UK weather and climate: characteristics and hazards

OCR J383 Paper 1 tests UK climate with questions on why the UK's weather is variable, the role of air masses and pressure systems, and the impacts of named weather events. Expect describe-the-weather-map questions and case-study questions on recent extreme events.

The UK's climate

Temperate maritime climate: moderate temperatures; rainfall throughout the year; changeable conditions.

• Temperature range: mild (London: average 5 degrees C in January, 22 degrees C in July).
• Rainfall: 600–1,000 mm/year in most of England and Wales; 2,000–3,000 mm in the Lake District/Scottish Highlands.
• Sunshine: south-east averages 1,800+ hours/year; north-west averages 1,200 hours/year.

Why is UK weather so changeable?

1. Location: 50°–60°N — between the cold polar air to the north and warm subtropical air to the south; frontal systems constantly cross from the Atlantic.
2. Westerly airflow: the UK lies in the path of the North Atlantic jet stream — a high-altitude fast-moving air current that steers low-pressure systems from west to east.
3. Mid-latitude position: in the Ferrel Cell zone — where Polar and Hadley cells interact, creating unstable frontal weather.

Air masses

An air mass is a large body of air with broadly uniform temperature and humidity characteristics, formed when air stagnates over a source region.

Air mass	Source	Temperature	Humidity	Effect on UK
Polar Maritime (Pm)	North Atlantic	Cold	Wet	NW England: heavy rain, low cloud
Tropical Maritime (Tm)	Subtropical Atlantic	Warm	Wet	SW England: mild, cloudy, drizzle
Polar Continental (Pc)	Siberia/N. Europe	Very cold	Dry	E England: cold, dry, snow in winter
Tropical Continental (Tc)	Sahara	Very hot	Dry	SE England: heatwaves in summer
Arctic Maritime (Am)	Arctic Ocean	Very cold	Wet	Scotland: very cold, snow

Pressure systems

Depressions (low pressure)

• Formed when warm and cold air meet → frontal systems.
• Characteristics: cloudy, wet, windy; associated with weather fronts (warm front → warm sector → cold front).
• UK receives ~200+ named low-pressure systems per year from the Atlantic.
• Depressions track NE across the UK in 1–3 days.

Synoptic chart features:

• Closely-spaced isobars → steep pressure gradient → strong winds.
• Warm front (red semicircles): light/moderate rain advancing ahead; temperature rises after passage.
• Cold front (blue triangles): heavy, showery rain; rapid temperature fall; wind veer.

Anticyclones (high pressure)

• Sinking, stable air; clear skies; light winds.
• Summer anticyclones: hot, sunny, dry → drought risk; heatwaves.
• Winter anticyclones: cold, clear nights → frost; radiation fog; icy roads.

Weather hazards

1. Flooding

Types:

• River (fluvial) flooding: rivers overflow their banks — excessive rainfall saturating the catchment.
• Surface (pluvial) flooding: intense rainfall exceeds drainage capacity; runoff floods urban streets.
• Coastal flooding: storm surges from deep depressions; rare in UK interior but major risk in Thames Estuary, Somerset Levels.

Case study: Somerset Levels floods (2014):

• December 2013 – February 2014: the wettest UK winter since records began.
• 65 km2 of farmland flooded; 600 homes affected; villages (Moorland, Burrowbridge) cut off for weeks.
• Estimated cost: £100 million.
• Causes: blocked drainage channels (failure to dredge rivers Tone and Parrett for 20 years); rapid urbanisation increasing runoff; exceptional rainfall.
• Response: emergency dredging; temporary pumping; flood defences upgraded; Somerset Levels Flood Action Plan.

2. Drought

UK drought (2022):

• England experienced its driest summer since 1976.
• Hosepipe bans in 8+ water company areas.
• UK temperature record: 40.3 degrees C at Coningsby, Lincolnshire (19 July 2022) — driven by Tropical Continental air mass from the Sahara.
• Thames Water declared drought emergency; river flows at record lows.
• Agricultural losses: 20–30% reduction in potato and vegetable yields.

3. Storms

Storm Desmond (December 2015):

• Low-pressure system brought record 24-hour rainfall: 341.4 mm at Honister Pass, Cumbria — UK record.
• Flooding across Cumbria, Lancashire, Yorkshire; Carlisle city centre flooded.
• 50,000+ homes without power; 500+ flood warnings; £500 million damage.
• Climate change link: warmer atmosphere holds more moisture → more intense rainfall.

Storm Eunice (February 2022):

• 196 km/h gust recorded at Needles, Isle of Wight — UK's highest ever recorded.
• Widespread damage across England and Wales; 4 deaths; 1.4 million without power.

Climate change and UK weather hazards

Climate change is projected to:

• Increase summer temperatures and drought frequency (more Tropical Continental air mass episodes).
• Increase intensity of winter storms and rainfall events.
• Raise sea levels by 0.3–1.0 m by 2100 → greater coastal flooding risk.
• Reduce summer rainfall in the south-east; increase winter rainfall overall.

Common OCR exam mistakes

1. Confusing weather (short-term conditions) and climate (long-term averages) — the examiner will penalise this.
2. Not naming the specific air mass or pressure system causing a weather type.
3. Forgetting that winter anticyclones bring cold, frosty conditions — not just summer sunshine.
4. Not including named case studies with statistics — "a flood happened" scores less than "Somerset Levels 2014; 65 km2 flooded; £100 million cost."