GCSE · Geography · AQA · Spec 8035

Evidence weather is becoming more extreme in the UK

Is UK weather really getting more extreme, or does it just feel that way? Those are two different questions. Let's learn to tell them apart.

Weigh the evidence

Is UK weather really becoming more extreme?

The claim

The weather in the UK is becoming more extreme.

Place each piece of evidence to load the balance. Mark the strong ones — they count double.

There is a perception that floods are becoming more frequent or more severe in parts of the UK.
Evidence 1: does it support or challenge the claim?SupportsChallenges
Strong evidence
Studies show a general consensus that precipitation and river flood flows are increasing.
Evidence 2: does it support or challenge the claim?SupportsChallenges
Strong evidence
That consensus is general, but not universal: not every study agrees that precipitation and river flood flows are increasing.
Evidence 3: does it support or challenge the claim?SupportsChallenges
Strong evidence
Most modelling studies that use climate change scenarios expect increases in extreme rainfall and peak river flows.
Evidence 4: does it support or challenge the claim?SupportsChallenges
Strong evidence
For storm surge, the consensus is that over century timescales its distribution can be assumed to stay the same.
Evidence 5: does it support or challenge the claim?SupportsChallenges
Strong evidence
Studies find evidence that, under climate change, the future distributions of coastal flood sources will not stay the same as in the past.
Evidence 6: does it support or challenge the claim?SupportsChallenges
Strong evidence

Pin down the word

Hang on. What counts as 'extreme'?

You've just judged whether UK weather is becoming more extreme. But you can't judge 'more extreme' properly until you know exactly what 'extreme' means.

Which is closest to what you think 'extreme weather' means?

Weather that's dangerous or causes damage.One sudden, violent event, like a single storm.Weather that's significantly different from the average or usual pattern, over one day or longer.Any weather that's even slightly different from normal.

How sure are you?

I'm sureI think soI'm guessing

Weather that's dangerous or causes damage.

This is a common misconception

Damage is about what weather does to people and places. The definition is about the weather itself: an event that is significantly different from the average or usual weather pattern. Nothing in it mentions damage.

One sudden, violent event, like a single storm.

This is a common misconception

Extreme weather can take place during one day, but it can also take place over a longer period of time. What makes it extreme is how far it differs from the usual pattern, not how quickly it arrives.

Weather that's significantly different from the average or usual pattern, over one day or longer.

This matches the evidence

Yes. Two parts to hold on to: it's measured against the average or usual weather pattern, and it can last one day or a longer period of time.

Any weather that's even slightly different from normal.

This is a common misconception

Close, but the definition says significantly different. A slight difference from the usual pattern isn't enough to make weather extreme.

Extreme weather: significantly different from the average or usual pattern, over one day or a longer period. Keep 'significantly' and 'usual pattern' in every definition you write.

Stationarity

Reason it through

Why does a changing pattern raise questions about flood defences?

Link 1 of 3

First link · your turn

Methods that estimate how likely and how big floods at a place could be start from an assumption. What do they tend to assume?

Locked — reveal the link above first

Spot the clash

Where does the assumption clash with the evidence?

For each source of UK flooding, tick a cell if the statement is true. Then check your grid and look for rows with two ticks.

Extreme rainfall

Usually assumed stationary in UK flood estimatesEvidence says its distribution is changing or expected to change

River flood flows

Usually assumed stationary in UK flood estimatesEvidence says its distribution is changing or expected to change

Storm surge

Usually assumed stationary in UK flood estimatesEvidence says its distribution is changing or expected to change

Mean sea level

Usually assumed stationary in UK flood estimatesEvidence says its distribution is changing or expected to change

Write it, then mark it

Turn your judgement into an answer

Using evidence, assess how far weather in the UK is becoming more extreme. [6 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Defines extreme weather against the usual pattern: significantly different from the average or usual weather pattern. (1 mark)
Uses the study finding: a general consensus that precipitation and river flood flows are increasing. (1 mark)
Uses what modelling studies expect, and identifies it as a projection about the future. (1 mark)
Identifies the perception of worse floods as weaker evidence than a study finding. (1 mark)
Keeps a qualifier: the consensus is not universal, or storm surge can be assumed stationary over century timescales. (1 mark)
Reaches a reasoned 'how far' judgement rather than a plain yes or no. (1 mark)

Model answer

Extreme weather means an event significantly different from the usual pattern, so the real test is whether that pattern is changing. Studies give the best support: there is a general consensus that precipitation and river flood flows are increasing. Most modelling studies also expect more extreme rainfall and higher peak river flows, though that is a projection, not a record of the past. The perception of worse flooding is weaker, because it is a feeling rather than a finding. Two limits remain: the consensus is not universal, and storm surge can be assumed stationary over century timescales. So I mostly agree: the evidence is strongest for rainfall and river flooding, not for every flood source.

Name the kind of evidence each time: a feeling, a finding or a projection. Then keep a qualifier and commit to how far.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A feeling isn't a finding. Learn to weigh what the evidence actually says, and how far it goes.

What you need to know

Extreme weather is a weather event significantly different from the average or usual weather pattern. It may take place during one day or over a longer period of time.
There is a perception that floods are becoming more frequent or more severe in parts of the UK.
Studies show a general, but not universal, consensus that both precipitation and river flood flows are increasing.
Most modelling studies using climate change scenarios expect increases in extreme rainfall and peak river flows.
Flood estimation methods tend to assume stationarity: floods recorded at a place belong to the same statistical distribution. In UK practice only the mean sea-level component of total sea level is not routinely assumed stationary.
Studies find the future distributions of coastal flood sources non-stationary under climate change; for storm surge, the consensus is that over century timescales it can be assumed stationary.
If stationarity is incorrect, estimates of flood and rainfall extremes may be biased, raising questions about whether flood defences are designed appropriately for present and future risks.

The big picture

Extreme weather is a weather event significantly different from the average or usual pattern, over one day or longer, and there is evidence that UK weather is becoming more extreme. Beyond a perception that floods are becoming more frequent or severe, studies show a general, but not universal, consensus that precipitation and river flood flows are increasing, and most modelling studies expect more extreme rainfall and peak river flows. Flood estimates tend to assume stationarity; if that is incorrect, they may be biased, raising questions about whether flood defences are designed appropriately.

Key points

1Evidence has different weights: a perception is weaker than a study finding, and a model projection is about the future, not the past.

2Keep the qualifiers: 'general, but not universal', and the storm-surge exception.

3Where a method assumes a fixed pattern but the evidence says the pattern is changing, estimates may be biased.

4'May be biased' says nothing about which way. Never claim estimates are too high or too low.

5The strongest answer to 'is weather becoming more extreme?' is a 'how far' judgement, not a yes or no.

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Worked example

Problem

A flood estimate for a riverside town treats every flood recorded there as coming from the same statistical distribution. Studies show a general, but not universal, consensus that river flood flows are increasing. What can you say about the estimate, and what can't you say?

⚠ Watch out

Treating 'most studies agree' as proof. The consensus that precipitation and river flood flows are increasing is general, but not universal, and for storm surge the consensus is that its distribution can be assumed stationary over century timescales. Keep the qualifiers in.

🧠

Memory hook

Feel it, find it, forecast it. A perception (feel), a study finding (find) and a model projection (forecast): three kinds of evidence, three different weights.

✓

Check yourself

Without looking back: give one piece of evidence that supports the claim that UK weather is becoming more extreme, and one that qualifies it. Then say which carries more weight, and why.

Flashcards

(12)

What is extreme weather?

A weather event that is significantly different from the average or usual weather pattern.

How long can an extreme weather event last?

It may take place during one day or over a longer period of time.

What is the perception about floods in parts of the UK?

That floods are becoming more frequent or more severe.

What do studies show about precipitation and river flood flows?

A general, but not universal, consensus that both are increasing.

What do most modelling studies using climate change scenarios expect?

Increases in extreme rainfall and peak river flows.

Perception, finding or projection: 'models expect more extreme rainfall'?

A projection: it is about what is expected in future, not what has already happened.

What do studies find about the future distributions of coastal flood sources?

That they are non-stationary under climate change.

What is the consensus about storm surge?

Over century timescales, its distribution can be assumed to be stationary.

What does it mean to assume stationarity in flood estimation?

That floods recorded at a particular location belong to the same statistical distribution as each other.

Which variable is not routinely assumed stationary in UK practice?

The mean sea-level component of total sea level.

What happens to estimates if the stationarity assumption is incorrect?

Estimates of flood and rainfall extremes may be biased.

What question do possibly biased flood estimates raise?

Whether flood defences are being designed appropriately to protect communities against present and future risks.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Is UK weather really becoming more extreme?

Hang on. What counts as 'extreme'?

Where does the assumption clash with the evidence?

Turn your judgement into an answer

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