Chronic drought, not acute heatwave, drives record summer live fuel moisture lows in temperate heathland

Abstract Wildfire risk is increasing in temperate heathlands. These ecosystems have previously been protected from severe summer wildfires because of their phenologically-high live fuel moistures (LFMC), but extreme weather events are increasingly overriding this resistance, leaving heathlands vulnerable to wildfire. Here we show the impact of experimental and observed meteorological drought on the LFMC and flammability of Calluna vulgaris from 2024–2025 and compare this to the impacts of the acute July 2022 heatwave in the UK. The prolonged drought in 2025 disrupted the phenological green-up of Calluna , leading to the lowest summer LFMC (44%) ever recorded in temperate heathlands and exceeding the previously recorded low during the 2022 heatwave by ~ 50%. Our findings suggest chronic extreme drying rather than acute temperature extremes pose the greatest risk for wildfires in temperate heathlands and highlight the emergence of a new era of wildfires characterised by non-linear LFMC dynamics under extreme weather conditions.