Why are wildfires getting worse? UCLA researchers point to climate and fuel buildup

Are wildfires really getting worse?

Yes — wildfires in the western United States have significantly worsened over the past several decades, according to research led by UCLA. Forest fires now burn 10 times as much acreage annually as in 1985, and severity has increased even faster — high-severity fire alone increased thirtyfold in California between 1985 and 2024. Over the past century, the region has seen increases in forest area burned, burn severity, fire spread potential and fire season length. CalFire data show eight of the 10 largest wildfires in California's last 100 years occurred within the last 10 years.

"These high-severity, forest-replacing fires used to be uncommon, and now it's the dominant fire type," said senior author Park Williams, UCLA professor of geography.

What's driving the increase in wildfire severity?

Climate change is one of two leading drivers, according to the 2026 UCLA study published in PNAS. Researchers identified rising atmospheric dryness — measured by vapor-pressure deficit — as a key climate factor: the warmer and drier the atmosphere, the more high-severity fire occurred over the study's 40-year period. Because much of the western U.S. remains in a long-term "fire deficit" and continues to warm, fire is expected to remain an ongoing challenge for land management, ecological resilience and community preparedness.

Is climate change solely responsible, or does forest management play a role too?

Not entirely — atmospheric warming and drying are the primary drivers, but forest management still plays a meaningful role, according to 2026 UCLA research published in PNAS. Severe burning increased most rapidly in forests with the highest fuel density, suggesting that increases in fire severity have been promoted by decades of fire suppression that have allowed brush to accumulate across California's forests.

"Among the largest drivers of burn severity are the warming and drying of the atmosphere, which no amount of forest thinning can change," said Mitchell Hung, lead author of the study and a UCLA graduate student at the time of the research, now a doctoral student at Stanford. "But even though forest management alone can't solve the problem statewide, for individual locations, making good forest management decisions can help alleviate the risk of high-severity fire."

Learn more from the news release or the full study.