Burning soil and peat drove most emissions in Canada’s record 2023 wildfire season
McMaster University
Hamilton, ON, July 27, 2026 –Most of the carbon released during Canada’s record-breaking 2023 wildfire season came from burning soil and peat, rather than trees, according to new research from McMaster University.
The study, published in the journal Geophysical Research Letters, found that underground carbon stores accounted for 76 per cent of wildfire emissions, helping drive a fire season that released nearly a quarter of the world's wildfire emissions that year.
Researchers estimate the 2023 wildfires burned 15.1 million hectares - seven times Canada’s 20-year average – and released 554 million tonnes of carbon.
“Canada stewards 20 per cent of the world’s soil organic carbon in its peatlands and soils. Future wildfire risk is not just about losing forests, it’s about releasing these vast stores of carbon that have accumulated underground over millennia into the atmosphere,” explains Alemu Gonsamo, associate professor in the School of Earth, Environment & Society, who has long studied Canada’s land ecosystems.
Peatlands are waterlogged ecosystems that have traditionally helped stop fires from spreading. But hotter and drier conditions in recent years have lowered water levels, turning normally fire-resistant peatlands into massive smouldering fuel sources.
“When fires start under these conditions, they can burn deep into peat and soil, releasing carbon that took thousands of years to accumulate in a single fire season,” says Gonsamo.
Canada is home to about 1.1 million square kilometres of peatlands. The Hudson Bay Lowlands alone, which are the second largest peatland complex in the world, store an estimated 30 billion tonnes of carbon.
The findings highlight the vulnerability of Canada’s soil carbon stores to intensifying wildfires.
“For years we've focused mostly on the trees that burn. This study shows we must also pay attention to what's happening beneath the surface,” says Gonsamo. “While forest management remains important, its impact is limited because many of these fires occur in remote, unmanaged areas. Prolonged hot and dry conditions are allowing smoldering ground fires to persist and releasing significant amounts of stored carbon.
One-third of all wildfire carbon emissions in 2023 were linked to peatlands alone.
“What we’re seeing is a shift from these landscapes storing carbon to releasing large amounts of it during extreme wildfire seasons,” says Gonsamo. Once that carbon is released, it contributes to further warming and increases the risk of future fires.
The climate impact of the 2023 Canadian wildfires was enormous. In carbon dioxide terms, the emissions were roughly three times greater than Canada's annual human-caused greenhouse-gas emissions reported for 2022.
“There is no alternative to reducing global greenhouse gas emissions to slow climate change and curb the growing intensity of wildfire emissions in Canada and elsewhere,” says Gonsamo.
“Addressing the root cause of increasingly severe fire seasons requires coordinated global action on climate change. This cannot be done by Canada alone.”
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Journal
Geophysical Research Letters
Article Title
Three-fourths of Carbon Emissions from 2023 Record-Breaking Wildfires in Canada Traced to Soil and Peat Combustion
Article Publication Date
27-Jul-2026
UC Irvine researchers create California wildfire damage risk map
Predictive model uses factors most closely linked to severe property losses
Irvine, Calif., July 27, 2026 — By analyzing 100,000 California Department of Forestry and Fire Protection inspection records from 2013 to 2024, researchers at the University of California, Irvine have identified the key environmental and human factors responsible for the most destructive wildfires, and they have synthesized the knowledge into a high-resolution, actionable fire risk map for the Golden State.
The team, from UC Irvine’s Department of Civil and Environmental Engineering, learned that during the 12-year study period, nearly 55,000 buildings were completely destroyed or partially damaged by fire and that 86 percent of those structures were in wildland-urban interface zones where nature meets development. The findings are outlined in a paper published in Science Advances.
“We uncovered predictable features in how buildings are destroyed in California’s wildfires, which shows that the damage pattern is not random,” said lead author Somnath Bar, a UC Irvine postdoctoral scholar in civil and environmental engineering. “We have found that by identifying the precise combination of structural, environmental and weather factors involved, we can establish a comprehensive, physically interpretable framework to explain, model and project which buildings are most likely to be damaged or destroyed by fire.”
“As fire season stretches longer into the year and blazes devastate communities across California, the need for precise, actionable fire risk data has never been greater,” said Assemblywoman Cottie Petrie-Norris (D-Irvine). “Good policy starts with good data. UC Irvine’s new fire risk map gives California exactly that – a clear picture of where the danger is greatest, so we can invest in smarter building practices, targeted fuel reduction, and data-driven planning before disaster strikes rather than after.”
Connecting landscape fires to buildings
In the paper, the researchers point to environmental elements such as low dew-point temperatures, trackable by instruments, that indicate elevated atmospheric dryness. Coupled with high wind speeds, this aridity can greatly amplify the probability of property destruction in a fire. California’s natural environment, including its grasslands, mesic chaparral and mixed oak woodland areas, serves as a pathway connecting landscape fires to buildings.
The growing tendency of people to build homes in the wildland-urban interface, near the source of forest fires, has resulted in significant property damage, the researchers said. Construction in the WUI increased in the U.S. by roughly 33 percent between 1990 and 2010, adding over 12 million new structures. Between 2020 and 2022, more than 80 percent of new homes built in California were in high fire-risk areas. Many of these WUI zones exist in middle elevations, about 500 meters (1,640 feet) above sea level, where moderate slopes channel wind that can accelerate fire spread and intensity.
According to the researchers, the way buildings are designed and the materials used in their construction can also lead to heightened risk of fire damage. These elements include wooden fences, flammable siding, protruding eaves and vents that can catch burning embers as they drift through the air, resulting in ignitions.
“Fire risk is compounded when these building practices come face to face with environmental factors like atmospheric aridity, high heat, wind, and dry fuels such as trees, shrubs and grasses,” said co-author Tirtha Banerjee, UC Irvine associate professor of civil and environmental engineering.
The Palisades and Eaton fires in Southern California, which destroyed more than 16,000 structures in January 2025, demonstrated the catastrophic potential of Santa Ana wind-driven firestorms combined with topographical attributes such as proximity to forests, sloped terrain, and canyons that channel and accelerate airflow.
The UC Irvine team took these variables and more into account to develop its Wildfire Building Damage Risk Index, a first-of-its-kind, 100-meter-resolution, continuous damage probability map covering all of California. The WBDRI integrates satellite-derived environmental data, gridded fire-weather analyses and building-level structural attributes into a machine learning framework.
The researchers tested three successive model configurations, adding building flammability ratings, weather variables and environmental exposure factors, achieving as high as 88 percent prediction accuracy. Bar said the result is a spatially explicit, actionable tool for risk forecasting, defensible space planning and the development of climate-resilient infrastructure.
“Local jurisdictions and homeowners can use the WBDRI map to prioritize defensible space inspections and fuel reduction investments in zones where the probability of damage exceeds 0.55, the threshold where the return on investment for structural hardening and vegetation management is highest,” he said.
“The strong influence of building flammability on damage tells us something encouraging: Homeowners and communities are not powerless,” Bar continued. “Replacing wood fencing, upgrading siding to noncombustible materials, retrofitting eaves and installing ember-resistant vents can substantially reduce the probability that a structure is lost in a wildfire.”
He noted that the study’s findings carry actionable implications at multiple scales. At the state and regional levels, the WBDRI provides a map of damage risk that can be integrated into land-use planning, insurance risk pricing and emergency management frameworks. At the community level, fire agencies can use it to determine where pre-fire mitigation investments will have the greatest impact. At the household level, the research provides a clear, evidence-based checklist for structural hardening, starting with fences, siding, eaves and roofing.
The researchers say they would like to see agencies adopt strategies combining stricter building codes, forward-looking land-use planning and active vegetation management, particularly in WUI zones. As fire weather conditions intensify, the team argues, such integrated, data-driven approaches are essential for protecting California’s communities and built environment.
Joining Banerjee and Bar on this project was Shu Li, a UC Irvine Ph.D. candidate in civil and environmental engineering. Funding was provided by the National Science Foundation, the University of California Office of the President and the U.S. Department of Agriculture.
About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by U.S. News & World Report. The campus has produced five Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UC Irvine has more than 36,000 students and offers 224 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $7 billion annually to the local economy and $8 billion statewide. For more on UC Irvine, visit www.uci.edu.
Media access: Radio programs/stations may, for a fee, use an on-campus studio with a Comrex IP audio codec to interview UC Irvine faculty and experts, subject to availability and university approval. For more UC Irvine news, visit news.uci.edu. Additional resources for journalists may be found at https://news.uci.edu/media-resources.
Journal
Science Advances
Article Title
Explaining building damage from wildfires in California
Article Publication Date
24-Jul-2026
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