UK heatwave: What is a heatwave? Amber heat health alert issued for most of England

Many parts of the UK are experiencing hot weather at the moment, with temperatures in some areas forecast to reach 32C (89.6F) by midweek.

An amber heat warning is in place across eight regions in England until Sunday night. It means that the elderly and people with certain health conditions should be extra careful.

The regions included in the warning are: London, the South East, the South West, the East and West Midlands, the East, North West and Yorkshire and Humber.

The hot conditions will be also be felt in Wales, while parts of Scotland and Northern Ireland could see "unseasonably high temperatures".

What is a heatwave?

A heatwave describes a prolonged period of unusually hot weather

A heat wave is a period of unusually hot weather.

To be considered a heatwave, temperatures have to be above normal averages for the time of year in a specific area.

In the UK, a heatwave is declared when temperatures either reach or go beyond the threshold for a particular location for three days in a row.

This temperature threshold is different for each UK county, as it's generally warmer in southern parts of the UK than northern areas.

You can see the UK temperature threshold map provided by the Met Office, who monitor UK weather, below.

Why do heatwaves happen?

Heatwaves are most common in summer when high air pressure develops across an area.

High pressure causes warm air to sink. The result is a dome of hot air that traps the heat near the ground.

These heatwaves can occur in the UK due to the location of the jet stream.

A jet stream is a fast-flowing current of air that travels around the planet. It occurs when warmer air from the south meets cooler air from the north.

The one that affects weather in the UK is called the Polar Front Jet.

Jet streams play a big role in the amount of rainy (unsettled) weather we get, or if we are going to have warm and sunny (settled) weather.

When the jet stream is below the UK, it creates low pressure in the atmosphere, making wetter, windier and colder conditions.

But when the jet stream moves further north of the UK, we tend to get warmer weather.

How serious is a heatwave?

What do you do to keep cool in hot weather?

Very hot days and warm nights can affect our health so it's important to keep cool and stay hydrated - that means drinking more water than you might do normally and cooling down if you feel too hot.

In the UK, there are five different heatwave levels. These are:

Level zero: This covers long-term planning to reduce the risks of heatwaves and the impact of climate change in the future.

Level one (Green): This is put in place every year between the 1 June and 15 September. It means people, including those who work in healthcare know what to do if temperatures do rise and the alert level is raised.

Heat warning on a motorway from 2022

Level two (Yellow): This level is issued when forecasts show that there is a high chance temperatures will go above the threshold for an area within a few days. It's important for those working in healthcare to be aware of the yellow alert as they will act to be prepared to look after those who might be affected by the heatwave.

Level three (Amber): A level three warning is issued when the Met Office confirms threshold temperatures for one of more regions have been reached for one day and the following night, and the forecast for the next day shows a high likelihood that the threshold temperature will be met again.

Healthcare services will put things in place to look after high-risk groups, such as the elderly or those with certain health conditions, who are more likely to be affected by very hot weather.

Level four (Red): This level is reached when a when a prolonged hot spell becomes severe and could end up impacting people both inside and outside of high-risk groups.

Is climate change responsible for heatwaves in the UK?

Heatwaves are extreme weather events and although it's not unusual for heatwaves to happen, research shows that climate change is making them more frequent and extreme.

The Met Office says that heatwaves are 30 times more likely to occur now than before a time known as the industrial revolution more than 100 years ago - when the burning of fossil fuels and resulting release of greenhouse gasses into the atmosphere started to happen more often.

The Earth's surface temperature has risen by 1°C since that period and UK temperatures have risen by a similar amount in that time too.

A new record-high temperature for the UK of 40.3ºC was recorded at Coningsby in Lincolnshire on the 19 July 2022 and, although the UK experiences occasional heatwaves, they currently aren't as frequent or hot as elsewhere in the world.

But, global warming means that heatwaves in the UK are predicted to occur as often as every other year by the 2050s.