California High-Severity Wildfires Now Burn 30 Times More Area Than in 1985, Study Finds

A new study from UCLA published Monday in the journal Proceedings of the National Academy of Sciences has found that high-severity wildfires in California are now burning far more acreage than they did four decades ago, fundamentally altering the state's forest landscape. The research shows that between 1985 and 2024, the area burned by high-severity fires increased thirtyfold, while the total forest acreage burned annually increased tenfold.

High-severity fires, which kill entire stands of trees and often prevent natural forest recovery, have become the dominant fire type in California, surpassing lower-severity fires that historically allowed ecosystems to regenerate. According to the study, since 2012, high-severity fires have outnumbered low-severity fires every year.

"These high-severity, forest-replacing fires used to be uncommon, and now it's the dominant fire type," said the study's senior author. Lead author Mitchell Hung, a doctoral student at Stanford University who conducted the research while at UCLA, explained that hot and dry weather conditions increase the vapor-pressure deficit, causing the atmosphere to act like a sponge and draw moisture from the landscape.

"In general, the warmer and drier the atmosphere, the more high-severity fire we saw over the last 40 years," Hung said.

The increase in severe fires has been most pronounced in densely forested areas with high levels of biomass and combustible vegetation. Researchers warn that repeated high-severity fires could permanently alter California's landscapes by preventing forests from regenerating and encouraging the spread of grasslands and shrublands in formerly forested areas.

The loss of forests may also impact air quality, water management, tourism, and other sectors of the state's economy.

While forest-thinning projects and prescribed burns can help reduce the risk of severe fires in some areas, the study emphasizes that broader climate trends remain a major driver of wildfire behavior. The findings underscore the urgent need for comprehensive strategies to address the growing threat of high-severity wildfires in California.