As temperatures climb towards 34°C in southern England and yellow heat health alerts are issued across the Midlands and southern England, many Britons are asking: what exactly counts as a heatwave in the UK? The answer is more specific than you might think.
A heatwave in the UK is officially defined by the Met Office as a period of at least three consecutive days where the daily maximum temperature meets or exceeds a regional threshold. These thresholds vary across the country: in London and the south-east, the threshold is 28°C; in northern Britain it is 25°C; and other regions fall somewhere in between. When these criteria are met, a heatwave is declared.
“Explains what a heatwave is in the UK, how it's defined, and why health alerts and restrictions matter.”
Heatwaves are not just about discomfort. They trigger health warnings from the UK Health Security Agency (UKHSA), which issues yellow, amber or red alerts depending on severity. A yellow heat health alert, like the one currently in force for the East Midlands, West Midlands, east of England, London, south-east and south-west England, warns of an increased risk to health for vulnerable people, such as the elderly and those with underlying conditions. It also warns of greater pressure on health and social care services, and an increased risk of water-related incidents such as drowning due to cold water shock.
The UK has seen three heatwaves so far this year, including a record-breaking spell in June when temperatures reached 37.3°C, the highest June temperature on record. The current heatwave, which began in early July, is expected to peak at 34°C in the south-east, but unlike the June heatwave, it is forecast to last longer – potentially well into the middle of July. The prolonged heat is caused by a ridge of high pressure linked to the Azores High extending north-eastwards, blocking Atlantic low-pressure systems and bringing settled, sunny weather.
For UK readers, the implications are practical. Travel, work and daily routines can be affected. In some regions, hosepipe bans have already been imposed: Southern Water has announced a ban in Hampshire and the Isle of Wight from 10 July, following record-breaking heatwaves that left river levels 25% lower than expected; South East Water has a ban in Kent. The bans stop customers using hosepipes for non-essential activities such as watering gardens or filling paddling pools. There is also a north-south split: while southern England swelters, western Scotland, Northern Ireland, Lancashire and the Lake District are cooled by an Atlantic breeze, keeping temperatures in the low to mid-20s Celsius.
Q: Why does the UK have different heatwave thresholds for different regions? The thresholds reflect the fact that average summer temperatures vary across the country. The south-east is generally warmer, so a higher threshold is needed to define exceptional heat, while cooler northern areas have a lower threshold so that dangerous heat is flagged appropriately.
Q: Are heatwaves linked to climate change? The source material does not provide expert commentary on climate change, but notes that the UK has experienced multiple heatwaves this year, including a record June temperature of 37.3°C. Such extremes are consistent with a warming climate, though the sources do not make that explicit link.
Q: What should I do during a yellow heat health alert? The UKHSA advises checking on vulnerable friends and relatives, avoiding sun exposure during the hottest part of the day (11am–3pm), staying hydrated, and keeping homes cool by closing curtains. The alert is a warning to be aware of health risks, not a panic signal.
What happens next? The current heatwave is forecast to peak on Thursday or Friday of the coming week, with temperatures reaching 34°C in the south-east. The yellow heat health alert remains in place until 8pm on Saturday 11 July. Beyond that, some forecasting models suggest the hot spell could persist into the middle of July, but uncertainty remains. Hosepipe bans are likely to remain in force until river levels recover, which could take weeks.