Heatwaves in the UK have led to unseasonable drying of vegetation bypassing natural ecological processes that limit the spread of wildfires, a new study has found.
In a paper published in the journal Communications Earth & Environment , a team of researchers led by the University of Birmingham have been studying moisture levels in plant life and carbon-rich soil around the UK to understand variations that affect the risk of wildfire. Alongside their three-year sampling period, the first long term survey of vegetation and soils that acts as fuel in wildfires collected across the UK, the team collected samples during the 2022 heatwave that resulted in an unprecedented number of wildfires, with a 500% increase in 999 calls and 14 major incidents declared .
The team found that samples taken during the 2022 heatwave were unlike anything collected during the previous three years.
Samples of soil, dead vegetation and living vegetation collected during the previous three-year period suggest that the moisture content of dead heather is primarily affected by weather, while drier summer conditions actually sees living heather increasing their moisture content. Soil moisture meanwhile was not just impacted by climatic conditions, but also by geographical conditions including elevation and underlying substrate rock.
However, the usual variations in moisture values were missing during the heatwave as the extreme heat conditions have led to dry soil as well as living and dead vegetation all having significantly less moisture. The team highlight that future climate change-related extreme heat events are likely to increase the likelihood and severity of wildfires in the UK due to this unseasonable drying effect.
Dr Katy Ivison from the University of Birmingham and first author of the study said: "Man-made climate change is having a serious financial and ecological impact across the UK and leading to wildfires spreading in areas not traditionally at risk.
"Our latest study shows how extreme weather conditions which are becoming increasingly common are leading to heat that is overwhelming the typical ways that heathland areas protect themselves against destructive wildfires. The three-year survey our team conducted has found that there is a normal variation in moisture content between the three fuel sources we studied that by and large balances itself out. Dead heather is affected by weather conditions during the summer but the living heather generally tends to take on more moisture in the summer months during green up, after seeing drier conditions during the spring.
"The extreme heat of the 2022 heatwaves, and further dry conditions in the last few years including record breaking weather in 2025, are likely to become the new normal in the UK. This extreme heat leaves the UK at much greater risk of wildfires that are a threat to human life, our homes, infrastructure, ecosystems and their wildlife."
Spring usually sees most wildfires – but heatwaves changing this pattern
Live heather drying out during the spring is actually a driver of wildfire occurrences during the year, while greening during the summer provides a natural mitigation against fire spread in peatlands and heathlands.
However, the data from 2022 shows that live vegetation has a limit on its ability to weather hotter conditions. In such extreme hot weather, samples suggest that there is an increased risk of severe wildfires spreading from one ecosystem to another due to uniform conditions in which fires can take hold.
Samples taken from around the UK also showed that the South East and East Anglia were most affected by heatwave conditions, largely driven by the most extreme temperatures including 40oC heat recorded in Lincolnshire.
Professor Nick Kettridge from the University of Birmingham and senior lead author of the paper said: "This is an important study to better understand how extreme weather conditions change our usual understanding of wildfire risk.
"We may be substantially underestimating the danger posed by wildfire through the summer, considering the risk to be low in areas of the country that have been historically resistant to summer fire. But heatwaves this year as well as 2022 have demonstrated the threat we face."
The study was funded by the NERC Highlight project Towards a UK Fire Danger Rating System NE/T003553/1. Https://ukfdrs.com/
