.
ash	Fine fragments of rock thrown into the air. Ash falls over large areas, collapses roofs under its weight, blocks drains, damages engines and aircraft, blankets crops so they cannot photosynthesise, and is harmful to breathe.
gases	The syllabus names three: water vapour, carbon dioxide and sulfur dioxide. Carbon dioxide is denser than air and can collect in hollows. Sulfur dioxide is the one that leads to the next row.
acid rain	Sulfur dioxide released by the eruption dissolves in water droplets in the atmosphere to form an acidic solution, which falls as acid rain. It damages leaves, lowers the pH of soils and lakes, and corrodes stonework and metals.
volcanic bombs	Large lumps of molten or solid rock thrown out of the vent. They travel fast, land some distance away, and cause damage and injury on impact.
pyroclastic flows	A fast-moving mixture of very hot gas, ash and rock fragments that flows down the side of the volcano. It moves far faster than a person can run and is the feature responsible for the greatest loss of life in explosive eruptions.

Impacts of tectonic events (6.1.7) — the framework

Here is the list, and this is the one to learn thoroughly, because eight of these ten items reappear word for word in the cyclone and flooding sub-topics. Learn it once here with the mechanism attached, and 6.2 and 6.3 become short.

Impact	The mechanism — the “because” that earns the mark	Shared with 6.2 and 6.3?
damage to buildings and infrastructure	Ground shaking moves foundations sideways faster than walls can flex, so structures crack and collapse; roads, bridges, pipes and power lines break, which also stops help arriving.	shared
loss of crops, livestock and habitats	Ash blankets fields and blocks light so crops cannot photosynthesise; lava and pyroclastic flows destroy vegetation outright; animals are killed or their habitat is buried.	shared
evacuation of people and livestock	People and animals have to be moved out of the danger zone, which means lost homes, lost income, crowded temporary accommodation and animals that cannot be fed or milked.	shared
fire	Broken gas pipes and damaged electrical cables ignite, and fires spread through damaged buildings while broken water mains leave nothing to fight them with.	tectonic only
tsunamis	An earthquake beneath the sea floor displaces a large volume of water, which travels outwards and rises into destructive waves as it reaches shallow coastal water.	tectonic only
landslides	Shaking loosens rock and soil on slopes so that they fail and slide downhill, burying land and blocking roads and rivers.	shared
contamination of drinking-water supplies	Broken sewers mix with broken water mains; ash and debris enter reservoirs and wells. The supply is unsafe exactly when demand is highest.	shared
water-related disease	Drinking contaminated water spreads diseases such as cholera and typhoid, and crowded shelters with poor sanitation let them spread quickly.	shared
financial losses	Rebuilding costs, lost business while premises are shut, lost harvests, lost tourism, and insurance payments. Losses continue long after the event.	shared
human health	Injuries from collapsing structures, breathing problems from ash, disease from contaminated water, and the effects on mental health of losing homes and relatives.	shared

Managing the impacts (6.1.8, 6.1.9) — the framework

The same applies here: seven of these eight strategies reappear for cyclones and floods. Organise them by when they act — before, during, after — because that is how the objective is phrased and it stops you writing rebuilding as a preparation.

When	Strategy	What it involves
before	monitoring and warning	Instruments watch for the signs — ground swelling, small tremors, gas emissions before an eruption — and a warning system alerts people.
	land use zoning	Laws that decide what may be built where: no housing or hospitals on the most dangerous ground, which is kept for parks, car parks or farmland.
	structure of buildings	Designing buildings to survive the shaking — deep foundations, reinforced frames, cross-bracing, and lighter roofs that do less harm if they fall.
	disaster preparation	Emergency plans, practice drills, stockpiles of water, food and medical supplies, and trained rescue teams ready to be sent.
during	evacuation	Moving people out along planned routes to a safe distance once a warning is given.
during	shelters	Strong buildings people can move into, supplied with water, sanitation and medical care.
after	rebuilding of damaged areas	Restoring homes and services, ideally to a better standard and in safer places than before.
after	international aid	Money, supplies, equipment and specialist teams sent by other countries and organisations.

6.1.9 then asks you to discuss the benefits and limitations of those strategies. Both sides, properly. This table is the answer to a six-mark question and, because seven of the eight rows carry over, it is the answer to the equivalent question in 6.2 and 6.3 as well.

Strategy	Benefits	Limitations
monitoring and warning	Volcanoes give measurable warning signs over days or weeks, so an eruption can often be predicted well enough to evacuate. Saves lives at a relatively low cost once the instruments are installed.	Earthquakes cannot currently be predicted with useful accuracy — a warning arrives seconds before the shaking, not days. Equipment and trained staff are expensive, so poorer regions may have sparse coverage. A warning only works if people receive it and act on it, and a false alarm makes them less likely to act next time.
land use zoning	Removes people from the most dangerous ground altogether, which is the most reliable way to reduce deaths, and it costs little to enforce on land that is not yet built on.	Only works for new development; existing cities are already there. Volcanic soils and river valleys are exactly where people want to live, so pressure to build is strong. It needs land records, planning law and enforcement, which many places do not have.
structure of buildings	Protects people where they live and work, without requiring them to move or to receive a warning. A well-designed building keeps working through an event that would flatten an ordinary one.	Costs considerably more to build, so the poorest are least likely to have it, and they are usually the most exposed. Existing buildings must be strengthened, which is expensive and disruptive. Standards are only as good as the inspection that enforces them.
disaster preparation	Drills mean people react correctly in the first minutes, which is when most lives are saved or lost. Stockpiles and trained teams shorten the delay before help arrives.	Needs continuous funding and repetition for events that may not happen for decades, so attention drifts. Supplies expire and stores need replacing. Plans made on paper may not survive the loss of the roads they assumed.
evacuation	Physically removes people from the hazard, so it can prevent nearly all deaths if there is enough warning time.	Needs roads that are usable and enough time to use them. People are reluctant to leave homes, animals and possessions. Evacuated areas may be looted, and moving a large population creates its own problems of shelter, water and disease.
shelters	Give immediate protection, and can be stocked and staffed in advance. One strong building can protect a large number of people.	Expensive to build and maintain for rare use. Crowding spreads infection, sanitation is hard, and people may not go if the shelter is far away or will not take their livestock.
rebuilding	Restores homes, services and the local economy, and is the opportunity to build to a better standard and in a safer place.	Very expensive and slow, often taking years. If it is done quickly and cheaply the same vulnerability is rebuilt, and if it is done well people may be housed elsewhere for a long time. Deciding who pays is politically difficult.
international aid	Brings money, equipment and specialist skills that the affected country may not have, quickly, and can fund reconstruction beyond local means.	Can be slow to arrive and poorly matched to what is needed; unsolicited goods block ports and airports. Aid may bypass local organisations and weaken them, and long-term dependence on aid is a genuine risk. Attention and funding fall away once the event leaves the news.

The judgement sentence for a management question

“Discuss” needs both sides and a conclusion. A reliable one: “No single strategy is sufficient, because each fails in a different way. Monitoring only helps if there is warning time, building design only helps those who can afford it, and evacuation only helps if the roads hold. The most effective approach combines a strategy that acts before, one that acts during and one that acts after.” That sentence works for any hazard in Topic 6.

The opportunities volcanoes give people (6.1.10)

This is the objective most students skip, and it is the reason people live beside volcanoes at all. If you cannot say why anyone would choose to, you cannot write a balanced answer about managing the risk.

Opportunity	How it works
fertile soils	Weathered volcanic ash and lava release mineral nutrients into the soil, so farmland near volcanoes gives high yields. This is the main reason for dense rural populations on volcanic slopes.
extraction of minerals	Volcanic and geothermal activity concentrates minerals including sulfur, copper, gold and silver, which can be mined.
building materials	Volcanic rock is quarried for stone, aggregate and cement, and volcanic ash has long been used in construction.
geothermal power	Hot rock near the surface heats water to steam, which drives turbines to generate electricity, and hot water can be piped directly to heat homes. The energy is renewable and low in carbon dioxide emissions.
tourism	Volcanoes attract visitors for the landscape, hot springs and guided climbs, bringing income and jobs to areas that may have few other industries.

Worked example Explain why many people continue to live on the slopes of an active volcano. [4]

Step 1 — lead with the strongest reason and give its mechanism

Volcanic soils are fertile, because weathered ash and lava release mineral nutrients, so crop yields are high and a small area of land can support a family. For a farming household that is a decisive advantage.

Step 2 — add income from the volcano itself

There is work in tourism, in quarrying building materials and in mining minerals concentrated by volcanic activity, and geothermal power can supply cheap electricity and heat locally.

Step 3 — the risk judgement, which is the fourth mark

Eruptions are infrequent compared with a human lifetime, so the benefits are received every year while the risk is occasional. Add that many people have family, land and no realistic means of moving elsewhere, so it is not a free choice.

Fertile soils and yearly income against an occasional risk, plus limited ability to move.

Use this figure for Question 5 below. Work from the arrows alone.

Checkpoint 6.1

Answer, then read the explanation even when you were right.

Your Score 0 / 12

Question 1

What causes the tectonic plates of the crust to move?

A the pull of the Moon on the solid rock of the crust

B convection currents in the mantle below the crust

C the energy released by earthquakes along a boundary

D the rotation of the Earth once on its axis each day

Heat from the core drives convection in the mantle, and those currents drag the plates. C reverses cause and effect — earthquakes are what plate movement produces, not what produces it. A and D are real forces acting on the Earth but neither moves plates, and D is the one people reach for because rotation feels powerful.

Question 2

Which best describes the world distribution of volcanoes?

A spread fairly evenly across all seven of the continents

B found only in the tropics, where the crust is warmest

C scattered at random, with no pattern that can be seen

D in narrow belts that follow the edges of the plates

Belts, not a scatter, and the belts sit on plate boundaries — the word to use is “uneven”. B invents a link with climate that does not exist; the crust is not warmer at the Equator in any relevant sense. A and C are both versions of “no pattern”, which is precisely what the map disproves.

Question 3

A chain of volcanic islands lies in the middle of an ocean plate, thousands of kilometres from any boundary. What explains it?

A a hotspot, with the plate moving slowly over it

B a conservative boundary hidden below the sea bed

C subduction of the plate beneath its own thin crust

D an ocean trench formed where two plates collide

A hotspot is magma rising through the middle of a plate, and because the plate keeps moving over it a chain is built with the oldest volcano at one end. B would give earthquakes but no volcanoes, so it cannot explain islands. C is not a thing that happens — a plate cannot subduct beneath itself. D describes a convergent boundary, which the question has ruled out.

Question 4

At a convergent plate boundary, why does a line of volcanoes form on the plate that is not subducted?

A because a gap opens between the plates and fills with magma

B because friction between the plates sets the surface rocks alight

C because the subducted plate melts and the molten rock rises

D because the two plates lock together and then jerk suddenly

One plate is forced down into the hot mantle, melts, and the molten rock is less dense so it rises through the plate above. A describes a divergent boundary. D describes what happens at a conservative one and gives earthquakes only. B sounds mechanical but rock does not burn, and friction at depth melts rock rather than igniting it.

Question 5

Look at the three-panel diagram above. In which boundary would you expect earthquakes but no volcanic activity?

A boundary A, because the plates are moving towards each other

B boundary B, because the plates are sliding past each other

C boundary C, because the plates are moving away from each other

D none of them, since all plate boundaries produce volcanoes

In B the arrows are parallel and opposite, so the plates slide past one another: no plate is destroyed and no gap opens, so there is nothing to melt and nothing to fill. That is a conservative boundary. A has arrows meeting, which gives subduction and a line of volcanoes. C has arrows separating, which lets magma rise into the gap. D is the assumption the question is built to catch.

Question 6

Which pair of statements about an earthquake is correct?

A The focus is on the surface; the epicentre is below it.

B The focus and the epicentre are two names for one point.

C The epicentre is where the magnitude scale is measured.

D The focus is underground; the epicentre is above it.

The rock breaks at the focus, underground, and the epicentre is the point on the surface vertically above it. A is the same two words swapped over, which is the mistake examiners look for. B ignores the whole distinction. C sounds technical but magnitude is a property of the earthquake as a whole and is calculated from recordings taken at many stations.

Question 7

Which volcanic gas leads to the formation of acid rain?

A sulfur dioxide, which dissolves in water droplets

B water vapour, which condenses to form the raindrops

C carbon dioxide, which is denser than the air around it

D volcanic ash, which is carried a long way by the wind

Sulfur dioxide dissolving in atmospheric water droplets gives the acidic solution that falls as acid rain. B supplies the water but does not make it acidic. C is one of the three named gases and its density is a genuine hazard in hollows, but it is not the acid rain route the syllabus asks for. D is not a gas at all.

Question 8

Which feature of an eruption is a fast-moving mixture of hot gas, ash and rock?

A a lava flow moving down the side of the volcano

B a volcanic bomb thrown some distance from the vent

C a pyroclastic flow travelling down the volcano side

D an ash cloud drifting downwind from the eruption

A pyroclastic flow combines all three materials and moves faster than a person can run, which is why it causes the greatest loss of life. A is molten rock only and usually moves slowly enough to escape on foot. B is a single lump of rock. D is ash alone, which is dangerous over a wide area but is not a flow down the slope.

Question 9

Which impact appears in the list for tectonic events but not in the lists for cyclones or flooding?

A contamination of the supplies of drinking water

B tsunamis generated by movement of the sea floor

C landslides on slopes loosened by the disturbance

D evacuation of people and of livestock from an area

Tsunamis and fire are the two impacts unique to 6.1; everything else on that list also appears under cyclones and flooding. A, C and D are all in the shared eight. Knowing which items are shared is worth doing deliberately, because it tells you when you can reuse an answer and when you cannot.

Question 10

What is the main limitation of monitoring and warning as a way of managing earthquakes?

A The instruments needed have not yet been invented.

B Warnings are ignored by nearly everyone who gets one.

C Monitoring works for volcanoes but not for landslides.

D Earthquakes give almost no useful warning beforehand.

This is the contrast worth learning: a volcano usually swells, trembles and gives off gas for days or weeks, so monitoring can give real warning, whereas an earthquake gives seconds. A is false — the instruments exist, they simply cannot predict the timing. B overstates human behaviour, though repeated false alarms genuinely do reduce response. C introduces landslides, which the question did not ask about.

Question 11

Which is the strongest limitation of land use zoning in an area that is already a large city?

A The buildings at risk are there already and cannot be moved.

B Zoning costs more per person than strengthening buildings.

C Zoning laws cannot be enforced anywhere without satellites.

D The most hazardous ground is usually the least fertile land.

Zoning is a planning tool and works on land not yet built on, so it does very little in an existing city. B is the reverse: zoning is normally the cheaper option, which is exactly why it is attractive for new development. C invents a requirement. D is backwards — volcanic slopes and river floodplains are usually the most fertile land, and that is why people build there.

Question 12

Which opportunity provided by volcanoes gives a renewable source of electricity?

A quarrying volcanic rock for aggregate and cement

B mining the sulfur and copper concentrated by magma

C geothermal power from hot rock beneath the surface

D guided climbs and hot springs that attract visitors

Hot rock near the surface turns water to steam, which drives turbines, and the heat keeps being supplied, so it is renewable and produces little carbon dioxide. A, B and D are all genuine opportunities from 6.1.10, but quarrying and mining remove a finite resource and tourism produces income rather than electricity.

6.2 Tropical Cyclones ▼

▶ Watch: 6.2 Tropical Cyclones

Now the framework starts paying you back. 6.2 has four objectives, and two of them — impacts, and management strategies — are almost the same lists you learned in 6.1. So this section spends its time on the one thing that is genuinely new, the conditions a cyclone needs in order to form, and then tells you precisely what changes when you carry the framework across. Read the differences carefully; they are where the marks are.

Where cyclones form, and what they need (6.2.1)

First, the names. Storms, hurricanes and typhoons are the same kind of event under different regional names — hurricane in the Atlantic and eastern Pacific, typhoon in the western Pacific. Cambridge groups them together as tropical cyclones, so do not treat them as three different hazards.

Then three numbers, and they are the kind of thing a one-mark question is made of. Learn them exactly:

Three numbers: 5 to 30, 27, 60

A tropical cyclone forms between 5° and 30° latitude north or south of the Equator, over ocean with a surface temperature of at least 27 °C and a depth of at least 60 m. Not near the Equator itself, not in cool water, and not over shallow water.

Two shaded bands, a gap along the Equator, and warm deep water underneath.

Impacts (6.2.2) — the framework, plus one

Compare the cyclone list with the tectonic list you already know. The eight shared impacts are there again: damage to buildings and infrastructure, loss of crops, loss of livestock and habitats, evacuation of people and livestock, landslides, contamination of drinking-water supplies, water-related disease, financial losses and human health. What is different?

Difference	Detail
flooding is added	Cyclones bring extremely heavy rainfall and drive sea water inland ahead of the storm, so flooding is on the cyclone list where it is not on the tectonic one. In many cyclones the water causes more harm than the wind, which is a good point to make in an extended answer.
fire and tsunamis are dropped	Both were specific to tectonic events. Do not import them.
the mechanisms change even where the impact is the same	Buildings are damaged by wind and by water rather than by shaking — roofs are lifted off, windows broken by flying debris, walls undermined by flood water. Crops are flattened and salt water ruins farmland. Landslides are triggered by saturated soil rather than by shaking.

Same impact, different because

“Damage to buildings” scores the same in both sub-topics, but the explanation does not. Shaking for an earthquake; wind, debris and water for a cyclone; water and undermined foundations for a flood. If a question says explain, the mechanism is the mark and the impact is just the heading.

Managing the impacts (6.2.3, 6.2.4)

Now the detail that catches people out. The cyclone list has seven strategies, not eight: land use zoning is not on it. Everything else carries over unchanged — monitoring and warning, structure of buildings, disaster preparation, evacuation, shelters, rebuilding of damaged areas, and international aid. Check the list rather than assuming, because a question asking for strategies “from the syllabus list” is marked against that list.

Strategy	What is different about it for a cyclone
monitoring and warning	This is the strategy that works best here. Satellites see a cyclone form and track it, so its likely path and time of landfall can be forecast days in advance. That is a completely different situation from an earthquake, and it makes everything downstream possible.
structure of buildings	The design problem is wind and water, not shaking: roofs fixed down and steeply pitched, shutters over windows, and in coastal areas houses raised on stilts above flood level.
disaster preparation	Plans, drills, stockpiles and rescue teams, as before — but because the warning is measured in days, preparation extends to boarding up buildings, moving boats and livestock, and stocking shelters before the storm arrives.
evacuation	Realistic and widely used, because there is warning time and a known path. Large populations are moved inland or to higher ground along planned routes.
shelters	Purpose-built cyclone shelters, often raised on pillars above the expected flood level and strong enough to resist wind, sited within walking distance of the villages they serve.
rebuilding	The chance to rebuild to the wind and flood standards described above rather than restoring what blew down.
international aid	As in 6.1: money, supplies, equipment and specialist teams from other countries and organisations.

For 6.2.4, the benefits and limitations are the ones in the 6.1 table — that is the point of a framework — with two adjustments worth making explicitly, because they change the judgement:

Monitoring and warning is far more effective here than for earthquakes, because days of warning make evacuation and preparation possible. Its limitations are different too: forecast tracks have real uncertainty, so a wide area has to be warned, and a storm that turns aside leaves people who evacuated for nothing and are more reluctant next time.
Evacuation is more feasible but harder to complete. There is time, but a cyclone can affect a very large area, so a great many people must move at once along roads that may already be flooding, and people are reluctant to leave livestock and property behind.

Worked example Explain why deaths from tropical cyclones have fallen in some countries even though the storms have not become weaker. [4]

Step 1 — the strategy that starts the chain

Monitoring and warning. Satellites track the storm and forecast where and when it will make landfall, so warnings can be issued days ahead.

Step 2 — what the warning makes possible

The warning time allows evacuation of the coast and the movement of people into shelters raised above flood level, so far fewer people are in the path when the storm arrives.

Step 3 — the slower, structural change

Building structure and disaster preparation: houses on stilts with fixed roofs and shutters, practised drills, stockpiles and trained rescue teams reduce both the initial deaths and those that follow from injury and disease.

Step 4 — note what has not improved

Financial losses have often risen over the same period, because there is more property in the path than there used to be. Deaths and damage are two different measures, and saying so shows you are reading the question rather than reciting a list.

Warning time converted into evacuation, shelters and preparation, plus better-built housing — with damage costs still rising.

Checkpoint 6.2

Answer, then read the explanation even when you were right.

Your Score 0 / 8

Question 1

Which ocean conditions are needed for a tropical cyclone to form?

A surface at least 27 °C and water at least 60 m deep

B surface at least 17 °C and water at least 60 m deep

C surface at least 27 °C and water no more than 60 m

D surface at least 37 °C and water at least 16 m deep

Both numbers are minimums: 27 °C and 60 m. C keeps the right temperature but turns the depth into a maximum, which is the trap — a cyclone needs a deep layer of warm water, not a shallow one. B and D change the temperature; 37 °C does not occur as an open-ocean surface temperature.

Question 2

Between which latitudes do tropical cyclones form?

A between 0° and 30° north or south of the Equator

B between 30° and 60° north or south of the Equator

C between 5° and 30° north or south of the Equator

D between 5° and 60° north or south of the Equator

The band is 5° to 30°, so there is a gap along the Equator itself. A is the answer most people give from memory because they picture “the tropics” as starting at the Equator; the missing 5° is exactly what the question is testing. B puts the band too far from the Equator, where the sea is too cool, and D stretches it too far.

Question 3

What is the relationship between hurricanes, typhoons and tropical storms?

A They form at three different ranges of latitude.

B They are the same event named by the region.

C They are three stages in the life of one storm.

D They occur over land, sea and coast in that order.

Cambridge groups all three under tropical cyclones; the different words are regional names. C is a plausible-sounding idea — storms do intensify — but the three words are not defined as stages in this syllabus. A and D invent distinctions that do not exist.

Question 4

Which impact is listed for tropical cyclones but not for tectonic events?

A landslides on slopes above the affected area

B loss of crops, livestock and their habitats

C contamination of the drinking-water supply

D flooding of low-lying land near the coast

Flooding is the one addition to the cyclone list, caused by heavy rainfall and by sea water driven inland. A, B and C are all in the eight impacts shared across the three hazards. Working out what is added and what is dropped is quicker than learning three lists separately.

Question 5

Which management strategy is listed for earthquakes and for flooding, but not for tropical cyclones?

A providing shelters for people to move into

B rebuilding of the areas that were damaged

C land use zoning to control what is built

D disaster preparation, including drills

The cyclone list has seven strategies; land use zoning is the one missing. A, B and D are on all three lists. It is worth writing the three lists side by side once, because this is exactly the kind of detail an examiner can test in a single mark.

Question 6

Why is monitoring and warning more effective for cyclones than for earthquakes?

A A cyclone can be tracked for days before it arrives.

B A cyclone affects a much smaller area of the land.

C A cyclone causes less damage to roads and bridges.

D A cyclone occurs at the same time every single year.

Warning time is the whole difference: satellites see a cyclone form and forecast its path days ahead, where an earthquake gives seconds. B is the reverse of the truth, since cyclones affect very wide areas. C is not generally true. D confuses a season, which is broadly predictable, with a date, which is not.

Question 7

Which is a genuine limitation of evacuating a coast before a cyclone?

A There is rarely enough warning time to move anyone.

B Evacuation cannot reduce the number of deaths at all.

C Moving people increases the damage done to buildings.

D Roads may flood and people will not leave livestock.

Evacuation depends on usable roads and on people being willing to go, and both fail in practice. A describes earthquakes, not cyclones. B is the opposite of the evidence — evacuation is the main reason death tolls have fallen. C confuses evacuation with the storm; the wind damages buildings whether people are inside or not.

Question 8

Explain the route by which a cyclone leads to water-related disease.

A Strong winds carry bacteria inland from the open sea.

B Flood water mixes with sewage and enters the supply.

C Salt water damages crops and people become undernourished.

D Heavy rain cools people and lowers their resistance.

Flooding carries sewage into wells and mains, so drinking water is contaminated and diseases such as cholera and typhoid spread — and crowded shelters help them spread. C describes a real chain from cyclone to poor health, but the syllabus lists that under loss of crops rather than water-related disease. A and D are not mechanisms the syllabus recognises.

6.3 Flooding ▼

Flooding has five objectives and you already own two of them. The impacts list and the management list are the framework from 6.1 again, with small and precise changes, so this section spends almost all of its time on the part that is genuinely new: the causes. That is also where the marks are, because 6.3.1 is the only place in Topic 6 where Cambridge asks you to explain why a hazard happens in terms of the ground, the soil and what people have done to both.

Then there is 6.3.5, the opportunities flooding gives people. It is two lines in the syllabus and it is worth learning properly, for the same reason 6.1.10 was: without it you cannot explain why anyone farms a floodplain, and an answer that cannot explain that is not a balanced one.

Causes of flooding (6.3.1) — the new material

Start from one idea and everything else hangs off it. A river floods when water arrives in the channel faster than the channel can carry it away. So every cause on the list works by doing one of two things: getting water to the river more quickly, or leaving the ground with less capacity to hold water back. Keep asking “does this speed the water up, or reduce the store?” and the five lettered items organise themselves.

Rain that lands on the ground has three possible fates. It can infiltrate, soaking down into the pore spaces of the soil, which is slow and delays it for hours or days. It can be intercepted by leaves and evaporate straight back. Or it can run over the surface as surface runoff, which is fast and arrives at the channel almost at once. Flooding becomes more likely whenever the balance shifts from the first two towards the third.

Read this left to right. The rain does not change; what the ground does with it changes completely.

Cause	The mechanism — how it produces a flood
land relief (the shape of the land)	Steep slopes shed water quickly: it travels downhill under gravity with little time to infiltrate, so a large volume arrives in the channel at nearly the same moment and the river rises sharply. Flat, low-lying land causes the opposite problem — once water has spread across it there is no gradient to drain it away, so it stands for days. A narrow, steep-sided valley concentrates the runoff from a wide area into one channel.
saturated soil	Soil stores water in the pore spaces between its particles. After long rain or snowmelt those spaces are already full, so the soil can take no more and any further rain has to run over the surface. This is why the third day of rain floods and the first does not.
compacted soil	Heavy machinery, trampling by livestock and building work press the soil particles together and squeeze the pore spaces shut. The infiltration rate drops, so rain that would have soaked in runs off instead. Notice this is a different mechanism from saturation: saturated soil is full, compacted soil has nowhere for the water to get in.
soil erosion	Two effects. A thinner soil layer holds less water, so the store that would have delayed the rain is smaller. And the eroded material is washed into the river and deposited on the bed, which raises the bed and reduces the capacity of the channel, so a smaller flow is now enough to make it overflow.
deforestation	Trees intercept rain on their leaves, from which much of it evaporates; their roots open channels that help water infiltrate; and they return water to the air by transpiration. Remove them and all three are lost at once, so more rain reaches the ground, less of it soaks in, and the bare soil is then eroded, which brings in the row above as well.
agricultural practices	Ploughing furrows down a slope gives water ready-made channels to run along. Fields are left bare between crops, so rain hits the soil directly and compacts and erodes it. Machinery and livestock compact the ground. Field drains and ditches are installed deliberately to move water off the land quickly — which is good for the farmer and moves the problem downstream.
urbanisation	Roofs, roads, pavements and car parks are impermeable, so almost nothing infiltrates. Gutters, drains and sewers are designed to carry that water away fast, so it reaches the river in a fraction of the time it once took. The result is a higher peak that arrives sooner. Building on the floodplain then places people and property in the very area the river uses when it overflows.
climate change: rise in sea level	A higher starting sea level means coastal land floods on tides that were previously safe, storm surges push further inland from a higher base, and salt water pushes further up river channels, which also slows the escape of river water to the sea.
climate change: more extreme weather	A warmer atmosphere holds more water vapour, so rainfall events tend to be more intense. The same total rain delivered in a shorter time generates far more surface runoff, because infiltration has a maximum rate and rain falling faster than that rate simply runs off.
storm surges	The very low air pressure at the centre of a tropical cyclone lets the sea surface rise, and the strong winds drive that raised water ashore. The surge floods low-lying coast with salt water in minutes, and it arrives on top of the ordinary tide, so its timing relative to high tide changes everything.
tsunamis	An earthquake on the sea bed displaces a large volume of water, which travels outwards and rises into destructive waves in shallow coastal water. Note where this sits: a tsunami is an impact of a tectonic event in 6.1.7 and a cause of flooding in 6.3.1. The same event, seen from two sub-topics.

Saturated is not the same as compacted

Both leave water on the surface, and they are marked as different points. Saturated means the pore spaces are already full of water — the store exists but there is no room left in it. Compacted means the pore spaces have been squashed out of existence — the store itself has been reduced. A dry field that cattle have trampled all summer is compacted, not saturated.

Reading a flood hydrograph

Paper 2 is 40% AO3 and this is the graph it likes, because two catchments on the same axes let you compare rather than just describe. A hydrograph plots the discharge of a river — the volume of water passing a point each second — against time after a storm. Three things to read off it: how high the peak discharge is, how long the lag time is between the rain and that peak, and how steep the rising limb is.

Use this graph for Question 2 below. Compare the height of each peak and how long each one took to arrive.

Worked example Explain how building over a river catchment increases the height of a flood downstream. [4]

Step 1 — the surface changes

Roofs, roads and pavements are impermeable, so rain that would have infiltrated into soil cannot soak in and stays on the surface.

Step 2 — the water moves faster

Gutters, drains and sewers are designed to remove that water quickly, so it travels to the channel in a fraction of the time it would take to seep through soil. The lag time falls.

Step 3 — the mark that most answers miss

Because the water arrives sooner it also arrives together, instead of being spread over the following days. The same total volume concentrated into fewer hours gives a much higher peak discharge, and it is the peak, not the total, that decides whether the banks are overtopped.

Step 4 — add the second effect if the marks allow

Building also removes vegetation, so interception and transpiration are lost too, and building on the floodplain itself puts property in the area the river uses when it does overflow.

Impermeable surfaces and drains, so a shorter lag time, so the same water arrives together and the peak is higher.

Impacts of flooding (6.3.2) — the framework, minus two

Compare with the tectonic list. The flooding list has nine items and every one of them you have already met: damage to buildings and infrastructure, loss of crops, livestock and habitats, evacuation of people and livestock, landslides, contamination of drinking-water supplies, water-related disease, financial losses, and human health. Cambridge splits “loss of crops” and “livestock and habitats” into two lettered items here, so treating them separately does you no harm.

Difference from 6.1	Detail
fire and tsunamis are dropped	Both belong to tectonic events only. A tsunami still appears in 6.3, but as a cause in 6.3.1, not as an impact. Getting that the right way round is a small, easy mark.
contamination and disease move up the order	For an earthquake, contaminated water is one consequence among many. For a flood the water is the hazard, so it is the central one: flood water flows through sewers, latrines, animal waste, fuel stores and chemical stores and then stands in the streets and enters wells and mains. Diseases such as cholera and typhoid follow, and crowded shelters spread them further.
the mechanisms change again	Buildings are damaged by water rather than shaking: moving water carries debris that batters walls, currents scour soil out from under foundations, and everything below the water line is ruined and stays damp for months afterwards. Crops die because waterlogged soil has no oxygen for the roots, and salt water from a surge leaves fields unusable for years. Landslides here are caused by saturated soil losing its strength on a slope, not by shaking.
the losses last longer than the water	Financial losses continue after the water has gone: repairs, lost harvests, businesses shut, and insurance that becomes expensive or unobtainable in a flood-prone area. Human health includes drowning and injury during the event, disease afterwards, and the effect on mental health of repeated flooding of the same homes.

Managing the impacts (6.3.3, 6.3.4)

Eight strategies, and this time land use zoning is back on the list. That is exactly the trap the cyclone section warned about: the earthquake list has zoning, the cyclone list does not, the flooding list does. Check, do not assume.

What is not on the list

Most flooding pages you will find elsewhere are full of dams, embankments, levees, dredging and straightened channels. None of those is in 6.3.3, and the syllabus says limited to. A question asking for strategies for managing the impacts of flooding is marked against the eight items below, so answer from them. Dams and reservoirs do appear in Topic 6, but as a way of increasing water supply in the drought list, 6.4.4 — a different job entirely.

Strategy	What is different about it for flooding
monitoring and warning	Rain gauges, river-level gauges upstream and weather forecasts. How much warning you get depends entirely on the catchment: a large lowland river gives days, because the flood wave takes that long to travel down it, while a small steep catchment can flood within an hour of the rain and gives almost none.
land use zoning	Keep the floodplain for uses that can be flooded without much loss — grazing, playing fields, car parks, nature reserves — and put housing, hospitals and power supplies on higher ground. The flooding is not prevented; what is prevented is anything valuable being in the way of it.
structure of buildings	Raise the living floor above the expected flood level, or build on stilts. Use solid floors and water-resistant materials rather than plaster and chipboard, put electrical sockets and wiring high up, and fit barriers to doors and airbricks.
disaster preparation	Plans, drills, stockpiles and rescue teams as before, plus what is specific here: sandbags stored ready, boats and high-clearance vehicles for rescue, agreed routes and destinations for moving livestock to higher ground, and households knowing to move belongings upstairs.
evacuation	Moving people to higher ground. The difficulty is that the routes flood first — low roads and bridges go under before the houses do — so evacuation has to start earlier than it feels necessary.
shelters	Buildings above the expected flood level, stocked with clean water and sanitation, which matters more here than for any other hazard because contaminated water is the main follow-on risk.
rebuilding of damaged areas	Repair with the resistant materials and raised floors above, and the harder question of whether the worst-affected properties should be rebuilt at all or the land returned to floodplain.
international aid	As before: money, clean water, sanitation equipment, medical supplies and specialist teams.

For 6.3.4 the benefits and limitations table in 6.1 is your answer, with three adjustments that are worth stating because they change the judgement:

Land use zoning has its sharpest trade-off here. Floodplains are flat, fertile, well supplied with water and next to a transport route, which is precisely why settlements were built on them in the first place. So zoning asks a town to give up its most useful land, and in most places the town is already there. It protects future development well and does very little for the existing city.
Warning time is not a property of the strategy, it is a property of the catchment. The same monitoring network gives days of warning on a large river and minutes on a small steep one. So “monitoring and warning is effective” is only half an answer; say for which kind of catchment.
Building design protects the building, not the place. A house on stilts stays dry while the power, the water supply, the roads and the shops around it do not, so people may still have to leave. It reduces damage rather than disruption.

A river catchment covers 240 km². In 1990, 8% of its surface was built on; by 2020 this had risen to 31%. After a storm delivering 50 mm of rain, peak discharge at the town downstream was 62 m³ per second in 1990 and 108 m³ per second in 2020. The time between the storm and the peak fell from 14 hours to 5 hours over the same period.

Using the data, explain how the change in the catchment has affected flood risk, and suggest one management strategy the data supports.

▼

Quote the figures, and say what they are figures of

The built-up fraction almost quadrupled, from 8% to 31%. Over the same period peak discharge rose by 46 m³ per second, an increase of about 74%, and the lag time fell from 14 hours to 5 hours, a reduction of 9 hours. Marks are given for using the numbers, not for saying “it went up”.

Give the mechanism that links them

The new surfaces are impermeable, so infiltration is reduced and surface runoff increased, and drains carry that runoff to the channel quickly. Because the water arrives sooner it also arrives together, so the peak is higher as well as earlier. The rainfall in the two events was the same, which is what allows the change to be attributed to the catchment rather than to the weather.

Say what the risk change actually is

Two separate increases in risk. A higher peak means the channel is more likely to be overtopped. A shorter lag time means there are now five hours rather than fourteen between the rain and the flood, which is the time available to warn and move people — so the warning system that worked in 1990 may not work now.

Choose a strategy the data actually supports

Land use zoning, because the data identifies the cause as new building in the catchment, and zoning is the strategy that acts on that cause by restricting further development on the floodplain and keeping it for uses that tolerate flooding. A defensible second choice is improved monitoring and warning, since the fall in lag time is the change that most directly threatens the existing warning arrangements. Naming a strategy that is not on the 6.3.3 list would score nothing however sensible it sounds.

The opportunities flooding gives people (6.3.5)

Two lettered items, and like 6.1.10 this is the objective most students walk past. It is also the reason floodplains hold some of the densest rural populations on Earth. If you can only write about damage you cannot answer “discuss whether people should be moved off the floodplain”, because you will have nothing on one side of the argument.

Opportunity	How it works, and why it matters to people
deposition of nutrient-rich silt on farmland	The river erodes fine material from upstream and carries it in suspension. When it spills onto the floodplain the water is suddenly shallow and slow, so it loses the energy to carry that load and deposits the silt across the fields. The silt contains mineral nutrients and organic matter, so the flood renews soil fertility every year at no cost. That is why floodplain soils give high yields without bought fertiliser, and why farming communities settle on land they know will flood.
recharge of surface water and ground water stores	Flood water refills lakes, ponds and wetlands, and some of it infiltrates through the soil and rock to recharge the aquifer beneath. That stored water is what feeds wells, springs and the river itself later in the dry season, so a flood in the wet season is part of the water supply for the months after it. Refilled wetlands also support fish, which are a food source and an income.

Opportunity

How it works, and why it matters to people

deposition of nutrient-rich silt on farmland

The river erodes fine material from upstream and carries it in suspension. When it spills onto the floodplain the water is suddenly shallow and slow, so it loses the energy to carry that load and deposits the silt across the fields. The silt contains mineral nutrients and organic matter, so the flood renews soil fertility every year at no cost. That is why floodplain soils give high yields without bought fertiliser, and why farming communities settle on land they know will flood.

recharge of surface water and ground water stores

Flood water refills lakes, ponds and wetlands, and some of it infiltrates through the soil and rock to recharge the aquifer beneath. That stored water is what feeds wells, springs and the river itself later in the dry season, so a flood in the wet season is part of the water supply for the months after it. Refilled wetlands also support fish, which are a food source and an income.

Where the evaluation marks are hiding

Any “discuss” or “evaluate” question about flooding is asking you to weigh these two against the nine impacts. The judgement sentence that works: “The benefits of flooding are small, regular and reliable, while the harm is occasional and large. A farming household therefore gains every year and loses badly in some years, which is a rational trade to accept — and it explains why zoning the floodplain is resisted even where the risk is understood.” That sentence takes you from describing to judging, which is the difference between the middle and the top band.

Checkpoint 6.3

Answer, then read the explanation even when you were right.

Your Score 0 / 8

Question 1

A river catchment is built over with houses, roads and car parks. Why does this raise the flood risk downstream?

A Buildings warm the air above the town so that more rain falls on it.

B Drains hold rainwater underground and release it slowly for weeks.

C Rain cannot soak in and runs off to drains, reaching the river fast.

D Concrete soaks up rainfall and then passes it into the soil beneath.

Impermeable surfaces plus a drainage system built to remove water quickly means a shorter lag time and a higher peak. D is the opposite of impermeable, which is the word the mark scheme wants. B describes a soakaway system, which does the reverse of what ordinary drains do. A is a real effect of cities on climate but it is not on the 6.3.1 list and it is far too small to explain a flood.

Question 2

Look at the hydrograph above. Which statement about catchment P is best supported by the graph?

A Its peak discharge is lower and arrives later than in catchment Q.

B Its peak discharge is higher and comes sooner than in catchment Q.

C Its discharge stays steady all day, so the storm had little effect.

D It received far more rainfall than catchment Q during the storm.

Read the two peaks off the gridlines: P reaches roughly 108 m³ per second about 5 hours in, Q reaches roughly 62 about 14 hours in. A simply reverses both readings. C describes a flat line, which is what neither curve does. D is the trap worth noticing — the caption states both catchments received the same 40 mm, so a difference in rainfall is ruled out by the question, and that is exactly what makes the graph evidence about the land surface instead.

Question 3

How does steep land relief in the upper part of a catchment contribute to flooding?

A Water runs downhill fast and reaches the channel with little delay.

B Steep slopes hold rain in hollows until the whole store spills at once.

C Steep ground is always colder, so more of the rain falls there as snow.

D Slopes made of rock are permeable, so all the rain is stored in them.

Gravity moves the water downslope before it has time to infiltrate, so runoff from a wide area arrives at the channel at nearly the same moment. B has the geometry backwards: hollows that store water are a feature of flat land, not of steep slopes. C is true of altitude in general but it is not a cause on the list and snow delays a flood rather than causing one. D confuses steepness with rock type, and slopes are often steep precisely because the rock is hard and not very permeable.

Question 4

A dry field has been crossed by heavy machinery all summer. Why does rain now run off it instead of soaking in?

A The machinery has removed the nutrients that hold water in the soil.

B The soil is already saturated, so its pore spaces are full of water.

C The soil has been eroded away and the bare rock below repels water.

D The soil is compacted, so its pore spaces have been squeezed shut.

Machinery presses the soil particles together and closes the pore spaces, so the infiltration rate falls. B is the answer people give and it contradicts the question, which says the field is dry — saturated soil is full of water, compacted soil has had the spaces squashed out of it, and they are marked as separate points. C describes erosion, a different item on the list, and rock is not water-repellent. A invents a role for nutrients that they do not have.

Question 5

Which pair of causes of flooding both work by pushing sea water inland over the coast?

A soil erosion in the uplands and the silting up of a river channel

B a storm surge driven by a cyclone and a tsunami from an earthquake

C deforestation of a hillside and the ploughing of fields down a slope

D saturated soil after long rain and the compaction of soil by cattle

A surge is sea water driven ashore by cyclone winds and low pressure; a tsunami is sea water displaced by an earthquake on the sea bed. Both flood the coast with salt water from seaward. A, C and D are all real causes on the 6.3.1 list, but every one of them works on rain water arriving from the land side, which is the distinction the question is testing. Note also that the tsunami you met in 6.1.7 as an impact of a tectonic event appears here as a cause of flooding.

Question 6

Which of these is listed as an impact of a tectonic event but not as an impact of flooding?

A fire spreading from broken gas pipes and damaged electrical cables

B contamination of drinking water where sewage enters wells and mains

C landslides where slopes are saturated and then lose their strength

D loss of livestock and habitats where land is under water for days

Fire and tsunamis are the two impacts that belong to 6.1 alone. B, C and D are all on the flooding list, and B is the one that matters most for a flood because the water is itself the route by which the contamination spreads. The other half of this pair is worth holding on to: a tsunami is an impact in 6.1.7 and a cause in 6.3.1, so it appears in both sub-topics doing different jobs.

Question 7

What is the strongest limitation of using land use zoning to reduce flood damage in an old riverside city?

A Zoning has no effect on where new housing and hospitals are built.

B Floodplain land is too poor in nutrients for any use to be made of it.

C Zoning laws raise the flood level by narrowing the river channel.

D Most of the city is already built on the floodplain and cannot move.

Zoning decides what may be built where, so it works on development that has not happened yet. In a city that has stood for centuries the vulnerable buildings are already in place, which is the honest limitation to write. A states the opposite of what zoning does. B is false and worth correcting — floodplain soil is fertile, which is the reason the pressure to use it is so strong. C confuses zoning with embankments, which are not on the 6.3.3 list at all.

Question 8

Why can regular flooding be an advantage to farmers on a floodplain?

A Flood water washes the salt out of the soil and leaves the land drier.

B Flooding kills the pests in the soil and leaves the crop untouched.

C The water slows and drops silt, returning nutrients to the soil.

D Flooding raises the land each year and lifts farms above the river.

Once the water spreads onto the floodplain it is shallow and slow, so it can no longer carry its suspended load and deposits nutrient-rich silt across the fields. The second opportunity in 6.3.5 is worth adding in a written answer: the flood also recharges surface water and ground water stores, so wells and wetlands still hold water later in the dry season. A is wrong in both halves — a surge brings salt in rather than taking it out. B ignores the fact that flooding drowns the crop as well. D confuses a thin annual layer of silt with a change in the height of the land.

6.4 Drought ▼

Drought is the sub-topic where the framework stops working, and that is the most useful thing to know about it. The impacts list is largely new, the management list is a completely different shape — only five items, and no evacuation, no shelters, no building design, no zoning — and there is no opportunities objective at all, so do not go looking for one or invent one by analogy with volcanoes and floods.

The reason for all of that is a single property: a drought is slow. An earthquake takes seconds and a cyclone takes a day. A drought builds over months across an entire region, and nobody can say precisely when it started. That is why the response is to bring water to people rather than to move people away from a hazard, and why the first strategy on the list is monitoring.

What a drought is (6.4.1) — learn the wording

The definition, word for word

A drought is a period of dry weather that is longer or more severe than normal.

Three words are doing all the work. Period — it has a duration, so a single dry week is not one. Longer or more severe — either one will do, so an unusually intense short dry spell counts and so does a mild one that will not end. And than normal, which is the part people drop.

That last phrase is the whole idea. A drought is defined by departure from what is normal for that place, not by an absolute amount of rain. So a desert that receives its usual 60 mm in a year is not in drought, however dry it is, because 60 mm is normal there and everything living there is adapted to it. A temperate region that normally receives 700 mm and receives 400 mm is in drought, even though 400 mm is far more rain than the desert ever sees, because its farming, its reservoirs and its rivers are all built around the larger figure.

Define means reproduce, not paraphrase

“Define” is a one or two mark command word and the mark scheme is the syllabus sentence. Write it exactly: a period of dry weather that is longer or more severe than normal. Answers such as “when there is no rain” or “when a country runs out of water” lose the mark, the first because it omits the comparison with normal and the second because it describes a consequence rather than the thing itself. If the question offers two marks, add the point that normal is measured against the long-term average for that particular place.

Reading rainfall data

Because the definition is comparative, a drought question in Paper 2 almost always arrives as data with a long-term average drawn on it. What you are being asked to do is spot a run of years below that line, not the single lowest bar.

Use this chart for Question 2 below. The dashed line is the average of a fifty-year period before the years shown.

Causes of drought (6.4.2) — only two

Two lettered items, and that is genuinely all of them. Resist the temptation to write about wind belts and pressure systems; none of it is on this syllabus and none of it is marked.

Cause	The mechanism
lack of rain	Rainfall over a region falls below its normal amount and stays below it. Water is still leaving the region by evaporation, by transpiration from plants and by abstraction for people, farms and industry, but it is no longer being replaced at the usual rate. So soil moisture is used up first, then streams and rivers fall, then reservoirs and groundwater, which is why the effects appear in that order over months.
climate change: increase in global temperatures	Higher temperatures raise the rate of evaporation from soil, lakes and reservoirs, and the rate of transpiration from plants. So even where rainfall is unchanged, more of the water that arrives is lost back to the atmosphere and less remains available — the region becomes effectively drier without a fall in rainfall.
climate change: increase in extreme weather events	Climate change is expected to make rainfall less evenly spread in time: longer dry spells between heavier downpours. That produces droughts even where the annual total holds up, and it makes the rain that does fall less useful, because intense rain on dry hard ground runs off rather than infiltrating to recharge the soil and the aquifer.

Impacts of drought (6.4.3) — mostly new

Ten items, and only three are carried over from the framework: loss of crops, livestock and habitats; financial losses; and human health. The other seven belong to drought alone, and they run in a chain rather than sitting in a list, which is how they are best learned and how “explain” questions are marked.

Learn it as three routes: the water route on the left, the soil route in the middle, the fire route on the right.

Impact	The mechanism — the “because” that earns the mark
water sources dry up	Streams and rivers fall and may stop flowing; lakes, ponds, wells and reservoirs drop, and shallow ones empty. Water for drinking, washing, irrigation and industry becomes short exactly when demand for it is highest, and people, often women and girls, walk further to collect it.
loss of crops, livestock and habitats	Crops wilt and fail without soil water, so harvests are small or nothing. Livestock have no pasture and no drinking water, so they lose condition and die or are sold cheaply. Habitats such as wetlands and grassland dry out, so the species that depend on them decline or move.
soil erosion	When the plants die, their roots no longer bind the soil and their leaves no longer shelter it. Dry loose soil is then blown away by the wind, and when rain finally arrives it falls on hard bare ground and washes the surface layer off. Note that a drought causes erosion by both wind and water, which surprises people.
desertification	Once the fertile topsoil has gone, plants cannot re-establish even when the rain returns, so the land is permanently less productive and takes on the character of a desert. This is the impact that does not reverse when the drought ends, which makes it the most serious one to write about.
death of organisms	Plants and animals die from lack of water directly, from lack of food as the plants fail, and from the loss of aquatic habitat as rivers and ponds dry. Fish are lost when a river stops flowing or its remaining pools warm and lose oxygen.
famine	Widespread crop failure and livestock deaths over a whole region mean there is not enough food, and prices rise at the same moment that farming households lose the income they would have bought it with. Famine is the point at which a food shortage becomes a shortage people cannot buy their way out of.
increased risk of wildfires	Dry vegetation ignites easily and burns fast, so fires start more readily and spread further, destroying crops, timber, buildings, habitats and the animals in them.
decrease in air quality	Two routes. Smoke and fine particles from wildfires, and dust blown off dry bare soil. Both irritate the eyes and airways and make asthma and other respiratory conditions worse, and both can travel a long way from where they were produced.
financial losses	Lost harvests and livestock, higher food and water prices, industry limited by water restrictions, hydroelectric output cut by low reservoirs, and the cost of trucking in emergency water. Farming households lose their income and their capital at the same time, because the livestock they sell cheaply were their savings.
human health	Undernutrition weakens people, especially children. What water is left is drawn from fewer and lower sources, so it is more likely to be contaminated. Respiratory problems come from dust and smoke, heat-related illness from the high temperatures, and there is the mental strain of losing a livelihood over a period of months or years.

The three impacts that are not on the drought list

Damage to buildings, evacuation of people, and landslides all appear for earthquakes, cyclones and floods, and none of them is on the drought list. That is not an oversight: drought does not knock things down, and there is nowhere to evacuate to when the shortage covers an entire region. If you find yourself writing about collapsed buildings in a drought answer, you have imported the wrong list.

Managing the impacts (6.4.4, 6.4.5)

Five strategies, and the shape of the list tells you what kind of hazard drought is. There is no evacuation, no shelter, no building design and no zoning — because there is nothing to shelter from and nowhere to go. Instead there are two strategies about reducing demand and increasing supply, which are the moves you already met in Topic 3 on water resources. That link is deliberate and it is worth making it in an answer.

When	Strategy	What it involves
before	monitoring and warning	Rainfall records compared with the long-term average, river and reservoir levels, soil moisture measurements, and satellite images that show how vegetation is growing compared with a normal year. Because drought builds slowly the warning can come weeks or months ahead, which is long enough for farmers to plant a drought-tolerant crop, for reservoirs to be held back, and for restrictions to start early and gently instead of late and severely.
during	emergency water supplies	Getting water to people who no longer have any: tankers, bottled water, temporary standpipes, and boreholes drilled to reach deeper groundwater. Short-term and immediate, and aimed at drinking water first, livestock second.
	water conservation	Reducing demand rather than finding more supply. Repairing leaking mains, metering and pricing water, switching from flood irrigation to drip irrigation that delivers water to the roots, mulching soil to cut evaporation, re-using treated waste water, and restricting non-essential uses such as watering gardens and washing cars.
	increasing water supply	The syllabus names four routes. Dams and reservoirs store wet-season water for release in the dry season. Aquifers and wells reach groundwater, which is still there when the surface water has gone. Desalination removes salt from sea water, so a coastal country can use a supply that never runs out. Rainwater harvesting collects runoff from roofs and surfaces into tanks for use later.
after	international aid	Water, food, medical supplies, drilling equipment and money from other countries and organisations, and longer-term funding for wells, irrigation and drought-tolerant seed so the next drought does less harm.

6.4.5 asks you to discuss the benefits and limitations of those five. Same rule as before — both sides properly, then a judgement.

Strategy	Benefits	Limitations
monitoring and warning	Drought is the one hazard in this topic that can be seen coming weeks or months ahead, so a warning is genuinely useful: crops can be changed, reservoirs held back, herds reduced early while the animals are still worth something, and restrictions phased in. Instruments and satellite data are cheap compared with the losses avoided.	There is no agreed moment at which a drought begins, so a warning is a judgement and may be issued too late or not acted on. Acting early costs money for an event that may not arrive, which makes governments reluctant. And a warning does not make it rain — it only buys time to prepare.
emergency water supplies	Immediate and it keeps people alive, which nothing else on this list does in the short term. It can be directed to the worst-affected settlements, and it is the only option once local sources have already failed.	Expensive per litre and hard to sustain, because trucking water needs fuel, vehicles and roads. Quantities are small, so it covers drinking and cooking but not crops or livestock. It treats the shortage rather than the cause, and it can only run for as long as somebody is paying for it.
water conservation	Cheap, quick to introduce and it works everywhere, since saving a litre is exactly as useful as finding one. Repairing leaks in particular can free a large volume with no new construction. It reduces the pressure on aquifers and rivers permanently, not only during a drought.	Depends on many people changing behaviour, and voluntary restrictions are widely ignored. Metering and pricing reduce use but fall hardest on poor households, which use least to begin with. There is a floor below which demand cannot be cut, so conservation alone cannot cover a severe or prolonged shortage.
increasing water supply	Adds new water rather than rationing what is there, and a reservoir or an aquifer carries a supply across a dry season. Desalination is not affected by rainfall at all, so it is reliable in exactly the conditions that make everything else fail. Rainwater harvesting is cheap, small in scale and can be installed by a household without waiting for a national project.	Dams are expensive and slow to build, flood land and displace people, trap sediment that would have fertilised farmland downstream, lose water by evaporation from a large surface, and reduce the flow to countries and regions downstream. Wells fail if water is taken out faster than the aquifer is recharged, and the water table falls beyond the reach of shallow wells first, which are the ones poor households use. Desalination uses a great deal of energy, so the water is costly and the emissions are real, and it only helps a coast. Rainwater harvesting collects nothing in a drought long enough to matter.
international aid	Brings water, food, money and drilling equipment that the affected country may not have, and can fund the wells and irrigation that reduce the impact of the next drought.	Slow to arrive, and slow-onset events attract far less attention and funding than sudden ones, because there is no single day of dramatic news. Aid may arrive after the harvest has already failed, may be poorly matched to what is needed, and long-term dependence on food aid can undercut local farmers by lowering the price they can sell at.

Worked example A government can spend its limited budget either on one large dam and reservoir, or on rainwater harvesting tanks for many villages. Discuss which would better reduce the impact of future droughts. [6]

Step 1 — the case for the dam, at its strongest

A reservoir stores a very large volume, so it can carry a city, its industry and its irrigated farmland through a dry season and into a second one. It supplies a reliable quantity to a piped network, and it can also generate hydroelectricity and regulate flooding downstream, so one investment does several jobs.

Step 2 — the case against it, also at its strongest

It costs a great deal and takes years to build, so it does nothing about a drought in the next five years. The reservoir floods land and displaces the people living there. Evaporation from a large surface in a hot climate is a continuing loss. Sediment is trapped behind the dam instead of fertilising the floodplain below it, and the flow reaching downstream regions is reduced. And it delivers water through a network, so villages without a connection gain nothing.

Step 3 — the case for and against harvesting

Tanks are cheap, quick, and can be installed in hundreds of villages at once, reaching exactly the households a piped network misses, and each one is owned and maintained locally. But the volume is small, so it covers drinking and cooking rather than irrigation, and it only fills when rain falls — in a long drought there is nothing to harvest. It buys weeks of resilience, not years.

Step 4 — the judgement, which is where the last marks are

The two do different jobs, so the answer depends on the question the government is really asking. For short, frequent droughts affecting rural households, harvesting reaches more people per unit of money and reaches them sooner. For long, severe droughts affecting a city and its irrigated farmland, only large storage will do. If the budget must go one way, harvesting first is the more defensible choice, because it delivers within a year, spreads the benefit widely, and does not displace anyone — with water conservation, which is cheaper than either, running alongside it.

Both have a real case. Name the timescale, the scale of the drought and who benefits, then decide on those grounds rather than on which sounds more impressive.

Over 18 months a city reservoir fell from 92% full to 24% full. Rainfall over the same 18 months was 61% of the long-term average. The city introduced a ban on watering gardens, which reduced household demand by 6%, and repaired leaking mains, which reduced losses from the distribution network by 19%.

Using the data, evaluate the response of the city, and suggest what it should do next.

▼

Establish that this is a drought, using the definition

Rainfall was 61% of the long-term average and stayed there for 18 months, so this is a period of dry weather both longer and more severe than normal. Saying that explicitly is worth a mark, because the definition is comparative and the data gives you the comparison.

Compare the two measures on the numbers

Leak repair cut losses by 19%, more than three times the 6% saved by the ban on watering gardens. Both are water conservation, but the one that changed the pipes achieved far more than the one that asked people to change their behaviour. That is the finding in this data and it is the thing to lead with.

Say honestly what the data does not show

The percentages are reductions in demand and in losses, not in the same quantity, so they cannot simply be added; and the reservoir still fell to 24%, so neither measure was enough. There is nothing here about cost, so you cannot yet say which was better value. Naming the limits of the data is an AO3 skill and it is credited.

Recommend, from the 6.4.4 list

Continue and extend the leak repair programme, since it is the measure the data shows working. Add monitoring so that restrictions begin earlier in the next dry period rather than at 24%. Then plan an increase in supply for the longer term — aquifers and wells, or desalination if the city is coastal — while keeping emergency water supplies ready in case the reservoir keeps falling. Reducing demand and increasing supply are complementary, not alternatives, and saying so is the judgement the command word is asking for.

Checkpoint 6.4

Answer, then read the explanation even when you were right.

Your Score 0 / 8

Question 1

A desert region receives 60 mm of rain in a year, which is close to its long-term average. Is it in drought?

A Yes, because any region receiving under 100 mm a year counts as one.

B Yes, because a drought is measured by total rainfall, not by season.

C No, because a drought is only ever declared over a whole continent.

D No, because a drought is a departure from normal for that place.

The syllabus definition is a period of dry weather longer or more severe than normal, so it is comparative. Sixty millimetres is normal here, so the region is dry but not in drought. A and B are the same error in two forms — setting an absolute threshold — and it is the error the definition is written to rule out. C invents a rule about area; a drought can affect a single catchment.

Question 2

Look at the rainfall chart above. Which run of years best fits the definition of a drought?

A 2013 to 2015, when rainfall was above the long-term average

B 2018 to 2020, when rainfall stayed well below the average

C 2021 by itself, the year with the highest rainfall shown

D 2024 by itself, when rainfall was close to the average

Three consecutive years below the dashed line, reading roughly 430, 380 and 460 mm against an average of 700, so it is both longer and more severe than normal. C is the wrong direction entirely. D reads at about 660, which is a little below average for one year and not a drought. A is above the line throughout. Note that 2023, at about 520, is a single low year rather than a run — the definition wants a period, which is why one bar is not enough.

Question 3

Which of these is a cause of a drought rather than one of its effects?

A a long period in which little or no rain falls

B the drying up of the rivers, lakes and wells of a region

C the erosion of bare soil by the wind once the plants die

D the increase in the number of wildfires in dry vegetation

6.4.2 gives only two causes: lack of rain, and climate change through higher global temperatures and more extreme weather events. B, C and D are all on the impacts list in 6.4.3, and each is a stage of one of the three chains. Sorting causes from impacts is most of what a drought question tests, because the two lists are easy to blur when they are learned as one long set of bullet points.

Question 4

Why is evacuation not one of the strategies listed for managing a drought?

A Droughts affect only farmland, so nobody lives in the area at risk.

B Droughts always end before people run short of food and water.

C A drought builds slowly over a wide area, so water is brought in.

D Governments are given no warning at all that a drought is starting.

There is no sudden impact to escape and no nearby safe place, since the shortage covers the whole region, so the response is to move water to people rather than people away from water. D is the reverse of the truth and it is the reason monitoring is first on the drought list: this is the one hazard here that can be seen coming months ahead. A ignores the cities that depend on the same reservoirs. B is simply false, and famine is on the impacts list because of it.

Question 5

Explain the route from a drought to desertification.

A Dry air holds more dust, and the dust settles and buries the soil.

B Plants die, bare soil is eroded away, and the land degrades.

C Rivers dry out and their beds are exposed as new areas of bare sand.

D Wildfires burn the soil itself and turn what is left into sand grains.

The chain runs: no water, plants die, roots no longer bind the soil and leaves no longer shelter it, so wind and later rain strip the fertile topsoil, and without topsoil plants cannot re-establish even after the rain returns. That last step is what makes it desertification rather than temporary damage. C describes a real sight but a dry river bed is not degraded farmland. D and A both invent a way of making sand, which is not what the word means — desertification is loss of productivity, not the arrival of sand dunes.

Question 6

How does a drought lead to a decrease in air quality?

A Less rain falls, so no water vapour is left in the air to breathe.

B Water sources dry up, so the water that is left carries disease.

C Crops fail, so more land is ploughed and the soil is turned over.

D Dry vegetation burns easily and the smoke carries particles.

Two routes are worth writing, and the second one earns the extra mark: smoke and fine particles from wildfires, and dust blown off dry bare soil. Both make asthma and other respiratory conditions worse. B is a genuine impact of drought but it is about water quality, not air, and the question names air. A misunderstands what people breathe. C reverses the farming response, since land is not ploughed more when there is no moisture to plant into.

Question 7

Which of these is one of the strategies for managing a drought?

A increasing supply by desalination or rainwater harvesting

B strengthening the roofs of buildings against very high winds

C zoning the most exposed ground so that no housing is built

D moving people into raised shelters above the flood level

The drought list has five items and a different shape from the other three: monitoring and warning, emergency water supplies, water conservation, increasing water supply, and international aid. B belongs to cyclones, C to earthquakes and flooding, and D to cyclones and flooding. Every one of them is a real strategy in the wrong sub-topic, which is exactly how this mark is lost.

Question 8

What is the main limitation of desalination as a response to drought?

A It cannot produce water that is safe enough for people to drink.

B It can only be used by countries that have no coastline at all.

C It uses a lot of energy, so the water produced is costly.

D It removes so much sea water that sea level falls near the coast.

Removing salt from sea water takes a great deal of energy, so the water is expensive and the emissions from generating that energy are a real cost. Note the benefit side you should give alongside it: the supply does not depend on rainfall, so it works in exactly the conditions that make everything else fail. B reverses the requirement, since a coast is what desalination needs. A is false; the product is potable. D is not a scale of effect that occurs.

▶ Revise the whole topic

Whole-topic run-throughs, for when you have worked through every sub-topic above and want one sweep before a paper. Opens on YouTube in a new tab. The IGCSE 0680 videos follow the OLD chapter numbering, where this topic was Chapter 6, Managing Natural Hazards — the content matches this topic. The last two are general geography, not 0680 lessons, chosen for one diagram each. Nothing here teaches 6.3 Flooding or 6.4 Drought directly — those sub-topics are on the page above and nowhere in this list.