Three dead as California hit by a series of storms over Christmas period.

Three people have died and many others have been affected by flooding as California has been hit by a series of storms over the Christmas period. A 74-year-old man from Redding, in Shasta County, died on the weekend of 20-21 December 2025, after his car became trapped in floodwaters, despite efforts by local police officers to rescue him. On Monday 22 December a woman in her 70s died after being swept into the sea by a large wave at MacKerricher State Park in Mendocino County. On Wednesday 24 December a 64-year-old man from San Diego was struck by a falling tree.

A car partially buried by a mudslide in San Bernadino County, California. CBS News.

Many areas have been affected by flooding, with some communities in San Bernadino County facing evacuation orders in order to keep them safe. Several flash floods have been reported in Los Angeles County, where 27 cm of rainfall was recorded on Wednesday 24 December, with a large landslip reported in Altadena, on a slope which had been stripped of vegetation by wildfires in January this year. Around 130 households were evacuated due to concerns about flooding and landslides in Los Angeles, mostly in the Pacific Palisades neighbourhood, which was also hit by wildfires in January. Windspeeds gusting in excess of 100 km per hour have been recorded in San Francisco, where waves more than 7 m high have been reported. More than 100 000 people have been left without power due to the storms, mostly in the central part of the state.

The storms have been driven by a phenomenon called an atmospheric river, in which a narrow band of saturated air carries large volumes of moisture for long distances. Such streams typically originate in tropical regions, and typically travel along the boundaries between diverging weather systems. As with other storm systems, once they pass over land they lose momentum, and can be forced upwards by hills or mountains, causing them to cool and deposit their moisture as precipitation, causing high rainfall and often flooding.

A diagrammatic representation of an atmospheric river. National Weather Service/National Atmospheric and Oceanic Organization/Wikimedia Commons.

Atmospheric rivers are a common phenomenon on the west coast of the United States, and a significant driver of local weather conditions. However, these systems are becoming both more common and more severe as a result of the warming climate, which has led to rising temperatures over the tropical Pacific, and subsequently higher levels of atmospheric moisture, combined with a tendency form storm systems and other weather events to form and move much more quickly, making it harder for meteorologists to make long term predictions about where and when such storms will hit.

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At least five dead and more than 2000 homes destroyed as a series of wildfires sweep across Los Angeles County.

Five people have been confirmed dead and others may have lost their lives as more than 2000 homes have been destroyed in a series of wildfires which have swept across Los Angeles County in Southern California since Tuesday 7 January 2025. Around 180 000 further people have been ordered to evacuate their homes, with another 200 000 warned this may be necessary, amid concerns that these will also be lost, many of them in Los Angeles's wealthiest suburbs. Around 400 000 people have had their electricity supplies either disrupted or cut off completely.

A fire at the intersection of Temescal Canyon and Pacific Coast Highway in the Pacific Palisades neighbourhood of Los Angeles on 7 January 2025. Robyn Beck/AFP/Getty Images.

The second fire reported, now named the Palisades Fire, was reported at about 10.30 am on 7 January in the Palisades Hills to the northwest of Santa Monica. This has subsequently spread to cover an area of about 55 km², affecting the communities of Santa Monica, Malibu, and Calabasas, with initial efforts to contain it hampered by high winds, which both helped the fire to spread quickly and prevented fire fighting aircraft from approaching the area. The problems faced by firefighters worsened as the area's fire hydrant system became exhausted by the demand being placed upon it, causing pressure to fall and fire hoses to run dry.

Firefighters attempting to control the Palisades Fire in western Los Angeles County on 7 January 2025. Kyle Grillot/Bloomberg.

At about 6.20 pm the Eaton Fire was reported in the Eaton Canyon Falls area to the northeast of Pasadena. This fire has now spread to cover an area of about 40 km², again with high winds and an over-used fire hydrant system severely hampering efforts to contain the fire. All five known fatalities have been caused by the Eaton Fire in the Altadena neighbourhood, although local officials are warning that there are probably many more dead around the county.

A burning home in the Altadena neighbourhood of Pasadena on 8 January 2024. Josh Edelson/AFP/Getty Images.

At about the 10.30 the Hurst Fire was reported in the San Fernando Valley to the north of Los Angeles. This has spread to cover almost 3 km² of land and is only partially controlled, leading to a large area being evacuated. Some witnesses have reported seeing an explosion at an electrical distribution centre, possibly caused by high winds blowing power cables loose, but this is still under investigation,

Westward view of the Hurst Fire as seen from the Oakridge Manufactured Home Park. P Rivas/Wikimedia Commons.

The Lidia Fire was reported slightly after 6.00 am on Wednesday 8 January, close to the town of Ravenna to the north of the Angeles National Forest. This fire has spread to cover about 1.5 km² of land,  and is only partially under control, provoking some evacuations. The Woodley Fire was reported at 6.15 am on Wednesday 8 January in the Woodley Recreation Area,  to the north of Encino. This eventually burned about 121 400 m² of wood-  and parkland before being brought under control. The Sunset Fire was reported slightly before 6.00 pm on Wednesday 8 January, and has spread to cover 170 m² of land, provoking further evacuations and threatening some of Holywood's  most iconic landmarks. 

The fires affecting Los Angeles (and other parts of California) are largely a result of several years of unusually hot and dry weather, which in turn have been driven by rising global temperatures. However, they have also been driven by extremely strong Santa Ana winds, a form of katabaric (downhill) wind driven by the Californian landscape. The interior of California is elevated, and has a dry climate compared to coastal areas. During periods of cool weather high pressure zones can form in these dry highlands, and if these coincide with a low pressure system in coastal areas, then the winds flow downhill, gaining heat (and, typically, quite a bit of dust) before reaching lowland coastal areas.

Air from areas of high pressure inland flows toward sea level in Southern California. Paul Duginski/Los Angeles Times.

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Residents evacuated as landslip destroys homes in Los Angeles County, California.

Sixteen people were evacuated from twelve properties in the Rolling Hills Estate on the Palos Verdes Peninsula in Los Angeles County, California, after the properties began to slide into a canyon on Saturday 8 July 2023. The evacuations were carried out after fire officials called to investigate a leaking pipe realised the hillslope was moving, with people being given just 20 minutes to grab personal items and leave. Following the evacuations many of the properties, which are valued at upwards of $1 million each, have slowly cracked and slid into the canyon.

Homes sliding into a canyon on the Palos Verdes Peninsula in Los Angelese County. AP.

Although the Rolling Hills Estate was built in the 1970s and has not previously shown any stability problems, the Palos Verdes Peninsula is notorious for landslips, with Rolling Hills being very close to Portuguese Bend, an ongoing earthflow, rotational and translational slide, an ancient movement which was reactivated in 1956 and by 1961 had damaged or destroyed over 150 homes. This movement still requires an expenditure about $150 000 in repairs and mediation measures each year.

The geology of the Palos Verdes Peninsula is comprised largely of weakly consolidated Miocene sediments uplifted to form the peninsula, and overlain by Quaternary alluvial deposits. The Miocene sediments are not flat, but uplifted in a series of synclines and anticlines, giving the beds a 'WWW' structure. The problem is made worse by layers of bentonite (a clay formed from volcanic ash) within the Miocene deposits. Bentonites both expand and become very slippery when they become wet. forming a natural slide plain along which landslips can move. 

This year southern California suffered an exceptional series of winter storms, brining high levels of rainfall to normally arid areas, causing widespread flooding and many landslide events. Although the worst of the flooding has now passed, in many areas the excess water will have penetrated deep into the ground, potentially activating earth movements in areas which have until now seemed stable.

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Magnitude 3.7 Earthquake hits Los Angeles.

The United States Geological Survey recorded a Magnitude 3.7 Earthquake at a depth of about 11.9 km beneath the western part of the Greater Los Angeles urban area, California, slightly before 0.05 am local time (slightly before 7.05 am GMT) on Wednesday 22 April  2020 (slightly before 3.00 am on Monday 9 March GMT). There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of southern California.

The approximate location of the 22 April 202 Los Angeles Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

 Tectonic boundaries and faults in California and the surrounding area. USGS.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

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Wildfires kill at least nine in California.

Nine people have been confirmed dead in California this week and thousands more have been made homeless, as two major wildfires sweep across parts of the state. All of the confirmed deaths occurred in the town of Paradise in Butte County, which was largely destroyed by the Camp Fire, which started in the Plumas National Forest on Thursday and rapidly spread to the town, where it is reported to have destroyed about 90% of the buildings. So far five people have been found dead in vehicles in the town, three in buildings and one outside, though another 35 people are currently missing, so it is highly likely that the number of dead will climb.

Burned out vehicles near Paradise, California, after the town was destroyed by a wildfire on Friday 9 November 2018. Peter Desilva/EPA.

Elsewhere in the state the Woolsey Fire and Hill Fire have caused extensive damage to the communities of Thousand Oaks, Casabias and Malibu, though there are no reports of any casualties due to prompt evacuations of the areas affected. Around a quarter of a million people have been evacuated from their homes across the state.

A wildfire burning in Malibu, California, this week. Reuters.

The fires have a variety of causes and have been fuelled by dry winds blowing from the mountains in the northeast of the state, but are essentially due to a prolonged drought in the state, which has been experiencing dry conditions since 2011, the longest such drought in the state's recorded history. This drought has killed vegetation, including thousands of trees, across much of central California, providing dry tinder to fuel the fires, despite high rainfall that caused flooding in parts of the state in the winter of 2016-7. The draught has been made worse by the diversion of water to suit Human purposes, such as agriculture, industry and leisure, which has taken water away from other ecosystems, resulting in the build-up of dead, dry vegetation that has produced fuel for the fires.

 The extent of fires burning in California on Saturday 10 November 2018. Google/Esri/NASA/BBC.

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Landslides kill at least five in Santa Barbara County, California.

At least five people have died and a number of large number of homes have been damaged or destroyed in a series of landslides and flash floods in Santa Barbara and Los Angeles counties, California, on Tuesday 9 January 2018. All of the known deaths occurred in the Montecito and Carpinteria areas of Santa Barbara County, where a number of people, including several children have also reportedly been injured. Local authorities are so concerned by these events that evacuation orders have been put in place in parts of Los Angeles, Santa Barbara and Ventura counties.

A search dog enters a damaged building to look for survivors following a mudflow in Montecito, Santa Barbara County, on 9 January 2018. Santa Barbara County Fire Department.

The events occurred following a severe rain storm that brought over 12 cm of rain to many areas in the space of a few hours. Landslides are are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. In this case much if the rain fell in areas that had been badly affected by wildfires late in 2017. This made communities particularly vulnerable to landslips and mudflows, as the wildfires had destroyed much of the natural vegetation that covers hillsides in the area, the roots of which would normally help to stabilise the hillside during severe weather events.

A mudflow covering a road in Los Angeles County following a severe rainstorm on 9 January 2018. Los Angeles Police Department.

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