California's Devastating Winter Wildfires
- Briefing Note 511
Winter Wildfires have ravaged Southern California. In California, wildfires can occur year-round, however the intensity, severity and destruction of these fires is unprecedented. So far, the death toll is 28, with more than 16,000 residences destroyed and over 230 km2 burnt, with estimates of insured losses between $20-30 billion USD and total economic losses of $250 billion USD.
Californian Wildfires
On the 7th of January, after months of drought and below average rainfall (Figure 1), a fire began in Temescal Canyon. Strong 160 km/h winds then strengthened the blaze, leading to the Palisades fire which has now become the most destructive in LA’s history (Figures 2, 3 and 4). Three weeks later, the fire is still burning, with 95% containment. Later that day another fire began in Eaton Canyon (Figures 2, 3 and 5), and within a few days up to nine fires were burning through Los Angeles (Palisades, Eaton, Hurst, Kenneth, Woodley Sunset, Olivas, Archer and Lidia; Figure 2). The loss of life and destruction is historically the most catastrophic ever for the region, with 28 lives lost and more than 16,000 residences destroyed. During the peak of the event more than 200,000 residents were evacuated. To put this into perspective, the previous most deadly and destructive fire in southern California was the Cedar fire in San Diego County in October 2003. It killed 15 people and destroyed around 2,820 residences. It is also likely to exceed the costliest fire in US history, the Camp Fire in northern California in 2018, which killed 85 people and destroyed 13,500 homes, many in the town of Paradise, with an insured loss of $12.5 billion USD.
As fire rapidly spread out of Eaton Canyon around 6:30 p.m. on Jan. 7, many neighborhoods in eastern Altadena and surrounding areas received evacuation warnings and orders that night. However, it has been widely reported that Altadena neighborhoods west of north Lake Avenue (Figure 4) did not receive electronic evacuation orders until 3:25 a.m., nearly nine hours after the fire broke out. The area also never received electronic evacuation warnings before then, even as multiple fires broke out west of north Lake Avenue. All 17 deaths confirmed so far in the fire occurred in the area west of north Lake Avenue.
Some of the most heavily impacted neighborhoods are the Pacific Palisades, Altadena, and Malibu (Figure 3 and 4). These communities have been devastated, with more homes destroyed than standing. Many of the destroyed residences were luxury homes valued at over $5 million USD, including celebrity homes and exclusive properties that line the western Malibu shore. This is why, despite a similar number of homes destroyed, the estimated insured loss is expected to dwarf the insured loss from the Camp Fire. The recent November 2018 Woolsey Fire, which started in Santa Susana and spread south to Malibu and west to Ventura County, also had severe impacts in Malibu. It burned 390 km2 of land, destroyed 1,643 structures, killed three people, and prompted the evacuation of more than 295,000 people. For many Malibu residents, the Palisades fire caused their second total house loss in 6 years, raising questions like those raised about repeated hurricane losses in the eastern States.
More devastating is the large number of the impacted people who are of low-middle income. Not only have people lost their homes or places of employment, but their whole community. Schools, churches, community structures, support systems, and different aspects of life have all been lost. A lot of people lost everything and may never be able to recover. Those impacted could go into debt and face residual stressors that could lead to health and mental health issues. Access to some disaster assistance programs could take years and can be very complicated and difficult to access.
California’s fire risk
In the present climate, California is seeing larger fires than it did four decades ago. This is illustrated by the Monitoring Trends in Burn Severity (MTBS) data which records and monitors large fires occurring over most US soils (Figure 5). Over the past 40 years, the number of these large fires hasn’t materially changed, but their sizes have increased over the recent two decades.
Typically, California has a wildfires season running from May through to November which coincides with the dry season in the south and summer months in the north of the state. Overall, the season typically peaks between August and ends with the arrival of rain at the start of the wet season (Figure 5). However, this seasonal pattern is not uniform across the state where the southern counties are experiencing higher fire risk all year long relative to the northern region (Figure 6). Moreover, recurring droughts impacting Southern California are now exacerbating the fire risk in the region and blurring the distinction between fire seasons and wet seasons.
As the planet continues to warm, fire seasons are expected to extend in most fire prone regions of the earth. Extreme fire weather, mainly driven by temperatures, will become more common and more severe across the globe. Climate change also has some impact on regional fuel structures. This further adds to California’s increased fire threat where its ‘asbestos forests’ in the far north have lost their immunity to fire, with their protective layer of fog and mist no more, presenting dense forest as fuel for large fires.
Weather Preceding the Wildfires
Almost unprecedented climate conditions in Southern California led up to the devastating fires (Figure 7). This type of explosive fire event has never happened before in Southern California in January, and only once in December. A combination of weather, drought and strong winds created almost ideal wildfire conditions.
California’s past summer was one of the hottest on record, the third hottest since at least 1895. The southwestern United States is also undergoing the driest 22-year period in the last 1,200 years. There have also been extreme swings between wet and dry conditions over the past two years. The previous two winters have been wet which promoted heavy growth of brush. However, this current winter has been extremely dry, with Southern California having less than 10% of average rainfall since the 1st of October. This pattern of quick unpredictable changes in weather has only occurred three times on record for Southern California, occurring in 1992-1993, and 1907-1908.
This extremely dry weather has led to parts of California being in drought. Parts of Southern California are listed as ‘abnormally dry’ by a U.S. Drought Monitor index. It has had near-zero rainfall since May 2024. This has led to the ground and vegetation becoming parched and perfect fuel for fires. Across much of the region soil moisture levels hover between just 2-5% of average. Furthermore, the vapor pressure deficit, a measure the ability of air to draw moisture from the landscape, has extreme deficits across much of Southern California. On the 4th of January in Malibu Canyon, it was 12° C with 36% humidity. On January 7th , the day the fires began, it was 18° C with 13% humidity, more than doubling the vapor pressure deficit. These drought conditions have severely dried out vegetation. For example, the live fuel moisture content of chamise in the Santa Monica Mountains has dropped from 143% in May 2024 to around 60% in November. More recently on January 7th it was 61% for vegetation in Santa Barbara. For context, the average for the region this time of year is 77%, and the threshold at which vegetation can support a large fire is 79%. Thus, the vegetation was so dry in Southern California that it was significantly below the threshold and could support large fires.
On the 7th of January, California experienced severe Santa Ana winds which fanned the fires. These winds reached up to 160 km/h and were one of the driving factors in the catastrophe that occurred. The Santa Ana winds are strong, extremely dry katabatic easterly winds that originate inland and affect coastal Southern California. They are generated by the flow of a high altitude, high density air mass interacting with a lower density air mass below it. Between 10-25 Santa Ana wind events occur annually, with events typically lasting 1-7 days. They typically bring hot, dry conditions to Southern California.
The strong winds also made it extremely difficult to combat the fires. This, compounded by water shortage, and no rainfall in sight has presented extremely challenging conditions. The situation was so dire that LA’s super rich were paying for private fire trucks to protect their homes.
What started the fires?
The most common cause of fire ignitions in the USA is human activities, accounting for 84% of all wildfires. The most common of these are power line failures, campfires, and arson. Natural causes are typically lightning. Though the cause of the California fires is still under investigation, it appears likely that they were due to human activities.
The Palisades fire began in the Temescal Canyon, home of a popular mountainous hiking trail that overlooks the Pacific Palisades. It is currently a crime scene, with investigators believing it to be the origin of the fire, supported by a video from hikers recording the moment the fire began with a cloud of smoke rapidly growing in size and getting darker before flames becoming visible. This investigation will likely take some time to solve, possibly as long as a year.
A lot of the initial online sentiment has been pointing blame at the hikers who took the video of the fire starting, as they stated in the video “that’s right where we were standing” and “we were literally right there”. However, the group have been adamant they didn’t start the blaze.
Law enforcement officers are also speaking with firefighters who responded to a blaze that occurred nearby in the same canyon on the 1st of January. It is thought that this blaze was never fully extinguished and may have re-ignited with the assistance of the strong 160 km/h Santa Ana winds. Several hikers told US media they had smelled smoke before the fire began of the 7th. A security guard who works near the trail also reported that they had observed smoke or dust for several days in the area before the fire began. However, the Los Angeles County Fire Department (LACoFD) has dismissed the suggestion that the two fires are connected, noting such occurrences are rare. There is also the possibility that power company utilities also began the Palisades fire.
Meanwhile, the Eaton fire that began in the San Gabriel Mountains in the evening the same day the Palisades fire began is also undergoing a similar investigation. The current theory is it was started by powerlines, with a large metal utility tower the current focus or investigators. However, Southern California Edison has stated it has not found any evidence that its equipment was responsible for the fire. It has been widely reported that Altadena residents west of Lake Avenue did not get an evacuation warning until 9 hours after the fire began.
Insurance Impacts
In the U.S. homeowners with mortgages are typically required by banks to have property insurance. However, as the climate has been changing, several insurers have withdrawn from Florida and California. Others have hiked prices or cancelled coverage altogether. As a result, homeowners have been turning to home insurance plans of last resort offered by state governments, despite these being typically more expensive while offering less protection. For California, the number of policies offered through the state’s Fair plan has risen from about 200,000 to more than 450,000 policies since 2020. The areas hit by the fires rank as some with the highest uptake of these Fair plan policies. These fires are expected to have widespread, negative impacts on California’s broader insurance market, driving up premiums and potentially reducing property insurance availability, as well as putting strain on the State’s Fair plan where there have already been warnings of risks of solvency.
For the broader reinsurance market, the California fires’ financial effect on Bermuda’s reinsurance sector is anticipated to be manageable. To put the estimated $20-30 billion USD insured loss into perspective, the latest insured loss estimates for hurricanes Milton and Helene in 2024 are $17-50 billion USD and $8-14 billion USD respectively.
An Evacuation Experience
One of the authors (PS) saw the Eaton fire at about 4 am on January 8th from his house located about 4 km west of the Jet Propulsion Laboratory (JPL) (Figure 5), just west of the western extent of the Eaton Fire. He then received an evacuation warning at 5 am and was able to return three days later, on January 11, when the evacuation order was lifted and electric power had been restored. Knowing that the Eaton fire had started at about 6:30 pm on January 7, he had packed bags that evening before the electric power went down at 9 pm in what had seemed before then to be the unlikely event that he would need to evacuate. This avoided the harrowing experience of many others who had to prepare to evacuate in the darkness of blackout before dawn the next morning.
His experience was eerily like that in the 27 October 1993 Kinneloa fire, which burned the southern flank of Mount Wilson. He could see the fire about 2 km to the east before dawn. The fire spread to the west into Altadena, burning 196 structures, including 121 houses, and the evacuation zone came within one block of his previous house, whose location is shown in Figure 5 and indicates that the 2025 Eaton fire got within a few houses of his previous house,
Astronomical Impacts
The 22 km2 1993 Kinneloa fire was not the only one to have threatened Mount Wilson, whose summit houses numerous television, radio and cellular telephone antennas. It also houses multimillion-dollar astronomical facilities and several historically significant telescopes at the Mount Wilson Observatory that were used by James Hubble in 1929 to identify the expansion of the universe. The 650 km2 2009 Station Fire burned in the Angeles National Forest between August 26 and October 16, threatening Mount Wilson. In September 2020, the 470 km2 Bobcat fire burned to within 150 metres of the Mt Wilson Observatory. In the 57 km2 2025 Eaton fire, there was another narrow escape as flames licked the foundations of the communication towers (Figure 4).
References
https://en.wikipedia.org/wiki/Bobcat_Fire
https://en.wikipedia.org/wiki/2025_California_wildfires
https://en.wikipedia.org/wiki/Camp_Fire_(2018) (Paradise fire)
https://en.wikipedia.org/wiki/Kinneloa_Fire
https://en.wikipedia.org/wiki/Station_Fire_(2009)
https://en.wikipedia.org/wiki/Woolsey_Fire
About the author/s
Jacob Evans
Jacob has been involved in the development of our FloodAUS, CyclAUS and QuakeAUS Cat-Loss models. He specialises in data science and mathematics.
Jacob received his PhD in Condensed Matter Physics from Macquarie University. Jacob’s interests include data science, numerical modelling, physics and mathematics.
Joining Risk Frontiers in 2017, Jacob has worked across a range of projects from model development and climate risk management to resilience and portfolio modelling.
Notably, Jacob has employed techniques such as machine learning and statistical analysis to understand the vulnerability of risk across Risk Frontiers catastrophe suite, as well as applying machine learning algorithms for flood, cyclone and earthquake models. He also works on hazard and loss modelling.
Tahiry is a Software Engineer with years of experience working with multiple operating systems, container technology, programming languages and various software stacks. Tahiry holds degrees in Mathematics and a PhD in Computer Science.
Stuart Browning
Stuart is Risk Frontiers' Climate Risk Scientist, with extensive experience studying the weather and climate in Australian and the Asia-Pacific region. His focus is to understand the large-scale climatic drivers of extreme weather events to better quantify risk over seasonal to multi-decadal timescales, using reanalysis data, model simulations, and paleoclimate records.
Paul Somerville
Paul is Chief Geoscientist at Risk Frontiers. He has a PhD in Geophysics, and has 45 years experience as an engineering seismologist, including 15 years with Risk Frontiers. He has had first hand experience of damaging earthquakes in California, Japan, Taiwan and New Zealand. He works on the development of QuakeAUS and QuakeNZ.