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Heatwave Definition Change – Reading University Comment

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On the news that the Met Office has raised the temperature threshold to define a heatwave in parts of the UK, including Berkshire – https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2022/heatwave-threshold-changes 

Heatwave Definition Change


Professor Hannah Cloke, a natural hazards researcher at the University of Reading, said:

“The Met Office recalibration of the official heatwave definition for the UK shows how simple it is. It is an effort to maintain the idea that in the UK we call hot weather ‘a heatwave’ if it feels particularly hot, in the middle of the afternoon, for more than a couple of days in a row.

“With average temperatures rising across the UK, we have to shift the definition of what ‘particularly hot’ is, otherwise that definition becomes increasingly meaningless.

“There are benefits and downsides to having such a simple definition of a heatwave. It means that it is easier for people to understand. However, there are a series of different heat warnings, all triggered at different points to avoid heat impacts and deaths, depending on which nation of the UK you live in.

“People need to know what to do in advance and take action quickly when extreme weather is coming. If people don’t or can’t do anything to protect themselves against extreme heat, then people die. It doesn’t help to declare a ‘heatwave’ so often that people stop listening, but neither does having an array of poorly understood definitions of heat risk.

“As UK summers get hotter due to climate change, definitions will mean nothing at all if we continue to ignore the risks and fail to adapt our buildings and our habits to cope with the heat.”

Prof Nigel Arnell, Department of Meteorology, University of Reading, said:

“This is further and clear evidence of how climate change is affecting our weather here in the UK. We have to get used to a ‘new normal’ – what we previously thought of as an unusually hot summer will soon become common.

“We have to make sure that our homes, offices and infrastructure can cope now with the anticipated higher temperatures so that we can reduce the ill-health and disruption that heatwaves produce.

“And things are only going to get worse. In a few years we’ll probably have to change the definitions again otherwise we’ll have a heatwave every summer.

“Reducing greenhouse emissions will slow the increase over the long term, but we need to better prepare for heatwaves now.”



Chloe Brimicombe, a PhD heatwaves researcher at the University of Reading, said:

“In a world where temperatures are rising, it is inevitable we will have to redefine temperature extremes. This move is sensible in updating heatwave definitions according to hotter baseline temperatures and in line with recently-altered heat health thresholds.

“However, thresholds based on trends that don’t capture impact are pretty meaningless. It is likely to result in fewer heat warnings being issued in the UK, and these are important to encourage action both nationally and individually to protect people’s wellbeing and lives.

“Just because hot weather is no longer considered unusual, it does not mean it no longer poses a threat to our health and infrastructure. Temperatures in the mid twenties Celsius are more than enough to affect outdoor workers, increase death rates and damage crops.

“The time is now to use temperature and humidity to better address health risks. We need this early warning system as key adaptation measure along with other factors such as urban greening and climate education that includes heatwaves.”

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