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Climate change is heightening the threat of wildfires across various regions globally. This escalation is linked to specific climatic conditions—termed fire weather—that promote wildfire outbreaks. A collaborative research effort between the Helmholtz Centre for Environmental Research (UFZ) and scientists from Australia has identified an increase in the overlap of fire weather seasons between eastern Australia and western North America. Their findings, published in Earth’s Future, delve into the causes of this shift and its repercussions for cross-border fire service cooperation in Canada, the US, and Australia.
Both the west coast of North America and the east coast of Australia have faced significant wildfire challenges. A notable instance occurred in January 2025, when wildfires in Los Angeles resulted in over 10,000 building damages and 29 fatalities, as reported by various media outlets. Similarly, eastern Australia experienced one of its most catastrophic bushfire events from September 2019 to March 2020, which devastated more than 12 million hectares of forest and bushland. Firefighters from Canada, the US, and Australia have been instrumental in supporting one another during these emergencies and others.
This international team of scientists aimed to explore how climate change is altering the timing of fire weather seasons in these two regions. They employed the Canadian Fire Weather Index (FWI), a globally recognized meteorological tool for assessing fire risk by considering factors such as rainfall, temperature, relative humidity, and wind speed. Through this method, the researchers pinpointed days classified as high-risk for wildfires. Their analysis revealed a notable increase in the overlap of fire weather days since 1979.
The peak occurrence of overlap—approximately 75%—was identified between July and December. Over the past four decades, the simultaneous fire weather days in eastern Australia and western North America have been increasing at a rate of about one day per year. “The fire season in eastern Australia is now commencing earlier in the spring, leading to an overlap with the concluding fire season on the west coast of North America,” explains Dr. Andreia Ribeiro, UFZ climate scientist and primary author of the study, part of a project funded by the German Academic Exchange Service (DAAD).
The research team also assessed future projections for the duration of this seasonal overlap, employing four distinct climate models and numerous simulations to factor in uncertainties. The findings indicate a definitive trend: “The number of overlapping fire weather days in western North America and eastern Australia is likely to continue rising,” notes Ribeiro. Depending on the climate models considered and potential future global warming scenarios, this increase could range from 4 to 29 additional days per year by mid-century.
This overlap is influenced in part by fluctuations in the El Niño Southern Oscillation, which governs the atmospheric and oceanic circulation in the equatorial Pacific. Typically, fire weather in eastern Australia corresponds with El Niño conditions—characterized by elevated sea surface temperatures—resulting in droughts and heatwaves. Conversely, western North America’s fire weather is frequently associated with La Niña conditions, which represent the opposing climate pattern. “Even though these patterns are usually contrary, we observe that strong overlaps in fire weather are distinctly linked to pronounced El Niño conditions in the Central Pacific,” says Ribeiro. Nonetheless, the anticipated impacts of climate change are expected to eclipse the effects of El Niño in the medium term. “Climate change is driving global temperature increases and exacerbating droughts in certain areas, while the effects of El Niño are projected to remain relatively stable,” adds Prof. Dr. Jakob Zscheischler, UFZ climate scientist and co-author.
This situation presents significant challenges for collaborative efforts among fire services in the US, Canada, and Australia, which have historically aided each other by sharing personnel and resources during wildfire responses. Previously, fire seasons were distinctly timed: the west coast of North America typically experienced them from June to October, while eastern Australia’s season ranged from October to March. These intervals allowed ample opportunity for teams to lend support when necessary. “However, the diminishing differences in fire weather seasons between the US and Australia are shortening the window for international cooperation, complicating rapid responses to widespread wildfires,” explains Dr. Doug Richardson, lead author and researcher at the ARC Centre of Excellence for Climate Extremes, University of New South Wales (Australia). As a result, existing international agreements regarding firefighting cooperation, as well as national firefighting strategies, must be reassessed. Both Australia and the US may need to bolster their domestic firefighting resources to lessen dependency on international assistance.
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