January 2025 Los Angeles wildfires: A wake-up call as 'once-in-a-generation' events become frequent
RICHMOND HILL, CANADA – May 27, 2025 – A new publication by the United Nations University Institute for Water, Environment and Health (UNU-INWEH), January 2025 Los Angeles Wildfires: Once-in-a-Generation Events Now Happen Frequently, highlights the alarming trend of increasingly frequent and destructive urban wildfires, drawing critical lessons from the January 2025 Los Angeles wildfires. These events, the Palisades and Eaton fires, collectively destroyed nearly 16,250 structures and directly exposed approximately 41,000 people, ranking them as the 2nd and 3rd most destructive wildfires in California's history, according to the analysis.
The fires, which started on January 7, 2025, spread rapidly through urban areas of Los Angeles County, fueled by severe drought conditions and powerful Santa Ana winds. The rapid spread into densely populated areas resulted in 29 fatalities and widespread population displacement, underscoring the heightened risks posed by human development in wildfire-prone areas.
" Our study highlights the low-survival rate of buildings in the January 2025 Los Angeles fires due to compounding impacts of climate-related and direct human factors" says Dr. Mojtaba Sadegh, Climate and Wildfire Analytics Lead at UNU-INWEH and lead author of the publication.
The authors emphasize that while the burned areas were not exceptionally large, the significant portion impacting urban areas led to the high level of devastation. Key drivers identified include vegetation growth followed by dry conditions (hydroclimate whiplash), powerful Santa Ana winds, and human-caused ignitions during critical dry-hot-windy conditions. Climate change is noted for exacerbating these conditions.
In response to these growing threats, the UNU-INWEH's incident analysis puts forth several critical recommendations, including prioritizing policies to decrease human-caused ignitions, especially during high-risk weather; promoting home hardening, defensible space, and community preparedness to protect communities in the Wildland-Urban Interface (WUI); encouraging ecologically appropriate vegetation management to reduce fuel loads; investing in advanced technologies for early detection, prediction, and suppression to enhance wildfire prediction and response; and implementing stricter zoning regulations and promoting fire-resilient design to strengthen land-use planning.
"The investigation clearly tells us that disasters like the Los Angeles wildfires are multi-faceted. Analysts must be extremely careful and avoid introducing one single cause, such as climate change, bad management decisions, and poor response, for complex disasters like this," states Professor Kaveh Madani, Director of UNU-INWEH and a co-author of this publication. "Reductionist thinking leads to wrong policy advice and decisions," he adds.
The analysis utilized satellite and population data to assess the impacts of wildfires, highlighting that working-age adults accounted for more than half of the direct exposures, followed by minors and older adults. The January 2025 Los Angeles wildfires serve as a stark reminder of the urgent need for proactive measures to protect vulnerable communities in an era of increasing extreme events.
Read the Paper: Sadegh M, Seydi S. T., Abatzoglou J T, AghaKouchak A, Matin, M., Madani, K. (2025), January 2025 Los Angeles Wildfires: Once-in-a-Generation Events Now Happen Frequently UNU Institute for Water, Environment and Health (UNU-INWEH), Richmond Hill, Ontario, Canada, doi: https://doi.org/10.53328/INR25MOS003
The UNU research team is available for interviews:
Dr. Mojtaba Sadegh, Lead, Climate and Wildfire Analytics, mojtaba.sadegh@unu.edu
Dr. Mir Matin, Manager, Geospatial, Climate and Infrastructure Analytics Program, mir.matin@unu.edu
Professor Kaveh Madani, Director, kaveh.madani@unu.edu
Media Contacts
Shooka Bidarian, Media and Journalism Fellow, Sustainability and Climate, shooka.bidarian@unu.edu
Kyra Bowman, UNU Head of Communications, bowman@unu.edu
RICHMOND HILL, CANADA – May 27, 2025 – A new publication by the United Nations University Institute for Water, Environment and Health (UNU-INWEH), January 2025 Los Angeles Wildfires: Once-in-a-Generation Events Now Happen Frequently, highlights the alarming trend of increasingly frequent and destructive urban wildfires, drawing critical lessons from the January 2025 Los Angeles wildfires. These events, the Palisades and Eaton fires, collectively destroyed nearly 16,250 structures and directly exposed approximately 41,000 people, ranking them as the 2nd and 3rd most destructive wildfires in California's history, according to the analysis.
The fires, which started on January 7, 2025, spread rapidly through urban areas of Los Angeles County, fueled by severe drought conditions and powerful Santa Ana winds. The rapid spread into densely populated areas resulted in 29 fatalities and widespread population displacement, underscoring the heightened risks posed by human development in wildfire-prone areas.
" Our study highlights the low-survival rate of buildings in the January 2025 Los Angeles fires due to compounding impacts of climate-related and direct human factors" says Dr. Mojtaba Sadegh, Climate and Wildfire Analytics Lead at UNU-INWEH and lead author of the publication.
The authors emphasize that while the burned areas were not exceptionally large, the significant portion impacting urban areas led to the high level of devastation. Key drivers identified include vegetation growth followed by dry conditions (hydroclimate whiplash), powerful Santa Ana winds, and human-caused ignitions during critical dry-hot-windy conditions. Climate change is noted for exacerbating these conditions.
In response to these growing threats, the UNU-INWEH's incident analysis puts forth several critical recommendations, including prioritizing policies to decrease human-caused ignitions, especially during high-risk weather; promoting home hardening, defensible space, and community preparedness to protect communities in the Wildland-Urban Interface (WUI); encouraging ecologically appropriate vegetation management to reduce fuel loads; investing in advanced technologies for early detection, prediction, and suppression to enhance wildfire prediction and response; and implementing stricter zoning regulations and promoting fire-resilient design to strengthen land-use planning.
"The investigation clearly tells us that disasters like the Los Angeles wildfires are multi-faceted. Analysts must be extremely careful and avoid introducing one single cause, such as climate change, bad management decisions, and poor response, for complex disasters like this," states Professor Kaveh Madani, Director of UNU-INWEH and a co-author of this publication. "Reductionist thinking leads to wrong policy advice and decisions," he adds.
The analysis utilized satellite and population data to assess the impacts of wildfires, highlighting that working-age adults accounted for more than half of the direct exposures, followed by minors and older adults. The January 2025 Los Angeles wildfires serve as a stark reminder of the urgent need for proactive measures to protect vulnerable communities in an era of increasing extreme events.
Read the Paper: Sadegh M, Seydi S. T., Abatzoglou J T, AghaKouchak A, Matin, M., Madani, K. (2025), January 2025 Los Angeles Wildfires: Once-in-a-Generation Events Now Happen Frequently UNU Institute for Water, Environment and Health (UNU-INWEH), Richmond Hill, Ontario, Canada, doi: https://doi.org/10.53328/INR25MOS003
The UNU research team is available for interviews:
Dr. Mojtaba Sadegh, Lead, Climate and Wildfire Analytics, mojtaba.sadegh@unu.edu
Dr. Mir Matin, Manager, Geospatial, Climate and Infrastructure Analytics Program, mir.matin@unu.edu
Professor Kaveh Madani, Director, kaveh.madani@unu.edu
Media Contacts
Shooka Bidarian, Media and Journalism Fellow, Sustainability and Climate, shooka.bidarian@unu.edu
Kyra Bowman, UNU Head of Communications, bowman@unu.edu
DOI
New study analyzes air quality impacts of wildfire smoke
The comprehensive research examined air quality in Reno, Nevada during 106 wildfires to illuminate the atmospheric and public health impacts of smoke
Desert Research Institute
image:
Satellite images helped the researchers distinguish smoky days (August 19 and 20, 2020) and average days (July 10, 2018) in Reno, Nevada.
view moreCredit: Lu et al., 2025/DRI
With wildfires increasing in frequency, severity, and size in the Western U.S., researchers are determined to better understand how smoke impacts air quality, public health, and even the weather. As fires burn, they release enormous amounts of aerosols — the vaporized remains of burning trees and homes that enter the atmosphere and the air we breathe. Now, a new study dissects these aerosols and gases to pinpoint their potential effects on our health as well as the planet’s short and long-term weather.
The research, published in April's issue of Environmental Science: Atmospheres, measured air quality in Reno, Nevada over a 19 month period between 2017 and 2020 to capture both smoky and clear days. During this timeframe, smoke from more than 106 wildfires impacted the city’s air. DRI scientists Siying Lu and Andrey Khlystov led the research, which found increases in both fine aerosols (known as PM 2.5 for the size of the particulate matter) and carbon monoxide during smoky days. During the fire-prone late summer months analyzed during the study, wildfire smoke accounted for 56% to 65% of PM2.5 and 18% to 26% of carbon monoxide concentrations in Reno air. The results have implications for weather, cloud formation, and public health.
“We know that Reno is frequently impacted by wildfires in summer, so we wanted to compare smoky and non-smoky days and measure the impacts on local air quality,” said Lu, who completed the research as part of her PhD work. “Although we focused on Reno for this study, we developed the method so that it can theoretically be applied anywhere.”
The research team started on the roof of DRI’s Reno campus, where they set up equipment that could measure the size of atmospheric particles. This information is important because it determines how the particles interact with both the atmosphere and the human body. Larger particles can affect our upper respiratory tract, whereas fine aerosols can travel deeper into lungs.
The researchers also collected data from a downtown Reno EPA air monitoring station that provided hourly concentrations of PM2.5, ozone, carbon monoxide, and other air pollutants. The data also provided concentrations of potassium, an element released by burning trees and other wood which can be used to confirm the presence of wildfire smoke in the air.
The team further verified when air pollution was caused by wildfire smoke by using satellite images to identify visible smoke plumes and fire location information from NASA and NOAA. With an additional tool from NOAA, they could track Reno’s winds back in time to verify that they had indeed passed through a wildfire area.
Wildfire aerosols have a complicated effect on the weather. On one hand, they can act as a filter to scatter and reflect incoming sunlight, creating a cooling effect. On the other hand, they contain light-absorbing material, such as soot and brown organic compounds, that can cause warming. Larger aerosols can promote cloud formation and duration by acting as nuclei for water vapor to condense around. The data showed that smoky days contained aerosols that are likely to act as cloud nuclei at concentrations up to 13 times higher than average.
“We figured out that the size of particles is quite distinct during fires from a normal day in Reno, which has implications for cloud formation and how sunlight scatters, as well as public health,” said Khlystov, Research Professor of Chemistry at DRI.
The study also found carbon monoxide present in higher concentrations during smoky days. Breathing high concentrations of carbon monoxide can reduce the ability of blood to carry oxygen to your brain and other organs.
In contrast, concentrations of nitrogen oxides and ozone were present in Reno’s air at similar levels during both smoky and average days. They attribute this to their release by vehicle traffic and chemical reactions induced by sunlight.
“Our research offers one of the most comprehensive looks at how wildfire smoke is affecting air quality in the Western U.S.,” Lu said.
Lu is working on a machine-learning program to facilitate this kind of air quality research by automating the ability to identify when wildfire smoke is present in the air. This could potentially be used to build an automated app that can identify real-time smoke impacts by location and facilitate air quality research and public health messaging.
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More information: The full study, Particle size distributions of wildfire aerosols in the western USA, is available from Environmental Science: Atmospheres at https://doi.org/10.1039/D5EA00007F
Study authors include: Siying Lu (DRI), Chiranjivi Bhattarai (DRI), Vera Samburova (DRI, UNR), and Andrey Khlystov (DRI)
A visualization of the density of wildfire smoke on the same days as the satellite images above. Green represents light smoke concentration, with darker red showing higher concentrations. Reno's location is shown as a yellow star. From Lu et al., 2025.
This map shows wildfires that affected Reno, NV, during the study period, with the size of each wildfire dot representing the area burned (km2). Concentric black circles radiate from Reno, NV, with each circle representing a 100 km increment from the city. Figure 1 from Lu et al., 2025.
Credit
Lu et al. 2025/DRI
Downtown Reno under a smoky sky.
Credit
Jessi LeMay/DRI
About DRI
We are Nevada’s non-profit research institute, founded in 1959 to empower experts to focus on science that matters. We work with communities across the state — and the world — to address their most pressing scientific questions. We’re proud that our scientists continuously produce solutions that better human and environmental health.
Scientists at DRI are encouraged to follow their research interests across the traditional boundaries of scientific fields, collaborating across DRI and with scientists worldwide. All faculty support their own research through grants, bringing in nearly $5 to the Nevada economy for every $1 of state funds received. With more than 600 scientists, engineers, students, and staff across our Reno and Las Vegas campuses, we conducted more than $52 million in sponsored research focused on improving peoples’ lives in 2024 alone.
At DRI, science isn’t merely academic — it’s the key to future-proofing our communities and building a better world. For more information, please visit www.dri.edu.
Journal
Environmental Science Atmospheres
Article Title
Particle size distributions of wildfire aerosols in the western USA
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