The causes and impacts of the 2025 Southern California Wildfires

What happened?

The January 2025 Southern California wildfires began with the Sunset 1 Fire in Los Angeles at 10:09 on 7th January. Although initially small, it ignited amid exceptionally dry vegetation and a National Weather Service Red Flag ‘Particularly Dangerous Situation’ (PDS) warning.
Just 20 minutes later, the Palisades Fire began 10 miles away. Driven by strong Santa Ana winds, it rapidly advanced through the communities of Pacific Palisades and Malibu, ultimately killing 12 people, destroying 6,837 structures, and burning 23,448 acres.

By early evening (18:18) the Eaton Fire ignited in the foothills of the San Gabriel Mountains. Extreme downslope winds carried it into Altadena, Pasadena, and Sierra Madre, creating a second major conflagration within ten hours. The Eaton Fire caused 19 fatalities, destroyed 9,413 structures, and burned 14,021 acres.

In the days that followed, nine additional substantial fires ignited across Los Angeles and Ventura Counties. Two coastal fires in Ventura County (Olivas and Auto) caused further losses, including the 32nd fatality. 

What caused the 2025 Wildfires?

The January 2025 LA wildfires were driven by a combination of hydroclimate extremes, record‑dry conditions, high fuel loads, intense Santa Ana winds, and multiple structural failures.

Hyrdroclimate Whiplash

Southern California experienced “hydroclimate whiplash” - a shift between very wet and very dry periods. Two unusually wet winters (2022–23 and 2023–24) promoted vegetation growth, including fine fuels enhanced by the remnants of Hurricane Hilary in August 2023. This growth created abundant fuel heading into 2024–25.
These unusually wet years were followed by a record dry autumn – one of the driest since the 1950s. By late 2024, live vegetation had dried to levels not seen in nearly four decades (Figure 1). The region entered January 2025 experiencing the driest start to a wet season on record for many areas.

Recent Fire Activity

In the Palisades area, no major wildfire had occurred for over 45 years, while Tuna and Peña Canyons had not burned in the 32 years since the Old Topanga Fire. These long fire‑free intervals allowed Chaparral – California’s dense, drought‑tolerant shrubland – to grow into older, highly flammable stands. A key species in this landscape, Chamise, is the most widely distributed chaparral shrub in California. Even under moderate winds (around 20 mph), Chamise can produce large flame lengths, contributing to rapid fire spread. 

The combination of decades without fire, high fuel continuity, and severely desiccated vegetation created a landscape primed for ignition and high‑intensity burning – conditions that helped turn the January 2025 ignitions into large, destructive wildfires.

Santa Ana Winds

Wildfire behaviour in Southern California is strongly shaped by seasonal wind regimes, particularly the Santa Ana winds – dry, downslope winds that typically occur from September through May. These winds develop when high pressure over the inland deserts forces air westward toward lower pressure off the California coast. As this air descends through mountain passes, it compresses and warms, producing the hot, very dry winds characteristic of Santa Ana events.

Because these winds accelerate through narrow canyons and passes, they can reach damaging speeds and rapidly spread flames across the landscape. Their extreme dryness also reduces vegetation moisture, making ignition easier and fire intensity higher.

Structural Failures and the Built Environment

Several structural failures and weaknesses in the built environment intensified the January 2025 wildfires. Inadequate vegetation management, failure to de‑energise power lines, water shortages, limited firefighting capacity, and weak evacuation procedures all contributed to the scale of the disaster.

As fire historian Stephen Pyne notes, “California is built to burn,” and this was evident in the affected communities. Many homes were constructed within or beside wind‑channelling canyons, surrounded by dense vegetation that amplified risk during the Santa Ana wind event.

Will it happen again?

California’s wildfire record offers a clear warning: 18 of the state’s 20 most destructive fires have occurred since 2000, underscoring how recent decades have brought conditions increasingly favourable to large, damaging events (CAL FIRE, 2026). The January 2025 fires emerged from a sequence of extremes - two unusually wet years that produced abundant vegetation, followed by an exceptionally dry autumn and intense Santa Ana winds. This rapid shift from record wet to record dry reflects how climate change is amplifying Southern California’s natural climate variability.

Research by Daniel Swain and John Abatzoglou suggests that a warming atmosphere is intensifying both heavy precipitation and drying (Swain et al., 2025). In California, this has contributed to delaying the onset of the wet season by nearly a month over the past six decades. Combined with rising temperatures, these shifts are extending the fire season deeper into winter, overlapping with the peak Santa Ana wind period.

Attribution studies reinforce this trend. The World Weather Attribution (WWA) team estimates that today’s level of global warming (1.3°C) has increased early‑January fire weather intensity by about 6% and raised the likelihood of extreme conditions by 35% (Barnes et al., 2025). Taken together, these analyses indicate that events of comparable magnitude may occur again under continued warming.

The 1961 Bel Air–Brentwood Fire marked a turning point in California’s wildfire policy, shifting thinking from treating fire as an unpredictable disaster to recognising it as a predictable, hazard. Yet despite this shift, many of today’s discussions echo those of the 1960s. Communities often rebuild on the same footprints, making only minimal changes to reduce risk. Whether the January 2025 fires will mark a genuine change is still uncertain. By November 2025, the first rebuilt homes in the Palisades were completed, incorporating some resilience measures - such as closed eaves and plumbing for optional exterior fire‑defence systems (Los Angeles Times, 2025).

While wildfire conditions set the stage for disaster, the built environment ultimately determines the outcome. When suppression efforts are overwhelmed, ignition-resistant structures survive, vulnerable structures contribute to urban conflagration (Calkin et al., 2023). Without significant changes to rebuilding practices and land‑use planning, areas remain vulnerable to the next major wildfire event.

In conclusion, the January 2025 LA wildfires were driven by a sequence of multi‑year wet conditions that produced heavy fuel growth, followed by extreme drying and intense winds. This combination created the costliest wildfire disaster in history. Structural vulnerabilities further amplified losses. As the climate continues to warm, wildfire risk is becoming an increasingly critical peril for the (re)insurance industry, underscoring the need for stronger resilience measures and forward‑looking risk governance.

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Calkin, D.E., Barrett, K., Cohen, J.D., Finney, M.A., Pyne, S.J. and Quarles, S.L. (2023) ‘Wildland‑urban fire disasters aren’t actually a wildfire problem’, Proceedings of the National Academy of Sciences, 120(51), p. e2315797120.

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Los Angeles Times (2025) First home has been rebuilt in wake of Palisades fire. Available at: https://www.latimes.com/california/story/2025-11-21/first-home-has-been-rebuilt-in-wake-of-palisades-fire (Accessed: 4 March 2026).

Madakumbura, G.D., Moritz, M.A., McKinnon, K.A., Williams, A.P., Rahimi, S., Bass, B., Norris, J., Fu, R. and Hall, A. (2025) ‘Anthropogenic warming drives earlier wildfire season onset in California’, Science Advances, 11(32), p. eadt2041.

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Swain, D.L., Abatzoglou, J.T., Albano, C.M., Brunner, M.I., Diffenbaugh, N.S., Kolden, C., Prein, A.F., Singh, D., Skinner, C.B., Swetnam, T.W. and Touma, D. (2025) ‘Increasing hydroclimatic whiplash can amplify wildfire risk in a warming climate’, Global Change Biology, 31(2), p. e70075.

Swiss Re (2025) Wildfires and severe thunderstorms in the US drive global insured losses to USD 80 billion in first half of 2025, Swiss Re Institute estimates. Available at: https://www.swissre.com/media/press-release/pr-20250806-wildfires-thunderstorms-global-insured-losses-first-half-2025.html (Accessed: 4 March 2026).