Feeling hot, hot, hot: UK revises heatwave threshold

Heatwaves are common in several equatorial countries, less so in the temperate British climate, but climate change and rising temperatures prompted the Met Office on Tuesday to revise the threshold before a heatwave is declared.

A heatwave is described as an extended period of hot weather relative to the expected conditions of the area at that time of year, which may be accompanied by high humidity.

In August 2003, the UK experienced heatwave conditions lasting 10 days and resulting in 2,000 deaths. A record maximum temperature of 38.5 °C was recorded at Faversham in Kent.

As Britain prepares for summer this year, figures and maps show more areas in south-east England and the Midlands exposed to heatwave conditions since the early 1960s.

The Met Office said warming across the country has not been even with some regions experiencing more rapid change than others, with heatwave thresholds in eight counties in a band from Surrey to east Yorkshire changing.

The original heatwave thresholds were based on a reference climate period for 1981-2010. Under the most recent 1991-2020 climate averaging period introduced in January this year, six counties are moving from a 27°C threshold to 28°C, one from 26 to 27°C, and one from 25 to 26°C.

The UK experiences occasional heatwaves but of a lesser frequency and intensity of those seen elsewhere globally.

The summer of 2018 was the equal-warmest summer for the UK along with 2006, 2003 and 1976. The hottest day of the summer was on 27 July, with 35.6 °C recorded at Felsham, Suffolk. In July 2006, similar conditions occurred breaking records and resulting in the warmest month on record in the UK.

In the summer of 2019, the 2003 maximum temperature record was broken at Cambridge University Botanic Garden on 25 July, with 38.7 °C.

Mark McCarthy of the Met Office: “Climate statistics over time reveal an undeniable warming trend for the UK. Temperature rise has been greatest across parts of central and eastern England where they have increased by more than 1.0°C in some locations, while further north areas of Scotland and Northern Ireland have seen temperatures rise by closer to 0.7°C.”

Counties changing from a 27C to a 28C threshold: Surrey, Berkshire, Buckinghamshire, Bedfordshire, Hertfordshire, Cambridgeshire; counties changing from a 26C to a 27C threshold:

Lincolnshire; counties changing from a 25C to a 26C threshold: East Riding of Yorkshire.

McCarthy added: “Although heatwaves are extreme weather events research shows that climate change is making these events more likely. A scientific study by the Met Office into the Summer 2018 heatwave in the UK showed that it was 30 times more likely to occur now than in 1750 because of the higher concentration of carbon dioxide (a greenhouse gas) in the atmosphere”.

“As greenhouse gas concentrations increase heatwaves of similar intensity are projected to become even more frequent, perhaps occurring as regularly as every other year,” he said.

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