Study finds fire weather days nearly tripled worldwide in 45 years
The number of days marked by hot, dry and windy conditions that fuel extreme wildfires has nearly tripled globally over the past 45 years, with researchers concluding that human driven climate change accounts for more than half of the increase.
A study published Wednesday in Science Advances reports that between 1979 and 1993 the world experienced an average of about 22 days per year of what scientists call synchronous fire weather, periods when multiple regions simultaneously face conditions conducive to severe wildfires. By 2023 and 2024, that figure had risen to more than 60 days annually.
The research, led by scientists at the University of California, Merced and the University of East Anglia, represents the first global assessment of synchronized extreme fire weather events. These are instances in which dangerous fire conditions occur at the same time across different parts of the world, increasing the strain on firefighting systems.
John Abatzoglou, a fire scientist at UC Merced and coauthor of the study, said the observed shifts heighten the likelihood that many regions will confront blazes that are difficult to contain. He noted that the expansion of overlapping high risk periods reduces the window in which countries can assist one another with personnel and equipment.
Lead author Cong Yin explained that the growing overlap of fire seasons is narrowing opportunities for international cooperation. As an example, the study found that the United States and South Africa now experience an average of four days each year with simultaneous extreme fire weather, with that overlap increasing by about 1.2 days per decade.
To conduct the analysis, researchers examined global meteorological data from 1979 to 2024 and calculated daily values of the fire weather index, a measure used to estimate wildfire risk based on temperature, humidity, wind and precipitation. They then assessed long term climate trends and compared them with records of burned area and smoke pollution to evaluate real world impacts.
Using climate simulations, the team compared current conditions with a counterfactual scenario that excluded greenhouse gas emissions from fossil fuel combustion. The results indicate that more than 60 percent of the global rise in synchronous fire weather days can be attributed to climate change linked to the burning of coal, oil and natural gas.
The study highlights specific regions where pressure on cross border firefighting cooperation is intensifying. In Portugal and Spain, for instance, the number of days with simultaneous extreme fire weather has increased by more than 12 days since 1979.
Mike Flannigan, a wildfire expert at Thompson Rivers University in Canada who was not involved in the research, said the findings are significant because extreme fire weather is the primary driver behind the growing global impact of wildfires. He noted that regions which once had staggered fire seasons, allowing them to share resources, are increasingly facing concurrent outbreaks.
Abatzoglou warned that as synchronized fire conditions become more common, the capacity of countries to respond effectively may be tested. When multiple areas are burning at once, competition for aircraft, crews and equipment intensifies, raising the risk that fires will grow larger and more destructive.
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