High-risk conditions for fires are increasingly happening across countries at the same time, making wildfires even more challenging to tackle, new research reveals.
Scientists from UC Merced and the University of East Anglia found this synchronized extreme fire weather — characterized by exceptionally warm, dry and often windy conditions — has increased strongly worldwide since 1979, becoming more widespread throughout regions, not just in single locations.
When these widespread high-risk days occur, there is also more fire activity and worse air quality in several regions, not just locally. These days also narrow the window for firefighting coordination, potentially straining existing international firefighting cooperation between, for example, the United States, Australia, Canada, Europe and South Africa.
In many areas, the number of high-risk days occurring simultaneously has more than doubled, with extreme fire weather increasing fire danger by enhancing vegetation's susceptibility to ignition and promoting spread.
“This ultimately makes wildfires more difficult to deal with at the times when they are most threatening,” said Matthew Jones of the Tyndall Centre for Climate Change Research at UEA. “Addressing these challenges requires coordinated international efforts, including the implementation of early warning systems, enhanced wildfire management strategies and clear communication between agencies.”
Publishing its findings today in Science Advances, the team estimates that more than half of the observed increase is driven by human-caused climate change, while natural climate variability can strongly amplify synchronicity in some regions. The researchers warn there is an urgent need for “more robust and adaptive” strategies in global fire management.
Previous work mainly examined synchronous fire weather in a few regions, such as the western United States, Europe or Australia. This study is the first to measure and visualize the phenomenon globally, and to distinguish two types: synchronicity within a region, where many places in the same region experience extreme fire weather on the same day; and synchronicity between regions, where two or more regions experience it on the same day.
“Currently, regions such as Europe and Southeast Asia, and fire-prone countries such as the United States, Canada and Australia, have established bilateral and multilateral firefighting cooperation systems, which have been effective in managing recent major wildfires,” said Cong Yin, a postdoctoral researcher at UC Merced and the Chinese Academy of Sciences. “However, when extreme fire weather happens in many places at once, it increases the likelihood of widespread fire outbreaks and strains firefighting capacity, because crews, aircraft, and equipment can’t be easily shared when everyone needs help at the same time.
“A key takeaway is that the growing overlap in fire-danger seasons can shrink the ‘window’ when countries or regions can effectively support each other,” said Yin, who is affiliated with UC Merced’s Sierra Nevada Research Institute . “For example, the United States and South Africa average four same-day extreme fire weather days per year, increasing by 1.2 days per decade.”
These findings help in understanding concurrent extreme fire weather and preparing for an increasingly fire-prone future, Yin said. They also emphasize the compounding effects on air quality, public health, and fire management.
In one example of international cooperation during the 2023 Canadian fire season, firefighters from South Africa and other countries across the world helped tackle hundreds of devastating wildfires that destroyed homes and land.
The researchers found clear hotspots where the strain on cooperation networks that share firefighting resources is set to grow most rapidly. For example, in Portugal and Spain, same-day extreme fire weather days per year have increased by more than 12 since 1979.
In addition, natural climate variability can increase synchrony in specific regions, such as Equatorial Asia, which sees many more of these fire-weather days during El Niño years.
The analysis found North America, Europe, Boreal Asia, the Middle East and South America experience the highest levels of simultaneous inter-regional fire weather, occurring on the same day in at least one other region for an average of more than 30 days per year.
In lower- to mid-latitude regions, including South America, Central and East Asia, Africa and the mainland United States, the annual average number of these days during 2001–2024 was three to seven times higher than during 1979–2000.
Simultaneous fire weather tends to be more strongly associated with poorer air quality in boreal regions, Equatorial Asia, Africa and South America. In Europe, during the top 25% of years with the most synchronous fire weather days, population exposure to fire-sourced air pollution is almost 200% higher than in other years.
The team, which also included researchers from the University of Washington and Boise State University, used global weather data to calculate daily Fire Weather Index values worldwide from 1979–2024, and identified when extreme fire‑risk days occurred simultaneously across large or multiple regions. They examined how human‑driven climate change and natural climate patterns such as El Niño influenced these events, and then compared them with actual burned area and smoke pollution to assess real‑world impacts.
The research was supported by funding from the National Science Foundation, the U.S. Department of the Interior's Joint Fire Science Program and by a public grant via the UK Natural Environment Research Council.
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