What are the effects of the UK heatwaves?

Meera Mahesh

Did you know the hottest temperature ever recorded in the UK was on the 25th of July 2020? It was 38.7 Celsius in Cambridge – that’s hot enough to fry an egg on the pavement (use a frying pan if you’re trying this)! Let’s have a look at what causes these increased temperatures, and how we as humans are affected.

What is a heatwave?

The Met Office, the UK’s national weather service, defines a heatwave as at least three continuous days, where the highest temperatures each day are higher than the ‘heatwave temperature threshold’. This threshold temperature varies depending on which part of the UK you are in. These temperatures are much higher than the average ‘hot’ temperature in these areas usually.


Threshold Temperature (Celcius)

Scotland, Northern Ireland, Wales, North and South West England


Lincolnshire, Cheshire, Dorset


Midlands, East Anglia, the home counties (which surround Greater London)




Why do they happen?

The reasons for why different weather patterns occur are mostly due to pressure systems. In a heat wave, there is a space of higher atmospheric pressure, which stops the warm air near the ground from rising, trapping it in place. Without rising air, there is no rain and fewer clouds, which means the direct sunlight makes the hot air even hotter.

Why do they feel hotter in some countries than others?

Have you ever wondered why 25 degrees in the UK feels so much hotter than 25 degrees abroad? The reason for this is to do with the design of the buildings, and humidity. In the UK, there are high levels of humidity, which means that sweat does not evaporate as easily. Humidity is the level of water in the air, so when it is more humid there is more water in the air which makes it feel tropical. This is why you get drenched in sweat after going for a short walk during some very hot days!

Houses have been designed in the UK to keep the heat trapped inside because of the usual cold temperatures. There are high levels of insulation, and no shade stopping the sunlight coming through the windows. In hotter countries like Australia, the buildings aren’t built to retain any heat, with poor insulation, and architectural features such as eaves (see diagram) which stop the sunlight from entering the house.

How do heatwaves affect humans?

So how does this all affect you?

Your body works best in a certain temperature range (around 36.1°C to 37.2°C).

When the temperature is too hot outside, your body has to work harder to keep cool and within the temperature range. The way your body does this is through sweating, which evaporates and cools you down, and also through making the blood vessels nearer to your skin wider which also allows heat to evaporate, which is why your skin gets flushed and red when you are exercising.

Sometimes you can get very tired and may get headaches and dizziness when you are hot. This is because you are dehydrated and have lost fluids and salt because you are sweating a lot and not drinking enough fluids. You may even experience heat exhaustion, which is when your body has overheated for a long period, and you might experience headaches, dizziness, loss of appetite, cramps and other unpleasant symptoms. If you don’t cool down in half an hour, this can progress to heat stroke, which can end in a coma, or even death.

We’ve already talked about how there are very few clouds around during a heatwave. This means that the sunlight is even more powerful than usual and has nothing blocking it. This makes being ‘sun-safe’ even more important, as the UV light that is given off from the sun can cause skin cancer. Some practices that can help you keep safe in the sun during hot weather includes limiting the time you are in the midday sun, staying in the shade, wearing sun cream, and drinking lots of water. Make sure you are safe when enjoying the nice hot weather!