Smoke from fires that rage through wildland-urban interface (WUI) areas where human development meets wildland vegetation has a significantly higher health impact than smoke from wildfires in remote areas, according to a groundbreaking study published in Science Advances.
The research, led by scientists at the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), reveals that emissions from WUI fires are about three times more likely to contribute to premature deaths annually than emissions from wildfires in general. The reason: WUI fires burn closer to populated areas, exposing more people to harmful pollutants like fine particulate matter and ground-level ozone.
Rising Risk of WUI Fires
The wildland-urban interface has been expanding globally, now covering about 5% of the world’s land area, excluding Antarctica. As these regions grow, so does the risk of devastating fires. Some of the deadliest WUI blazes in recent history include:
- 2009 Black Saturday bushfires (Australia) – 173 deaths
- 2018 Attica fires (Greece) – 104 deaths
- 2023 Lahaina Fire (Hawaii) – 100 deaths
2025 Southern California fires – Over 16,000 structures destroyed, with financial losses estimated at $250 billion or more
A previous study led by NSF NCAR scientist Wenfu Tang used satellite observations and machine learning to show that WUI fires have become more frequent in recent decades. In this latest research Tang and her team went a step further quantifying the health impact of emissions beyond immediate fire-related deaths.
Why WUI Smoke Is More Dangerous
The researchers used an advanced atmospheric model, Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA), to simulate fire emissions and track pollutants. They ran four simulations No fires, Both WUI and wildland fires, WUI fires only, Wildland fires only
By comparing scenarios, they found that while WUI fires contributed just 3.1% of total fire emissions globally in 2020, their impact on premature deaths was disproportionately high at 8.8%. The numbers varied by region North America WUI fires made up 6% of all fires but caused 9.3% of premature deaths. Europe WUI fires accounted for 11.4% of fires but 13.7% of premature deaths
The study underscores that pollutants from WUI fires do not disperse over vast distances like those from remote wildfires. Instead, they linger in densely populated areas, significantly increasing health risks.
One critical unknown remains: how different burned materials impact health. Unlike wildland fires that primarily consume trees and vegetation, WUI fires burn buildings, vehicles, and household materials that release additional toxic substances.
Tang and her team are now focusing on developing a detailed emission inventory that accounts for the burning of structures. “We need to know what is being burned in order to determine what is going up in smoke,” Tang emphasized.
As WUI fires continue to rise worldwide, understanding their health impacts is becoming more urgent. With the study funded by NOAA and NSF, researchers hope their findings will inform stronger fire management policies and urban planning strategies to reduce exposure to harmful emissions.