London’s first red heat alert in four years reaches Putney

London faces its first red heat alert since 2022, the most serious warning there is, issued only when the heat becomes a risk to life even for healthy people. It covers Putney, Roehampton and the rest of SW15.

The heat is already here. Putney hit 36°C on Tuesday, which felt closer to 38°C in the humidity, and the Met Office expects the peak on Wednesday and Thursday, when the air itself reaches 38°C. The alert runs from 1am on Wednesday until 11pm on Thursday, and may be extended.

Red alerts are issued rarely. The last time London had one, in the July 2022 heatwave, an estimated 2,803 people aged 65 and over died from the heat in England. The reassuring part, as the UK Health Security Agency stresses, is that a few simple steps make a real difference.

If you can, stay home

South Western Railway is urging people to travel only if essential on Wednesday and Thursday, running fewer trains at reduced speeds. On the Underground, the District Line is already badly affected, with severe delays on the Richmond branch through East Putney and Southfields after a signal fault and heat-related speed limits. For most people, the simplest plan for the next two days is to stay out of the heat.

Cooling your home, and yourself

Close blinds and curtains on the windows that catch the sun, and keep windows shut while the air outside is hotter than the air indoors, opening them for a through-draught only once it cools down overnight. The relief will be limited this week, though, with the Met Office expecting overnight lows to stay above 20°C, the tropical nights that make it hard for homes and bodies to recover before the next hot day. Sleep in the coolest room you have. Here is the one most people get wrong: an electric fan only helps while the air is below about 35°C. Once it is hotter than that, a fan simply pushes hot air around and speeds up dehydration, so on the worst of Wednesday and Thursday it can do more harm than good. Do not point one straight at you, for the same reason.

Drink water steadily through the day rather than waiting until you feel thirsty; a good check is that your urine should stay a pale straw colour. Fruit juices, smoothies and sugary drinks actually dehydrate you, so reach for water or diluted squash instead, and go easy on alcohol. Keep half an eye on your medicines, too, because some need to be kept below 25°C or in the fridge, which is easily forgotten in a heatwave. And never leave anyone in a parked car, where the temperature climbs dangerously fast, least of all children, older people or pets. Pets feel the heat as much as we do, so keep them indoors through the hottest hours with shade and a full water bowl, and walk dogs early or late rather than at midday, when pavements get hot enough to burn their paws.

The signs to watch for

Heat exhaustion shows as heavy sweating, tiredness, dizziness, cramps, a headache or feeling sick. Move the person somewhere cool, get them sipping water, and cool their skin with a cold pack or a cloth wrung out in cold water, held under the armpits or on the neck, which brings the temperature down fast. They should feel better within 30 minutes. If they do not, or if someone becomes confused, stops sweating or feels very hot to the touch, that is heatstroke, a medical emergency, and you should call 999. The NHS has the full list of signs to watch for.

Where to cool down, and where not to

Putney Library, a supermarket or a place of worship will often be cooler than a flat when home becomes unbearable, and Wandsworth Council’s heatwave guidance page links to a map of registered cool spaces across the borough. What looks like the obvious answer, a dip in the Thames or the ponds on the Common, is not one: open water is far colder than it looks even on a baking day, the river runs on strong tides, and trying to cool off there is how summer days turn into emergencies.

Check on the people nearby

The people most at risk are older neighbours, babies and young children, anyone with a heart, breathing or other long-term condition, people on certain medications, and those sleeping rough or living alone. Wandsworth Council has asked community and voluntary groups to check in on them, and Thamesfield’s neighbourhood police have emailed residents directly with the same request. The same goes for the rest of us. A knock on a neighbour’s door costs nothing.

Bins, schools and what is off

If you are a parent you have probably already received an email letting you know what your child’s school is doing to deal with the heat. A quick review of messages from a number of schools shows that some schools are closing early at lunchtime, some have cancelled games and sports days, and most have moved lessons out of the hottest classrooms. It is worth checking to see if your school is ending early today and tomorrow.

A number of events have also been cancelled, including the Poets in Putney anniversary night, due on Thursday. So if you have tickets for anything, this week it is worth checking to see if it is still on. You should receive a full refund if it is cancelled.

There is fuller advice on the UKHSA’s hot-weather guidance.