UK Extreme Weather File

The wettest day ever recorded here

On 5 and 6 December 2015, 341.4 mm of rain fell on Honister Pass in the Cumbrian fells in 24 hours. Nowhere in the United Kingdom had ever recorded more in a single day. At Thirlmere, a few miles away, over 400 mm fell across 38 hours. The storm that delivered it had been named Desmond under a scheme the Met Office had introduced only that autumn, and it drew its moisture from a long plume of warm, wet air streaming north-east out of the subtropical Atlantic. The UK sits where it does for a reason. It lies in the mid-latitudes, on the western edge of a continent, in the path of the polar front jet stream, and at the meeting point of air masses with completely different characters: warm moist air off the Atlantic, cold moist air from the north-west, cold dry air from the Eurasian interior in winter, hot dry air from north Africa in summer. Which of them is in charge this week decides whether the country is flooded, frozen, becalmed or on fire. That is why British weather is not merely a national obsession but a genuine hazard. This module does three things. It sets out the kinds of extreme weather the UK actually gets, it works through Storm Desmond as the named example an exam answer needs, and it looks at the evidence that UK weather is becoming more extreme. That last one is the hardest, because it is not a question about how bad the last storm was. It is a question about whether the pattern is changing, and answering it well means understanding the difference between a dramatic event and a trend.

Five terms, including two traps

The first three explain why UK weather behaves as it does. The last two are the ones that catch out answers on this topic every year.

Order the Storm Desmond sequence

These six stages describe what happened in Cumbria in December 2015. Put them in order.

• A corridor of very moist air streams north-east across the Atlantic towards north-west Britain
• It meets the Cumbrian fells, is forced to rise and cool, and rain falls at extraordinary rates
• Ground already wet from a wet November cannot absorb any more, so almost all of it runs off
• Rivers including the Eden rise to record levels and overtop or outflank their defences
• Thousands of homes and businesses flood, bridges are destroyed and a substation failure blacks out a city
• Defences are reviewed and raised, and flood plans are rewritten for a higher standard

Why is UK weather so changeable?

Which answer best explains why the UK gets such a wide range of weather hazards?

• Its position puts several very different air masses within reach of the same island: warm wet Atlantic air, cold showery polar maritime air, bitter dry continental air in winter and hot dry air from north Africa in summer. The polar front jet stream runs overhead, steering Atlantic depressions across the country, and small shifts in where it sits change which air mass dominates. Being a western-facing island also means moist air is forced over high ground on arrival, concentrating rainfall in the uplands.
• The Gulf Stream alone makes the UK unpredictable.
• Islands always have unpredictable weather.
• Climate change created UK weather hazards.

Storm Desmond: effects and responses

The map asks for effects split into primary and secondary and responses split into immediate and long-term, so that is how this is laid out. These are the figures to carry into a named-example answer.

Match each detail to what it shows

Answering the evidence question

The hardest question on this key element asks you to argue from evidence, not from drama. It is not asking how bad Storm Desmond was. It is asking whether the pattern itself is shifting, and there are two ways to answer it badly. The first is to retell a single storm. However spectacular one event was, weather has always thrown up records, so no individual episode settles anything. The second is to announce that things are getting worse without putting a single measurement behind the claim. What scores is measured change over decades: how often something happens, how intense it gets when it does, and whether the season it arrives in has moved. Reach for the longest series you can name. England and Wales have a rainfall record running back to 1766, and the winter of 2013 to 2014 was the wettest in the whole of it. The nuance that lifts an answer is honesty about the limits of what a record can show. Say that an event of a given severity has grown more probable; do not say that a warming atmosphere produced one particular storm. Examiners notice the difference, and it is one of the clearest signals of a grade-9 grasp of the subject. Finally, mind the return period. If you argue that Carlisle suffered two once-in-a-century floods within ten years and conclude from that alone that the statistics have broken, you have made an arithmetic mistake rather than a geographical argument.

Complete the UK weather facts

Storm Desmond dropped _____ mm of rain on Honister Pass in 24 hours in December 2015, a UK record, because a corridor of very moist Atlantic air was forced to rise over the Cumbrian fells. Around 5,200 homes flooded, and a secondary effect of the flooding was the loss of power to roughly _____ properties when a substation in Lancaster went under. Evidence that UK weather is becoming more extreme comes from the long record rather than from any one storm: the UK passed _____ degrees Celsius for the first time in July 2022, and the ten warmest UK years have all occurred since _____. A one-in-a-hundred-year flood means a one _____ cent chance in any given year, not one flood per century.

Spot the three sound evidence statements

Select the THREE statements that could be used as they stand in an answer about UK weather becoming more extreme.

• The ten warmest years in the UK temperature record have all occurred since 2003, and the UK exceeded 40 degrees Celsius for the first time in July 2022 when Coningsby reached 40.3.
• Warmer air can hold more water vapour, so a warming climate is expected to produce more intense rainfall events, which is consistent with the record 24-hour totals seen during Storm Desmond.
• Sea level around the UK has risen by roughly 16 cm since 1900, so any given storm surge now starts from a higher base and reaches further inland.
• Storm Desmond was very severe, which proves that UK weather is becoming more extreme.
• Carlisle flooded twice in ten years, so the once-in-a-century statistics must have been wrong.
• Climate change directly caused Storm Desmond.

A named-example answer, marked

Use a named example of a recent extreme weather event in the UK to explain its effects and the responses to it. [9 marks] Storm Desmond struck north-west England on 5 and 6 December 2015, drawing moisture from a corridor of warm, wet Atlantic air that was forced to rise over the Cumbrian fells. The primary effects came directly from the rainfall, which reached 341.4 mm at Honister Pass in 24 hours, a UK record, with over 400 mm at Thirlmere across 38 hours. Because November had already saturated the ground, almost all of it ran off rather than soaking in, so rivers including the Eden rose to record levels and around 5,200 homes and businesses were flooded, with Carlisle inundated again only ten years after the 2005 floods and the 200-year-old Pooley Bridge swept away entirely. The most striking secondary effect reached people the water never touched: flooding of an electricity substation in Lancaster cut power to roughly 55,000 properties, closing schools and businesses, and total damage came to around 1.3 billion pounds. Responses divided the same way. Immediately, the Environment Agency issued severe flood warnings and mountain rescue teams, the fire service and the armed forces evacuated residents by boat, while rest centres and emergency generators were brought in. In the longer term the defences themselves were reconsidered, because Carlisle had been protected to a standard this storm exceeded, so schemes were reviewed and raised and catchment plans were rewritten to hold water back upstream through tree planting and upland storage rather than relying on walls in the town. The event therefore shows both how quickly the UK can respond and how a defence designed against yesterday's worst case can be overtaken. What earned the marks: a named event with precise dates and figures; effects separated into primary and secondary and responses into immediate and long-term, as the mark scheme expects; a causal link drawn between the saturated ground and the runoff rather than a list of what happened; and a closing sentence that says what the example shows.

Find the two secondary effects

Five things that happened during or after Storm Desmond. Two of them are secondary effects, meaning harm that followed on from the flooding rather than being caused directly by the water or the rain. Tap those TWO.

• Tens of thousands of properties across Lancaster lost electricity when the substation supplying them was inundated.
• A stone bridge that had stood over the River Eamont for two centuries was swept away by the flow.
• Schools and businesses across the area closed for days, and pupils lost teaching time while buildings were dried out.
• More rain fell on the fells in a single day than had ever been recorded anywhere in the UK.
• Around 5,200 homes and businesses were flooded across Cumbria and Lancashire.

Write the attribution sentence carefully

Assemble a sentence that links the storm to climate change without overclaiming.

Four decisions around a flood

Each stage is a real choice made before, during or after an event like Storm Desmond.

• 4 December 2015. Forecasts show an atmospheric river aimed at Cumbria and the ground is already saturated from a wet November. Issuing the highest level of warning disrupts thousands of lives, and forecasts can be wrong.
• The night of 5 December. Water is rising fast in residential streets, several roads are already impassable and the local substation is threatened.
• Spring 2016. Carlisle's defences, built after 2005, were overtopped. Raising them further is expensive, and higher walls in the town push the problem downstream.
• A local paper asks whether climate change caused the flood. You want to be accurate and still useful.

Argue from the evidence

Use evidence to suggest that weather in the UK is becoming more extreme. [9 marks]

• Open by distinguishing weather from climate, so it is clear you know a single storm is not a trend
• Give at least three pieces of evidence drawn from the long record, with figures and dates, such as the first 40 degree Celsius reading or the ten warmest years
• Use your named event, Storm Desmond, as an illustration of intensity rather than as proof on its own
• Explain the physical mechanism, that warmer air holds more moisture, so the evidence is linked to a cause rather than just listed
• Close with a careful judgement: say what the evidence does support and what it cannot show, and avoid claiming that climate change caused any particular storm