Spotlight on Wildfire Risk – How Wind, Weather, and Development Patterns are Fueling Extreme Events

The recent wildfires in Los Angeles County, especially Eaton and Palisades, were incredibly devastating with over 11,000 structures burned, 29 lives lost, and unprecedented economic impacts. These fires were particularly scary given their location and proximity to densely populated urban areas, and could have caused even more damage. 

Several factors contributed to the disaster – a wet growing season followed by drought-created conditions ripe for fire ignition, and strong downslope winds, drove the fires to enormous destruction while grounding firefighting aircraft, allowing for significant expansion. Similar environmental conditions have played a role in the Carolina wildfires that started in early March. The LA fires and other destructive fires in the recent past implore us to pause and consider fire risk across the US, how it may be changing, and what can be done to save lives and keep property safe from the standpoints of homeowners, businesses, jurisdictions, government agencies, and a broader society.

A Historical Context

Records of the most damaging or deadly wildfires in US history show fires falling into two time periods: from the late 1800s to the early 1900s, and the past twenty years. The late 1800s saw the deadliest fires in US history including Peshtigo (Wisconsin, 1871), Hinckley (Minnesota, 1894), and Cloquet and Moose Lakes (Minnesota, 1918). Poor forestry practices such as clear-cutting and leaving branches on the ground, a lack of modern firefighting capabilities, and the inability to evacuate quickly led to deadly fires in the upper Midwest. Modern advancements reduced the occurrence of fires during the 1900s.

However, wildfires have been getting more intense and damaging over the past twenty years, and especially the last decade. Numerous devastating wildfires have each destroyed thousands of structures and taken dozens of lives. According to the National Interagency Fire Center, the annual area burned has more than doubled over the past forty years despite the frequency of fires remaining relatively constant. This doubling has occurred entirely in the Western US, with little change in the East. 

What is Making Recent Fires so Damaging?

There are commonalities among recent fires that we’ll explore in detail here, including high wildfire risk, drought conditions following wet years, and downslope wind events. Below, we can see some of the driving factors involved in three of the largest recent fires – the Marshall Fire in Colorado, the Maui Fires in Hawaii, and the Palisades and Eaton Fires in Los Angeles County. 

Table 1. Common drivers of three recent devastating wildfires.

Downslope Wind Events

As air rises over a mountain range it loses moisture and gains heat. As it descends and accelerates on the leeward side of a mountain the air is compressed by increasing air pressure, resulting in warming and a reduction in relative humidity. These warm, dry winds can accelerate to very high speeds, causing damage and greatly increasing fire risk. The Chinooks around the Colorado Front Range and the Santa Ana winds in Southern California are examples of this phenomenon.

Fires spread by downslope wind events are particularly destructive. While they make up only 14% of wildfires and 11% of the total burned area in the Western US, they account for 60% of structures lost and over 50% of fatalities. Furthermore, downslope fires are more than twice as likely to be caused by human-ignitions such as debris burning, recreation, or energy systems.¹² High winds also contribute to fire risk by damaging infrastructure such as powerlines.

Why downslope wind event fires are so damaging:

• These winds tend to be hot and dry, enhancing the flammability of the fuel. 
• Fires usually burn up slopes and away from urban areas, but downslope winds can drive fires from wildlands into more urban areas.
• Wildfires driven by high winds move fast and jump barriers, making them harder to control on the ground.
• High winds ground firefighting aircraft that are important for creating defensible barriers ahead of the fire, and tactical firefighting in areas that are inaccessible to ground crews.

Downslope winds occur in very specific areas on the leeward side of mountain ranges, and have been identified by the American Society for Civil Engineers (ASCE) as special wind regions. Below, we map US Forest Service wildfire burn probability overlaid with the special wind regions. The Western US has several areas of high burn probability within special wind districts, indicating regions with high damage potential. 

Wet Then Dry Weather Conditions

The West has been experiencing a multi-year drought with years of low precipitation and persistent unusual warmth. Drought conditions make ignition and fire spread more likely. Dry conditions existed during each of these events, and locations with more history of drought are more at risk. However, all three of these fires also had anomalously wet conditions during the preceding growing seasons. Prior wet conditions have been shown to increase fire probability, and in Hawaiian grasslands at least, they increase the probability more so than drought during the fire year.¹³ 

The Colorado, Maui, and Los Angeles County fires were primarily not in forested areas, but grass and shrub lands, in which a single growing season can dramatically change the relative fuel load. Because grass grows back annually, the return period of fires in grasslands can be much shorter than in forests. Thus, areas that recently burned from grass fires have a higher fire risk than areas affected by recent forest fires. 

Below, we map drought risk, as the monthly probability of severe drought, along with the ASCE special wind regions. Similar to burn probability, the West has high drought potential, including in many special wind regions.

Other Places at Risk

To pinpoint other urban areas that may also face this uniquely dangerous combination of downslope wind events, high fire risk, and drought conditions, we combined data on ASCE special wind regions, severe drought, and wildfire burn probabilities. Focusing on the western contiguous US, we then identified cities with populations of 15,000 or more within these high-risk areas. This analysis reveals several urban centers facing significant wildfire danger, including:

• Los Angeles and San Bernardino metro areas
• Palm Springs and surrounding areas 
• Colorado Front Range including Denver, Boulder, and Fort Collins
• Reno, NV and the Lake Tahoe area
• Klamath Falls and Redmond, OR

Below, we show close-ups of the Southern California and Reno-Lake Tahoe areas, highlighting the location of cities in ASCE special wind regions with high wildfire risk.

What sets these areas apart from the many western cities with high wildfire risk is the possibility of strong downslope winds that make fires much harder to control, and much more destructive. 

Growth in the Wildland-Urban Interface

Growth in the wildland-urban interface (WUI), where development meets or is interspersed with undeveloped wildland, compounds the risk of wildfires. Today, 52 million Americans – one in six – live in these wildfire-prone areas, a result of decades of expansive growth. With this growing population in the WUI and the intensification of drought and extreme temperatures, future wildfire probabilities are projected to rise, placing more people and property at risk. The number of catastrophic fires around the world is projected to increase by 30% by 2050, according to the United Nations.¹⁴ Our modeling suggests a 20% increase in annual burn area by 2050 over the Contiguous United States.

What Can be Done to Mitigate Risk?

Combating escalating wildfire risk demands a blend of proactive solutions, beginning with data-driven insights to pinpoint high-risk areas and assess the exposure of people, property and businesses. This comprehensive risk assessment should guide the prioritization of both immediate and long-term adaptation and mitigation efforts. These efforts can include ignition reduction strategies like home hardening and vegetation management, urban planning and policy to control growth in high-risk zones, and robust emergency management plans to ensure safe evacuations.

While it is impossible to predict where and when the next devastating wildfire will occur, it is possible to identify places at significant risk and take measures to reduce that risk. Contact us about how you can use data-driven insights to understand wildfire risk and inform planning and policy-making.

Footnotes

1. https://wildfirerisk.org/
2. https://droughtmonitor.unl.edu/Maps/MapArchive.aspx
3. https://wwa.colorado.edu/resources/intermountain-west-climate-dashboard/briefing/compound-hazards-and-marshall-fire-january
4. https://droughtmonitor.unl.edu/Maps/MapArchive.aspx
5. https://research.fs.usda.gov/firelab/products/multimedia/webinars/meteorology-2023-maui-wildfire
6. https://droughtmonitor.unl.edu/Maps/MapArchive.aspx
7. https://www.weather.gov/wrh/climate?wfo=lox
8. https://storymaps.arcgis.com/stories/83af63bd549b4b8ea7d42661531de512
9. https://research.fs.usda.gov/firelab/products/multimedia/webinars/meteorology-2023-maui-wildfire
10. https://www.nytimes.com/interactive/2025/01/18/us/los-angeles-fires-palisades-eaton-timeline.html
11. https://ascehazardtool.org/
12. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EF003471″
13. https://pubmed.ncbi.nlm.nih.gov/30199690/
14. https://www.unep.org/resources/report/spreading-wildfire-rising-threat-extraordinary-landscape-fires