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Climate change significantly heightens the threat of wildfires across various global regions, primarily due to specific weather conditions termed “fire weather,” which promote the spread of these fires.
Recent collaborations between researchers at the Helmholtz Center for Environmental Research (UFZ) and their Australian counterparts have revealed that fire weather seasons are increasingly overlapping in eastern Australia and western North America. This study underscores potential impacts on cross-border coordination among firefighting agencies in Canada, the United States, and Australia. The findings are published in Earth’s Future.
Both the western regions of North America and the eastern parts of Australia have faced severe wildfire challenges. A notable incident occurred in January 2025 when wildfires in Los Angeles led to the destruction of over 10,000 structures and resulted in 29 fatalities. Similarly, between September 2019 and March 2020, eastern Australia experienced one of its worst bushfire seasons, with more than 12 million hectares of forest and grassland lost. Fire crews from Canada, the United States, and Australia have a history of supporting each other during such disasters.
The team aimed to discern how the fire weather seasons are shifting due to climate change. Utilizing the Canadian Fire Weather Index (FWI)—a widely recognized index for evaluating fire risk that considers factors like rainfall, temperature, humidity, and wind speed—they identified what they termed “fire weather days,” days when wildfire risk is elevated.
From their analysis, the researchers observed a growing overlap in fire weather days since 1979, suggesting an increased wildfire risk. The highest overlap, around 75%, occurs between July and December, with the number of overlapping fire weather days rising by an average of one day per year over the last four decades.
Dr. Andreia Ribeiro, a climate scientist at UFZ and lead author of the study, notes, “This pattern emerges because the fire season in eastern Australia is beginning earlier in the spring, coinciding with the tail end of the fire season in western North America.”
Further analysis utilizing four climate models projected that this trend is likely to continue. Depending on the chosen model and future global warming scenarios, the overlap in fire weather days could increase by anywhere from 4 to 29 days per year by mid-century.
The variability of the El Niño Southern Oscillation—a climatic phenomenon influencing oceanic and atmospheric circulation—plays a key role in this overlap. Eastern Australia’s fire weather is generally associated with El Niño conditions, which bring elevated sea surface temperatures, often resulting in droughts and heatwaves. Conversely, western North America’s fire weather is more frequently associated with La Niña conditions, which represent opposite climatic scenarios.
Dr. Ribeiro elaborates, “Despite these generally diverging conditions, we have observed that when fire weather overlap is pronounced, El Niño patterns become particularly notable in the Central Pacific.” Nonetheless, the researchers anticipate that the effects of climate change will dominate over El Niño impacts in the foreseeable future.
Prof. Dr. Jakob Zscheischler, also from UFZ, emphasizes that climate change is driving global temperature increases and exacerbating drought conditions, while the El Niño effect is likely to remain stable. This evolution poses significant challenges for the firefighting collaboration among US, Canadian, and Australian services, which traditionally assist each other during emergencies by sharing resources and personnel. Previously, the distinct timings of fire seasons—June to October in North America and October to March in Australia—allowed sufficient time for international support.
Dr. Doug Richardson, lead author and researcher at the ARC Center of Excellence for Climate Extremes, warns, “The shifting fire weather seasons in the US and Australia are compressing the timeframe for cooperation and complicating rapid responses to major wildfire outbreaks.”
As a result, there is an urgent need to reassess international firefighting agreements and national capacities to adapt to these new realities. Both Australia and the US will need to enhance their domestic firefighting capabilities to decrease dependency on international support.
More information: Doug Richardson et al., “Increasing Fire Weather Season Overlap Between North America and Australia Challenges Firefighting Cooperation,” Earth’s Future (2025). DOI: 10.1029/2024EF005030
Source
phys.org