The number of days when weather conditions align in ways that help wildfires ignite and spread is rising across the globe, according to a study published in Science Advances on Wednesday. The research team focused on “fire weather,” defined by conditions including heat, strong winds and dry air and ground—factors that can make it easier for fires to erupt and spread widely. The authors say the pattern is becoming more synchronized, so multiple regions can face fire-friendly weather at the same time, reducing the ability of one area to rely on assistance from neighbors that are also dealing with fires.
In the analysis, the researchers did not examine specific blazes. Instead, they calculated how often the planet’s different regions meet the weather criteria for what they call “synchronous fire weather,” meaning conditions are favorable for fires across large areas at the same time. They report that in 1979 and over the following 15 years, the world averaged 22 synchronous fire-weather days a year for flames confined within large global regions. In recent years, the annual average rose to more than 60 days in 2023 and 2024.
Cong Yin, a fire researcher at the University of California, Merced and the study’s lead author, said the findings reflect a shifting likelihood of widespread outbreaks as the right weather aligns more often. “It increases the likelihood of widespread fire outbreaks, but the weather is one dimension,” Yin said. He added that other ingredients matter as well, including oxygen, fuel such as trees and brush, and ignition sources such as lightning, arson or human accidents.
John Abatzoglou, a fire scientist at UC Merced and a co-author, warned that the trend makes suppression harder in many places. “These sorts of changes that we have seen increase the likelihood in a lot of areas that there will be fires that are going to be very challenging to suppress,” Abatzoglou said. He argued in the study’s framing that when more regions experience fire-favorable weather concurrently, the global system for managing wildfire disruptions can start to strain.
The authors attribute the increase in synchronous fire-weather days to human-driven warming, according to the study’s findings. Abatzoglou and Yin said the research shows more than half of the global increase is caused by human-caused climate change, and Yin said more than 60% of the increase can be traced to warming driven by emissions from burning coal, oil and natural gas. The researchers said they used computer simulations to compare recent conditions with a counterfactual “fictional world” without the added greenhouse gases from fossil-fuel burning.
The study’s regional results show larger changes in some places than others. For the continental United States, the researchers reported that from 1979 to 1988 the region averaged 7.7 synchronous fire-weather days per year. They said that in the last 10 years that average rose to up to 38 days per year. The changes are even steeper in parts of South America, the study found.
Yin said southern South America averaged 5.5 synchronous fire-weather days per year from 1979 to 1988. Over the last decade, he said that number rose to 70.6 days per year, including 118 days in 2023. Of 14 global regions analyzed, Yin said only Southeast Asia saw a decrease in synchronous fire-weather days, which he attributed “probably” to increasing humidity in that area.
The study highlights why timing matters for wildfire impacts and resource planning, even though it does not model individual fires. Fire scientist Mike Flannigan of Thompson Rivers University in Canada, who was not part of the study, said the work is important because extreme fire weather is a major driver—though not the only one—behind rising wildfire impacts worldwide. Flannigan said the overlapping timing can also matter for logistics: regions that used to have fires in different seasons could share resources, but as fire weather shifts toward synchronization, that coordination becomes harder, he said.
The findings arrive as countries and agencies face increasingly intense and overlapping wildfire seasons that can test firefighting capacity. By tying the rise in risk to a quantified increase in synchronized fire-weather conditions—and by linking much of that increase to climate change—the study provides a framework for anticipating how often multiple areas could face fire-favorable conditions at once.