Fire weather seasons are overlapping more than ever before

Climate change is making wildfires more frequent and intense. A key factor behind this surge is the rise in “fire weather” – specific conditions that make it easier for fires to ignite and spread. Heat, dry air, low rainfall, and strong winds are all part of this volatile mix.

Recent research from the Helmholtz Center for Environmental Research (UFZ) and the University of New South Wales shows that the timing of fire weather seasons is shifting. Eastern Australia and western North America are now experiencing more overlap in their fire seasons than ever before.

The study, published in the journal Earth’s Future, reveals how this change could complicate international firefighting efforts.

Catastrophic fire seasons

Wildfires have devastated coasts on both continents. In January 2025, Los Angeles saw one of its worst fire disasters, with 29 lives lost and over 10,000 buildings destroyed.

Between September 2019 and March 2020, eastern Australia faced a catastrophic bushfire season that burned more than 12 million hectares of forest and bushland.

In times of crisis, countries have leaned on each other. Firefighters from Canada, the United States, and Australia have flown across the globe to offer support. These collaborations have saved lives and resources. But the window for such cooperation is shrinking.

Fire seasons are rising together

To understand what’s changing, the researchers analyzed global fire weather trends using the Canadian Fire Weather Index (FWI). This tool considers rainfall, temperature, humidity, and wind speed to flag days when wildfires are more likely.

Since 1979, the number of fire weather days that occur simultaneously in eastern Australia and western North America has been rising. Most of the overlap happens between July and December. In fact, the number of these simultaneous fire-prone days has been increasing by about one day per year.

“This is because the fire season in eastern Australia is starting earlier in spring and overlapping with the end of the fire season on the west coast of North America,” explained Dr. Andreia Ribeiro, a climate scientist at UFZ and lead author of the study.

Preparing for the future

The team didn’t stop at historical data. Using four climate models and multiple simulations, they explored what the future might look like.

The result? A continued rise in overlapping fire weather days – by as much as 4 to 29 days per year by the middle of this century.

“The number of overlapping fire weather days in western North America and eastern Australia will continue to increase,” said Dr. Ribeiro.

One key driver behind fire season timing is the El Niño Southern Oscillation. El Niño often leads to droughts and heatwaves in eastern Australia. Meanwhile, La Niña tends to bring drier, hotter conditions to western North America.

“Despite these generally opposing patterns, we found that during strong fire weather overlap, El Niño conditions are especially pronounced in the Central Pacific,” said Dr. Ribeiro. But even this climate system may not be enough to offset the bigger picture.

“Climate change is causing global temperature rises and increasing drought in some regions while the El Niño effect is expected to remain largely unchanged,” noted study co-author Dr. Jakob Zscheischler.

Overlapping fire seasons

The traditional schedule once worked in favor of cooperation. Western North America usually battled fires between June and October. Eastern Australia faced them from October to March. This left a gap that made it possible for countries to send help, but the gap is closing fast.

“These increasingly overlapping fire weather seasons in the US and Australia are narrowing the window for international cooperation and making it harder to respond quickly to large-scale wildfires,” said study lead author Dr. Doug Richardson from the ARC Center of Excellence for Climate Extremes at UNSW.

Rethinking firefighting strategies

The study suggests that current international agreements may no longer be enough. With shrinking timeframes for mutual aid, countries may need to rely more on their own fire services.

Australia and the United States will likely need to boost domestic resources – more personnel, more aircraft, and stronger infrastructure. The stakes are high.

As climate change continues to stretch fire seasons longer and push them closer together, the ability to act swiftly and independently could save thousands of lives and ecosystems.

The full study was published in the journal Earth’s Future.

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