Santa Monica City Council
November 18, 2025

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(including those built prior to the 1973 Hospital Act) and affects approximately 2,500 buildings on 475 campuses statewide.

SB 1953 directed OSHPD, in consultation with the Hospital Building Safety Board, to develop emergency regulations including “…earthquake performance categories with subgradations for risk to life, structural soundness, building contents, and nonstructural systems that are critical to providing basic services to hospital inpatients and the public after a disaster” (Health and Safety Code Section 130005).

In 2001, recognizing the continuing need to assess the adequacy of policies and the application of advances in technical knowledge and understanding, the California Seismic Safety Commission created an Ad Hoc Committee to re-examine the compliance with the Alquist Hospital Seismic Safety Act. The formation of the Committee was also prompted by the evaluations of hospital buildings reported to OSHPD that at the time revealed that a large percentage (40 percent) of California’s operating hospitals were in the highest category of collapse risk.” Both hospitals in Santa Monica have been seismically strengthened and/or replaced, and have been assigned high marks for structural performance. For the most recent information on these rankings for hospitals in the state refer to https://hcai.ca.gov/facilities/building-safety/seismic-compliance-andsafety/seismic-performance-ratings/#SPC.

Earthquake Education
Earthquake research and education activities are conducted at several major universities in the southern California region, including (but not limited to) CalTech, University of Southern California (USC), University of California at Berkeley, Los Angeles (UCLA), Santa Barbara (UCSB), Irvine (UCI), and San Diego (UCSD) locations, and the California State University system, including locations at Northridge (CSUN), Long Beach (CSULB), Fullerton (CSUF), San Diego (SDSU), and San Bernardino (CSUSB).

The local clearinghouse for earthquake information is the Statewide California Earthquake Center (SCEC. SCEC is currently transitioning to become the Statewide California Earthquake Center, is a community of scientists and specialists who actively coordinate research on earthquake hazards associated with the entire transform boundary between the North America and Pacific tectonic plates, and communicate earthquake information to the public. SCEC is a National Science Foundation (NSF) Science and Technology Center and is co-funded by the United States Geological Survey (USGS).

Los Angeles County, along with 13 other southern California counties, sponsors the Emergency Survival Program (ESP), an educational program for learning how to prepare for earthquakes and other disasters (https://lacounty.gov/emergency/). Survival guides in 15 different languages can be downloaded from https://ready.lacounty.gov/emergency-survival-guide/. Many school districts have very active emergency preparedness programs that include earthquake drills and periodic disaster response team exercises. Many schools also participate in the Great ShakeOut earthquake scenario drills sponsored by the Southern California Earthquake Center, typically in October of every year. For additional information about resources and how to participate in these drills, refer to www.shakeout.org.

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Earthquake Resource Directory
Local and Regional Resources
Statewide California Earthquake Center (SCEC)
SCEC compiles new information about earthquakes in southern California, integrates this information into a comprehensive and predictive understanding of earthquake phenomena, and communicates this understanding to end-users and the general public in order to increase earthquake awareness, reduce economic losses, and save lives.

University of California
3651 Trousdale Parkway, Suite 169, Los Angeles, CA 90089-0742 Ph: 213-740-5843
www.scec.org
Earthquake Country Alliance (ECA)
Public-private-grassroots partnership of people and organizations that work together to improve earthquake and tsunami preparedness, mitigation and resiliency. This organization is administered by SCEC (see above).

Ph: 213-740-1560
http://www.earthquakecountry.org
State Resources
California Department of Transportation (Caltrans) – District 7 CalTrans is responsible for the design, construction, maintenance, and operation of the California State Highway System, as well as that portion of the Interstate Highway System within the state's boundaries. Alone and in partnership with Amtrak, Caltrans is also involved in the support of intercity passenger rail service in California.
100 S. Main Street, 10th Floor, Los Angeles, CA 90012
Ph: 213-897-1200
http://dot.ca.gov/caltrans-near-me/district-7
California Resources Agency
The California Resources Agency restores, protects and manages the state's natural, historical and cultural resources for current and future generations using solutions based on science, collaboration and respect for all the communities and interests involved. 715 P Street, 20th Floor, Sacramento, CA 95814
Ph: 916-653-5656
https://resources.ca.gov/
California Geological Survey (CGS)
The CGS develops and disseminates technical information and advice on California’s geology, geologic hazards, and mineral resources. In addition to providing technical and mapping services on landslide, earthquake and burned watersheds, the CGS is the state’s scientific representative on tsunami preparedness, mitigation, and response programs. 715 P Street, Sacramento, CA 95814
Ph: 916-445-1825
www.conservation.ca.gov/cgs

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California Geological Survey: Southern California Regional Office Junipero Serra Building
320 W. 4th Street, Suite 850, Los Angeles, CA 90013
Ph: 213-239-0877
California Department of Conservation
The Department of Conservation provides services and information that promote environmental health, economic vitality, informed land-use decisions and sound management of our state's natural resources.
715 P Street, Sacramento, CA 95814
Ph: 916-322-1080
www.conservation.ca.gov
California Seismic Safety Commission
The Seismic Safety Commission investigates earthquakes, researches earthquake-related issues and reports, and recommends to the Governor and Legislature, policies and programs needed to reduce earthquake risk. Some of the duties of the Commission include managing California’s Earthquake Hazards Reduction Program, reviewing seismic activities funded by the State, providing a consistent policy direction for earthquake-related programs for all agencies at all government levels, proposing and reviewing earthquake-related legislation, conducting public hearings on seismic safety issues, recommending earthquake safety programs to governmental agencies and the private sector, and investigating and evaluating earthquake damage and reconstruction efforts following earthquakes
3650 Schriever Avenue, Mather, CA 95655
Ph: 916-263-5506
https://ssc.ca.gov
California Governor’s Office of Emergency Services (Cal OES) Cal OES coordinates overall state agency response to major disasters in support of local government. The office is responsible for assuring the state's readiness to respond to and recover from natural, manmade, and war-caused emergencies, and for assisting local governments in their emergency preparedness, response and recovery efforts.
3650 Schriever Avenue, Mather, CA 95655
Ph: 916 845- 8910
www.caloes.ca.gov/
Federal and National Resources
Building Seismic Safety Council (BSSC)
The BSSC develops and promotes building earthquake risk mitigation regulatory provisions for the nation. Provides a forum that fosters improved seismic safety provisions for the use by the building community in the planning, design, construction, regulation and utilization of buildings. 2121 K Street NW, Suite 800
Washington, DC 20037
Ph: 202-289-7800
www.nibs.org/bssc

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Federal Emergency Management Agency (FEMA), Region 9
An agency within the U.S. Department of Homeland Security, FEMA is tasked with responding to, planning for, recovering from and mitigating against disasters. FEMA provides extensive resources to help communities, businesses, and residents prepare for disasters. It is also a major source of funding through grants for hazard mitigation and hazard preparedness. coordinates the federal response agency support of state and local jurisdictions during disaster events. FEMA also provides reimbursement to jurisdictions for their disaster response costs and facilitates programs to implement mitigation improvements post-disaster.
1111 Broadway, Suite 1200, Oakland, CA 94607-4052
Ph: 510-627-7100
www.fema.gov
United States Geological Survey (USGS)
The USGS provides scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.
12201 Sunrise Valley Drive, Reston, VA 20192
Ph: 650-853-8300, 1-800-ASK-USGS
Pasadena Field Office
525 South Wilson Avenue, Pasadena, CA 91106-3212
Ph: 626-583-7811
http://www.usgs.gov/
Publications
“Land Use Planning for Earthquake Hazard Mitigation: Handbook for Planners” by Wolfe, M.R., Bolton, P.A., Heikkala, S.G., Greene, M.M., and May, P.J., 1986: Special Publication 14, Natural Hazards Research and Applications Information Center, University of Colorado, Institute of Behavioral Science, National Science Foundation. This older but still applicable handbook provides techniques that planners and others can utilize to help mitigate seismic hazards. It provides information on the effects of earthquakes, sources on risk assessment, and effects of earthquakes on the built environment. The handbook also gives examples on application and implementation of planning techniques to be used by local communities.

Available online from several sites including https://digitalcommons.usf.edu/fmhi_pub/82/. “Local Mitigation Planning Handbook,” FEMA (March 2013). This handbook was prepared by FEMA to help local governments in the preparation of their local hazard mitigation plans.

According to FEMA, the Handbook is a companion to the Local Mitigation Plan Review Guide released by FEMA in 2011. While the Plan Review Guide is intended to help State and Federal officials review and approve local hazard mitigation plans, the Handbook is intended to help local officials develop these plans. The Handbook is available from https://www.fema.gov/sites/default/files/2020-06/fema-local-mitigation-planninghandbook_03-2013.pdf. “Public Assistance Debris Management Guide,” FEMA (July 2000). The Debris Management Guide was developed to assist local officials in planning, mobilizing, organizing. and controlling large-scale debris clearance, removal, and disposal operations, Debris management is generally associated with post-disaster recovery. While it should be compliant with local and county emergency operations plans, developing strategies to ensure strong debris management

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is a way to integrate debris management within mitigation activities. The “Public Assistance Debris Management Guide” is available in hard copy or on the FEMA website. “A Safer, More Resilient California: The State Plan for Earthquake Research,” California Seismic Safety Commission (2004). This is a 5-year statewide earthquake research plan that contains identifies research activities, and provides strategies to receive federal funding to implement the plan. For additional information and to review many more publications issued by the CSSC, refer to their website at http://www.seismic.ca.gov/pub.html. “Staying Safe Where the Earth Shakes” are undated regional publications prepared by the Earthquake Country Alliance, the California Earthquake Authority and the California Governor’s Office of Emergency Services and available from the Earthquake Country Alliance website. The Southern California Coast regional guide that includes Los Angeles, Orange and Ventura counties with an emphasis on the coastal region, and thus includes the hazard of tsunami, is available from https://www.earthquakecountry.org/southerncaliforniacoast/.

Pamphlets available for other California regions are also available from www.earthquakecountry.org.
“Putting Down Roots in Earthquake Country,” Southern California Earthquake Center, 2011. This is an updated version of a classic booklet that discusses the earthquake risk in California and provides homeowners with specific information on how to earthquake-proof their homes and be prepared for an earthquake. The document is available online from https://www.earthquakecountry.org/booklets/. A Spanish version of the pamphlet is also available from the same site.
“7 Steps to an Earthquake Resilient Business – A Supplemental Guide to Putting down Roots in Earthquake Country,” Southern California Earthquake Center, 2008. This booklet provides information helpful to business owners to earthquake-proof their place of business, keeping their employees safe, and prevent work stoppages or business closure. This document is also available from www.earthquakecountry.org/roots/.

Refer to the References section (Appendix I) for a listing of the reports referenced in this section and other resources.

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SECTION 7: TSUNAMIS
WHY ARE TSUNAMIS A THREAT TO THE CITY OF SANTA MONICA?
As discussed in more detail later in this section, the historical record, albeit short, includes several tsunamis that have been observed and/or measured in the Santa Monica Bay region, including along the Santa Monica coastline. Most of these tsunamis have amounted to small waves about 1 foot (0.30 m) or less in height, but a few have exceeded 3 feet (1 m). For the most part, these tsunamis have been generated by distant earthquakes. Extensive and constant monitoring of the ocean basins now provide warnings up to hours in advance of the arrival of a tsunami for distant earthquake sources; this in turn allows for evacuation efforts that help to significantly reduce loss of life.

However, as discussed in Section 6, several offshore Holocene-active faults extend across the Santa Monica Bay (see Figure 6-1). Surface rupture during an earthquake on any of these faults could generate a local tsunami that could impact Santa Monica and other coastal communities. An earthquake-generated landslide along the continental slope or in the canyons offshore, in the bay (Figure 7-1), could also generate a tsunami. These local tsunamis would reach the coastline in a short period of time, measured in minutes rather than hours, limiting evacuation efforts, with the potential to result in significant loss of life, injuries, and damage to coastal structures and infrastructure. All coastal structures, including residential and commercial buildings on the seaward side of Pacific Coast Highway, in addition to the Santa Monica Pier and other tourist attractions, could be damaged. This could have a significant impact on the local economy.

Figure 7-1: Bathymetric Map of Santa Monica Bay Showing Continental Slope and Offshore Canyons that Could Be a Source of Tsunami-Generating Landslides

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TSUNAMI BASICS – DEFINITIONS AND CAUSES
What is a Tsunami?
A tsunami (pronounced (t)soo-NAH-mee, a Japanese composite word meaning “harbor wave”) is a series of sea waves caused by a sudden displacement of the ocean water. Tsunamis are characterized by their length, speed, low period, and low observable amplitude: the waves can be up to 125 miles (200 km) long from one crest to the next, they travel in the deep ocean at speeds of typically about 600 mi/hr (950 km/hr), and have periods of between 5 minutes and up to a few hours (with most tsunami periods ranging between 10 and 60 minutes). Their height in the open ocean is very small, a few meters at most, so they pass under ships and boats undetected (Garrison, 2002).

However, as a tsunami approaches a coastline and enters shallow water, its speed decreases to about 20 to 30 mi/hr (which is still much too fast for a person to outrun), and the height of the waves increases as the water piles up, with the potential to reach heights of 30 m (100 ft) or more. The effect of these waves can be amplified where a bay, harbor or lagoon funnels the waves as they move inland. Although 30-foot-plus waves are obviously extremely damaging, even tsunamis only 1 to 3 feet high can be very destructive and cause many deaths and injuries.

Terminology (see Figure 7-2) related to observations or measurements of the reach of a tsunami on normally dry land include “water height or tsunami height,” “runup, wave runup, or uprush,” and “inundation.” Tsunami height is the maximum elevation, typically in meters, of the wave above a reference sea level, such as mean sea level, at the shoreline. Runup is the maximum elevation, also typically reported in meters relative to the same reference level, of ground wetted by the tsunami.

Inundation is the horizontal distance of the inland reach of the tsunami.

Figure 7-2: Diagram Showing Terms Commonly Used in Tsunami Studies Source: From Lekkas et al., 20130F
1 , their Figure 2.

It is important to note that a tsunami wave may first arrive at a coast as a trough, with water receding and exposing the sea floor over a much larger area than is typical during extremely low tide. Public education efforts need to stress that this is an important warning sign and the public needs to head 1 Lekkas, E.L., Andreadakis, E., Kostaki, I., and Kapourani, E., 2013, A proposal for a new integrated tsunami intensity scale (IT IS-2012): Bulletin of the Seismological Society of America, Vol. 103, No. 2B, pp. 1493-1502, doi:10.1785/0120120099; accessed December 2, 2024.

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inland or to higher ground as soon as possible. The receding water will rush back in, likely in a few minutes, typically as a bore, with the fast-rising flood potentially causing significant damage and loss of life if people are trapped within the flooded zone.

What Causes a Tsunami?
The most frequent causes of tsunamis are underwater earthquakes and submarine landslides that cause a sudden disturbance or displacement of the sea floor and the column of water above.

However, tsunamis can also be caused by underwater volcanic explosions, oceanic meteor impacts, glacier calvings, underwater nuclear explosions, and even meteorological conditions. Tsunamis caused by weather events or meteorological conditions are called meteotsunamis.

Earthquake-generated tsunamis have been studied more extensively than any other type. The earthquakes that often generate tsunamis typically, though not always, occur along subducting plate boundaries, where one tectonic plate is being subducted under another. Subduction zones are typically characterized by deep ocean trenches, with a zone of volcanoes paralleling the plate boundary (referred to as a volcanic arc). The volcanoes are the surface manifestation of the subducted crust being heated as a result of increased temperatures and pressures with increasing burial depth. The heated crust heats and melts the overlying mantle, forming magma. The magma then rises through the mantle to the surface, forming volcanoes.

The margins of nearly the entire Pacific Ocean basin, with the exception of the coastline along Canada and most of California and Baja California, are defined by subducting plates and associated volcanoes, in a zone referred to as the Ring of Fire, Rim of Fire, or the Circum-Pacific Belt (Figure 7-3). The belt runs along the north edge of the Aleutian Bay in Alaska, the western coast of Washington, Oregon and northern California, the western coast of Mexico and Central America, and parallels the coastline of Ecuador, Peru and Chile. On the west side of the Pacific Ocean basin, subducting plates occur along the east side of Russia, Japan, Taiwan and the Philippines, through Papua New Guinea and south of the Solomon Islands and Vanuatu, to the north and east of Tonga and the North Island in New Zealand. Earthquakes generated along any of these subduction plates have the potential to generate tsunamis.

Other regions in the world, including some parts of the Indian and Atlantic Oceans and the Mediterranean Sea, can also generate tsunami-inducing earthquakes. For example, the devastating 2004 earthquake and tsunami that occurred in the Indian Ocean, off the west coast of Sumatra, and the 1755 Lisbon earthquake and tsunami are thought to have originated on a fault under the Atlantic Ocean, offshore of the Iberian Peninsula.

Early researchers found that there is a correlation between the depth and size of the earthquake and the size of the associated tsunami: the larger the earthquake and the shallower its epicenter, the larger the resulting tsunami (Imamura, 1949; Iida, 1963, as reported in McCulloch, 1985). The size of the tsunami is also related to the volume of displaced sea floor (Iida, 1963). Tsunamis can travel across an entire ocean basin (called teletsunamis1F
2 ), or they can be local.

2 A teletsunami originates from a distant source, defined as more than 1,000 km away or at least three hours travel from the area of interest, sometimes travelling across an ocean.

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Figure 7-3: World Map Showing Approximate Location of Ring of Fire (pink shaded areas), Subduction Trenches (blue lines), Active Volcanoes (yellow triangles), and Large Earthquakes Between 1900 and 2013 (red, green and blue dots). Cascadia Subduction Zone also shown.

Source: Modified and combined from two open-source maps available from https://en.wikipedia.org/wiki/Ring_of_Fire, accessed in May 2024.

Tsunamis can also be caused by underwater or water-adjacent volcanic eruptions; these are called volcanic tsunamis or volcanogenic tsunamis. These tsunamis can be caused by a variety of phenomena associated with volcanic eruptions, including earthquakes, collapse of the volcano’s caldera, landslides or avalanches along the sides of the volcano consisting of either older material or new hot lava, pyroclastic flows or lahars, and shock waves or airwaves associated with underwater eruptions. Most of these tsunamis are fairly local, but they can be devastating to communities adjacent to the source. For example, the waves generated by the 1883 eruption of Krakatou (Latter, 1981) were nearly 135 ft (41m) high, destroying coastal towns and villages along the western coast of Java and the southern coast of Sumatra, with a death toll of nearly 35,000.

More recently, an undersea volcano called Hunga Tonga-Hunga Ha’apai in the Kingdom of Tonga erupted violently on January 15, 2022. The explosions triggered tsunamis in the adjacent Tongan islands that were almost 65 ft (20m) high, destroying hundreds of buildings, displacing 1,500 people and killing four. The volcanic explosion also created atmospheric waves that caused pressure changes in the ocean water, causing meteotsunamis. The atmospheric waves travel faster than a typical tsunami, with the fastest of these, referred to as Lamb waves, travelling at the speed of sound.

As a result, the first of the teletsunamis observed in Japan arrived more than 2 hours earlier than expected. Many tide gauges around the world, including the Indian Ocean, the Mediterranean, and along the west coast of the United States also recorded the arrival of meteotsunamis related to this volcanic eruption, typically followed by regular tsunami waves hours later. These waves ranged in

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height between a few inches to about 8 feet (2.5 m)2F
3 . Tsunami runups related to this volcanic
eruption were observed in Santa Monica.

Meteotsunamis are typically generated by air pressure disturbances associated with fast-moving weather systems, like squall lines. The development, direction and magnitude of these meteotsunamis are controlled by the intensity, direction, and speed of the air pressure disturbance as it travels over a body of water deep enough to enhance wave magnification. Unlike the volcanicrelated meteotsunamis described in the previous paragraph, most weather-related tsunamis tend to be regional, and do not affect entire ocean basins. Moreover, certain parts of the world appear to be prone to meteotsunamis due to a combination of factors, including local weather patterns, the depth and shape of the ocean floor near the coast (bathymetry), and coastal elevation and features (topography), although the record is probably not long enough to be certain of this. In the United States, locally generated meteotsunamis have been observed in Hawaii, Alaska, California, the Gulf of Mexico, Florida, from Pennsylvania to southern New England, Maine, and in Lake Erie. Most meteotsunamis are too small to be noticed, with maximum water heights of less than 1 foot, but large meteotsunamis can generate dangerous waves, flooding, and strong currents that can cause damage, injuries, and even death. For example, a meteotsunami in Daytona Beach, Florida on July 3, 1992 with a reported maximum water height of 3 m (9.8 ft) injured 75 people (Churchill et al., 1995).

HISTORICAL, LOCALLY SIGNIFICANT TSUNAMIS
As described above, most of the Pacific Ocean Basin is bordered by prominent submarine trenches related to the ongoing subduction of tectonic plates. It has been estimated that between 80 and 90 percent of all tsunamis worldwide are generated in the subduction zones along the Pacific Rim.

Review of the data presented in Table 7-1, and the sources used to prepare this table, show that tsunami-generated runups that have been observed along the southern California coastline have originated from all around the Pacific Ocean, including the Aleutian Islands and Bay of Alaska, the western coast of Central and South America, offshore eastern Russia and Japan, and southeastern Asia. Some portions of southern California are partly protected from tsunamis by the Channel Islands, which deflect east- and northeast-trending waves, and by Point Arguello, which deflects waves coming in from the continental area of Alaska. However, tsunami waves up to about 6 feet (2 meters) high sourced from the Pacific Ocean Basin have been recorded in the Santa Monica Bay region.

Although the historical record for southern California is short, over 150 tsunamis have been recorded in southern California since the early 1800s. Most of these were minor and barely noticeable, but at least 40 made an impression, causing damage to harbors, boats and other coastal structures, and a few caused loss of life (Table 7-1; only tsunamis with reported maximum water height equal to or greater than 0.1 meter are included therein). The earliest tidal gauges in southern California date from 1906 in San Diego, 1923 in Los Angeles, 1924 in La Jolla, and 1932 in Santa Monica3F 4 ; thus,
wave heights for tsunami events prior to these dates were estimated based on historical accounts, sometimes written down one or two generations after the fact.

Table 7-1 also shows that tsunamis generated by local earthquakes and/or landslides, and

3 https://www.usgs.gov/centers/pcmsc/news/depth-surprising-tsunamis-caused-explosive-eruption-tonga; accessed in April 2024. 4
https://tidesandcurrents.noaa.gov/stations.html?type=Historic+Water+Levels#California; accessed April 24, 2024.

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meteotsunamis have historically posed a risk to southern California. Because the water height measurements in many early cases are based on passed-down recollections, there are uncertainties in the numbers reported. However, the data suggest that the highest sea waves historically recorded in the southern California area caused by a locally generated tsunami, the result of an earthquake and/or offshore landslide, is either 11.2 feet (3.4 m) in Gaviota (in 1812), or 19.7 ft (6 m) in Santa Monica (in 1930). The records for Santa Monica, in particular, are questionable, with other sources indicating water height values of 2 ft (0.6 m4F
5 ) and 10 feet (3.05 m5F
6 ) for the same event. The largest
historically reported meteotsunami along the southern California coastline likely occurred in Newport Beach on August 21, 1934, where waves 30 to 39 feet (9-12 m) high were reported.

Text associated with tsunamis that are inferred or known to have been observed in Santa Monica is in bold on Table 7-1. Local or world-wide significant tsunamis described further in the following sub-sections are shown in bold across the table entry.

Table 7-1: Significant Historical Tsunami Record for Southern California – 1812 to January 2024
Date Source Water Height
March 26, 1806 Possibly an earthquake offshore
southern California
Unknown, but boats reportedly beached in
Santa Barbara
December 21, 1812 Possibly an earthquake and/or
landslide in Santa Barbara Channel
Gaviota (El Refugio): 3.4 m (11.2 ft)
Santa Barbara: ~2-3 m (6.6-9.8 ft)
Ventura: ~2-3 m (6.6-9.8 ft)
November 1853 Earthquake in Kuril Islands Unknown; possibly observed in San Diego May 31, 1854 Possibly an earthquake offshore
southern California; possibly same as
July or December events
Unknown; observed in Santa Barbara
July 24, 1854 Unknown; possible meteorological
origin
San Diego: ~0.3 m (~1 ft)
December 23-24,
1854
Earthquake offshore Japan San Diego: 0.1 m (0.3 ft)
July 11, 1855 Possible offshore landslide caused by
earthquake in Los Angeles
Unknown; two unusually large waves
surged on shore at San Juan Capistrano
May 27, 1862 Estimated M 5.9 earthquake near San
Diego
San Diego: 1.2 m (4 ft)
April 3, 1868 Earthquake in Hawaii San Diego: 0.1 m (0.3 ft) August 13, 1868 Earthquake offshore Chile San Diego: 0.3 – 0.8 m (0.6-2.6 ft) San Pedro: 0.76 - 1.8 m (2.5 - 5.9 ft)
Wilmington: 0.76 - 1.8 m (2.5 - 5.9 ft)
April 16, 1877 Central and southern California;
possible meteotsunami or small
offshore earthquake
Cayucos: 1.8 m (5.9 ft) (mild tremor(s) felt
there that morning)
Seal Beach: 1.8 m (5.9 ft)
May 10, 1877 Earthquake offshore Chile Gaviota: 1.83 m (6 ft) San Pedro: 2.07 m (6.8 ft)
Wilmington: 1.68 m (5.5 ft)

5 Legg, M.R., Borrero, J.C., and Synolakis, C.E., 2003, Evaluation of Tsunami Risk to Southern California Coastal Cities: Earthquake Engineering Research Institute Report PF2002-11; available from https://www.eeri.org/images/archived/wp-content/uploads/FinlRept.pdf. 6 https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/eventdata?regionCode=88&maxYear=2024&maxEventValidity=4&area=CA&minYear=1600&country=USA&minEvent Validity=0; accessed April 2024.

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Date Source Water Height
Seal Beach: 1.52 m (5 ft)
November 22, 1878 Central California landslide At least 9 runups recorded in Avila Beach, Pismo Beach, Morro Bay, Port Harford,
Surf and other localities: 1 m (3.05 ft);
damage to wharfs reported.

Wilmington: 2 m (6 ft) high wave; record
deemed questionable.

August 10, 1879 Possible undersea landslide caused
by earthquake in San Fernando area?
Unknown; tsunami reported at Santa
Monica following shaking felt therein
December 25, 1899 Possible underwater landslide
generated by earthquake in San
Jacinto area or meteotsunami?
Unknown; large wave reported along
southern California coast
February 26, 1902 Earthquake offshore El SalvadorGuatemalaUnknown; large wave reported in San Diego; record considered questionable
December 11, 1913 Unknown disturbance offshore Santa
Barbara; submarine landslide,
earthquake or meteotsunami
Waves 4.6 m (15 ft) high, strong surf;
dislodged the wreckage of an old ship
thought to be >100 years old, and the
bones of a mastodon that washed onshore
May 1, 1917 Earthquake in Kermadec Islands,
New Zealand
Unknown; large waves reported in La Jolla
San Diego: 0.1 m (0.3 ft)
November 11, 1922 Earthquake offshore Chile San Diego: 0.2 m (0.7 ft) February 3, 1923 Earthquake offshore Kamchatka,
Russia
San Diego: 0.2 m (0.7 ft); strong “tides”
reported in Los Angeles and Santa Cruz
April; 13, 1923 Aftershock offshore Kamchatka,
Russia
Los Angeles: 1.8 m (5.9 ft)
San Diego: 0.1 m (0.3 ft)
October 4, 1925 Unknown; possible meteorological
origin or submarine volcanic event
Long Beach: 0.34 m (1.1 ft)
January 1, 1927 Southern California; possibly a
submarine landslide caused by an
earthquake in Imperial Valley
Unknown; large waves reported along
southern California coast
Long Beach: oscillations of 0.34 m (1.1 ft)
November 4, 1927 Central and southern California;
offshore earthquake off Lompoc,
Santa Barbara County
La Jolla: 0.2 – 0.3 m (0.7 – 1 ft)
Surf: 1.8 m (5.9 ft)
Port San Luis: 1.5 m (4.9 ft)
June 17, 1928 Earthquake in Oaxaca, Mexico La Jolla: 0.1 m (0.3 ft) August 31, 1930 Southern California; offshore
earthquake in Santa Monica Bay
Tsunamis reported in Redondo Beach,
Santa Monica and Venice. Max. water
height in Santa Monica & Venice: between

0.6 m (2 ft) and 6 m (20 ft) depending on
source, with preferred value of 3.05 m (10
ft)
June 3, 1932 Earthquake offshore Central Mexico Long Beach: 0.1 m (0.3 ft) Santa Barbara: 0.1 m (0.3 ft)
March 2, 1933 Earthquake offshore Sanriku, Japan Los Angeles: 0.1 - 0.2 m (0.3 - 0.7 ft) Long Beach: 0.1 m (0.3 ft)
Santa Monica: 0.07 - <2 m (0.2 - 6.6 ft)
March 11, 1933 Earthquake offshore Newport Beach,
California (Long Beach earthquake)
but marigrams show wave activity
starting before earthquake and
lasting for >36 hours after,
suggesting meteorological source
Long Beach: 0.1 m (0.3 ft)

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Date Source Water Height
August 21, 1934 Unknown; possibly caused by
earthquake near Balboa, or of
meteorological origin
(meteotsunami or rogue waves)
Newport Beach: 3 m rise (10 ft)
9-12 m (30 –39 ft) waves
Damage in Long Beach
November 10, 1938 Earthquake offshore Alaska San Diego: 0.1 m (0.3 ft) Santa Monica: 0.05 m (0.15 ft)
Crescent City: 0.18 m (0.6 ft)
December 7, 1944 Earthquake offshore Kii Peninsula,
Japan
La Jolla: 0.1 m (0.3 ft)
Santa Monica: 0.07 m (0.23 ft)
April 1, 1946 Earthquake offshore Unimak Island,
Alaska
Avila Beach: 1.3 m (4.3 ft)
Long Beach: 0.2 m (0.66 ft)
Los Angeles: 0.4 m (1.3 ft)
San Pedro: 0.38 m (1.25 ft)
December 20, 1946 Earthquake offshore Honshu, Japan Los Angeles: 0.1 m (0.3 ft) March 4, 1952 Earthquake offshore Hokaido Island,
Japan
Long Beach: 0.1 m (0.3 ft)
Los Angeles: 0.13 m (0.4 ft)
November 4, 1952 Earthquake offshore Kamchatka
Peninsula, Russia
La Jolla: 0.19 m (0.62 ft)
Los Angeles: 0.38 m (1.25 ft)
Santa Monica: 0.48 m (1.6 ft)
March 9, 1957 Earthquake offshore Andreanof
(Aleutian) Islands
San Diego: 0.2 – 1.0 m (0.7–3.3 ft)
Los Angeles: 0.1 – 0.5 m (0.3 – 1.6 ft)
Santa Monica: 0.46 m (1.5 ft)
May 22-23, 1960 Earthquake offshore Valdivia, Chile Alamitos Bay: 0.61 m (2.0 ft) Long Beach: 0.88 m (2.9 ft)
Los Angeles: 0.76 – 0.95 m (2.5 – 3.2 ft)
Santa Monica: 1.4 m (4.6 ft)
October 13, 1963 Earthquake offshore Kuril Islands,
Russia
La Jolla: 0.1 m (0.3 ft)
Los Angeles: 0.1 m (0.3 ft)
March 28, 1964 Earthquake offshore Gulf of Alaska
(Prince William Sound)
Alamitos Bay: 0.43 m (1.4 ft)
Crescent City: 4.8 m (15.75 ft)
Los Angeles: 0.49 m (1.6 ft)
Santa Monica: 1.03 m (3.4 ft)
San Diego: 0.53 – 0.99 m (1.74 – 3.25 ft)
February 4, 1965 Earthquake offshore Rat (Aleutian)
Islands, Alaska
Los Angeles: 0.1 m (0.3 ft)
Santa Monica: 0.08 m (0.26 ft)
San Diego: 0.1 m (0.3 ft)
October 17, 1966 Earthquake offshore Peru Long Beach: 0.1 m (0.3 ft) Los Angeles: 0.1 m (0.3 ft)
Newport Bay: 0.1 m (0.3 ft)
May 16, 1968 Earthquake offshore Honshu Island,
Japan
Crescent City: 0.61 m (2.0 ft)
Santa Monica: 0.2 m (0.7 ft)
Los Angeles: 0.1 m (0.3 ft)
Long Beach: 0.1 m (0.3 ft)
July 26, 1971 Earthquake offshore Papua New
Guinea in Bismarck Sea
Long Beach: 0.1 m (0.3 ft)
Los Angeles: 0.05 m (0.2 ft)
November 29, 1975 Submarine landslide generated by
earthquake offshore Hawaii Island
La Jolla: 0.15 m (0.5 ft)
Los Angeles: 0.15 m (0.5 ft)
Catalina Island: 1.4 m (4.6 ft)
June 22, 1977 Earthquake in the Tonga Trench,
South Pacific
Los Angeles: 0.05 m (0.2 ft)
Long Beach: 0.12 m (0.4 ft)
San Diego: 0.08 m (0.26 ft)

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Date Source Water Height
1979 and 1989
Unknown source affecting Santa
Monica Bay; most likely associated
with offshore earthquakes in the bay
Local oscillations; no water heights
reported.

July 30, 1995 Earthquake offshore North Chile
Santa Monica: 0.13 m (0.43 ft)
Los Angeles: 0.05 m (0.2 ft)
San Diego: 0.05 m (0.2 ft)
June 23, 2001 Earthquake offshore South Peru
Santa Monica: 0.1 m (0.3 ft)
Los Angeles: 0.05 m (0.15 ft)
La Jolla: 0.05 m (0.15 ft)
December 26, 2004 Earthquake offshore west coast of
Sumatra
Los Angeles: 0.13-0.27 m (0.43-0.9 ft)
La Jolla: 0.06-0.12 m (0.2-0.4 ft)
San Diego: 0.16 m (0.52 ft)
Santa Monica: 0.19-0.41 m (0.62-1.35 ft)
May 3, 2006 Earthquake offshore Tonga Islands
La Jolla: 0.04 m (0.13 ft)
Los Angeles: 0.08 m (0.26 ft)
Santa Monica: 0.10 m (0.3 ft)
November 15, 2006 Earthquake offshore South Kuril
Islands, Russia
Crescent City: 0.88 m (2.9 ft); $20 M in
damages to Inner Harbor
Los Angeles: 0.11 m (0.36 ft)
La Jolla: 0.1 m (0.3 ft)
Santa Monica: 0.15 m (0.5 ft)
April 1, 2007 Earthquake offshore Solomon Islands San Diego: 0.1 m (0.3 ft) Santa Monica: 0.11 m (0.36 ft)
September 29, 2009 Earthquake offshore Samoa Islands Los Angeles: 0.13 m (0.43 ft) Santa Monica: 0.15 m (0.49 ft)
February 27, 2010 Earthquake offshore Maule, Chile La Jolla: 0.6 m (2.0 ft) Dana Point: 0.7 m (2.3 ft)
Los Angeles: 0.42 m (1.38 ft)
Santa Monica: 0.64 m (2.1 ft)
Damaged boats and docks in southern and
central California; damage to harbor
structures estimated at >$1M
March 11, 2011 Earthquake offshore Honshu, Japan Santa Barbara: 1.02 m (3.3 ft) Port Hueneme/Ventura harbors: 1-1.5 m
(3-4.5 ft)
Santa Monica: 0.85 m (2.8 ft); wave front
travelled at least 2.5 km (1.6 mi) up
Ballona Creek channel; barges broke loose
from their moorings in Alamitos Bay.

Los Angeles/Long Beach: 0.5-0.7 m (1.7-

2.3 ft)
La Jolla: 0.5 m (1.4 ft),
San Diego Harbor: 0.5 m (1.7 ft). One
dock was submerged and boat sank near
Shelter Island.

April 1, 2014 Earthquake offshore North Chile Santa Barbara: 0.21 m (0.69 ft) Santa Monica: 0.12 m (0.39 ft)
September 16, 2015 Earthquake offshore Central Chile Santa Monica: 0.21 m (0.69 ft) Santa Barbara: 0.34 m (1.12 ft)
Los Angeles: 0.16 m (0.52 ft)
January 15, 2022 Hunga-Tonga volcanic eruption Ventura: 1.2 m (3.94 ft)

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Date Source Water Height
Santa Monica: 0.61 m (2 ft)
Los Angeles: 0.43 m (1.4 ft)
San Diego: 0.42 m (1.38 ft)
Santa Barbara: 0.64 m (2.01 ft)
Sources: Compiled from Lander and Lockridge (1989), McCulloch (1985), Ewing (2011); https://en.wikipedia.org/wiki/List_of_tsunamis (accessed February 2023); https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/event-search (accessed February 2023 & April 2024).

Santa Barbara Tsunami of 1812
The second of two strong earthquakes in the Santa Barbara area on December 21st, 1812 produced a tsunami that caused damage in Santa Barbara and Ventura counties and was reported along the coast of southern California. The most likely source for the earthquakes is a fault zone in the Santa Barbara Channel, although onshore faults east of Santa Barbara cannot be ruled out.

While some historical accounts suggest the tsunami produced a maximum one-mile runup and wave heights of 50 ft (15 m) at Gaviota, 30 to 35 ft (9 to 10.5 m) at Santa Barbara and 11.2 ft (3.4 m) at Ventura, contemporary records from the missions at Santa Barbara and Ventura do not mention tsunami runup or damage to nearby coastal communities (Lander and Lockridge, 1989). The mission records describe only a disturbed ocean and fear of tsunami, suggesting that the accounts of high waves, most of which were recorded years after the event, may have been exaggerated (Lander and Lockridge, 1989). For example, an account of “an old trader” printed in the San Francisco Bulletin 52 years after 1812, reported a 1-mile runup in Gaviota. From this account, a 50 ft (15 m) wave height was derived using topographic maps.

Accounts collected by Trask (1856), 44 years after the event, reported that waves damaged the lower part of the town of Santa Barbara, half a mile inland. Trask (1856) also recorded reports of a ship damaged by a tsunami wave near San Buenaventura (present day Ventura). This may be the same vessel reported by Los Angeles Star in 1857 to have been swept up a canyon at El Refugio Bay, near Gaviota. A third-hand account of tsunami damage to the mission in Ventura, located 15 ft (4.5 m) above sea level, is not corroborated by the mission records (Grauzinis et al., unpublished report).

Grauzinis et al. (unpublished, based on data from Soloviev and Go, 1975; McCulloch, 1985; Marine Advisors, 1965; Iida et al., 1967; Wood, 1916; Heck, 1947; Toppozada et al., 1981), concluded that the most reliable historical data support a tsunami height of less than 10 ft (3 m) at Santa Barbara and Ventura, 11.2 ft (3.4 m) at El Refugio, and lower elsewhere in southern California. This is roughly consistent with analysis of predicted tidal data for the region by Long (1988) who suggested a wave height of 6.6 ft (2 m) at Santa Barbara and Ventura.

Tsunami of May 10, 1877
A magnitude 8.3 earthquake off the coast of northern Chile generated a tsunami that was detected along the California coastline from Sausalito south to at least Seal Beach (referred to at the time as Anaheim Landing). At Gaviota, the water level rose 12 feet6F 7 , then fell, then rose and fell three more
times in a span of 20 minutes. At Anaheim Landing, “swift currents carried 2 sailors in a rowboat upstream beyond their destination, then were suddenly rushed back again. . .” Water rushed in and out of the beach every five minutes, covering the beach with 6 to 8 feet of water, and leaving sharks

7 Maximum water height is considered half of this value, i.e., 6 feet.

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and fish on dry land when the water retreated, before being washed off again when the water rushed back in (Lander et al., 1993).

Tsunami of April 13, 1923
A magnitude 7.2 earthquake that is considered an aftershock of a magnitude 8.4 earthquake that occurred in the same region off Kamchatka, in Russia, on February 3, 1923, generated a tsunami that was observed in the Los Angeles harbor, with swells that ebbed and flowed for four hours, rising and falling at least twelve times during that time period. The swirling currents caused havoc at the harbor, causing several ships to collide with other ships or with docks, and causing several smaller fishing boats to break their moorings. Damage at the port was estimated at about $5,000 (equivalent to about $90,750 in 2024). Note that tsunami runups associated with this smaller earthquake were larger than those reported two months earlier.

Earthquake and Tsunami of August 31, 1930
A magnitude 5.2 earthquake occurred in Santa Monica Bay, causing building damage in Venice, Los Angeles, Chatsworth, Hollywood, and Pasadena, among other localities. The earthquake was felt throughout the Los Angeles Basin, as far north as Kern County, San Diego County in the south, and Palm Springs in the east. Ground cracks, small landslides and rockslides were reported along the edge of the Palisades Bluff in Santa Monica. A tsunami variously reported as between 0.6 m (2 feet) and 6 m (20 feet) high was observed in Santa Monica7F 8 . One man was overtaken by the waves
and killed south of Redondo Beach, and “scores” of swimmers were rescued from the surf by lifeguards at Santa Monica.

Possible Tsunami of August 21, 1934
On August 21, 1934, large destructive waves were reported along the coast of southern California from Malibu to Laguna Beach. The true source of the waves is not known; however, several causative events have been suggested. Although official records show no large earthquakes in the area on the day of the waves, a small, magnitude 3 tremor was reported in the Balboa (Newport Beach) region before the waves struck. Submarine landsliding, volcanic activity, and unusual meteorological conditions (meteotsunami or rogue waves?) have also been suggested as possible explanations for the waves. A runup of 890 ft (270 m) inland, 10 ft (3 m) above mean high tide level was recorded at Newport Beach, which flooded part of that city to a depth of 3.3 ft (1 m). Four people were injured near the channel entrance to Newport Bay, at the western pier. Many houses were destroyed, including a two-story home in Balboa that was detached from its foundation. Part of the pavement on Balboa Peninsula was washed away, temporarily isolating the residents of this area from the mainland. Thousands of tons of debris were tossed onshore. The waves also flooded a moorage in Balboa Island and collapsed part of the breakwater in Long Beach (Lander and Lockridge, 1989).

Damage was estimated at $75,000.00 ($1.74 million in 2024). In a later publication, Lander et al., 1993) considered this event to have been triggered by remote storms and aggravated by high tides.

Aleutian Islands Tsunami of March 9, 1957
A magnitude 8.6 earthquake in the Aleutian Islands on March 9, 1957 generated a small tsunami in the San Diego area that damaged two ships in San Diego Harbor and caused minor damage at La

8 https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/runup-data?sourceMaxEventValidity=4&sourceMaxYear =2024&sourceArea=CA&sourceMinYear=1800&sourceMinEventValidity=2&sourceCountry=USA and https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/6619; accessed April 2024.

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Jolla (McMulloch, 1985; Iida et al., 1967; Salsman, 1959; Joy, 1968). A wave height of up to 3.3 ft (1 m) was reported at Shelter Island, off the San Diego coast, although the tide gauge there recorded only a 0.7 ft (0.2 m) wave. No reports of damage were recorded in the Los Angeles area. Tsunamis generated by this earthquake caused extensive damage in Oahu and Kauai, Hawaii, and near the source at Scotch Cap on Umnak Island.

Chilean Tsunami of May 23, 1960
On May 22, 1960, a moment magnitude (Mw) 9.5 earthquake off the coast of Chile produced a tsunami that damaged coastal communities in southern California between Crescent City and San Diego. A wave height of 4.6 ft (1.4 m) was recorded in Santa Monica and the tidal gauge in San Diego was carried away by the tsunami waves (Lander and Lockridge, 1989). Significant damage was recorded in the Los Angeles and Long Beach Harbors, where 30 small craft were sunk and over 300 were set adrift. Over 340 boat slips, valued at the time at $300,000, were also damaged in the area. At Santa Monica, eight small boats were swept away and a surge of 300 ft (90 m) flooded a parking lot along the Pacific Coast Highway. Damage of $20,000 was reported in the Santa Barbara area. At San Diego, two passenger ferries were knocked off course by the waves; the first ferry was pushed against a dock in Coronado, destroying 260 ft (80 m) of the dock, and the second was rammed into a flotilla of anchored destroyers. The waves also rammed a 100-ton dredge into the Mission Bay Bridge, knocking out a 70-ft (21-m) section and sinking a barge at Seaforth Landing (Lander and Lockridge, 1989; Iida et al., 1967; Talley and Cloud, 1962; Joy, 1968).

Good Friday (March 28) Earthquake Tsunami of 1964
On March 28, 1964, a Mw 9.2 earthquake in the Gulf of Alaska produced the largest and still, to date, the most damaging historical tsunami to ever hit the West Coast. The tsunami killed 16 people in northern California and Oregon and caused $8 million ($80.6 million in 2024 dollars) in damage in California. Although damage was primarily focused in coastal areas north of San Francisco, southern California experienced hundreds of thousands of dollars in losses. In Los Angeles Harbor, the wave damaged six small-boat slips, pilings, and the Union Oil Company fuel dock. It scoured the harbor sides, causing an estimated $175,000 to $275,000 in damage. The tsunami also destroyed eight docks in the Long Beach Harbor at a loss of $100,000 (Spaeth and Berkman, 1972). A wave amplitude of 3.3 ft (1 m) was recorded in Santa Monica, and eight surges of water were reported in Marina del Rey between 1:45 AM and 7:00 AM. In Santa Monica, one 16-foot outboard boat was sunk, and in Marina del Rey, several boats, a fueling station and floating anchorage were damaged, for an estimated $100,000 (>$1 million in 2024) in losses. Minor damage was reported elsewhere along the southern California coast.

Boxing Day (December 26) Earthquake and Tsunami of 2004 On December 26, 2004, a magnitude 9.1 to 9.3 earthquake off the northwest coast of Sumatra, Indonesia caused tsunamis in the Indian Ocean that resulted in nearly 228,000 confirmed fatalities in the region, with about 170,000 of those in Indonesia alone. The earthquake and resulting tsunamis displaced more than 1.1 million people in ten countries in South Asia and East Africa, making it one of the most devastating natural events in recorded history. The staggering loss significantly increased the world’s awareness of tsunamis as a potentially devastating natural hazard. The highest wave recorded as a result of this earthquake had a height of 167 ft (50.9 m). The tsunami was felt in coastal communities around the globe, in both the Pacific and Atlantic Oceans, making it a “global tsunami.” In Santa Monica, waves as high as 1.35 ft (0.4m) in height were recorded.

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As a result of this event, an international tsunami monitoring system was developed and deployed in the Indian Ocean with earthquake sensors on the ocean floor that trigger early warnings. This event also led coastal communities worldwide, including many cities in southern California, to identify evacuation routes, and develop training programs to teach people how to recognize a possible tsunami, with emphasis on evacuation and disaster response.

Chilean Earthquake and Tsunami of February 26-27, 2010
Approximately 4 hours after the February 26 (at 10:34 PM PDT) magnitude 8.8 earthquake off the coast of Chile occurred, the West Coast Alaska Tsunami Warning Center (WCATWC) issued a Tsunami Advisory for the entire California coast. The tsunami arrived in southern California approximately 10 hours after the advisory was issued, on the 27th, with highest wave amplitudes reported one to six hours after the first wave arrival. The forecast estimated a maximum tsunami amplitude of 3.87 ft in Santa Monica, but the actual observed amplitude was 2.01 ft. The highest tide gauge readings were reported in Pismo Beach (2.95 to 3.94 ft), Oxnard (3.28 ft), Santa Barbara (2.99 ft), and Santa Cruz (2.95 ft). Minor damage to docks and marine infrastructure was reported in Marina del Rey, Two Harbors (Catalina), Los Angeles, and Oceanside. Moderate damage to docks, concrete piers and boats was reported in North Shelter Island (San Diego Bay). No damage was reported in Newport Beach, Huntington Beach, Seal Beach, Long Beach, and La Jolla (Wilson et al., 2011). The tsunami advisory was cancelled by the WCATWC at 8:03 PM PDT.

Tohoku, Japan Earthquake and Tsunami of March 11, 2011
The magnitude 9.1 earthquake that occurred offshore along the northeast coast of Japan triggered a tsunami that caused widespread damage in northern Japan. The tsunami breached existing sea walls and caused the meltdown of three reactors at the Fukushima nuclear power plant, which in turn caused the discharge of radioactive materials into the surrounding area. Waves as high as 133 ft (40.5 meters) were recorded in Miyako, and in the Sendai area, the runup traveled inland 6 miles (10 km). In total, more than 22,000 deaths were reported, and four years later, in 2015, a survey showed that more than 228,000 people were still displaced.

The tsunami traveled throughout the Pacific Ocean region, arriving at the west coast of the United States about 10 hours after the initial shock, with tsunami activity lasting as much as 24 hours after the first wave arrived. Evacuation orders were issued for some US coastal areas, but at least five people in Oregon and California were swept out to sea (four were rescued), and several boats were torn off their moorings8F
9 . About $100 million in damages were reported for California ports and harbors, including Moss Landing, Ventura, and San Diego. Specifically, the tsunami waves destroyed a dock and damaged 13 boats in Mission Bay, a boat was sunk and a dock was damaged in south Shelter Island (San Diego), a pylon was damaged when hit by a boat in Dana Point, a boat was pulled off its moorings in Huntington Beach, and minor damage to docks and boats was reported in Los Angeles and Long Beach (Wilson et al., 2011). A Tsunami Advisory was issued for Santa Monica for over 24 hours and emergency response personnel closed the Santa Monica beach, adjacent parking lots and the Santa Monica Pier during the advisory. Maximum wave heights in Santa Monica were recorded at 2.8 ft.

9 https://www.bbc.com/news/world-us-canada-12714558, accessed in 2023 and April 2024.

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Tonga Volcanic Eruption and Tsunami of January 15, 2022 On January 15, 2022, violent eruptions from volcanic vents below the ocean surface generated a plume of gas, steam and ash that rose 36 miles (58 km) into the atmosphere; the plume eventually covered all of the Tongan islands. The explosions generated two different types of tsunamis: “classic” tsunamis produced by “the displacement of large volumes of water, and meteotsunamis caused by fast-moving pressure disturbances in the atmosphere.”9F 10 The tsunamis triggered by the eruption
reached up to 65 feet above sea level, destroyed hundreds of structures, displaced more than 1,500 people, and caused four deaths in the Tongan Islands. The tsunami waves propagated across the Pacific Ocean, causing damage in Fiji, Japan, New Zealand, Russia, Hawaii, Chile, and California.

In Peru, it caused an oil spill and two deaths. The relatively low number of deaths is attributed to an improvement in global tsunami preparedness.

The first tsunamis arrived hours earlier than expected in many shores around the Pacific Ocean, travelling at an unprecedented speed of more than 700 mph, and radiating in all directions.

Eventually these waves were observed all around the globe, circling the world approximately threeand-a-half times. These were determined to be meteotsunamis. The “classic” tsunamis arrived later.

In California, tsunamis associated with this volcanic eruption were reported in several areas, with water heights of between about 1.4 and nearly 4 ft recorded in some areas (see Table 7-1). These tsunamis are now thought to have been caused by pyroclastic flows emanating from the caldera and flowing down the underwater slopes of the volcano10F

11. A Tsunami Advisory that lasted approximately
19 hours was issued for the California coastline, including Santa Monica. Across Los Angeles County, people were directed to stay off the beach and out of the ocean.

TSUNAMI HAZARD ASSESSMENT FOR SANTA MONICA
Hazard Identification
Identifying hazardous locations is an essential step towards implementing more informed mitigation activities. Recognition that the southern California region is susceptible to tsunamis dates to at least the early 1960s, following the 1964 Alaska earthquake and tsunami. Early researchers looked at the long-term worldwide historical data and combined that information with mathematical models to estimate distantly generated, 100-year and 500-year probability teletsunami runup elevations for the west coast of the United States (Houston and Garcia, 1974, 1978; Garcia and Houston, 1975; Houston et al., 1975; Houston, 1980; as presented in McCulloch, 1985). The 100-year (R100) and 500-year (R500) teletsunami runup heights first predicted for the Santa Monica area were approximately 4.9 to 6.6 ft (1.5 to 2.0 m) and 8.2 to 10.8 ft (2.5 to 3.3 m), respectively (Houston, 1980, based on Figure 208 in McCulloch, 1985).

The 100- and 500-year risk levels selected were used by the Federal Insurance Administration in the 1980s to calculate flood-insurance rates, similar to storm flooding. As with flooding, the 100- and 500-year designations do not mean that these tsunamis occur only once every 100 or 500 years, but rather, these terms describe the tsunami that has a 1 percent (for 100-year) or 0.2 percent (for 500- year) probability of occurring in any one year. The 100-year and 500-year tsunami runup elevations were thought to have the potential to cause significant damage to harbors and upland areas, whereas

10 https://www.usgs.gov/centers/pcmsc/news/depth-surprising-tsunamis-caused-explosive-eruption-tonga; accessed December 3, 2024. 11 Ibid.

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smaller 50-year events could cause damage to boats and harbor facilities, with onshore damage restricted to very low-lying areas. Houston (1980) did not have the technology available to quantify the effect that estuaries, the offshore zone where water is 15 to 30 ft (5 to 10 m) deep, and the shoreline have on tsunami runup. Furthermore, Houston’s (1980) predicted heights were based on mean sea level elevation data, and thus did not consider the maximum credible heights possible if a teletsunami coincides with peak high tide, or with storm-induced high water.

Then, in the early 1990s, McCarthy et al. (1993) reviewed the historical tsunami record for California and suggested that the tsunami hazard in the southern California region from the Palos Verdes Peninsula south to San Diego, is moderate. However, as discussed previously, the southern California historical record is very short. Given that the recurrence interval for many of the faults in the world is in the order of hundreds to thousands of years, it is possible that southern California has been impacted by tsunamis for which there are no records. There are also several faults immediately offshore of the southern California area that are either thrust faults, or have some component of vertical motion, and are thus capable of triggering a local tsunami if they rupture in an earthquake.

Similarly, several submarine landslides and landslide-susceptible areas have been mapped offshore, within 2 to 9 miles (3.5 to 15 km) of the coastline (Field and Edwards, 1980; McCulloch, 1985; Clarke et al., 1985), and movement on any of these landslide-susceptible areas could also generate a local tsunami.

Synolakis et al. (1997) reviewed the McCarthy et al. (1993) study and other data, and concluded that not only do the early methods used to estimate tsunami runups yielded results that were in some areas more than 50% lower than anticipated but, as discussed above, the early models did not consider near-shore tsunami events. Synolakis et al. (1997) argued that near-shore tsunamis should be considered worst-case scenarios, as these have the potential to cause high runups that would impact the coastline with almost no warning. For example, Borrero et al. (2001) found that an earthquake in the Santa Barbara channel could generate a 6.6-ft (2-m) runup, whereas an earthquake-induced submarine landslide could generate a runup of as much as 66 ft (20 m). These analyses prompted the California Seismic Safety Commission (2005) to issue a report on tsunami threats where they indicated that both teletsunamis and locally generated tsunamis pose a significant threat to life and property in California.

In response to these concerns, in 2009 the University of Southern California Tsunami Research Group published tsunami inundation maps for a large section of coastal California. The maps showed the worst-case scenario based on an analysis of both local and distant tsunami sources and their impact on 33 coastal populated areas along the California coastline (Wilson et al., 2008).

Sources used to develop these maps included surface-rupturing earthquakes on offshore faults based on studies by Legg et al. (2003), submarine landslides off the Palos Verdes peninsula, and earthquakes in the Aleutians and Chile subduction zones. These models highlighted the concern with local tsunami sources; specifically, that the time it takes between the local, tsunami-generating earthquake and the arrival of the first waves along the coastline is estimated at 10 to 20 minutes.

This does not allow much time for broadcasting warnings and evacuation orders, so people in lowlying coastal areas need to be educated about these risks and to recognize that if they feel strong ground shaking they should evacuate to higher ground immediately.

The 2016 edition of the American Society of Civil Engineers (ASCE) building standard (ASCE 7-16), entitled “Minimum Design Loads and Associated Criteria for Buildings and Other Structures,” was the first edition of this building standard to contain a chapter on tsunami loads and design impacts.

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The standard included tsunami design maps for Hawai’i, Alaska, Washington, Oregon and California developed by Thio et al. (2010, 2017) and Wei et al. (2017). The tsunami design zones were mapped using a horizontal resolution of 60 meters (~200 ft), and considered several probabilities of occurrence in 50 years ranging from 2% to 50% (equivalent to annual frequencies of exceedance of between 1/2475 and 1/72 per year). The maps were based on subduction zone sources around the Pacific Ocean, and did not consider local tsunami sources such as crustal faults or offshore landslides. The ASCE 7-16 and 7-22 tsunami design zone maps used in the California Building Code are based on what is referred to as the Maximum Considered Tsunami, with ~2,500-year return period (approximately equal to a 2% probability of being exceeded in 50 years). The tsunami design zone, 3-ft inundation depth, and runup elevation limits for Santa Monica and any other area along the Pacific Coast of North America can be viewed online, here. The tsunami design zone or tsunami hazard zone is the area susceptible to being flooded by the Maximum Considered Tsunami. Updated tsunami hazard maps are expected to be issued as part of the ASCE-7-28 building standard.

On March 22, 2021, the California Geological Survey (CGS, also referred to as the State) issued new tsunami inundation maps for several coastline areas in Los Angeles and Orange counties, including Santa Monica (Figure 7-4) that were prepared by AECOM (Thio, 201911F 12). The tsunami hazard area
maps were created using a probabilistic tsunami hazard analysis approach similar to that used for the ASCE-7 standard that considered the tsunami waves generated by a variety of tsunami sources around the Pacific Ocean using several average return periods ranging from 72- to 3,000-year annual return probabilities. The maps issued to the public are based on a 975-year average return period (equivalent to a 5% probability of exceedance in 50 years), a smaller event than that used for the ASCE-7-16/22 maps. The probabilistic tsunami model used computes wave evolution as a result of changes in bathymetry and topography, with the maps from the CGS relying on 10-meter (~30-ft) resolution topographic data rather than the 30- to 90-meter (~100- to ~300-ft) resolution used for the older 2009 maps. The inundation limits developed were then smoothed to create a realisticlooking inundation boundary, modified to consider levees or other features not recognized by the topographic data that would limit the reach of the inundation zone, and matched to geographic features or city streets. The final inundation boundaries presented in the published maps also rely on input from local emergency managers, first responders and other experts and stakeholders that were asked for advice regarding the “placement of the final hazard area in places that would help the public and government safely evacuate during a tsunami event” (CGS, 2021). For a more indepth description of the process refer to Thio et al. (2010), Thio (2019) and Graehl et al. (2019)12F

13. The tsunami hazard zone and evacuation area defined by the CGS for the Santa Monica area (red shaded region on Figure 7-4) extends approximately 700 to 1,500 ft (215 to 460 m) inland from the coast, and places all structures and parking lots west of the Pacific Coast Highway (PCH) and Appian Way within the area susceptible to tsunami inundation. These structures include the Santa Monica Pier and buildings associated with it, in addition to the residential and commercial buildings on the west side of the roads mentioned above. North of the Pier, the inundation limits are defined by the base of the sea bluffs, as the height of the bluffs provide a natural constraint to the inland

12 https://docftppub.blob.core.windows.net/temp/202305042119/AECOMProbabilisticTsunamiHazardMapsForCalifornia-Phase2.pdf?sv=2020-02-10&st=2024-12- 06T23%3A51%3A30Z&se=2024-12-
20T23%3A51%3A30Z&sr=b&sp=r&sig=/Q6BXk7HEm2w7qOEr2iOjOECgP3DIfeSXRe1kZxStks%3D, accessed in December 2024. 13 https://www.conservation.ca.gov/cgs/Documents/Tsunami/Tsunami-inundation-map-methodology-2019.pdf, accessed in December 2024.

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advancement of the runup. Significant damage to the base of the bluffs and PCH can be expected.

In the southwestern portion of the city, the inundation limits extend locally to Neilson Way. This places several multi-family residential structures within the hazard zone. In addition to the Pier, Cityowned or managed facilities located in the inundation hazard zone include Beach Maintenance, the Santa Monica Urban Runoff Recycling Facility, and the Annenberg Community Beach House.

Note that the 2021 tsunami hazard zone identified by the CGS extends offshore past the beach and into the inner shelf area of Santa Monica Bay. Swimmers, surfers, and mariners within this area are at risk because a tsunami causes strong currents that can sweep people and objects out to sea.

Floating debris can also cause extensive damage. A common occurrence as a tsunami travels over the continental slope and approaches the shore is the formation of a trough, with the sea receding from the shore. Beach goers that observe this phenomenon should immediately run inland and to higher ground, before the tsunami runup occurs. A tsunami typically causes strong surges and rapid changes in sea level that may persist for hours after the first wave arrives. Furthermore, the first wave may not be the largest wave to hit the shoreline, so people should avoid the beach for, at a minimum, several hours after the tsunami first hits the area. Computer simulations for the northern and central California coastlines showing the complicated tsunami wave pattern that may develop are available at the link provided.

As indicated above, the State-issued tsunami hazard map presented on Figure 7-4 is based on a tsunami event with an approximately 975-year return period, which is a smaller tsunami event than the ~2,500-year-return-period event used in the ASCE-16/22 standard (and the 2022 edition of the California Building Code [CBC], which is based on the ASCE standard). As a result, the maps in the CBC in general show a wider inundation zone that extends east of PCH north of the California Incline, and along a stretch between approximately Arizona Avenue and just north of the Pier.

However, because there are no structures east of PCH along the northern portion of the city (just the bluffs), the anticipated losses in this section of the Santa Monica are the same for both events. In the southern portion of the city, the CBC map includes in the inundation zone several buildings on the east side of Barnard Way, between Strand Street and Hill Street, and between Barnard Way and Neilson Way from Hill Street south to the city boundary. However, in the southwestern portion of the city, the State (CGS, 2021; Figure 7-4) map is locally more conservative than the CBC map because the inundation limits were modified to match city streets, locally extending the inundation zone inland to Neilson Way.

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Vulnerability and Risk
A vulnerability assessment for tsunamis can help predict how different types of property or infrastructure and population groups will be affected by the hazard of tsunamis. As mentioned in previous sections, some of the most important factors defining the hazard of tsunamis include the source (offshore fault or submarine landslide, volcanic eruption, or some other cause), the location and distance of the source relative to the city’s coastline, the slope of the continental shelf, and whether or not there are canyons, bays, or other bathymetric features that could funnel the tsunami inland or cause complicated (and dangerous) wave patterns and currents. The wide, relatively shallow continental shelf in Santa Monica Bay, in front of Santa Monica, helps to slow down incoming tele-tsunami waves and decrease their wavelength, which in turn can increase the runup height. Depending on the location of the tele-tsunami source relative to Santa Monica Bay, the offshore Channel Islands could shield the bay from the waves, or could interfere with the pattern of the waves, intensifying their effect as they approach the coastline. All of these conditions complicate the development of tsunami models used to estimate the impact that a tsunami may have on the region. Modelers typically compare the analytical results developed from these models with the historical record to evaluate the reliability of their results (Arcas, 2015).

The data presented in Table 7-1 suggests that teletsunamis sourced in Chile, Central America, Alaska and Japan have created significant historical runup inundations in Santa Monica and other nearby coastal areas. The tsunami hazard maps issued by both the CGS and the ASCE (see the Hazard Identification section above) are based on teletsunamis sourced out of Alaska and the Cascadia Subduction Zone, as these analyses showed that these sources pose the greatest risk to the California coastline. This certainly seems to be the case given the widespread geographic reach of a tsunami generated from a distant source, with the entire California coastal zone at risk of being inundated, and the fact that both of these subducting areas are seismically active and have a high probability of generating a significant tsunami-generating earthquake during the time-frame considered for the probabilistic analyses. Significantly, the most recent tsunami hazard maps that have been prepared for California do not include a tsunami-generating earthquake in the West Melanesian Trench, a slow-moving to potentially currently inactive subducting trench north of Papua New Guinea. A tsunami forecast model for Santa Monica (Arcas, 2015) considered tsunamis sourced from 20 different locations around the Pacific Ocean basin, and found that a tsunami generated along the West Melanesian Trench could generate maximum runups of more than 7.5 meters (~25 ft) in Santa Monica. These runup levels are three times higher than the second-largest runups modeled, which originated along the New Zealand-Kermadec-Tonga trench.

However, the highest water levels that have been reported historically in the Santa Monica Bay (based on Table 7-1) appear to have been associated with nearby tsunami sources, including earthquakes generated by faults in the bay or in the Santa Barbara Channel, and possible offshore submarine landslides mobilized by earthquakes on faults in the southern California region. These local tsunami sources are particularly concerning because a tsunami could reach the coastline in minutes rather than the hours it takes for a teletsunami to reach the area, and a tsunami warning may not be issued in time to evacuate the inundation hazard zone. Moreover, depending on the volume of water displaced by the fault rupture or submarine landslide, the tsunami-generated water heights (runups) could be higher than the modeled runups used to generate the tsunami hazard zone maps discussed in the previous section, meaning that an area larger than that delineated in the tsunami hazard zone could be impacted. Finally, the time of day when the tsunami hits the coast would also have an impact on the number of people exposed. All of these unknowns make it difficult to conduct a reliable analysis of possible tsunami losses. Nevertheless, as discussed in the section

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below, this report summarizes the results of three different analyses that provide generalized information on the impact that a tsunami could have on the coastal area of Santa Monica.

Risk Assessments - Methodology
For this report, we relied on three different sources or methods to obtain estimates of the impact that a tsunami would have on the city of Santa Monica. These include:

1. Loss analyses conducted and reported by the CGS (Becker et al., 2023) using FEMA’s HazUS Version 6.0 Tsunami Model and the tsunami hazard zone shown on Figure 7-4, which is based on a tsunami with a 975-year return period generated by an earthquake in the subduction zone along Alaska’s Aleutian Islands. This teletsunami is estimated to take approximately 320 minutes (5 hours and 20 minutes) to reach the coastline along Los Angeles County, providing ample time for evacuation orders to be issued. Significantly, these analyses were conducted at the County level, so Santa Monica-specific results are not available. The results provided apply to all of Los Angeles County.

2. Loss analyses conducted for this study also using FEMA’s Version 6.0 HazUS Tsunami Model and a similar inundation hazard zone as above, but with the tsunami generated by an earthquake on the offshore section of the Palos Verdes fault in Santa Monica Bay. The tsunami generated by this hypothetical earthquake would take only a few minutes to reach the coastline, so advanced warnings of the incoming tsunami are unlikely. This analysis was conducted specifically for the City of Santa Monica.

3. Economic analysis conducted by the City of the properties in Santa Monica within the tsunami inundation zone identified by the CGS (2021) and shown on Figure 7-4, using the damage assessment software Crisis Track. The software allows calculation of the minimum and maximum cost for residential and commercial properties within the specified hazard zone. Different damage levels based on FEMA’s Preliminary Damage Assessment 4-Point Terminology were applied to generate a range of loss amounts based on the most recent tax assessment values (2023) available at the time of the analysis rather than market valuations.

As discussed further below, all three of these methods have limitations, so the results provided should be considered carefully and judiciously, recognizing that the true impact of a tsunami on Santa Monica is likely to have severe, long-term implications on the economy of the City that were not fully captured here. Similarly, because it is difficult to estimate the total number of people that may be in the city at the time of a tsunami, especially one sourced nearby, the casualty estimates may significantly underestimate the total actual counts should a tsunami impact the area.

Risk Assessments - Results
County-Level Loss Estimates Published by the California Geological Survey The County-level HazUS results published by the CGS (Becker et al., 2023) indicate that if all individuals within the tsunami inundation zone heed the evacuation orders within 15 minutes of receiving the notification, no casualties would be reported in Los Angeles County. Casualties are defined as the projected sum of fatalities and injuries resulting from the number of people exposed to the tsunami, with the population estimates based on 2020 Census data and advanced demographic at-risk population profile data from Esri. If, on the other hand, people take 30 minutes to depart after receiving orders to evacuate (referred to as “evacuation departure delay time”), an estimated 197 casualties are expected if the tsunami occurs during daylight hours. If the tsunami occurs at night, an estimated 117 casualties are estimated. A larger number of casualties can be

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expected for longer evacuation departure delay times. The daytime Los Angeles County population count within the tsunami hazard zone used in the analyses was 85,162. This figure includes residential, commercial and institutional populations within the tsunami hazard zone. The figure however does not account for day visitors to the coastal areas, so higher casualty numbers are likely.

For the casualty analyses, 99% of the population exposed to a flood height of 2 meters (~6.6 ft) are expected to perish, with only 1% being injured. For flood heights of less than 2 meters, the fatality and injury rates are each estimated at 50%.

As will be discussed in more detail in the next sub-section, the HazUS Tsunami Model estimates building damage counts, classifying damaged buildings into four categories as follows:

1. Buildings that incur losses that amount to less than 5% of their value are considered to be Affected.

2. Buildings that incur losses that amount to between 5 and 30% of their total value are considered to have Minor damage.

3. Major damage means that the losses incurred amount to 30 to 50% of the building’s value, and the

4. Destroyed category captures all buildings with damage that exceeds 50% of their value.

These categories generally correspond to the tagging nomenclature used in the post-disaster inspection of buildings (green, yellow and red), hence the colors assigned to each column in the table below. The loss value includes both structural and non-structural elements, but does not include the value of the land. Total building damage counts and residential building damage counts for Los Angeles County are presented in Table 7-2 below.

Table 7-2: Total Building and Total Residential Building Damage Counts for Los Angeles County Based on a HazUS Tsunami Analysis of the CGS (2021) Tsunami Hazard Maps for California Damage Category
Building Type
Affected
(Green Tag)
Minor
(Green Tag)
Major
(Yellow Tag)
Destroyed
(Red Tag)
Total Buildings 7,348 996 9 34
Residential Buildings 6,394 875 1 26
Source: Extracted from Becker et al. (2023)
Total statewide losses as a result of this tsunami scenario are estimated at $12.6 billion. Losses in Los Angeles County alone amount to about $600 million, with approximately half of that associated with residential structures. It is difficult to estimate what percentage of this total amount would pertain specifically to losses in Santa Monica, but a conservative estimate would be about 10 to 20% of the total, which amounts to between about $60 and $120 million.

Loss Estimates Due to a Local Tsunami Using HazUS
As discussed in far more detail in Section 6, HazUS is a GIS-based loss estimation methodology funded by and available through FEMA. The software includes several components or modules, with tsunami being one of them. The tsunami modeled for this study was sourced in the Santa Monica Bay, as a result of fault rupture on the offshore section of the Palos Verdes fault, and was assumed to generate a 6-meter- (~20-ft-) high runup that would essentially inundate the same area identified in the State-issued tsunami hazard map. The principal difference between this analysis and that conducted by the State and described in the sub-section above is that the tsunami generated in the

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bay would arrive at the coastline in 10 minutes, with maximum inundation occurring in 15 minutes.

An official tsunami warning alert within this time could potentially be issued within 5 to 10 minutes of the earthquake, but that really would limit the amount of time people would have to evacuate. In this case, as directed in tsunami education, the strong shaking generated by the earthquake itself should be considered the tsunami warning, with people evacuating to higher ground immediately after shaking subsides.

As discussed above, the tsunami module estimates the number of people that will be injured and killed by the hypothetical tsunami event. To do this, three community tsunami preparedness levels are considered: “Good,” “Fair” and “Poor.” The “Good” level represents a well-prepared community that has invested on education programs, signage showing evacuation routes, and/ or is otherwise prepared because of prior experience (a “Tsunami Ready” community), whereas a community with a “Poor” level has had very little experience and has not prepared its local population to respond to the hazard of tsunamis. Given the large number of out-of-town beachgoers (visiting population) in Santa Monica that may not be aware of the tsunami hazard and may not know to respond immediately upon feeling shaking, different preparedness levels are considered appropriate for the analysis.

The casualty estimates also consider two different times of the day when the tsunami occurs: 2:00 AM and 2:00 PM. These times represent the periods of the day when different sectors of the community are at their peak occupancy loads. Specifically, during the 2:00 AM scenario the residential load is considered to be at its maximum, whereas the 2:00 PM scenario time considers the educational, commercial and industrial sector loads to be at their maximum. The population estimates use Census 2020 data, and do not include the significant seasonal and daytime increase in population due to regional and out-of-town visitors. Therefore, the casualty estimates are likely to undercount the total number of casualties. Pedestrian travel time using standard walking speeds and reduction factors based on the local demographics, such as population 65 years old and older, and estimated number of individuals in the evacuation zone with mobility limitations, are considered in the analysis. The estimated travel times are then combined with the estimated tsunami travel time, warning time and community reaction time to estimate the number of potential casualties. The casualty results are summarized in Table 7-3 below.

Table 7-3: Estimated Tsunami Casualties in Santa Monica by Time of Day, Exposed Population and Community Preparedness Level (for a Local Tsunami Scenario) Day Casualties (2:00 PM)
Exposed Population
Community Preparedness Level
Good Fair Poor
Under
65 65
and
Over
Total
Population Fatalities Injuries Total Casualties Fatalities Injuries Total Casualties Fatalities Injuries Total Casualties 1,857 166 2,023 281 281 561 931 545 1,476 1,392 324 1,716 Night Casualties (2:00 AM)
Exposed Population
Community Preparedness Level
Good Fair Poor
Under
65 65
and
Over
Total
Population Fatalities Injuries Total Casualties Fatalities Injuries Total Casualties Fatalities Injuries Total Casualties 729 119 848 80 80 160 376 237 613 572 145 717

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The estimates calculated by HazUS indicate that about 2,023 people would be within the tsunami inundation zone during the day, including residential, commercial and institutional occupancies.

These numbers are based on Census (2020) data, and thus do not include visitors to the beach, pier, and adjacent roads and businesses, nor motorists on PCH and other roads adjacent to the beach.

Given that on a regular summer day, thousands of people visit the beach and the pier, the population counts likely grossly underestimate the number of people that would have to evacuate the area upon feeling strong ground shaking, and thus the total number of casualties. The population count for the nighttime scenario is based on maximum residential loads and estimates that 848 people within the tsunami hazard area would have to evacuate. These numbers are expected to be much closer to the true values on any given night in the area.

Depending on the level of preparedness considered, the number of casualties during a daytime tsunami event are estimated at between 516 and 1,716 (with these numbers again representing only the Census-counted individuals within the tsunami hazard area). The number of fatalities ranges between about 281 (for a community preparedness level of “good”) and 1,392 (for a community preparedness level of “poor”). Total number of casualties as a result of a nighttime tsunami event ranges between 160 and 717, with the total number of fatalities ranging between 80 and 572.

The HazUS tsunami model estimates that a total of three (3) structures would be completely destroyed, with total building losses estimated at $15 million. Note that this estimate is lower than the estimates obtained using other methods. Nearly 78% of this value pertains to loss of contents, and 7% accounts for business-interruption losses including loss of income and inventory, and relocation expenses. Residential occupancies are estimated to account for about 41% of the estimated $15 million in total losses.

As discussed in both Section 6 (Earthquakes) and Section 9 (Landslides), an earthquake on the offshore section of the Palos Verdes fault, which was used as a source for the local tsunami scenario described above, could result in damage of the slopes along PCH, which in turn would impact the use of PCH as an evacuation route. A sudden tsunami runup onto PCH is also likely to severely impact traffic patterns and result in additional casualties, with closures or limited access on PCH anticipated to result in major disruptions to emergency services, including the mobilization of people in need of emergency services to the local hospitals Loss Estimates Using Crisis Track®
Crisis Track®, a damage assessment software used by local governments, including the City of Santa Monica, was also used to develop estimates of the monetary impact that a tsunami event would have on Santa Monica. This software also classifies monetary losses based on the nomenclature used in post-disaster inspection of structures, as described on page 7-20. The software calculates the economic losses to residential and commercial structures within a user-designated zone. For this analysis, the City used the tsunami hazard area on Figure 7-4. The results of this analysis are summarized on Table 7-4 below.

Table 7-4: Estimated Economic Losses to Residential and Commercial Buildings in Santa Monica Using Crisis Track® Software
Damage Category Affected
(Green Tag)
Minor
(Green Tag)
Major
(Yellow Tag)
Destroyed
(Red Tag)
Total Cost $18,254,688.90 $45,636,722.25 $109,528,133.40 $182,546,889.00

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The estimated losses calculated using this approach are also expected to be on the low end as the software does not compute damage to public infrastructure such as roadways, utilities, and beaches, and the tax assessment valuations used are likely to under-report the true value of the structures. It is also important to note that this analysis does not consider the structural characteristics of individual buildings or their location within the tsunami inundation zone; instead, the same damage level is considered for the entire inventory of structures, with total loss estimates calculated for each of the four different damage levels assumed for the entire study area. Given that different damage levels can be expected depending on the structure type and distance from the coastline, the true cost of the anticipated damage to the residential and commercial structures impacted by the tsunami is likely to be somewhere between the minimum and maximum values considered (between about $18 million and $182.5 million).

TSUNAMI MITIGATION ACTIVITIES
Tsunamis, like earthquakes, cannot be avoided, and their occurrence cannot be predicted. However, extensive instrumentation of the ocean floors in the Pacific Ocean following the 1948 Alaska earthquake, and increased instrumentation following the 2004 Indian Ocean tsunami now means that immediately after an earthquake, tsunami warning centers can detect whether or not a tsunami has been generated, and if so, predict where and when the tsunami is likely to reach different shorelines. These messages are transmitted to local agencies as needed, allowing local emergency managers to implement tsunami evacuation warnings or orders, as appropriate. The Tsunami Center at the National Oceanic and Atmospheric Administration (NOAA) uses a four-category system to convey information about the potential for a tsunami to impact a region following an earthquake, as summarized on Table 7-5 below.

Table 7-5: Tsunami Alerts and Appropriate Responses
Alert Type Potential Hazards Appropriate Action
Warning
DANGER! TSUNAMI IMMINENT!
Dangerous coastal flooding and
powerful currents are possible. Wave
heights > 3 ft or unknown.

Get to high ground or inland
IMMEDIATELY. Follow tsunami
evacuation signage.

Advisory

STRONG CURRENTS AND
DANGEROUS WAVES in or very near
coastal water. Wave heights of 1 -3 ft.

Stay out of the water, and away from
beaches and waterways.

Watch
TSUNAMI IS POSSIBLE. Alert level
may change once more information is
known.

Be prepared to take action. Stay tuned
to local radio / TV / NOAA “alert”
weather radios
Information
Statement
NO TSUNAMI IMPACT EXPECTED.

Alert level may change once more
information is known.

No action needed.

Sources: https://www.weather.gov/safety/tsunami-alerts and https://www.tsunami.noaa.gov/pmeltheme/forecast-warning Some communities, like Japan, which has been impacted by tsunamis dozens of times, have built seawalls designed to stop or reduce the impact of tsunamis. The difficulty in the design of these

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structures, however, is to predict the maximum wave height likely to be experienced in a given area, and build walls that are high enough. Japan has a long historical record of tsunamis, with markers that show the limits of previous, historical tsunami runups, and yet, the 2011 tsunami was larger than expected, and overtopped the existing seawalls. That in turn trapped water on the landward side of the seawall, adding to the overall damage and loss of life. Some communities, especially since the 2004 Indian Ocean tsunami, have recognized the importance of protecting and enhancing mangroves, sand bars, and other natural systems that slow down the waves and protect inland areas from debris carried by the tsunami. Avoiding the construction of buildings and infrastructure within the hazard area, building instead on areas inland or elevated above the projected inundation levels, is recommended and now often considered in site planning, but these mandates are generally not retroactive and do not apply to structures already built within the hazard zone. Note that the most recent California Building Code, which is based on the ASCE-7/16-22 standard, requires that tsunami loads be considered for new structures built within the tsunami hazard area. Building types that perform best in tsunamis include concrete, masonry and heavy steel frames if built to modern building code standards. In Japan some buildings within the tsunami hazard zone that have been built to withstand tsunami loads have been used as vertical evacuation areas, with people converging in the upper floor or roof, which has been built to be above the anticipated water level.

Other communities have invested significant resources in education and outreach efforts to prepare their population for future tsunamis. These programs may include some or all of these items:
• preparing evacuation plans that identify roads and pathways to be used to reach higher ground in the event of an evacuation
• installing signs showing the tsunami evacuation routes and the intended destination areas outside of the potential tsunami inundation zone
• deploying alarm systems and/or reverse 911 communication systems that can be used to provide evacuation instructions and other pertinent important information • preparing and disseminating educational pamphlets or other materials that describe when and what to do if an evacuation order is issued
• conducting regular drills to test the preparation level of first responders, identify bottlenecks and procedures that could be improved, and increase the awareness of residents and workers in the tsunami hazard zone
These efforts work best when disaster mitigation is community-based, with local residents involved in the planning process and emergency drills. These efforts allow community members to define specific concerns and problems, and identify potential solutions. World Tsunami Awareness Day is on November 5th. Many communities organize educational drills and other activities on that day to raise awareness of the dangerous effects of tsunamis and to highlight the importance of having tsunami evacuation plans in place. Communities that implement a series of disaster-preparedness activities can become certified as a TsunamiReady community. The guidelines that need to be met to obtain this certification are described here.

As discussed in the previous sections, the California Geological Survey (CGS) in collaboration with the Governor’s Office of Emergency Services (Cal OES) and other partners, have prepared maps showing the tsunami hazard zones in the State. The map that covers the Santa Monica area is included here as Figure 7-4. Together with these products, these agencies have also prepared and provided several resources designed for emergency managers in areas susceptible to tsunami hazards. These resources are described in the paragraphs below. Information on these products was

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extracted from this website. For additional information and links to download the Special Reports discussed below, refer to the link provided.

1. Maritime Tsunami Response Playbooks (CGS Special Report 241; Wilson et al., 2016): This report and the individual “playbook” plans were developed in response to the impact that the 2010 Chile and 2011 Japan tsunamis had on the California coastline and the harbors and ports therein. Authorities in charge of these facilities were interested in more detailed information on the estimated hazard and impact that a future tsunami would have on these maritime communities. In response, the California Tsunami Program developed and provided harbor-specific maps and other products detailing the estimated currents, wave heights, and damage potential, the minimum offshore safe depth for vessels to evacuate to in advance of an incoming tsunami, and specific recommendations for each harbor to follow depending on the estimated size and damage potential for tsunamis of different sizes.

The “playbooks” provide harbor and marina officials with a variety of response maps for different-sized tsunamis and different source origin locations, with guidance regarding actions that can be taken based on the anticipated in-harbor hazards (such as strong currents and eddies, damage potential to docks, piles and other infrastructure) and the areas offshore where boats can sit out the tsunami without being damaged (remember than in open, deep seas tsunamis are almost imperceptible). The decisions taken, including tsunami evacuations and response activities, are made by each maritime community, but these decisions can be guided by the instructions recommended in their Playbook Plan.

The California Tsunami Program, together with FEMA and other partners involved in the preparation of these documents also envisioned that the Playbooks would be used not only for tsunami response, but for pre-disaster planning and preparedness, including the identification of mitigation measures and infrastructure improvements that would make their facilities more disaster-resilient. Funding to make some of the identified improvements could then be sought, including, possibly, through additions to their Local Hazard Mitigation Plans.

2. Tsunami Emergency Response Playbooks and FASTER Tsunami Height Calculation:

Background Information and Guidance for Use (CGS Special Report 236; Wilson and Miller, 2014): These products are similar to the playbooks described above, but are meant to help communities susceptible to tsunami hazards prepare for an incoming tsunami by providing implementation actions tailored to that individual tsunami event. As with the maritime tsunami response playbooks, these products were also developed in response to the impacts to the California coast from both the 2010 Chile and 2011 Japan tsunamis.

Typical tsunami evacuation plans at that time identified the evacuation area for a worst-case tsunami event, which typically included areas at elevations below 30 to 50 feet. In some communities, this amounted to a large evacuation area that was not applicable to most tsunami events and required significant resources to implement. The alternative was to not issue an evacuation order at all, placing individuals near the coastline in danger when the tsunami arrived.

To address these concerns, the California Tsunami Program developed the approach referred to by the acronym FASTER, which allows emergency managers to estimate tsunami flood conditions, including runup and flood elevation, at given locations for specific tsunami

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events, which in turn helps determine which areas should be evacuated. Input variables used by FASTER include:

FA = Forecasted amplitude (i.e., wave heights), which are calculated and provided by the National Tsunami Warning Center in the first few hours after a tsunami is generated Storm = Storm surge or existing ocean conditions. These values are predicted and issued by the regional NOAA Weather Forecast offices
T = Maximum Tidal height anticipated in the first 5 hours of a tsunami hitting the coastline. These values are also issued by NOAA
E = Forecast modeling Error potential which, based on an analysis of past historical events (Wilson et al., 2012), has been calculated to be about 30% of the forecast amplitude
R = Site-specific amplified Runup potential, a value calculated from existing State tsunami modeling.

The City of Santa Monica has a Tsunami Playbook prepared by the CGS that emergency managers in the City use to estimate runup elevations and evacuation areas when a teletsunami warning is issued. Public safety personnel are prepared to use the local Tsunami Playbook is to implement evacuations during a tsunami event. In addition, the Playbook is used to educate public safety personnel on potential tsunami impacts, design local tsunami evacuation plans and maps, and assist in the design of realistic disaster drills. The City’s tsunami hazard zone, evacuation routes, and evacuation sites are reviewed regularly by Office of Emergency Management, Santa Monica Police, and Santa Monica Department of Transportation personnel and are publicly available online.

The City of Santa Monica is designated a TsunamiReady Community by the National Weather Service based on established program criteria. It regularly participates in statewide tsunami drills, testing notification procedures and use of the Playbook. The City has pre-scripted alerts and warnings that can be quickly distributed to the public using overhead speakers on the Santa Monica Pier, reverse 911 communications, or even Wireless Emergency Alerts (WEA) to anyone who is within the hazard area. The City participates in National Tsunami Preparedness Week and World Tsunami Awareness Day by educating the public and staff on tsunami inundation zones and actions to take during a tsunami event. The City includes tsunami education in its general public outreach activities, including a designated tsunami preparedness website that provides direct access to tsunami hazard maps, meanings of tsunami terminology, and general preparedness information.

TSUNAMI RESOURCE DIRECTORY
City Resources
City of Santa Monica Office of Emergency Management
City agency that administers the implementation of disaster planning, training and community-based preparedness programs to ensure that Santa Monica is a disaster-resilient community. City-prepared information on tsunami preparedness is available from this link.

County Resources
Los Angeles County Emergency Response Website
When a disaster occurs, this website is activated to provide information in real-time about the incident, evacuation instructions, shelter locations and other important information.

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Los Angeles County Office of Emergency Management (OEM) This agency is responsible for comprehensively planning for, responding to and recovering from large-scale emergencies and disasters that impact Los Angeles County. OEM’s work is accomplished in partnership and collaboration with first response agencies, as well as non-profit, private sector and government partners.
500 W. Temple Street, Room 358,
Los Angeles, CA, 90012
Ph: (213) 974-1311
State Resources
California Geological Survey, Southern California Regional Office 320 W. 4th Street, Suite 850
Los Angeles, CA 90013
Ph: 213-239-0877
Fax: 213-239-0894
California Geological Survey, Headquarters
801 K Street, MS 12-30
Sacramento, CA 95814
Ph: 916-445-1923
Fax: 916-445-5718
Governor’s Office of Emergency Services (Cal OES)
Website provides information on disaster planning, preparedness and prevention; disaster response; getting assistance following a disaster, and recovery operations. 3650 Schriever Avenue
Mather, CA 95655
Ph: 916-845-8510; Fax: 916-845-8511
www.caloes.ca.gov
California Tsunami Program (CTP)
Collaboration between Cal OES and the CGS Tsunami Unit that also partners with the National Weather Service and other agencies at the local level (including counties, cities, and community workgroups) to lead California’s efforts to assess the tsunami hazard and risks of California’s coastal communities. Their website is the gateway to a variety of tsunami products, including maps, preparedness guides, educational materials, technical reports and data, and publications. New tsunami maps for California can be accessed from this site.

TsunamiZone.org
A consortium of state and Federal partners including NOAA, the National Tsunami Hazard Mitigation Program, the USGS, Cal OES and the Statewide California Earthquake Center (SCEC), with support from the CGS, FEMA, the University of Southern California and the Earthquake Country Alliance. The TsunamiZone website provides information on how to understand the warnings, how to better prepare for earthquakes and tsunamis, including materials on preparedness drills, and registering as a tsunami-ready individual, family, business, school, group, or organization.

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Federal Resources and Programs
National Oceanic and Atmospheric Administration –
National Tsunami Hazard Mitigation Program
U.S. Tsunami Warning System
Lists tsunami warnings, advisories, watches or threats in real-time, around the world. 910 S. Felton Street
Palmer, AK 99645 USA
Ph: 907-745-4212
Federal Emergency Management Agency (FEMA) – Region IX
For information on disaster declarations and disaster assistance, and the use of HazUS. 1111 Broadway, Suite 1200
Oakland, CA 94607-4052
Ph: 510-627-7100
Fax: 510-627-7112
Southern California Field Office Ph: 626-851-7900
Tsunami Page at Ready.gov
A website of the U.S Government that provides information on what to do before, during and after a tsunami.

Publications
The resources presented in the previous section include links to many publications and educational materials.

For the References cited in this section, refer to Appendix I.

There are hundreds of publications on tsunamis, and many more are published every year. The modeling of tsunamis is evolving rapidly as computer power increases and better bathymetric models are developed. The publications below set the stage for many of the more recent models that were used to develop the CGS Tsunami Hazard Maps and the ASCE-7-16/22 and ASCE-7-28 tsunami section.

Ross, S., and Jones, L. (editors), 2013, The SAFRR (Science Application for Risk Reduction) Tsunami Scenario: U.S. Geological Survey Open-File Report 2013-1170 and California Geological Survey Special Report 229; available from https://pubs.usgs.gov/of/2013/1170/. Similar to the ShakeOut San Andreas fault earthquake scenario, this report addresses a hypothetical tsunami scenario generated by an earthquake offshore the Alaska Peninsula, and its impacts on the California coast.

Wilson, R., Hemphill-Haley, E., Jaffe, B., Richmond, B., Peters, R., Graehl, N., Kelsey, H., Leeper, R., Watt, S., McGann, M., Hoirup, D., Chague-Goff, C., Goff, J., Caldwell, D., and Loofbourrow, C., 2014, Chapter C: The search for geologic evidence of distant-source tsunamis using new field data in California, in Ross, S.L., and Jones, L.M., editors, The SAFRR (Science Application for Risk Reduction) tsunami scenario: U.S. Geological Survey Open-File Report 2013–1170–C, 122 p., doi:10.3133/ofr20131170c.

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Wood, N.J., Ratliff, J. and Peters, J., 2012, Community Exposure to Tsunami Hazards in California:

U.S. Geological Survey Scientific Investigations Report 2012-5222; available at https://pubs.usgs.gov/sir/2012/5222/.

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SECTION 8: FLOOD HAZARDS
WHY ARE FLOODS A THREAT TO THE CITY OF SANTA MONICA?
Floods are natural and recurring events that only become hazardous when human activities and structures encroach onto floodplains, modifying the landscape and building structures in the areas meant to convey excess water during floods. Flooding is one of the most destructive natural hazards in the world, and average annual flood losses have increased steadily over the last decades as development in floodplains has increased. Thus, in 2005, the U.S. Department of Homeland Security reported that flood damage costs nationwide exceeded $5 billion per year, while in 2022, the National Centers for Environmental Information0F
1 , a division of the National Oceanic and
Atmospheric Administration (NOAA), reported that flooding has an average cost of $4.6 billion per event, and is the fourth most costly natural hazard in the US (cyclones, drought and wildfires occupy the first three rankings. In short, flooding poses a threat to life and safety, and can cause severe damage to public and private property.

Under the National Flood Insurance Program, a flood is:
a) a general and temporary condition or partial or complete inundation of normally dry land areas from:
(1) the overflow of inland or tidal waters,
(2) the unusual and rapid accumulation or runoff of surface waters from any source, or (3) mudslides (i.e., mudflows) which are caused by flooding and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, or b) the collapse or subsidence of land along the shore of a lake or other body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels or suddenly caused by an unusually high water level in a natural body of water, accompanied by a severe storm, or by an unanticipated force of nature, such as flash flood or abnormal tidal surge, or by some similarly unusual and unforeseeable event which results in flooding.

This very broad definition of flooding is used in this document to address the potential for partial or complete inundation of normally dry areas in Santa Monica as a result of storms and catastrophic failure of reservoirs. Inundation resulting from tsunamis is discussed in Section 7, and mudflows are discussed in Section 9.

Like most of southern California, the city of Santa Monica and surrounding areas are subject to unpredictable seasonal rainfall. Most years, the scant winter rains are barely sufficient to turn the hills green for a few weeks, but every few years, the region is subjected to periods of intense and sustained precipitation that results in flooding. The variability in annual rainfall amounts is illustrated on Figure 8-1, which shows the annual rainfall measured in the city of Los Angeles, California for the period between 1877 and 2022. Notable historical flood events reported in southern California occurred in 1862, 1884, 1916, 1938, 1969, 1978, 1980, 1983, 1988, 1992, 1995, 1998, 2005, 2019, and 2023.

1 https://www.ncei.noaa.gov/access/monitoring/dyk/billions-calculations, accessed Nov.-Dec. 2023.

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Figure 8-1: Annual Rainfall in the City of Los Angeles, California for the Period Between 1877 and 2023

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Notice that whereas in the 19th and first half of the 20th century the significant flood events appear to have been spaced about 20 to 30 years apart, in the last decades damaging flood events have been spaced between two and 14 years apart. The list of flood events provided in Table 8-1 below suggests that frequency of flooding in the region has not changed much in the past approximately 250 years, however the increased occupation of low-lying areas has likely increased exposure, resulting in an increase in losses to property and life as a result of flooding. Specifically, as the population in the region has increased, there has been an increased pressure to build on flood-prone areas and upstream of already developed areas. Increased development in turn increases the amount of impervious surfaces, such as asphalt and concrete. Water that used to be absorbed into the ground now becomes runoff to downstream areas. If storm drain systems are not designed or improved to convey these increased flows, areas that may not have flooded in the past are now subject to flooding or may be subject to flooding in the future. This is especially true for developments at the base of the mountains and downstream from canyons that have the potential to convey mudflows.

The city of Santa Monica lies at the western edge of the Los Angeles basin and the greater floodplain of the Los Angeles and San Gabriel rivers. When Spanish explorers first encountered the basin in the late 1700s, the Los Angeles River floodplain was heavily vegetated and dotted with vast marshes, shallow lakes, and small ponds. The rivers, which collected runoff from the surrounding mountains, were rarely confined to a distinct channel and often radically changed their courses spreading storm water and sediment loads across the basin. Then, in the late 1800s and early 1900s, as the region became increasingly urbanized, several of the marshes were drained to increase acreage for agricultural purposes. During wet winters, however, the basin was subject to several episodes of severe flooding. In response, natural channels were dredged and major rivers in the basin were confined to artificial channels to control flooding and sedimentation. These efforts included channelization of the Los Angeles River and lining with concrete or grout the channels of Santa Monica Canyon, Rustic Canyon, and the eastern, upstream portion of Ballona Creek, east of Centinela Avenue. West of Centinela, the banks of Ballona Creek were paved or lined with boulders, but its bottom was left unpaved.

Today, the 50-plus miles-long Los Angeles River begins in the foothills of the San Gabriel and northern Santa Monica Mountains, then flows east across the San Fernando Valley, where it is joined by major tributaries draining the western San Gabriel Mountains. It then turns south, passing through the Hollywood Hills and the Glendale Narrows, onto the broad coastal plain where it receives water from several more tributaries. The river then flows south, eventually reaching the Long Beach Harbor and draining a total watershed of about 834 square miles. Prior to 1825, the Los Angeles River used to flow westward across the northern portion of the Los Angeles Basin, through the Ballona Gap, and into what has been referred as both the Ballona Lagoon or Ballona Lake (Dark et al., 2011), in the area now occupied by Marina del Rey. Given that the river has now been channelized and the region has been extensively developed, the likelihood of the Los Angeles River changing course again and flowing through the Ballona Gap area is very low to nil.

Much of the work described above regarding the channelization of the Los Angeles River and other drainages was conducted by the U.S. Army Corps of Engineers and Los Angeles County. Both of these agencies continue to maintain numerous regional flood control structures within the Los Angeles River system, including channels, levees, flood-control basins, and debris basins. Today, this flood-control effort is also tied to water conservation: it is now the policy of both the County and cities therein, including Santa Monica, to capture as much storm runoff as feasible and store the water in either water treatment plants to use as reclaimed water, or return it to the underlying aquifers

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is no flow data for these channels. Flows in
Ballona Creek, however, are measured,
with the majority of the flow in this
channel occurring between the months of
November and March, reflective of the
“Mediterranean climate” typical for coastal
southern California.

The closest U.S. Geological Survey stream
gaging station near the city of Santa
Monica is on Ballona Creek in Culver City
(Site Number 111035001F
2 ), approximately
3 miles to the southeast of Santa Monica
Airport. Daily measurements were made at
this station for 50 water years between
1928 and 1978. These records are used
here to illustrate and discuss the significant
variability in daily discharge on Ballona
Creek, and thus in the region. A tile plot
that shows the monthly discharges for the entire 50-year period is shown on Figure 8-2. Darker blues indicate higher discharge amounts, whereas white cells indicate little to no discharges. This figure illustrates the statement made above that most flows occur between November and March, and that there is significant variability in discharge from year to year. 2 https://maps.waterdata.usgs.gov/mapper/ accessed on December 18, 2023. via soft-bottom channels and spreading grounds. In the densely urbanized Santa Monica area, like most of the Los Angeles Basin, runoff is now largely controlled by streets, retention basins, storm drains, and flood control channels.

HISTORY OF FLOODING IN THE CITY OF SANTA MONICA
Floods of consequence in and around the city of Santa Monica are typically flash floods, caused by short-duration but heavy rainfall events. These flood events generally have high peak volumes and high velocities. This type of flooding occurs in response to the local geology and geography and the built environment (human-made structures). When a storm approaches, runoff from the Santa Monica Mountains to the north and the Baldwin Hills to the southeast collects rapidly into the natural and artificial channels in the built environment. The flood control channels then direct the runoff directly into the Pacific Ocean. A few of these high-discharge flood events have impacted the city of Santa Monica historically. For example, heavy rains in 1938 resulted in flooded streets, flooded sumps and depressions, and mudflows in the vicinity of Santa Monica Canyon. More recently, as a result of tropical storm Hilary in August 2023, the Pico-Kenter storm drain overflowed its top and flooded some areas of the beach.

There are no major streams in the city limits of Santa Monica; channels of the Santa Monica and Rustic Canyons roughly define the
northern boundary of the city but are not Figure 8-2: Tile Plot Showing Monthly Discharges in located in the city proper. These streams Ballona Creek at Site 11103500 for Years 1928-1978 are not currently being monitored, so there

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Historic Flooding in Los Angeles County
There are several rivers in the southern California region, but the river with the best-recorded history is the Los Angeles River. The flood history of the Los Angeles River is generally indicative of the flood history of much of southern California. Records show that the Los Angeles River floods, on average, about once every six to seven years. But averages are deceiving, for the Los Angeles Basin goes through periods of drought and then periods of above-average rainfall. For example, between 1868 and 1884, a period of 16 years, there were no major floods, but this was followed by a series of wet years with floods in 1885, 1886, 1889 and 1891. A similar cluster of wet years was recorded in the 1990s, and more recently, flooding events were recorded in 2005, 2014, 2017, 2022, and 2023. The history of floods in Los Angeles County is summarized on Table 8-1 below. The entries in bold text are flood events that likely impacted the Santa Monica coastal region. FEMA began to record disaster declarations in 1953; flood events in Los Angeles County that prompted a disaster declaration are identified in the table.

Table 8-1: Historical Floods in Los Angeles County
Date Comments
1770-1771 Great flooding on the Los Angeles River recorded by Father Juan Crespi. River overflowed its channel.
1771-1772 Flooding recorded by Spanish Mission Fathers. San Gabriel Mission crops destroyed. 1775-1776 Due to heavy flooding, San Gabriel Mission was moved about 6 miles back from the river. 1779-1780 Flooding recorded by Spanish Mission fathers. Flows filled riverbed and flooded the lowlands where wheat and barley had been planted.
1811 Flooding reported, although records are sparse.
1815 Flooding washes away the original Plaza in Los Angeles. River changes course at Alameda and 4th Street to cut west and join Ballona Creek. From there it emptied into Santa Monica Bay.
1822 A great flood on the Los Angeles River “covered all the lowlands and reached a greater height than was ever known before.”
1824-1825 Los Angeles River changed its course back from the Ballona wetlands to San Pedro. Before this storm, the river would spread over the entire area, filling depressions at the surface and forming lakes, ponds and marshes, rarely discharging its waters into the sea. The 1825 floods cut a riverway to the ocean, draining the marshlands and causing the forests to disappear. 1832 Heavy flooding caused the drainage near Compton to change so that many lakes and ponds that “had been permanent, became dry a few years thereafter.” Drainage of these ponds and lakes completed the destruction of the forests that used to cover a large part of southern Los Angeles County.
1849-1860 Floods of various magnitudes occurred in 1849-1850, 1851-1852, and 1859-1860. 1861-1862 The “great flood” or the “Noachian deluge of California.” Fifty inches of rain fell during December and January, with rain falling every day for 43 days. The entire valley from Los Angeles to the ocean was a great lake. Part of the Los Angeles River split and drained into Ballona Creek. The San Gabriel River also overflowed its banks and started a new channel. 1867-1868 Floods spilled over the river channel and created a large, temporary lake out to Ballona Creek. The San Gabriel River broke out of its channel and washed out thousands of acres of land.
1884 Two periods of intense rainstorms separated by 6 to 8 days. The first storms caused little damage. The second washed out all but one of the bridges across the Los Angeles River, washed away many houses, and drowned several people. Parts of Los Angeles flooded 3 to 4 feet deep.

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Date Comments
1886-1887 A good part of Los Angeles was inundated. The levees were damaged and railway communication was impossible for 2 to 3 weeks.
1889 Flood on Christmas Day caused much damage; bridges and levees washed away; the old San Gabriel, new San Gabriel and Los Angeles Rivers joined near Downey and formed one body of water. Los Angeles River overtopped its channel. 1914 Heavy flooding in January and February. Great damage to Los Angeles harbor. 1916-1938 Flooding in 1916. Minor floods causing damage in certain areas reported in 1918, 1921- 1922, 1926, 1927, 1931, 1932, 1934, 1936, and 1937.
1934 Moderate to severe flooding starting January 1. Over 40 dead in La Cañada – Glendale area.

Debris flow killed 12 people who had taken shelter in the Montrose Legion Hall. 1938 Series of storms beginning December 1937. March floods exceeded all previous floods for which records were available. Large tracts inundated; bridges, highways and railroads severely damaged. 87 people killed, over $78 million (1938 dollars, approximately equivalent to $1.7 billion in 2025) in damages.
1941-1944
Los Angeles River floods five times.
1952 Moderate flooding.
1969 Disaster declaration due to recurrent precipitation during January and February that nearly approached the largest total since 1884. Nearly 40 people died as direct result of the floods in southern California, and more than 10,000 had to be evacuated. 1978 Two moderate floods prompted a disaster declaration issued in February. 1979 Los Angeles experiences severe flooding and mudslides. 1980 Disaster declaration issued in response to flooding. Flood tops banks of river in Long Beach.

Sepulveda Basin spillway almost opened.
1983 Disaster declaration issued in response to a coastal storm that caused flooding; six people died.
1992 Disaster declaration issued as a result of 15-year flood. Motorists trapped in Sepulveda basin, resulting in six deaths.
1994-1995 Disaster declarations issued as a result of heavy flooding throughout California. The total damages were estimated at $2 billion.
1997-1998 The 1997 floods caused extensive damage in 48 California counties, including Los Angeles County, prompting a Disaster declaration. Total damages estimated at $1.8 billion. The 1998 El Niño storms also caused damage, but this was less than it could have been because many had taken measures to reduce their risk following the 1997 storms. Still, a Disaster declaration was issued for the Feb. 2, 1998 storms.
2003-2004 Disaster declaration issued for Los Angeles County due to flash floods. The rains followed the extensive fires of 2003; in many areas, canyons chocked with ashes and debris caused debris flows that did substantial damage downstream.
2004-2005 The second-wettest year on record in the Los Angeles Basin; the rains caused extensive damage in some areas, triggering landslides and debris flows. In January 2005, flooding and landsliding caused 28 deaths, 8 injuries, affected 500, and caused $200 million in damages.

Between 17-23 February, flooding in Los Angeles County alone killed 9 people, affected 150, and caused $250 million in damages. The 2005 storms triggered two Disaster declarations for Los Angeles County.
2005-2006 Flooding due to intense precipitation between Dec. 31 and Jan. 18 killed 3 people, affected 3,600, and caused $245 million in damages in northern and southern California, and in Nevada.

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Date Comments
2010-2011 California winter storms caused flooding, debris flows and mudflows in several counties, especially along the foothills, and in areas previously burned by wildland fires. Major Disaster Declarations issued on March 10, 2010 and January 26, 2011. Another powerful winter storm caused flash floods in March 2011.

Oct. 2012 A cold and unstable air mass produced strong thunderstorms and flash floods across Los Angeles County. The strongest storms occurred across the San Fernando and San Gabriel Valleys. Water flooding 3 to 4 feet high was reported along all lanes of I-710 in the Bandini neighborhood of Commerce.

Feb.- Mar.
2014
Strong winter storm generated heavy showers and thunderstorms that produced flash flooding and debris flows across Los Angeles County. Flash flooding and debris flows were reported near the Colby fire burn area in the San Gabriel Valley near Glendora and Azusa.

Several homes were damaged. In Lakeview Terrace, two women were trapped when a wall of water swept across their driveway into the street.

Dec. 2014 Disaster declaration due to severe storms, flooding and mudslides impacting the Soboba Band of Luiseño Indians, with damage primarily impacting roads and bridges. Event occurred Dec. 4-6; declaration issued on Jan. 27, 2015. A strong thunderstorm on Dec. 16th over the city of Torrance produced intense rainfall and flash flooding. Streets were flooded and numerous cars were stranded.

Jan. 2017 Disaster declaration issued in response to severe winter storms, flooding and mudslides throughout several counties in California, including Los Angeles County. The event occurred January 18-23, 2017; declaration issued on March 16, 2017. The dollar amount obligated to assist the public exceeded $57 million. Between 2 and 6 inches of rain fell across the region, resulting in flash flooding across Los Angeles County. Flash flooding was reported at the intersection of Pacific Coast Highway with I-710.

Feb. 2017 Disaster declaration issued in response to severe winter storms, flooding and mudslides, with nearly all counties north of and including Santa Barbara affected. The event occurred February 1-23, 2017; disaster declaration was issued April 1, 2017. The dollar amount obligated by FEMA to assist the public was almost $428 million.

Dec. 2022
– Jan. 2023
Disaster declaration issued in response to severe winter storms, flooding and mudslides, with the event occurring Dec. 27, 2022 to Jan. 31, 2023. Declaration issued on Jan. 14, 2023. All coastal counties, with the exception of Orange County, were included in the declaration.

Jan. 2023 Disaster declaration issued in response to severe winter storms, flooding and mudslides impacting all coastal counties from Humboldt south to San Diego, and dozens of counties inland, including San Bernardino and Riverside counties in southern California. Los Angeles County included in the impacted area. Storms occurred Jan. 8-31, 2023, and declaration was issued Jan. 9, 2023.

Feb. 24-
25, 2023
Powerful winter storm brought 2-5 inches of rain to coastal areas and valleys, and 4-10 inches of rain to foothill and mountain areas. Heavy rain caused flash flooding, mudslides and debris flows in several areas in the region. These include flash flooding on I-5 near Burbank where a couple of vehicles were flooded. Flash floods also closed Highway 101 near Campo de Cahuenga, with all lanes experiencing significant flooding.

Mar. 2023 Disaster declarations issued in response to severe storms, flooding and mudslides impacting a large portion of California, including Los Angeles County. The declarations were issued on March 10th and April 3rd, and covered storm damage that began on March 9th.

Aug. 20,
2023
Heavy rain brought on by Tropical Storm Hilary; numerous reports of flash flooding, mudslides and debris flows throughout the region. Flooding impacted I-10 at various locations including Culver City, stranding numerous vehicles. Also in the Culver City area, small streams overflowed their banks and flooded several backyards. Heavy rains flooded the I-405 near Sherman Oaks, leaving numerous vehicles stranded on the flooded roadway.

Mud and debris flows reported on Piuma Road near Malibu Canyon Road.

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Date Comments
Feb. 4-8th,
2024
Slow-moving atmospheric river dropped between 6 and 12 inches of rain in the southern California region, from Santa Barbara south to San Diego, with areas in the Santa Monica Mountains reporting about 12 inches of rain in three days. A Disaster declaration was issued for the storms in early February, to address damage caused by the winter storms and their after-effects, including flooding, landslides and mudslides.

Sources: http://www.em-dat.net/disasters/ (accessed at various times in 2014-2017; https://www.emdat.be in 2023, but no longer available to consultants without an annual fee; http://www.fema.gov (accessed at various times in 2014, 2017, 2022, and 2023); https://www.ncdc.noaa.gov/stormevents/ accessed various times in Aug.-December 2023; https://www.fema.gov/data-visualization/disaster-declarations-states-and-counties accessed in March 2025
WHAT FACTORS CREATE FLOOD RISK?
Climate
Flooding occurs when climate, geology, and hydrology combine to create conditions where water flows outside of its usual course. In the city of Santa Monica, geography and climate may combine to create seasonal flooding conditions. The Santa Monica, Santa Susana, and Verdugo Mountains for the most part do not reach heights above three thousand feet. In contrast, the western San Gabriel Mountains reach elevations of more than seven thousand feet, and to the southwest, the San Bernardino Mountains reach elevations of more than 11,500 feet. These higher ridges, given their elevations, often trap east-moving winter storms approaching from the Pacific Ocean side. As a result, downtown Los Angeles and the ridges to the north (including the Santa Monica Mountains) typically average just about 13 to 15 inches of rain a year, whereas the northern part of the Los Angeles Basin receives about 23 to 24 inches per year, and the mountain peaks in the San Gabriel and San Bernardino Mountains receive more than 40 inches of precipitation annually. “Averages” however, are not particularly representative of rainfall in the southern California area, as illustrated with the following discussion about downtown Los Angeles: the average annual rainfall in Los Angeles for approximately the past 125 water years is 14.75 inches, but rainfall during this period ranged from only 3.21 inches in 2006-2007 to 38.18 inches in 1883-1884 (see Figure 8-1).

This makes the Los Angeles Basin a land of extremes in terms of annual precipitation.

Rainfall that falls on the mountains and hillsides moves rapidly downstream, often with severe consequences for anything in its path. The intensity of the runoff increases in hillside areas recently burned by wildfires, where vegetation has not yet formed a protective ground cover that helps keep the soil in place. Furthermore, the oils in many of the plants native to southern California, when burned, react with the soils, making them water repellant. As a result, less rainwater than usual infiltrates the ground, and instead makes its way downstream as runoff, carrying ashes and other burned debris with it. Several of the mudflow and debris flows that prompted the enactment of Disaster declarations in the past decades (see Table 8-1) occurred at the base of the San Gabriel Mountains, in areas burned by wildfires, such as the communities of Azusa, Glendora, and Burbank.

Runoff often also concentrates in major roadways, leading to flash floods in low-lying sections of freeways, including the interstates (I-5, I-10, I-405) and Highway 101.

There are three main types of storms that produce precipitation in southern California: winter storms, local thunderstorms, and summer tropical storms (or monsoons). These are briefly described below.

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• Winter Storms are characterized by heavy and sometimes prolonged precipitation over a large area. These storms usually occur between November and April and are responsible for most of the precipitation recorded in southern California. Most of these storms have been found to be associated with atmospheric rivers (ARs). The storms originate over the Pacific Ocean and move eastward (and inland), with the mountains forming a rain shadow, as described before. A significant portion of the moisture drops on the mountains as snow. If large storms are coupled with snowmelt from these mountains, large peak discharges can be expected in the main watersheds at the base of the mountains during the spring. Atmospheric rivers are discussed further in the following pages.

Some of the severe winter storm seasons that have historically impacted the southern California area have been related to El Niño events. El Niño is the name given to a phenomenon that starts every few years, typically in December or early January, in the southern Pacific off the western coast of South America, but whose impacts are felt worldwide. Briefly, warmer than usual waters in the southern Pacific are statistically linked with increased rainfall in both the southeastern and southwestern United States, droughts in Australia, western Africa and Indonesia, reduced number of hurricanes in the Atlantic Ocean, and increased number of hurricanes in the Eastern Pacific. Atmospheric rivers are also statistically linked to El Niño events, with an increase in both frequency and intensity of ARs in the western and southwestern United States during El Niño years.2F 3 Two of the
largest and most intense El Niño events on record occurred during the 1982-1983 and 1997- 1998 water years. These were also two of the worst storm seasons reported in southern California.
• Thunderstorms and Monsoons: Relatively infrequent sources of heavy rainfall in the southern California region are tropical storms (or monsoons related to hurricanes in the Pacific Ocean), with rainfall generally reported in the mountains, inland deserts and adjoining cities. These rains typically occur in the summer or early fall. The storms originate in the warm, southern waters off Central America, Mexico, or Baja California, in the Pacific Ocean, and move northward into southern California. During El Niño years, southern California can also experience increased thunderstorm activity and higher-than-average precipitation during the summer months. Thus, El Niño can result in increased rainfall both during the winter and summer months. This is reflected in Table 8-2 below. Occasional hurricanes and tropical storms that have dropped significant rainfall in the southern California area in the last 150 years or so are also listed in Table 8-2. Thunderstorms related to storms in the Gulf of Mexico, Gulf of California, or the southern Pacific Ocean can occur at any time but are usually more prevalent in the higher mountains and deserts during the summer. During La Niña years the jet stream tends to shift to the north, typically resulting in drier-than-average conditions in southern California. However, weather patterns are highly variable and occasionally during La Niña events, the area is still impacted by summer thunderstorms, as shown on Table 8-2. The summer and early fall storms that potentially impacted the Santa Monica area are highlighted with bold text. Storms that resulted in flooding and are listed in both Tables 8-1 and 8-2 are identified with an asterisk (*) after the date.

3 Kim, H-M., Zhou, Y., and Alexander, M.A., 2017, Changes in atmospheric river and moisture transport over the Northeast Pacific and western North America in response to ENSO diversity: Climate Dynamics, Vol. 52, pp. 7375-7388, doi:10.1007/200382-017-3598-9.

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Table 8-2: Tropical Storms That Affected Southern California Between 1858 and August 2023
Date Source of Storm; Area(s) Affected Rainfall
(inches)
Oct. 2-3, 1858
The only known historical hurricane that made a landfall in southern California; 75 mph winds estimated in San Diego, tropical storm along the coastline north to Long Beach; intense rain reported from San Diego to Santa Barbara.
>7
July 20-21, 1902 Deserts and southern mountains. El Niño of 1901-1902. up to 2 Aug. 18-19, 1906 Deserts and southern mountains. El Niño of 1905-1906. up to 5 Sept. 15, 1910 Mountains of Santa Barbara County. 2
Aug. 20-21,
1921* Deserts and southern mountains. La Niña of 1920-1921. up to 2 Sept. 30, 1921* Deserts. La Niña of 1920-1921. up to 4
Sept. 18, 1929 Southern mountains and deserts. up to 4
Sept. 28 – Oct. 1,
1932* Mountains and deserts, 15 fatalities. El Niño of 1932-1933. up to 7 Aug. 25, 1935 Southern valleys, mountains and deserts. up to 2 Sept. 4-7, 1939 Southern mountains, southern and eastern deserts. All storms in September 1939 associated with the El Niño of 1938-1939. up to 7 Sept. 11-12, 1939 Deserts, central and southern mountains. up to 4 Sept. 19-21, 1939 Deserts, central and southern mountains. up to 3 Sept. 25, 1939
Tropical cyclone that made a landfall in San Pedro, with sustained winds of 50 mph. Only known tropical cyclone to make a landfall in Southern California. 93 people died; 45 onshore and 48 offshore, at sea. Ten houses washed away in Belmont Shores.
5 Sept. 25, 1939 Surrounding mountains. 6 to 12
Sept. 9-10, 1945 Central and southern mountains. up to 2 Sept. 30 – Oct. 1,
1946 Southern mountains. up to 4
Aug. 27-29, 1951 Southern mountains and deserts; many roads washed out in the Imperial Valley. El Niño of 1951-1952. 2 to 5
Sept. 19-21,
1952* Central and southern mountains. El Niño of 1951-1952. up to 2 July 17-19, 1954 Deserts and southern mountains. El Niño of 1953-1954. up to 2 July 28-29, 1958 Deserts and southern mountains. El Niño of 1957-1958. up to 2 Sept. 9-10, 1960 Hurricane Estelle dissipated west of Central Baja California; southern mountains at and near Julian. 3.40
Sept. 17-19, 1963 Tropical storm Katherine made landfall in northern Baja California; impacted central and southern mountains. El Niño of 1963-1964. up to 7 Sept. 1-3, 1967 Hurricane Katrina in Baja California; impacted southern mountains and deserts. 2
Sept. 3, 1972
Remnants of Hurricane Hyacinth made landfall between Los Angeles and San Diego with 25-mph winds and rainfall in the central and southern mountains. El Niño of 1972-1973.
up to 1
Oct. 6, 1972
Hurricane Joanne made landfall in northern Baja California; maintained tropical storm strength into Arizona; rain in southeast deserts. El Niño of 1972-1973.
up to 2

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Date Source of Storm; Area(s) Affected Rainfall
(inches)
Sept. 10-11, 1976
As a result of the tropical storm Kathleen; impacted the central and southern mountains; sustained winds of 57 mph at Yuma. Killed 12 people in the U.S.; 70-80% of Ocotillo was destroyed; caused millions of dollars in damage. El Niño of 1976-1977.
6 to 12
Aug. 1977
Hurricane Doreen dissipated over the southern California coastal waters. Widespread flooding in Los Angeles and south; extensive crop damage. Also impacted the mountains. El Niño of 1977-1978. up to 2 in the
valleys, up to 8
in the
mountains
Oct. 6-7, 1977 Remnants of Hurricane Heather tracked into southern Arizona; impacted southern mountains and deserts. up to 2
Sept. 5-6, 1978 Remnants of Hurricane Norman impacted the mountains. El Niño of 1977-1978. 3
Sept. 24-26, 1982 Remnants of Hurricane Olivia; impacted the mountains. Strong El Niño of 1982-1983. up to 4
Sept. 20-21,
1983*
Hurricane Manuel dissipated off west coast of northern Baja California; impacted the southern mountains and deserts. Strong El Niño of 1982-1983.
up to 3
Oct. 7, 1983 Remnants of Hurricane Priscella scattered light rain across southern California. n/a
Sept. 10-11, 1984 Hurricane Marie dissipated off the west coast of northern Baja California; scattered rain in coastal areas.
n/a
Aug. 17-19, 1997
Tropical storm Ignacio dissipated near the south-central California coast with gale-force winds over coastal waters. Part of the strong El Niño of 1997-1998.
n/a
Sept. 1997
Hurricane Linda, the strongest storm recorded in the eastern Pacific with 180 mph winds, threatened to come ashore southern California as a subtropical storm. The storm turned away, but caused high surf, 18-foot high waves, showers and thunderstorms.
n/a
Sept. 25, 1997
Hurricane Nora crossed into southern California and Arizona from Baja California. Brought heavy rain to parts of the region, causing millions of dollars in damage to agriculture.
n/a
Sept. 10-19, 2004 Mid-level moisture from hurricane Javier spread over northern Mexico and southwestern United States. n/a
July 31, 20-22,
2006
Remnants of Tropical storm Emilia brought rain to southern California that helped extinguish the House Fire. n/a
Sept. 2007 Thunderstorms and showers; flooding watch in Santa Catalina Island; rain throughout the southern California area. n/a July 18-20, 2012 Remnants of Hurricane Fabio generated scattered showers and thunderstorms in the Los Angeles basin. n/a
Aug. 25-26, 2013
Moisture from the remnants of Tropical storm Ivo caused flash flooding and mudslides in San Bernardino County and Arizona. One motorist drowned in Needles. In the Antelope Valley, flash flooding was reported in the communities of Quartz Hill and Leona Valley. 3 to 4
Aug. 20, 2023* Tropical Storm Hilary swept north from Baja California, bringing winds and rains throughout the southern California area.

13.5 in San
Bernardino Co.
>7 in Los
Angeles Co.

Source: https://www.ncdc.noaa.gov/stormevents/ accessed various times in Aug.-December 2023 and January 2025.

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Much research in the last decade has focused on the study of a meteorological phenomenon called the Atmospheric River (AR). ARs are narrow streams of water vapor transported in the lower atmosphere that are now recognized as responsible for most of the very large storms on the west coast of the United States. Typically packing high wind speeds, ARs are about 400 to 500 kilometers wide and thousands of kilometers long, sometimes extending across whole ocean basins. When these sub-tropical jet streams carrying moisture-laden air directly from the tropics to the western U.S. collide with the mountain ranges in the west coast, the vapor is forced upwards, where it condenses and rains out, leading to significant flooding3F 4 . Because the jet stream passes over the
Hawaiian Islands, these events used to be called the “Pineapple Express.” The storms that occurred 1861-1862 (see Table 8-1) are now thought to have been a series of ARs.

These storms caused state-wide flooding that left the central coast impassible, the State capital underwater for three months, and the State bankrupt. Thousands of people are thought to have died, and one quarter of the cattle in California perished by drowning. These storms were significantly wetter than the 2022-2023 winter storms that caused extensive damage along the entire west coast.

A storm today similar to the 1861-1862 storms would be devastating as the region is now home to millions of people, and produces a large percentage of the U.S. crops. Geologists studying sediments offshore have found evidence that suggests that six “megastorms” have occurred in California in the last 1,800 years – all more severe than the 1861-1862 event. Other studies suggest that similar storms occur once every 100 to 200 years.4F
5 The U.S. Geological Survey’s (USGS) Multi Hazards Demonstration Project (MHDP) has been combining various science disciplines to test and improve the resiliency of communities to natural disasters. To do this, they develop disaster scenarios with feedback from scientists, engineers, and other experts, and in the process engage emergency planners, first responders, businesses, universities, insurance companies, government agencies and the public in preparing for a major natural disaster. The first project of the MHDP was the 2008 ShakeOut earthquake scenario on the San Andreas fault discussed in Section 6. Their second major project was a catastrophic winter storm scenario consisting of a series of hypothetical (but probable) Pacific storms striking the west coast of California for 23 days, which is a shorter period than the 1861-1862 storms.

Named the ARkStorm (for Atmospheric River 1,000 – the name is meant to convey the magnitude of the event, and not its return period), the hypothetical storm was projected to overwhelm the State’s flood protection system, which is normally designed to control the 100- to 200-year storm runoff. In 2011, when the study was first released, property damages and business disruptions from the ARkStorm scenario were estimated to be about $725 billion (Porter et al., 2011). Adjusted for inflation and increase in population, the cost of this hypothetical storm in 2023 was estimated at $1.7 trillion (Masters, 2023). Such a storm would be many times more destructive and costly than a magnitude 8.0 earthquake on the San Andreas fault. The products of the ARkStorm Scenario are intended to be used by emergency planners, policymakers and others to review disaster preparedness, conduct risk assessments and disaster drills, explore ways to adequately fund response and recovery, plan future hazards mapping, and educate the public. The December 2022/January 2023 ARs that impacted California, although significant and costly (responsible for 22 deaths and

4 Ralph, F.M., and Dettinger, M.D., 2011, Storms, floods, and the science of atmospheric rivers: Eos, Transactions of the American Geophysical Union, Vol. 92, No. 32. 5
Dettinger, M.D., and Ingram, B.L., 2013, Megastorms could drown massive portions of California: Scientific American, January 1, 2013, available from https://www.scientificamerican.com/article/megastorms-could-downmassive-portions-of-california/.

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estimated at more than $30 billion in losses), did not approach the rainfall and flooding levels expected from the ARkStorm scenario.

The scientists that ran the ARkStorm scenario described above have been conducting a revised study referred to as ARkStorm 2.0. This new study considers recent advances in the fields of climate, weather and hydrology, uses the latest in modeling tools, and takes into consideration the effects of climate change (Huang and Swain, 2022; Swain, 2022). ARkStorm 2.0 considers two megastorm scenarios: 1) an ARkHist scenario that is based on present-day climate using climatological data collected between 1995 and 2005, and 2) an ARkFuture scenario that considers a warmer climate.

The ARkHist event is anticipated to generate between about 10 and 15 inches of precipitation in Santa Monica in a 30-day simulated storm event, whereas the ARkFuture event would produce between about 15 and 20 inches of rain during a 30-day period in Santa Monica. The storms modeled in the ARkHist scenario produce less precipitation than the rainfall events that led to the 1861-1862 floods; the scenario is thought to have a recurrence interval of about 90 to 100 years.

Flooding in the Santa Monica area as a result of an ARkStorm event could result in flooded streets, overtopping of the concrete-lined channels in Rustic Canyon and Santa Monica Canyon, erosion and hillslope damage along the bluffs, and severe storm swells that may cause coastal inundation and erosion. The ARkFuture scenario is estimated to have a recurrence interval of about 400 years in the present climate. However, findings of the Fourth National Climate Assessment (USGCRP, 2017) include the conclusion that the frequency and severity of ARs impacting the west coast of the United States will increase with increasing temperature, as the warmer weather will result in an increase in evaporation and higher atmospheric water vapor. The economic and societal impacts of these new ARkStorm 2.0 models are being developed (Swain, 2022).

Geography and Geology
The mountains bordering the Los Angeles Basin are very steep and consist of rock types that are fairly impervious to water. Consequently, little precipitation infiltrates the ground; rainwater instead flows across the surface as runoff, collecting in the major drainages that drain into and pass through the basin. Specifically, when a major storm moves in, water collects rapidly and runs off quickly, making a steep, rapid descent from the mountains into man-made and natural channels within developed areas. Because of the steep terrain, scarcity of vegetation, and the constant shedding of debris from mountain slopes (primarily as dry ravel and rock falls), floodwaters often carry large amounts of mud, sand, and rock fragments. Sheet flow occurs when the capacities of the existing channels (either natural or man-made) are exceeded and water flows over and into the adjacent areas.

The greater Los Angeles Basin has been shaped by erosion and sedimentation for millennia. Most of the mountains that ring the basin are still being uplifted at a (geologically) fast rate in response to earthquakes on the region’s many active faults. The rapid uplift has resulted in steep, rugged slopes underlain by brittle, fractured rock, thereby creating a landscape that is very susceptible to erosion.

Over time, rivers and streams emanating from the mountain front have carried boulders, rocks, gravel, sand, and silt down these slopes to the valleys and coastal plain where sedimentary deposits are locally as much as twenty thousand feet thick. This sediment generally acts as a sponge, absorbing vast quantities of water received as precipitation in those years when heavy rains follow a dry period. But like a sponge that is near saturation, the same soil fills up rapidly when a heavy rain follows a period of relatively wet weather. So, in some years of heavy rain, flooding is minimal because the ground is relatively dry. The same amount of rain following a wet period, when the ground is already saturated, can cause extensive flooding.

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Built Environment
The greater Los Angeles Basin is essentially built out, with vast swaths of land covered by impervious surfaces such as concrete and asphalt. This leaves scant open land to absorb rainfall. This lack of open ground forces water to remain on the surface and accumulate rapidly. If it were not for the massive flood control system that has been built over the years, with its concrete-lined rivers and stream beds, flooding in the Los Angeles Basin would be a much more common occurrence. And the tendency is towards even less and less open land. In-fill building is becoming a much more common practice in many areas: This increase in impervious surfaces (including concrete walkways, and roofs) results in a direct increase in runoff.

Another potential reason for recurrent storm flooding in developed areas is “asphalt creep.” The street space between the curbs of a street is a part of the flood control system. Water leaves the adjacent properties and accumulates in the streets, where it is directed towards the underground portion of the flood control system. The carrying capacity of a given street is determined by the width of the street and the height of the curbs along the street. Often, when streets are being resurfaced, a one- to two-inch layer of asphalt is laid down over the existing asphalt. This added layer of asphalt subtracts from the rated capacity of the street to carry water. Thus, the original engineered capacity of the entire storm drain system is marginally reduced over time. Subsequent re-paving of the street will further reduce its engineered capacity.

When structures or fill are placed in the floodway or floodplain, water is displaced. Developments in these locations raise river levels by forcing the river to compensate for the flow space obstructed by the inserted structures and/or fill. When structures or materials are added to the floodway or floodplain and no fill is removed to compensate, serious problems can arise. Flood waters may be forced away from historic floodplain areas. As a result, other existing floodplain areas may experience floodwaters that rise above historic levels. Local governments must require engineer certification to ensure that proposed developments will not adversely affect the flood-carrying capacity of the Special Flood Hazard Area (SFHA). Displacement of only a few inches of water can mean the difference between no structural damage occurring in a flood event, and the inundation of many homes, businesses, and other facilities. Careful attention should be given to development that occurs within the floodway to ensure that structures are prepared to withstand base flood events.

In highly urbanized areas, increased paving can lead to an increase in volume and velocity of runoff after a rainfall event, exacerbating the potential flood hazards. Care should be taken in the development and implementation of storm water management systems to ensure that these runoff waters are dealt with effectively.

STORM FLOODING CHARACTERISTICS
There are several types of flooding that have historically affected the southern California region, including the Los Angeles Basin: coastal flooding, fluvial (riverine) flooding, pluvial (urban) flooding, and hillside debris flows. The first three types of flooding are covered below. Debris flows are discussed in Section 9 - Landslides.

Coastal Flooding
Coastal flooding, or the inundation of land areas along the coast, is the result of higher-than-average high tide and worsened by heavy rainfall and onshore winds (i.e., wind blowing landward from the

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ocean). Flooding is the costliest natural disaster in the United States, with coastal flooding due to coastal storms and hurricanes being responsible for a significant amount of the total loss.

Coastal communities face a range of unique flooding hazards including storm surge, waves, and erosion—all of which can cause extensive damage to homes, businesses, and infrastructure. As of 2018, about 40 percent of the United States’ population was estimated to live in a coastal county5F 6 ,
and that number is expected to grow. As the coastal population continues to increase, more people and properties will be at risk from coastal storms and flooding.

Coastal environments are dynamic and are constantly reshaped by the forces of nature. Land use changes and rising average temperatures and sea levels are anticipated to increase the risk of coastal flooding. Many communities are already being impacted more often by flooding from high tides.

This can lead to road closures, overwhelmed storm-water systems, and disrupted business districts.

By 2050, high tide flooding along some United States coastlines is estimated to occur, on average, 25 to 75 days per year.

Fluvial (Riverine) Flooding
Riverine flooding is the overbank flooding of rivers and streams. This process in a natural environment adds sediment and nutrients to the flooded area, cyclically enhancing the fertility of the soils, which is why floodplains have been the breadbaskets of civilizations through the ages.

However, large floods have the potential to cause significant damage to man-made structures and cause significant loss of life. Flooding in large river systems typically results from large-scale weather systems that generate prolonged rainfall over a wide geographic area, causing flooding in hundreds of smaller streams, which then drain into the major rivers.

Shallow area flooding is a special type of riverine flooding. FEMA defines shallow flood hazards as areas that are inundated by the 100-year flood with flood depths of only one to three feet. These areas are generally flooded by low-velocity sheet flows of water.

Pluvial (Urban) Flooding
Pluvial flooding occurs in direct response to intense and/or prolonged rainfall, with flooding occurring in areas that are not normally part of an existing body of water such as a stream or lake.

Urban flooding usually occurs as a result of land being converted from agricultural fields or woodlands to roads and parking lots, in the process losing its ability to absorb rainfall. Urbanization of a watershed changes the hydrologic systems of the basin. Heavy rainfall collects and flows faster on impervious concrete and asphalt surfaces. The water moves from the clouds to the ground, and either ponds at the surface, in level ground, resulting in what is referred to as a surface flood, or if there is some relief, into a flash flood, with floodwaters potentially rising very rapidly and peaking with violent force. The flooding of developed areas often occurs when the amount of water generated from rainfall and runoff exceeds the capability of the storm drain system to remove and transport it. Oversaturated ground due to two or more back-to-back storms can also contribute to this type of flooding, as the wet soil cannot absorb the water dropped by later storms.

6 https://coast.noaa.gov/states/fast-facts/economics-and-demographics.html; accessed on 01/31/2024.

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HOW FLOOD-PRONE AREAS ARE IDENTIFIED
The Federal Emergency Management Agency (FEMA) is mandated by the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973 to evaluate flood hazards. To promote sound land use and floodplain development, FEMA prepares and provides Flood Insurance Rate Maps (FIRMs) for local and regional planners. Flood risk information presented on FIRMs is based on historic, meteorological, hydrologic, and hydraulic data, as well as topographic surveys, openspace conditions, flood control works, and existing development.

Rainfall-runoff and hydraulic models are utilized by the FIRM program to analyze flood potential, adequacy of flood protective measures, surface-water and groundwater interchange characteristics, and the variable efficiency of mobile (sand bed) flood channels. It is important to realize that FIRMs only identify potential flood areas based on the conditions at the time of the study, and do not consider the impacts of future development. To prepare FIRMs that illustrate the extent of flood hazards in a flood-prone community, FEMA conducts engineering studies referred to as Flood Insurance Studies (FISs). Using information gathered in these studies, FEMA engineers and cartographers delineate Special Flood Hazard Areas (SFHAs) on FIRMs. SFHAs are those areas subject to inundation by a “base flood,” which FEMA sets as a 100-year flood (see definitions below).

Flood Terminology
Floodplain
A floodplain is a land area adjacent to a river, stream, lake, estuary, or other water body that is subject to flooding. This area, if left undisturbed, acts to store excess floodwater. The floodplain is made up of two sections: the floodway and the flood fringe.

Floodway
Floodways are defined for regulatory purposes. Unlike floodplains, floodways do not reflect a recognizable geologic feature. For National Flood Insurance Program (NFIP) purposes, floodways are defined as the channel of a river or stream, and the overbank areas adjacent to the channel. The floodway carries the bulk of the floodwaters downstream and is usually the area where water velocities and forces are the greatest. NFIP regulations prohibit all development in the floodway, keeping the area free from development or other structures that would obstruct or divert flood flows onto other properties. The NFIP floodway definition is "the channel of a river or other watercourse and adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one foot.” Floodways are not mapped for all rivers and streams but are generally mapped in developed areas.

Flood Fringe
The flood fringe refers to the outer portions of the floodplain, beginning at the edge of the floodway and continuing outward. Generally, the flood fringe is defined as "the land area which is outside of the stream floodway but is subject to periodic inundation by regular flooding.” This is the area where development is most likely to occur, and where precautions to protect life and property need to be taken.

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100-Year Flood
The 100-year flood, also called the Base Flood, is the flood having a one percent chance of being equaled or exceeded in magnitude in any given year; it is not a flood occurring once every 100 years. The 100-year floodplain is the area adjoining a river, stream, or watercourse covered by water in the event of a 100-year flood. A 100-year flood is defined by looking at the long-term average period between floods of a certain size, and identifying the size of flood that has a 1 percent chance of occurring during any given year. This base flood has a 26 percent chance of occurring during a 30-year period, the length of most home mortgages. However, a recurrence interval such as “100 years” represents only the long-term average period between floods of a specific magnitude; rare floods can in fact occur at much shorter intervals or even within the same year.

Development
For floodplain ordinance purposes, development is broadly defined as "any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation, or drilling operations located within the area of special flood hazard." The definition of development for floodplain purposes is generally broader and includes more activities than the definition of development used in other sections of local land use ordinances.

Base Flood Elevation (BFE)
The term "Base Flood Elevation" refers to the elevation (normally measured in feet above sea level) that the base flood is expected to reach. Base flood elevations can be set at levels other than the 100-year flood. Some communities choose to use higher frequency flood events as their base flood elevation for certain activities, while using lower frequency events for others. For example, for the purpose of storm water management, a 25-year flood event might serve as the base flood elevation, whereas the 500-year flood event may serve as base flood elevation for the tie down of mobile homes. The regulations of the NFIP focus on development in the 100-year floodplain.

Special Flood Hazard Area (SFHA)
Using information gathered in Flood Insurance Studies, FEMA engineers and cartographers delineate Special Flood Hazard Areas on FIRMs. SFHAs are those areas subject to a high risk of inundation by a “base flood” which FEMA sets as a 100-year flood. As discussed further in the next section, SFHAs are regulated zones, requiring the mandatory purchase of flood insurance. They are also subject to special standards and regulations that apply to new construction, and in some cases, existing buildings. Floodplain regulations required by the NFIP apply only to properties located in a SHFA.

However, these are minimum requirements, and local jurisdictions may regulate areas outside of the SHFAs, based on knowledge specific to their area.

Flood Mapping Methods, Products and Programs
Flood Insurance Rate Maps and Flood Insurance Studies
Flood Insurance Rate Maps (FIRMs) and Flood Insurance Studies (FISs) are the basis for implementing floodplain regulations and for delineating flood insurance purchase requirements given that these studies assess the probability of flooding at a given location. FIRMs are developed using water surface elevations combined with topographic data and illustrate areas that would be inundated during a 100-year flood, floodway areas, and elevations marking the 100-year-flood level. In some cases, these maps also include base flood elevations (BFEs) and areas located within the 500-year

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floodplain. Significantly, and of relevance to the urban environment, these maps are prepared only for areas susceptible to coastal and fluvial (riverine) flooding, not pluvial flooding.

FIRMs are the official maps produced by FEMA that delineate Special Flood Hazard Areas (SFHAs) in communities where National Flood Insurance Program (NFIP) regulations apply. FIRMs are also used by insurance agents and mortgage lenders to determine if flood insurance is required and what insurance rates should apply. Communities find it particularly useful to overlay flood hazard areas on tax assessment parcel maps and land use maps. This allows a community to evaluate the flood hazard risk for a specific parcel during review of a development request. FIRM maps can be imported directly into GIS, which allows for GIS analysis of flood hazard areas. Coordination between FEMA and local planning jurisdictions is the key to making a strong connection with GIS technology for the purpose of flood hazard mapping.

In addition to their original purpose of setting insurance rates and regulating flood hazards, FIRMs are used by local and regional planners for other purposes, including land-use planning, emergency preparedness and response, natural resource management, and risk assessment. Given their wide usage, it is important to note that there are many uncertainties inherent in the establishment of FEMA flood zones (Larson, 2009). Furthermore, several recent studies 6F 7 have shown that FIRMs are
inaccurate, which in turn can lead to poor, potentially damaging, planning decisions. Specific limitations of FIRM maps that communities should be aware of are discussed below:
• FIRMs only identify potential flood areas based on the conditions at the time of the Flood Insurance Study (FIS) that led to the development of the maps. As a result, FIRMS do not consider the impacts of changes to the area since the maps were developed, or the impacts that future changes may have on the flood hazard. Conditions that affect the maps and the decisions made on their basis may include changes in corporate boundaries, changes in population, man-made and natural changes to the landscape, removal of vegetation, changes to hydrologic systems, construction of flood control facilities, and climate change. These modifications to the environment may increase or reduce the area susceptible to flooding. Many Flood Insurance Studies that were first completed in the late 1970s and early 1980s have not been updated since, and thus significantly under-estimate the current flood risk in areas where extensive development has occurred since the maps were created.
• The level of detail studied and presented on the maps, as well as the boundaries of the area studied, depend on the type of flood hazard, the funding available, and the risk of flood damage at the time that the FIS was conducted. For instance, areas studied by approximate methods do not provide base flood elevations on the map, and some study areas are limited in extent.

Essentially, not all 100-year and 500-year floodplains have yet been mapped. • The maps typically do not identify all areas susceptible to flooding, such as areas crossed by small drainages, areas of localized ponding during storms, or areas where drainages are restricted by temporary or permanent structures. As mentioned above, FIRMs only cover areas known to be impacted by coastal or fluvial flooding, not areas flooded by standing water or flash

7 https://www.smithsonianmag.com/smart-news/federal-flood-maps-are-outdated-because-of-climate-change-femadirector-says-180980725/ https://www.washingtonpost.com/climate-environment/interactive/2022/fema-flood-risk-maps-failures/ Sanders et al., 2023, Large and inequitable flood risks in Los Angeles, California: Nature Sustainability, https://www.washingtonpost.com/climate-environment/interactive/2022/fema-flood-risk-maps-failures/

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floods following a rainstorm. This is important in Santa Monica where pluvial flooding may locally impact some areas not identified in the FIRMs.
• The analytical process used to construct these maps relies on many assumptions and limited data. The data used may be too old, incomplete, interpolated, and/or inaccurate. For example, in relatively flat floodplains, small elevation errors in the topography can result in large errors in flood zone boundaries.
• One major drawback is the very short time period for which we have meteorological records.

Research on some parts of southern California has shown that slight climate fluctuations between wet and dry cycles have occurred since the late 1800s (Hereford and Longpre, 2009). The effects of global climate change, which appears to be responsible for significant rainfall events, and large swings between dry and wet periods, are not currently considered and modeled for. • Long-term changes in the watershed or floodplain, primarily as a result of human activities, are also difficult to anticipate. Flood control structures, such as berms and levees, can actually increase the flood risk to other areas. The design of high-density developments often requires taking drainages that used to be spread over a wide area and constricting them into narrow channels, thereby increasing the velocity and erosive power of the flow, and perhaps leading to overtopping. Consequently, there are clearly limitations in using hydrologic calculations based on past, imperfect records to predict the future.
• Larson (2009) also argued that the process of placing a line on a map (flood zone boundaries) incorrectly conveys a sense of certainty about the risk. Since the public and policy makers typically make decisions based on flood zone boundaries, the potential risk to adjacent properties outside the margins defined by those lines is often underestimated. This has recently become apparent in many areas throughout the US that have been impacted by flooding where FEMA mapping showed no hazards 7F
8 . This also means that millions of people that live in areas susceptible to flooding currently have no flood insurance. This became a poignant issue for many homeowners who were impacted by the mudslides and flooding resulting from the atmospheric rivers that hit southern California in 2022-2023, and in early February 2024.

Partly as a result of several of these known issues with FIRMs, FEMA recommends that most property owners, whether residential or commercial, purchase and keep flood insurance even if they are not located in a mapped flood hazard zone. It is important to note that approximately 40 percent of all flood claims occur outside of mapped high flood risk areas, and typical homeowner or business insurance policies do not cover flooding. Temporary situations, such as a storm drain inlet or culvert that becomes blocked by storm debris, can cause localized flooding and property damage. Residents or business owners that rent property can also purchase coverage for the contents of their homes or business inventories. In low to moderate risk areas, property owners should ask their agents if they are eligible for the FEMA Preferred Risk Policy, which provides inexpensive flood insurance protection. Insured property owners can be reimbursed for all covered losses, even if the flood is not officially declared a Federal disaster area.

FEMA also recommends that residents do not forgo purchasing insurance, assuming instead that Federal disaster assistance will pay for flood damage. This is because in order to receive assistance, a community must first be declared a Federal disaster area, and these declarations are issued in less than 50 percent of flood events. Furthermore, Federal assistance is usually in the form of a loan,

8 https://www.washingtonpost.com/climate-environment/interactive/2022/fema-flood-risk-maps-failures

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which must be repaid with interest. If uninsured property owners do receive Federal assistance, they must purchase flood insurance to remain eligible for future disaster relief.

Mapped Flood Areas Outside of the 100-Year Flood Zone
Although many communities rely exclusively on FIRMs to characterize the risk of flooding in their area, there are some flood-prone areas that are not mapped but remain susceptible to flooding.

These areas include locations next to small creeks, local drainage areas, topographically low spots, and areas susceptible to man-induced and pluvial flooding. In order to address this lack of data, jurisdictions can make efforts to develop more localized flood hazard maps. One method that has been employed includes using high-water marks from flood events or aerial photos to better reflect the true flood risk.

Community Rating System
The Community Rating System (CRS) is a voluntary part of the National Flood Insurance Program (NFIP) that seeks to coordinate all flood-related activities, reduce flood losses, facilitate accurate insurance ratings, and promote public awareness of flood insurance by creating incentives for a community to pursue beyond-the-minimum requirements of the NFIP. Any community that is in full compliance with the NFIP’s minimum floodplain management requirements may apply to join the CRS. CRS ratings are on a ten-point scale, from 1 to 10, with 1 being the best rating. Residents of CRS communities who live within FEMA’s Special Flood Hazard Areas (SFHAs) receive a 5 percent reduction in flood insurance rates for every one-point improvement in the community’s CRS rating.

As of October 1, 2023, the City of Santa Monica is not included in the list of CRS-eligible communities8F
9 . For additional information on the Community Rating System, including how to go about becoming eligible, refer to https://www.fema.gov/national-flood-insurance-programcommunity-rating-system.

Risk Mapping, Assessment and Planning (Risk MAP) Program With the Risk MAP Program approved in March 2009, FEMA has moved away from simply portraying flood hazard zones on maps to more accurately communicating and assessing risk to the local community. Building on the digitized maps, FEMA developed a five-year plan to fill in data gaps, increase public awareness, increase their outreach on flood risks, support state and local agencies in risk-based mitigation planning, and provide an enhanced digital platform that improves communication and sharing of risk data.9F
10 Then, in 2011, FEMA started a multi-year project to
improve their guidelines and standards for flood risk analysis and mapping with the goal of bringing overall consistency, clarity, and efficiency to the mapping process. The result of this work was publication, in 2013, of a compendium document covering all standards applicable to the Risk MAP program. This document has been updated since, with the most recent version dating from 2024.10F 11 Today, Risk MAP is meant to be a collaborative effort between FEMA and federal, state, tribal and local partners across the U.S. to identify flood risk, promote informed planning and development practices, and in the process reduce the risk. The process includes several steps that allow for stakeholders (including planners, engineers, real-estate and insurance specialists, and even

9 https://www.fema.gov/floodplain-management/community-rating-system#participating, accessed on 02/08/2024. 10 https://www.fema.gov/pdf/rebuild/map_mod_fact_sheet.pdf 11 https://www.fema.gov/flood-maps/guidance-reports/guidelines-standards/guidance-femas-risk-mappingassessment-and-planning

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homeowners and business owners) to be involved in the discovery and recording of flood-prone areas, create a community outreach plan, and review and comment on preliminary flood maps prepared in response to the discovery phase. The end goal of this program is to inform property owners of their flood risk and most importantly, develop and implement hazard mitigation strategies for flood-prone areas to increase community resilience. Flood risk products that may be created as a result of these efforts include non-regulatory Flood Risk Maps (FRMs), Flood Risk Reports (FRRs), and Flood Risk Databases (FRDs).

FLOOD HAZARD ANALYSIS FOR THE SANTA MONICA AREA
Los Angeles County, including the Santa Monica region, was analyzed by FEMA fairly recently, with the current FIS for the area most recently issued on June 2, 2021. This document can be accessed from https://pw.lacounty.gov/floodzone/moreinfo.cfm with the nine volumes that comprise the study accessible from the section labeled “FEMA Flood Zones.” The FIS includes community descriptions, flooding sources (such as the Los Angeles River), information on historical flooding, existing flood protection measures, hydrologic and hydraulic analyses, and definition of potential flood areas.

The City’s most current FIRM maps became effective on April 21, 2021.11F 12 The 2021 FIRMs include
several revisions for coastal areas such as Santa Monica that reflect updated ocean and topographic measurements at the coastline, physical changes in the watersheds, and in some areas, corrections to an inadvertent “shift” of the flood zone boundaries that occurred in 2008 when the 1980s-era paper maps were converted to digital form.12F
13 The FIRM panels that cover the city of Santa Monica include: 06037C1567G, 06037C1569G, 06037C1588G, 06037C1589G, 06037C1590G and 06037C1751G. The FIRM identifies Special Flood Hazards Areas within Santa Monica that occur along and east of Pacific Coast Highway and extend west into the Santa Monica Bay. The Special Flood Hazards Areas (SFHAs) mapped in Santa Monica are described in Table 8-3 and are shown on Figure 8-3. Note that the section of the Santa Monica coastline that is approximately north of Wilshire Boulevard is classified as both Zone AE and Zone VE, whereas the coastline approximately south of Wilshire Boulevard is only classified as Zone VE.

Table 8-3: Flood Zones Mapped in Santa Monica
Santa Monica
Special Flood
Hazard Areas
Description Area of Santa Monica Map Reference
Zone AE
100-year flood zone along
coastline susceptible to storm
flooding
Coastline north of
Wilshire Blvd.

Figure 8-3,
Bright Pink
Zone VE
100-year flood zone susceptible
to coastal flooding due to storm
surges
Coastline north and
south of Wilshire Blvd.

Figure 8-3,
Light Purple

12 https://www.dpw.lacounty.gov/wmd/NFIP/OPCFEMAMapRevision.aspx 13 https://www.dpw.lacounty.gov/wmd/NFIP/documents/OPCFMR/Open%20Pacific%20Coast%20Study%20FAQ% 20Sheet%20June%202021.pdf

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According to an analysis by City Staff13F
14, 85 beach-front properties along Pacific Coast Highway are located within a SFHA. Owners of these properties are required to purchase flood insurance in order to secure financing if they intend to build or improve their structures. New property owners are required to purchase flood insurance to secure financing to buy the property in the SFHA. Lending institutions that are federally regulated or federally insured must determine if the structure is located in a SFHA and must provide written notice requiring flood insurance. Santa Monica became a participating member of the NFIP in 1983 (City ID No. 060159F), which means that flood insurance is available to any property owner in the city. Being a NFIP member also means that all NFIP-related building code regulations apply. NFIP regulations (44 Code of Federal Regulations (CFR) Chapter 1, Section 60, 3) require that all new construction in floodplains must be elevated at or above base flood level.

The FIRMs that encompass the city of Santa Monica and surrounding jurisdictions also identify areas with a moderate to low risk of flooding. The flood having a 0.2 percent annual chance of occurring (also called the 500-year flood) is usually the basis for these categories, with moderate risk defined as the zone between the limits of the 100-year and 500-year floods, and low risk defined as the area outside of the 500-year flood limits. These zones may also include areas where the base flood is less than one-foot deep, where the drainage basin is small (less than one square mile), or areas that are protected from the base flood by levees. Most of Santa Monica is mapped as having a minimal flood hazard with the majority of the city located outside the 500‐year flood zone (Zone X, unshaded on Figure 8-3). Note, however, that flood-prone areas have been identified just outside the City limits; this could have an impact on motorists attempting to arrive or depart from Santa Monica. For example, sections of Rustic Canyon in Pacific Palisades are designated by FEMA as either a 1% or

0.2% chance of flooding. Likewise, relatively low depressions along Bundy Drive and San Vicente Boulevard near the Brentwood Country Club are considered to have a 0.2% chance of flooding.

Flood insurance is available for properties in these zones, but is not mandated by the NFIP.

14 City of Santa Monica, Staff Report 4422, March 9, 2021 online at https://santamonicacityca.iqm2.com/Citizens/Detail_LegiFile.aspx?Frame=&MeetingID=1262&MediaPosition=&I D=4422&CssClass=

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Figure 8-3: Flood Zones Mapped In and Near Santa Monica

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The fluvial (riverine) flood hazard in the city is deemed low to nil because there are no floodways extending through Santa Monica today. As mentioned before, prior to 1825, the Los Angeles River flowed through the Ballona gap area, and into the Ballona Lagoon, which historically extended north to what is today the area near the intersection of Main Street and Abbott Kinney Boulevard in Venice (Dark et al., 2011), less than 0.5 miles from Santa Monica. Ballona Creek is now confined to a channel that flows into the Pacific Ocean just south of Marina del Rey. Moreover, geologic maps and older topographic maps of the area suggest that streams draining the foothills of the Santa Monica Mountains in the area east of Brentwood Knoll converged in what today is the east-central part of Santa Monica and then drained west following the low-lying area now mostly occupied by the I-10 freeway.

Pluvial (urban) flooding in Santa Monica is managed by an extensive drainage system that consists of over 2,400 catch basins and 64 storm drain lines, with the Los Angeles County Flood Control District retaining ownership of about 9 to 10 miles of storm drain lines and inlets within the city of Santa Monica. The City’s storm drain pipes range from 16 inches to 11 feet in diameter and are mainly constructed of reinforced concrete; a few structures consist of brick arch drains, concrete open channels, or corrugated metal pipes. Only a small section in the southeast corner of the city drains to Ballona Creek. Historically, the majority of the urban runoff in Santa Monica has drained untreated into Santa Monica Bay via the underground storm drain system described above and five outfalls within City limits. The largest of these outfalls is located at the western terminus of Pico Boulevard and is known as the Pico-Kenter outfall. In addition to runoff from Santa Monica, this outfall discharges runoff from parts of Brentwood and West Los Angeles, and flow conveyed by the 120-inch Santa Monica Freeway storm drain that runs through a portion of the city and drains portions of Los Angeles County as well. Both of these drains come together and empty into the ocean at the western end of Pico Boulevard, along the southern end of the Civic Center. The other four outfalls are located on the beach at Montana Avenue, Wilshire Boulevard, the Santa Monica Pier, and Ashland Avenue. The Montana and Wilshire outfalls typically only discharge runoff to the ocean during heavy rains. The Pico-Kenter, Santa Monica Pier and Ashland Avenue outfalls discharge yearround during both wet and dry periods. In 2022, the City completed construction of the Sustainable Water Infrastructure Project (SWIP) at the Civic Center, which is designed to capture millions of gallons of storm water runoff that once would have flown into the Santa Monica Bay.

The storm drain system in the city of Santa Monica was designed for the 50-year storm (referred to as the “capital flood”) in accordance with the requirements in the Los Angeles County Hydrology Manual (Chapter 4, Section 4.2 Capital Flood Protection14F 15). However, new data indicate that
flooding associated with a 50-year storm (and a 100-year storm) is likely to be more intense than previously thought, which means the values used in the design of the storm drain system may be too small. Specifically, in 2014, the National Oceanic and Atmospheric Administration (NOAA15F 16)
issued supplementary stream gage data that expanded the existing dataset typically used in hydrology analyses. The old stream gage data covered the time period between 1897 and 1970, whereas the new data, published in what is referred to as the NOAA Atlas 14, covers the time period between 1970 and 2010. As a result of the 2014 analyses, NOAA found that precipitation levels in

15 Los Angeles County Department of Public Works, January 2006, Hydrology Manual, available from https://dpw.lacounty.gov/wrd/publication/engineering/2006_Hydrology_Manual/2006%20Hydrology%20Manual -Divided.pdf 16 Perica, S. et al., 2014 (revised), NOAA Atlas 14, Precipitation-Frequency Atlas of the United States, Volume 6, Version 2.3: California: National Oceanic and Atmospheric Administration, 233p.; available from https://www.weather.gov/media/owp/oh/hdsc/docs/Atlas14_Volume6.pdf

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the south-facing flank of the Santa Monica Mountains are generally about 1 to 2 inches higher for the 100-year 6-hour estimates using the revised Atlas 14 values than the values previously used. In the Los Angeles Basin itself, including Santa Monica proper, the Atlas 14 values are about the same or slightly lower (0 to -0.25 inches) than the previously used values. Combined with the precipitation levels in the mountains, however, the overall runoff input into the storm drain system draining the region is expected to be higher than the previous estimates used in the design of the system.

Moreover, considering that future storms in southern California are expected to be more intense as a result of climate change, with higher maximum 1-day precipitation amounts, as evidenced most recently with the early February 2024 rainfall totals, the storm drain system is anticipated to be under-designed for the unusual but high-intensity storms the region is expected to experience in the future. This in turn means that flood mitigation measures may be limited if the storm drain system is under-designed and does not have adequate capacity to handle the increased flows expected due to climate change.

INUNDATION DUE TO CATASTROPHIC FAILURE OF WATER STORAGE

STRUCTURES
Seismically induced inundation refers to flooding that occurs when water retention structures (such as dams and their associated reservoirs and above-ground water tanks) fail as a result of an earthquake, overtopping, foundation defects, construction errors, or some other reason. Loss of life and damage to structures, roads, and utilities may result from a dam failure. Economic losses can also result from a lowered tax base and lack of utility profits (if the dam is part of a hydroelectric project).

Flooding Due to Dam Failure
Statutes governing dam safety are defined in Division 3 of the California State Water Code (California Department of Water Resources, 1986). These statutes empower the California Division of Dam Safety to monitor the structural safety of dams that are greater than 25 feet in dam height or have more than 50 acre-feet in storage capacity. Dams under Federal ownership and operation, such as those owned by the U.S. Army Corps of Engineers, are not reviewed by, nor are they under the jurisdiction of the California Division of Dam Safety.

There are several reasons why dams can fail. The most common causes include: 1) overtopping (meaning water spills over the top of the dam), 2) foundation defects, 3) cracking caused by natural settling, faulting, landsliding or other deformation of the ground supporting the structure, 4) inadequate maintenance of the structure, and 5) piping (internal erosion of the dam caused by seepage). Combined, overtopping, foundation defects and piping are responsible for approximately 84% of all dam failures that have occurred over the years in the United States.16F 17 Overtopping alone
is responsible for nearly 130 dam failure incidents between 2010 and 2019, based on a database compiled by the Association of State Dam Safety Officials (ASDSO), with the main driver of these incidents being hydrologic events that led to flooding.17F 18 These numbers are sobering considering
that the existing California water storage infrastructure (dams and reservoirs, debris basins, catchment basins, and the causeways and storm drains downstream) are thought to be severely

17 Based on percentages for each cause listed in the Association of State Dam Safety Officials website at https://damsafety.org/dam-failures accessed on October 25, 2023. 18 https://damsafety.org/dam-failures accessed in Oct. – Nov. 2023.

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under-designed for the amount of precipitation and storm frequency expected as a result of climate change, including ARkstorm events such as those experienced in 2023 and 2024.

There have been between 82 and 92 dam failures in California since the 19th century18F 19, with 82 of
those events known to have resulted in uncontrolled release of water from the reservoir. Table 8-4 lists those events known to have occurred in southern California; the list may be incomplete as data on the locations of numerous dams is not available. Three of these dam failure events prompted the enactment of strict dam safety legislation at the State level.19F 20 These dam failures are: 1) St. Francis
dam, 2) Baldwin Hills dam, and 3) Lower San Fernando dam. These dam failures are described further in the following pages.

Table 8-4: Dam Failures in Southern California
Dam Name Location Year Failure Mechanism; Casualties
Sweetwater and
Sweetwater Main
San Diego 1916 Overtopping due to intense rainfall event; 8 deaths.

Lower Otay San Diego 1916 Overtopping during first filling due to inadequate spillway capacity; 30 deaths.

Garfield Avenue South Pasadena 1924 Unknown, but surmised to be related to construction errors
Sheffield Santa Barbara 1925 Earthquake slide or liquefaction Puddingstone Pomona 1926 Overtopping during construction Sweetwater Main San Diego 1927 Inflow flood; hydrologic event Lake Hemet Hemet 1927 Overtopping due to intense rainfall Saint Francis San Francisquito
Canyon
1928 Sudden failure at full capacity through foundation, >450 deaths.

Cogswell Monrovia 1934 Breaching of concrete cover
Baldwin Hills Los Angeles 1963 Leak through embankment due to seepage, internal erosion; 5 deaths, 16,500 evacuated.

Matilija Ventura County 1965 Unknown if it resulted in an uncontrolled release of water from the reservoir; failure mode also unknown.

San Fernando San Fernando
Valley
1971 Seismic shaking and liquefaction; near-failure; 80,000 evacuated.

Wohlford Lake San Diego County 1980 Unknown if it resulted in an uncontrolled release of water from the reservoir; failure mode also unknown.

St. Francis Dam, completed in 1926 in the San Francisquito Canyon near Saugus, was originally 185 feet high and 600 feet long. In response to increased population pressures, the storage capacity of the dam was increased by raising the dam’s height to 205 feet. This was accomplished without increasing the width of the base to compensate for the increased height, a significant issue since this was a curved concrete gravity dam, with its stability derived from a balance between the vertical and horizontal loads. Around midnight on March 12-13, 1928, a massive landslide occurred along the dam’s left abutment; more than 1.5 million tons of schist bedrock slid down and against the dam’s 271 tons of concrete. That, combined with the already unstable dam base resulting from the increased height, led to the catastrophic failure of the dam. A flood wave more than 140 feet high

19 https://npdp.stanford.edu/sites/default/files/reports/npdp_dam_failure_summary_compilation_ v1_2018.pdf; http://npdp.stanford.edu/dam_incidents, both accessed on February 22, 2024. 20 https://water.ca.gov/Programs/All-Programs/Division-of-Safety-of-Dams/History, accessed in October 2023.

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swept down the Santa Clara valley toward the Pacific Ocean. Even 42 miles down-canyon, by Santa Paula, the wall of water was estimated at 25 feet high. Almost everything in its path was destroyed:
livestock, structures, railways, bridges, and orchards. By the time it was over, parts of Ventura County were under 70 feet of mud and debris. The death toll is unknown as there were many undocumented families living in the floodplain below the dam. Some accounts say 420 people were killed; others estimated more than 600.20F
21 Damage estimates topped $20 million (equivalent to more than $366 million in 2024).

The failure of this dam resulted in several positive changes, including the requirement for engineering geologic input in dam projects (it had been absent before then), increased dam safety legislation in California, the review of all federal dams, professional engineering registration, and state-mandated arbitration hearings for all victims of natural disasters (Rogers, 2007). Specifically, and in response to failure of the St. Francis Dam, the State legislature created the Dam Safety Program on August 14, 1929, which required, among other things, the examination and approval of dams built prior to 1929; the review and approval of plans and specifications for new and existing dams; and the supervision during construction and maintenance of all dams under the jurisdiction of the State. Today, this program is managed by the Division of Safety of Dams (DSOD) under the California Department of Water Resources (CDWR).

The Baldwin Hills dam, an earthen dam that created a 20-acre, 70-foot-high reservoir, failed on Saturday, December 14, 1963 at 3:38 in the afternoon (see Photo 8-1). The dam was constructed between 1947 and 1951 for the purpose of storing water for west Los Angeles. The “off-stream” dam did not impound a natural river course, and thus, under the rules at the time, was not a jurisdictional dam under the purview of the DSOD. As a result of this dam failure, in 1965 the California Water Code was modified by the legislature to include off-stream storage reservoirs in the DSOD’s list of jurisdictional dams.

This hilltop reservoir was built in 1951 across the surface trace of several faults and cracks associated with the Newport-Inglewood fault zone and uplift of the Baldwin Hills. A water-injection program to enhance the recovery of petroleum in the adjacent Inglewood oil field was begun in 1954, with a full-scale program instituted in 1957. The injection program caused renewed movement on the faults, including one under the reservoir that experienced normal movement. Movement on the fault caused the reservoir lining to fail; a pencil-thin crack widened to a 75-foot-wide gash, allowing 250 million gallons of treated water to surge out, with the flood sweeping northward in a V-shaped path roughly bounded by La Brea Avenue and Jefferson and La Cienega boulevards. The residences within a square-mile area were inundated with mud and debris, 65 homes were completely destroyed, and more than 200 additional homes and apartments were damaged. Five lives were lost and 27 people were injured; the loss of life would have been much greater had a caretaker not given the alarm approximately three hours beforehand, allowing the police just barely enough time to evacuate the area. Total property damages were estimated at $12 million (approximately $120.7-150.9 million in 2023 dollars), in addition to the loss of the reservoir itself.21F 22 21 https://web.mst.edu/rogersda/st_francis_dam/Impacts%20of%20St.%20Francis%20Dam%20Failurecompressed.pdf accessed at various times in 2024 and March 2025. 22 Hamilton, D.H. and Meehan, R.L., 1971, Ground rupture in the Baldwin Hills: Science, Vol. 172, pp. 333-344; and https://damsafety.org/Incidents

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Photo 8-1: Failure of the Baldwin Hills Dam
Dark spots in the water and upper right-hand quadrant
show the location of the break in the dam.

This is one of the first disaster events documented in a live helicopter broadcast – the live telecast of the collapse from a KTLA-TV helicopter is considered the precursor to airborne news coverage that is now routine everywhere. It took 77 minutes for the impounded reservoir to empty, but it took a generation for the neighborhood below to recover, illustrating the severe, long-term impact of these disasters. Furthermore, failure of this reservoir foreshadowed the end of urban-area earthen dams as a major element of the Department of Water and Power’s water storage system. It also prompted a tightening of Division of Safety of Dams control over reservoirs throughout the State.

The third southern California dam failure (near-failure in this case) that prompted legislative changes occurred as a result of earthquake-induced liquefaction (see Section 6). The Lower and Upper Van Norman (or San Fernando) dams were built in the 1910s to collectively store the water brought into the area by the Los Angeles Aqueduct. Combined, the two dams could store about 80% of the water for the city of Los Angeles. The bulk of these dams were constructed with hydraulic fill; this involves pumping a sludge of sediment and water into place, contained in between embankments or dikes.

The sludge is deposited in layers, with water allowed to drain before a new layer is laid; this causes the finer-grained sediments in the sludge to settle in the center of the dam, creating a clay core. If the water flow is not managed correctly, however, layers or tongues of coarse-grained material may be deposited across the width of the dam, with these layers then allowing for seepage to occur.

Uncompacted hydraulic fill is susceptible to liquefaction when shaken, which is what happened to these dams when the 1971 San Fernando earthquake hit.

Fortunately, at the time, the Upper San Fernando dam was only about one-third full, and the Lower San Fernando dam was about half full. The Lower dam, in particular, had undergone a seismic hazard review in 1966, and by 1967, its operating height had been reduced in response to that analysis. The lower water levels helped avert disaster to areas downstream. Specifically, as a result

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of the earthquake, the Upper San Fernando dam dropped 3 feet and was laterally displaced about 5 feet. The Lower dam experienced damage to its crest and upstream face, with a large liquefactioninduced shallow landslide that originated from the upstream face failing into the reservoir. To keep the dam from failing catastrophically, the dam operators reduced the water level as quickly as possible. At the same time, the neighborhoods within the potential inundation area were evacuated; an estimated 80,000 people were evacuated from their homes for at least three days. In response to the near-failure of these embankments, the DSOD revisited its seismic evaluation program, and revisited all hydraulic fill dams under their jurisdiction, an effort that resulted in the seismic retrofit of numerous dams in the state. The near-failures also prompted civil engineering departments at various institutions to conduct liquefaction research.22F 2323F24
Flooding Due to Failure of Above-Ground Water Storage Tanks Seismically induced inundation can also occur if strong ground shaking causes structural damage to above-ground water tanks. If a tank is not adequately braced and baffled, sloshing water can lift a water tank off its foundation, splitting the shell, damaging the roof, and bulging the bottom of the tank (elephants foot) (EERI, 1992). Movement can also shear off the pipes leading to the tank, releasing water through the broken pipes. These types of damage occurred during southern California’s 1992 Landers, 1992 Big Bear, 1994 Northridge, and 2019 Ridgecrest earthquakes. The Northridge earthquake alone rendered about 40 steel tanks non-functional (EERI, 1995), including a tank in the Santa Clarita area that failed and inundated several houses below. As a result of lessons learned from those earthquakes, new standards for design of steel water tanks were adopted in 1994 (Lund, 1994). The new tank design includes flexible joints at the inlet/outlet connections to accommodate movement in any direction. However, an analysis of water tanks following the 2003 Paso Robles earthquake found that the design standards should be modified further in seismically active areas to make tanks more earthquake resistant.24F 25 Below-ground water tanks are less likely to be impacted by ground shaking, but are still susceptible to surface ground deformation resulting from fault rupture, liquefaction, or slope failures. Water lost from tanks during an earthquake can significantly reduce the water resources available to suppress earthquake-induced fires. Damaged tanks and water mains can also limit the amount of water available to residents after a severe earthquake. Groundwater wells can be damaged during an earthquake, limiting the water available to the communities dependent on those wells. Therefore, it is of paramount importance that the water storage tanks in the area retain their structural integrity during an earthquake, so water demands after an earthquake can be met. In addition to evaluating and retrofitting to meet current standards, this also requires that the tanks be kept at or near full capacity as much as practical.

23 https://water.ca.gov/Programs/All-Programs/Division-of-Safety-of-Dams/History; https://damsafety.org/incidents/ca00000-124, both accessed on Nov. 6, 2023. 24 Castro et al., 1989, Re-Evaluation of the Lower San Fernando Dam, available from https://apps.dtic.mil/sti/tr/pdf/ADA214589.pdf, accessed on Nov. 6, 2023. 25 Eidinger, J., 2009, Magic R: Seismic Design of Water Tanks: paper accessed from https://www.geengineeringsystems.com/ewExternalFiles/Magic%20R%20%20Seismic%20Design%20of%20Wate r%20Tanks.pdf on Feb. 19, 2023.

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HAZARD ASSESSMENT
Hazard Identification
Hazard identification is the first phase of flood-hazard assessment, and involves estimating the following:
1) the geographic extent of the area at risk from flooding; 2) the intensity of the flooding that can be expected in specific areas of the floodplain; and 3) the probability of occurrence of flood events.

This process usually results in the creation of a floodplain map, with FEMA being the agency that generally creates these products. Floodplain maps often provide detailed information that can assist jurisdictions in making policies and land-use decisions, although communities should recognize that as a result of the limitations in the mapping process and the impacts of climate change, these maps may not capture all flood-prone areas. Maps that show the extent of inundation if a water reservoir fails are also now required for all dams in California under the jurisdiction of the State. We refer to both the FEMA map and the inundation maps available for dams near Santa Monica to address the risk of flooding in the city.

Flood Hazard Mapping and Flooding Potential in the City of Santa Monica The City of Santa Monica has participated in the National Flood Insurance Program since 1974. The potential flood zones mapped by FEMA in the city are shown on the Flood Insurance Rate Maps (FIRMs). The FIRM panels that cover Santa Monica include: 06037C1567G, 06037C1569G, 06037C1588G, 06037C1589G, 06037C1590G and 06037C1751G. The most recent Flood Insurance Study (FIS) for Los Angeles County, which includes Santa Monica, was issued by FEMA on June 2, 2021. Overall, FEMA assigns a Very Low Coastal Flood Risk Index rating to the Los Angeles County region, including Santa Monica25F
26, as discussed further below.

Specifically, the only area in Santa Monica mapped as within the 100-year flood zone is the beach west-southwest of Pacific Coast Highway north of the Pier, and approximately west of the Marvin Braude Bike Trail south of the Pier. Figure 8-3 shows the inundation limits for 100-year flood events as a result of both storm flooding (AE zones in bright pink), and coastal flooding due to storm surges (VE zones in light purple). Zone VE is the coastal area with a 1% or greater chance of flooding with an additional hazard associated with storm waves. The section of the Santa Monica coastline that is approximately north of Wilshire Boulevard is classified as both Zone AE and Zone VE, whereas the coastline approximately south of Wilshire Boulevard is only classified as Zone VE. Based on an analysis by City Staff26F
27 of the 2021 FIRM maps, 85 beach-front properties are located within the 100-year flood zone. The properties adjacent to the coast are also at significant risk of flooding due to tsunamis, as discussed in Section 7.

FIRMs typically also show the estimated limits of areas with moderate to low risk of flooding. The flood having a 0.2% annual chance of occurring (also referred to as the 500-year flood) is usually the basis for these categories, with moderate risk defined as the zone between the limits of the 100- year and 500-year floods, and low risk defined as the area outside of the 500-year flood limits. These

26 https://hazards.fema.gov/nri/coastal-flooding, accessed on 01/31/2024. 27 City of Santa Monica, Staff Report 4422, March 9, 2021 online at https://santamonicacityca.iqm2.com/Citizens/Detail_LegiFile.aspx?Frame=&MeetingID=1262&MediaPosition=&I D=4422&CssClass=

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zones may also include areas where the base flood is less than one-foot deep, where the drainage basin is small (less than one square mile), or areas that are protected from the base flood by levees.

Figure 8-3 shows that most of Santa Monica is mapped as having a minimal flood hazard, with the majority of the city located outside the 500‐year flood zone (Zone X, unshaded). Flood-prone areas are mapped just outside the City limits; this could have an impact on motorists attempting to arrive or depart from Santa Monica. For example, sections of Rustic Canyon in Pacific Palisades are designated by FEMA as either a 1% or 0.2% chance of flooding. Likewise, relatively low depressions along Bundy Drive and San Vicente Boulevard near the Brentwood Country Club are considered to have a 0.2% chance of flooding. Flood insurance is available for properties in these zones, but is not mandated by the NFIP.

Urban Flooding and Existing Flood Protection Measures
in the City of Santa Monica
Santa Monica, like the rest of the extensively developed Los Angeles basin, has a high concentration of impervious surfaces that both collect and concentrate the flow of water. During periods of urban flooding, some streets may concentrate water flow leading to swift currents, and low-lying areas may fill with water. Storm drains, especially if clogged with vegetation and debris, can also result in unintentional localized flooding.

Urban runoff in Santa Monica is captured in a drainage system that consists of over 2,400 catch basins and 64 storm drain lines, and the Los Angeles County Flood Control District also owns about 9 to 10 miles of storm drain lines and inlets within Santa Monica. The City’s storm drain pipes range from 16 inches to 11 feet in diameter and are mostly constructed of reinforced concrete; a few structures consist of brick arch drains, concrete open channels, or corrugated metal pipes.

Historically, urban runoff would be carried by this underground storm drain system and drain untreated into Santa Monica Bay via five outfalls within City limits. A small fraction of the runoff drained into Ballona Creek. The largest of these outfalls is the Pico-Kenter which, combined with the 120-inch Santa Monica Freeway storm drain, empties into the ocean at the western end of Pico Boulevard. Other outfalls are located on the beach at Montana Avenue, Wilshire Boulevard, the Santa Monica Pier, and Ashland Avenue. Since 2022, however, with the construction of the Sustainable Water Infrastructure Project (SWIP) at the Civic Center, millions of gallons of storm water runoff are now captured, treated and used for irrigation and other gray-water purposes, limiting the amount of water that flows into the Santa Monica Bay.

As mentioned before, the FEMA mapping shows that flooding in Santa Monica is generally a concern only along the coastline. However, small and localized flooding may occur in the inland areas of the city, especially if the storm drains are clogged or prove to be inadequate to manage runoff from a large or protracted storm like the one in February 2024. Areas that occasionally flood reportedly include the general vicinity of Wilshire Boulevard to Idaho Avenue, from 4th Street to 7th Street, and along the I-10 freeway, the Pacific Coast Highway, and at the McClure Tunnel. Ponding has also been reported following heavy rain by Michigan Avenue and 16th Street, at Main Street between Hill Street and Ashland Avenue, and by Virginia Avenue Park and Douglas Park.

Proper maintenance of the extensive underground storm drain system is recommended to ensure that urban street flooding remains a relatively low hazard. City staff prepare for storms by closely monitoring storm activity and if there is a forecast of high-volume storms, work to ensure that storm drains are clear, especially in areas prone to ponding. The City may also direct people to stay off the

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roads during flood/flash flood events. City staff typically address issues of localized ponding with paving or drainage improvement projects.

Inundation Due to Catastrophic Failure of Water Storage Structures Water-Retaining Structures In and Near Santa Monica
The City of Santa Monica owns and operates four drinking water storage reservoirs (Mt. Olivette, Riviera, San Vicente, and Arcadia), two stormwater/urban runoff harvesting tanks, and one treated urban runoff storage tank. These reservoirs and tanks are identified in Table 8-5, and are described further below.

Table 8-5: Water Storage Reservoirs In and Near Santa Monica Owned by Santa Monica Drinking Water Storage Reservoirs and Tanks
Name Address
Storage Capacity
(millions of
gallons)
Type Date
Construction
Mt. Olivette 924 Franklin Street 5 underground 1924
Riviera 1252 Capri Drive,
Pacific Palisades 25 off-stream covered reservoir 1962
San Vicente San Vicente Blvd.
and 26th Street 5 underground 1958
Arcadia 1228 South Bundy Dr.,
Los Angeles 5 partially underground Pre 1927
Reclaimed Water Harvesting and/or Storage Tanks
Clean Beaches Tank 1623 Appian Way 1.6 underground 2018 Sustainable Water
Infrastructure Project (SWIP) –
Stormwater Harvesting Tank
1771 Main Street 5 underground 2022
Marine Park Underground
Storage Tank 1406 Marine Street 0.025 (25,000 gallons) underground 2017 Mt. Olivette Reservoir
The Mt. Olivette Reservoir is located in the northeastern part of the city, along Franklin Street. This subsurface reservoir was built in 1924 and holds up to 5 million gallons (15.3 acre-feet) of water.

This site is not within an Alquist-Priolo Earthquake Fault Zone, but several geologists have mapped a trace of the Santa Monica fault zone along the north side of the Brentwood Knoll, the elevated hill where the reservoir is located, and within 300 feet of the site. At least one published fault map27F 28 shows a trace of the Santa Monica fault through the southeastern corner of the reservoir site. The northeast-sloping face of the knoll, including the northeastern portion of the reservoir site, is also in an area identified by the California Geological Survey (CGS) as susceptible to earthquake-induced slope damage. The slopes in this area could also sustain surficial slope instability following an intense and/or prolonged precipitation event. Due to its location relative to the CGS-defined earthquake fault and landslide zones, the Mt. Olivette Reservoir may be impacted during an earthquake. In August 2023, the Santa Monica City Council approved a contract for engineering upgrades and improvements to the Mt. Olivette Reservoir and all other water storage reservoirs in

28 Yerkes, R.F., and Campbell, R.H., 2005, Preliminary Geologic Map of the Los Angeles 30’ x 60’ Quadrangle, Southern California, Version 1.0: U.S. Geological Survey Open-File Report 2005-1019; available from http://pubs.usgs.gov/of/2005/1019

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the city, with the work expected to be completed over the next two to four years.28F 29 Riviera Reservoir
The Riviera Reservoir, located at 1252 Capri, is located along the northern wall of Santa Monica Canyon in the city of Los Angeles, next to the Riviera Country Club and about two miles north of the city of Santa Monica. Although outside City limits, the dam and reservoir are owned by the City of Santa Monica, and managed by the City’s Department of Public Works. The Riviera Reservoir (California State Dam Number 1043-000, National ID No. CA00876) was constructed in 1962, has a storage capacity of about 25 million gallons (approximately 76 acre-feet), and is an off-stream, covered storage reservoir built with vertical concrete walls with a dam height of 40 feet. Because of its size, this reservoir is considered a dam and is therefore under the purview of the California Division of Dam Safety. Statutes governing dam safety are defined in Division 3 of the California State Water Code.29F
30 These statutes empower the California Division of Dam Safety to monitor the structural safety of dams that are greater than 25 feet in dam height or have more than 50 acre-feet in storage capacity.

According to the Division of Safety of Dams30F
31, the dam is best described as a reinforced concrete
tank. The length of the dam crest is 1,280 feet. As of 2022, this reservoir had been certified, meaning that the dam is considered to safely impound water to the elevation specified in the Certificate of Approval, and is considered satisfactory, meaning that no existing or potential dam safety deficiencies are recognized. This also means that the dam is expected to perform in an acceptable manner under all loading conditions in accordance with the minimum applicable state or federal regulatory criteria.

The Riviera Reservoir is located in an area that the CGS has mapped as susceptible to liquefaction, and adjacent to a slope that could fail as a result of earthquake-induced seismic shaking. If the reservoir failed during an earthquake, then the structures located immediately below the dam at the Riviera Country Club would be impacted. Moreover, flood waters released during the reservoir failure would empty onto the Riviera Country Club golf course, eventually flowing into the Santa Monica Canyon. Thus, inundation from Riviera Reservoir would mainly be confined to Santa Monica Canyon and not cross over into the city. Santa Monica Canyon is a concrete-lined channel that is dry most of the time; the flood control channel will likely contain the increased flow from the dam failure and direct it to the Pacific Ocean. Damage to any homes adjacent to the golf course is considered unlikely, and the travel time of the flood flows to the flood control channel is estimated at 15 minutes. According to the California Division of Safety of Dams, this reservoir has a “high” downstream hazard, defined as expected to result in the death of at least one person should the dam fail when operating with a full reservoir.

San Vicente Reservoir
The San Vicente Reservoir is also located in the northeastern part of the city, in the median of San Vicente Boulevard, near its intersection with 26th Street. The reservoir is entirely underground and

29 https://santamonicacityca.iqm2.com/Citizens/FileOpen.aspx?Type=1&ID=1351&Inline=True, accessed November 8-9, 2023. 30 California Department of Water Resources (DWR), 1986, Statutes and Regulations Pertaining to Supervision of Dams and Reservoirs: Division of Safety of Dams, 46p. 31 https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-ofDams/Files/Publications/Dams-Within-Jurisdiction-of-the-State-of-California-Listed-Alphabetically-by-NameSeptember-2022.pdf

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has a capacity of 5 million gallons of water. This tank is not located in an area mapped as susceptible to fault rupture or slope instability, but it is located near the Santa Monica fault. As a result, this reservoir could experience significant ground shaking if the Santa Monica fault caused an earthquake. In 2018, this reservoir, together with the other three drinking water storage facilities that serve the city, was reviewed by the California State Water Resources Control Board Division of Drinking Water. As a result of that routine survey, several reliability and operational improvements to the reservoir were recommended. These improvements will be conducted under the contract approved by City Council in August 2023, with the work anticipated to be completed by 2028.

Arcadia Reservoir and Water Treatment Facility
The Arcadia Reservoir and Water Treatment Facility is located east of the city of Santa Monica near the intersection of Wilshire Boulevard and Bundy Drive, in the city of Los Angeles. The storage tank has a storage capacity of 5 million gallons and is part of a water treatment facility that removes methyl tertiary butyl ether (MTBE) from the City’s Charnock Well Field and volatile organic compounds (VOCs) from groundwater pumped from the City’s Olympic Well Field. The facility is currently being expanded with the goal of reducing Santa Monica’s reliance on imported water. The multi-barrier treatment facility includes greensand filtration, ultraviolet light advanced oxidation processes, granular activated carbon, and reverse osmosis systems.

Because the Arcadia reservoir is partially buried, failure of the structure may inundate surrounding areas located at lower elevations, with the released water expected to flow to the southwest and possibly south on Bundy Drive. The Arcadia Reservoir is located within the CGS-defined AlquistPriolo Earthquake Fault Zone for the Santa Monica fault, with several different geologists having mapped the fault through this site. Significantly, this fault trace is the same fault previously investigated at both the Veteran’s Administration property in Los Angeles and at University High School, with both studies indicating that this fault has moved in the past 11,700 years and is therefore Holocene-active. The southwestern portion of the Arcadia reservoir is also located in an area mapped as susceptible to liquefaction.

Stormwater and Urban Runoff Harvest Tanks
The City completed construction of two stormwater/urban runoff harvesting tanks aimed to protect water quality in the Santa Monica Bay and increase local water reuse. One of these is the Clean Beaches Tank completed in 2018 that is located in the surface parking lot north of the Santa Monica Pier. Stormwater/urban runoff captured from the Pier drainage area is stored in the 1.6-million-gallon tank and sent to the existing Santa Monica Urban Runoff Recycling Facility (SMURRF) for treatment; the treated water is then used for non-potable and potable reuse. The second is the Sustainable Water Infrastructure Project (SWIP) Stormwater Harvesting Tank located underneath the surface parking lot adjacent to the Santa Monica Courthouse. This tank has the capacity to store 1.5 million gallons of captured stormwater and urban runoff. The stormwater/urban runoff is purified in the SWIP’s Advanced Water Treatment Facility where the final purified water is used for non-potable uses (e.g., irrigation and toilet flushing) and potable reuse (e.g., groundwater recharge via direct injection).

Additional storage tanks like these are reportedly planned throughout the Los Angeles region to alleviate some of the water demands and reduce the need for imported water. One of these tanks was built by the City of Los Angeles at Penmar Park, under the baseball field, just outside Santa Monica city limits. The tank is reportedly not currently operational, but is still there and could thus be used in the future. When the tank was proposed, the water stored there was to be used to irrigate

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Penmar Recreation Center, Penmar Golf Course, and transferred to a 25,000-gallon storage taken at Marine Park in Santa Monica to irrigate the peak daily needs of the park.31F 32 For these reasons, this
tank is included in Table 8-5 above.

These stormwater harvesting tanks are located in areas of the city considered to be relatively safe from seismic and geologic hazards. This means that these tank locations are not known to be underlain by faults, and are not expected to be impacted by liquefaction or slope instability. The SMURFF is also outside the area expected to be impacted by coastal flooding or a tsunami. Although all three locations (the two storage tanks and the SMURFF) are expected to experience ground shaking as a result of an earthquake on any of the regional active faults, the buried cisterns in particular are expected to perform well. Damage could occur at the piping connections if not fitted with flexible piping or tubing designed to accommodate some movement when the ground is shaking. This is discussed further below.

Water Tank Failure Impacts
The tanks located within Santa Monica are at risk of experiencing very strong ground shaking if the Santa Monica, Palos Verdes, Newport-Inglewood, or Hollywood faults generate an earthquake with its epicenter at or near the city. For this reason, these tanks should be regularly evaluated and their inundation paths should be defined, if at all possible, to determine whether or not habitable structures, and especially essential facilities, such as schools, are located within the inundation zone.

Ideally, in the event of catastrophic breakage, the water stored in these tanks is either contained within the site, or is discharged to a storm drain or channel that limits the impacted area.

It is unclear whether the reservoirs mentioned above are fitted with flexible joints and pipe connections that could withstand shaking associated with an earthquake on a nearby seismic source.

However, if the main water lines leading from the reservoirs to the city are sheared or damaged during an earthquake, Santa Monica could be without water for several days to weeks after the earthquake, depending on the scale of damage. An earthquake on the Santa Monica fault could result in extensive damage to the network of water mains and pipelines that distribute water to all buildings in the region. Rupture of the water mains could also result in the flooding of the areas immediately surrounding, and down-gradient of the failed pipes since several of the reservoirs drain by gravity. These potential ruptures would allow little time to evacuate the areas immediately downgradient from the reservoirs, with the potential for loss of life and damage to property.

Because the entire metropolitan area of Los Angeles, including the city of Santa Monica and neighboring communities, is susceptible to strong seismic ground motion, all above-ground water storage tanks in and upstream from Santa Monica should incorporate earthquake-resistant designs.

These should include flexible pipe joints that can accommodate some movement during seismic events, reducing the potential for breakage of the pipes, leading to accidental releases of water.

The City is currently evaluating design options for the rehabilitation of four water storage reservoirs that serve the community. The evaluation includes failure modes that are caused by seismic events and identify potential mitigation measures to minimize interruption to providing continuous water service to the community.

32 https://yovenice.com/2016/07/09/green-irrigation-for-penmar-park-and-golf-course/

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Stone Canyon Reservoir
The Stone Canyon Reservoir, which is located about 4.1 miles northeast of Santa Monica near the residential neighborhood of Bel Air, is owned and operated by the Los Angeles Department of Water and Power. This earthen embankment reservoir (California State Dam Number 6-025; National ID No. CA00083) was constructed in 1924, has a storage capacity of about 3.4 billion gallons (approximately 10,372 acre-feet), is 188 feet tall and 1,150 feet long. Given its size, this dam is also under the jurisdiction of the Division of Dam Safety. The dam is discussed here because if it failed, the flood waters released from the reservoir would inundate portions of the city of Santa Monica, in addition to impacting a significant section of Los Angeles and Culver City. Neighborhoods of the city of Los Angeles that would be impacted include Bel Air, Westwood, West Los Angeles, Mar Vista, Playa del Rey, Westchester, Palms, Venice, and Marina del Rey,.

Roth et al. (200432F
33) evaluated the seismic performance of the Stone Canyon Reservoir with two- and three-dimensional nonlinear effective-stress models using the explicit finite-difference program FLAC. They modeled the reservoir response to shaking levels experienced during the 1994 Mw6.7 Northridge earthquake, and during a hypothetical regional and local Maximum Credible Earthquake (MCE) of moment magnitude (Mw) 8 and Mw 6.5, respectively. Based on these parameters, their analyses suggest that Lower Stone Canyon Dam can be operated safely with the reservoir level at its design elevation of 865 feet.

However, if the reservoir failed during a larger local earthquake, then the eastern portion of the city of Santa Monica, in the area between about Olympic and Pico Boulevards, would be inundated.

Specifically, the flood waters from Stone Canyon Reservoir are expected to have a peak velocity of 1 to 3 feet per second, have a maximum depth of 1 to 10 feet, and arrive in the eastern part of Santa Monica approximately an hour to an hour-and-a-half after the dam failure.33F 34 Significant more
damage is expected to adjacent communities including Bel Air, Los Angeles, Culver City and Venice; refer to Figure 8-4. As of 2022, the California Division of Safety of Dams lists this reservoir as certified, with a satisfactory assessment, and with an “extremely high” downstream hazard. The extremely high downstream hazard is assigned to reservoirs that are “expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more”34F

35. 33 Roth, W.H., Dawson, E.M., Somerville, P., Davis, C.A., and Plumb, C.C., 2004, Evaluating the seismic performance of Stone Canyon Reservoir with 2-D and 3-D analyses: Paper No. 3249 presented at the 13th World Conference on Earthquake Engineering, Vancouver, B.C. Canada, 1-6 August 2004; available from https://www.iitk.ac.in/nicee/wcee/article/13_3249.pdf. 34 GENTERRA Consultants, Inc., 2018, Stone Canyon Dam Sunny Day Dam Failure Scenario, Los Angeles County, California State Dam # 06-025, National Dam ID # CA00083; consulting report prepared for Los Angeles Department of Water & Power, dated June 29, 2018. 35 https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-ofDams/Files/Publications/Dams-Within-Jurisdiction-of-the-State-of-California-Listed-Alphabetically-by-NameSeptember-2022.pdf

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Figure 8-4: Dam Inundation Map

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The Los Angeles Department of Water and Power (LADWP) shares its Emergency Action Plan (EAP) for Stone Canyon Dam with Santa Monica emergency response partners regularly. The LADWP conducts regular safety inspections of the dam and monitors water levels in the reservoir to quickly activate response measures if an issue is identified. Its EAP was last revised in February 2024, describing local public safety emergency responsibilities and emergency alerting and communication processes, including regular patrols of the dam as part of its security plan. Areas of Santa Monica that are not directly affected may be indirectly impacted due to large portions of West Los Angeles rapidly evacuating or needing support services, including critical facilities such as schools, hospitals, and college campuses. A major flooding incident would also impact Santa Monica’s mutual aid agencies in Culver City. An imminent failure scenario would result in major long-term recovery impacts for Santa Monica, as the scenario could hinder access to Santa Monica from the east and south for an extended period of time and would result in the relocation of a large portion of the West Los Angeles population, likely impacting the city’s workforce, housing demands, school communities, and business activity.

VULNERABILITY ASSESSMENT – COMMUNITY FLOOD ISSUES
Vulnerability assessment is the second step of flood-hazard assessment. It combines the floodplain boundaries recognized during the hazard identification phase with an inventory of the properties and infrastructure within the floodplain. Understanding the population and property exposed to this hazard can assist in reducing risk and preventing loss from future events.

The vulnerability assessment of the impact flooding would have in Santa Monica considered two separate possible scenarios, as follows: 1) a 100-year coastal flooding event, and 2) inundation of the eastern portion of the city as a result of a “sunny day” failure of Stone Canyon reservoir. The assessment used two separate approaches to calculate the anticipated damage, including cost. The first approach is based on HazUS, a regional multi-hazard loss estimation model and software application developed by FEMA and the National Institute of Building Sciences used to develop multi-hazard losses at a regional scale. Local, state and regional officials can use these loss estimates to evaluate the area’s vulnerability to multi-hazards and prepare for emergency response and recovery.

The coastal floods vulnerability assessment was conducted using a GIS-based version of the most current Flood Insurance Rate Map for Santa Monica (see Figure 8-3), and a Level 1 analysis that relies on the baseline inventories of structures and population counts based on the 2022 National Structure Inventory, and 2020 Census Data and 2022 U.S. Census American Community Survey, respectively. The dam inundation scenario was developed using a user-developed and supplied hazard map that considered only that portion of Santa Monica impacted by the dam inundation event, based on data extracted from the inundation map for a “sunny-day” dam failure event prepared by Genterra Consultants, Inc. (2018; see Figure 8-4). Both analyses considered and provided information on the number and types of buildings within the pathway of the coastal flood events and the inundation zone, that would thus be damaged. Additional information regarding HazUS, including its uses and limitations, is provided in Section 6 – Earthquake Hazards. The HazUS results were deemed to not capture the current value of the properties found to be impacted by the flood and inundation hazards evaluated, so the areas in the City anticipated to be affected by the flood and inundation scenarios were revisited using Crisis Track®, a GIS-based disaster management software that uses tax data to estimate the cost of a disaster. The results of the analyses are presented below and in the following Risk Analysis section.

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What is Susceptible to Damage During a Flood Event?
The Santa Monica region is approximately 8.4 square miles in area and contains 1,250 census blocks. The region contains over 47,000 households and has a population of about 93,000 people (based on 2020 U.S. Bureau Census data estimates). There are an estimated 27,495 buildings in the region, with a total building replacement value, excluding contents, of $19,682 million (based on 2022 regional population and building value data). The building data used by HazUS estimates that approximately 84.3 percent of the buildings, and 68.7 percent of the building value, are associated with residential housing. For a breakdown of the building exposure by occupancy type and construction type, refer to Section 6.

Critical facilities include police stations, fire stations, hospitals, emergency operation centers, shelters, and other facilities that provide important services to the community. These facilities and their services need to be functional after a flooding event. The database used by HazUS for the Santa Monica region was modified to include two (2) hospitals with a total combined capacity of 531 beds, 27 schools, five (5) fire stations, one (1) police station, and two (2) emergency operation centers (EOCs). The EOC at the Main Library was not included in the analysis. The flood and inundation zones shown on Figures 8-3 and 8-4 were also visually compared to the map of critical and essential facilities in Santa Monica to identify those facilities that could be impacted by these hazards. 100-Year Coastal Flood Event
Only a small portion of this region, and by City staff estimates, 85 buildings, are located within the FEMA-designated floodways (see Figure 8-3). Areas outside of the 100-year flood zone are known to occasionally flood during intense precipitation events, as mentioned previously, but these areas were not considered in the vulnerability assessments as their boundaries are not well-defined.

Critical facilities, and economically important buildings and infrastructure within or very close to the 100-year flood zone include Fire Station 7, the Harbor Patrol, the Santa Monica Pier, the Annenberg Beach House, and the Santa Monica Urban Runoff Recycling Facility (SMURRF). As discussed previously, coastal flooding can impact Pacific Coast Highway (PCH), whereas urban flooding may impact some sections of PCH, the tunnel connecting PCH with the I-10 freeway (McClure Tunnel), and low points along some of the local streets, including Wilshire Boulevard, Michigan Avenue, Idaho Avenue, and 16th Street, to name a few.

Stone Canyon Inundation Event
The portion of the city within the dam inundation failure zone for Stone Canyon reservoir is larger than the area susceptible to coastal flooding, but is still limited. The area considered for the dam inundation analysis is the area of Santa Monica shown on Figure 8-4 shaded in purple. HazUS estimates that there are about 320 structures within the potential zone of inundation. A review of GoogleEarth images of the area suggests, however, that this figure underestimates the total number of buildings in the zone. The HazUS-derived estimates of building exposure by occupancy type to inundation as a result of the catastrophic failure of Stone Canyon dam are summarized on Table 8- 6 below. Note that residential and commercial structures are estimated to comprise nearly 84% of the total number of structures exposed. The potential losses to these structures as a result of a Stone Canyon dam failure event are discussed in the risk analysis section.

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Table 8-6: Building Exposure by Occupancy Type – Stone Canyon Dam Inundation Event Occupancy Type Stone Canyon Dam Inundation
Exposure (in thousands of $) Percent of Total
Residential 325,263 45.1
Commercial 277,601 38.5
Industrial 103,567 14.3
Agricultural 279 0.0
Religion 5,785 0.8
Government 4,629 0.6
Education 4,649 0.6
Totals 721,773 100.0
The only critical facility located within Santa Monica’s Stone Canyon dam inundation zone is the LA Metro Division 14 facility at the boundary between the cities of Los Angeles and Santa Monica.

The dam inundation maps (GENTERRA Consultants, 2018) also show a private school, New Roads School on Olympic Boulevard, near to or just within the inundation zone. However, there are several critical facilities and infrastructure near the zone that could be impacted as a result of increased traffic during evacuation and potential minor flooding. These include three schools (Edison Language Academy, the Santa Monica College Center for Media and Design, and the Santa Monica College District Offices), the Santa Monica City Yards, the Fire Training Academy, and the I-10 freeway, including several bridges and connector ramps.

RISK ANALYSIS
Risk analysis is the third and most advanced phase of a hazard assessment. It builds upon the hazard identification and vulnerability assessment. A flood risk analysis should include two components: 1) the population and value of the properties that may incur losses from a flood event (defined through the vulnerability assessment; see Table 8-6 above); and 2) the number and type of flood events expected to occur over time.

As mentioned above, the HazUS results presented here for the hazard of coastal flooding are based on an analysis of the FEMA maps available for Santa Monica, combined with results obtained using Crisis Track®, a disaster management software that can help jurisdictions like cities and counties estimate the costs of a disaster (designed for real events). The Crisis Track® software allows calculation of the minimum and maximum cost for residential and commercial properties within the specified hazard zone. Different damage levels based on FEMA’s Preliminary Damage Assessment 4-Point Terminology are applied to generate a range of loss amounts based on the most recent tax assessment values (2023) available at the time of the analysis rather than market valuations. Results provided by both methods are included below.

The dam inundation analysis was also done using HazUS with a user-supplied GIS-based map of the area anticipated to be impacted by failure of the dam, including depth of the flood waters. The HazUS results are supplemented with a Crisis Track® estimate of the cost of the residential and commercial properties located within the inundation zone, based on tax valuations. The results of these analyses are presented in the following sections.

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General Building Stock Exposure and Potential Building-Related Losses The largest impact on communities from flood events is typically loss of life and property damage.

Nationwide, data from the National Weather Service shows that between 2010 and 2023 included, 101 people on average died each year as a result of flooding.35F 36 Between 2010 and 2022, annual
economic losses in the United States have ranged between about $494 million (2012) and $60.7 billion (2017).36F
37 In California, as a result of the 2022-2023 atmospheric river events, at least 22 people lost their lives and property losses were estimated at about $4.6 billion.37F 38 The type of property damage caused by flood events depends on the depth and velocity of the floodwaters. Faster moving floodwaters can wash buildings off their foundations and sweep cars downstream. Pipelines, bridges, and other infrastructure can be damaged when high waters combine with flood debris. In some regions, extensive damage can be caused by basement flooding. Most flood damage is caused by water saturating materials susceptible to loss (i.e., wood, insulation, wallboard, fabric, furnishings, floor coverings, and appliances). In many cases, flood damage to homes renders them unlivable.
100-Year Coastal Flood Event
Based on data previously obtained by City staff, 85 buildings are known to be located within the FEMA-mapped 100-year flood zone along the Pacific Ocean, west of Pacific Coast Highway. Several of these properties are City-owned and important to the community and the local economy. Coastal flood damage to these structures costs the City both to repair the structures, and as revenue lost if the structures have to be closed to the public while being repaired. For example, the intense rains in early February 2024 caused damage to City-owned property in Santa Monica, which in turn required the expenditure of City funds to pay City staff and subcontractors to clear and clean up debris from flooded areas, and repair damaged fencing and support beams at the Santa Monica Pier.38F
39 The potential cost to private structures within the flood zone as a result of a 100-year coastal flood event is anticipated to cost in the thousands to even millions of dollars.

The HazUS 100-year flood analysis for Santa Monica yielded a potential loss to commercial structures in the coastal flood zone of $4.6 million. The Crisis Track analysis for the area of the city within the 100-year flood zones shown on Plate 8-3 returned the values shown on Table 8-7 below.

Table 8-7: Estimated Economic Losses to Residential and Commercial Buildings in Santa Monica Within the 100-Year Flood Zone Using Crisis Track® Software Damage
Category
Affected
(Green Tag)
Minor
(Green Tag)
Major
(Yellow Tag)
Destroyed
(Red Tag)
Total Cost $4,027,299.20 $10,068,248.00 $24,163,795.20 $40,272,992.00

36 https://www.weather.gov/arx/usflood accessed on March 12, 2024. 37 https://www.statista.com/statistics/237420/economic-damage-caused-by-floods-and-flash-floods-in-the-us/, accessed on March 12, 2024. 38 https://www.ncei.noaa.gov/access/billions/events/US/1980-2024?disasters[]=all-disasters, accessed on March 12, 2024. 39 Based on email correspondence forwarded by Lindsay Call, Chief Resilience Officer, Santa Monica Office of Emergency Management, on February 8, 2024.

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Thus, the true value of economic losses related to a 100-year coastal flood event in Santa Monica are expected to range between about $4 million and $40 million. Note that these estimates are only for physical damage to the structures, and do not include the cost of damaged utilities or infrastructure. Furthermore, these estimates also do not include damage to the contents of the buildings or loss of inventory, loss of revenue, and the costs of relocation and/or rental while repairs to the damaged structures are done.

Stone Canyon Inundation Event
For the Stone Canyon dam failure scenario, HazUS estimates that about 214 buildings will be at least moderately damaged. This is over 67% of the total number of buildings in the region impacted by the scenario. This figure includes an estimated 23 buildings that will be completely destroyed.

Table 8-8 summarizes the expected damage by occupancy type, and Table 8-9 summarizes the expected building damage by building type. These tables show that residential structures comprise a large number and percentage of the total number of buildings impacted, with all of the “completely destroyed” buildings being residential. The impact to residential and commercial structures is also shown graphically on Figure 8-5.

Table 8-8: Expected Building Damage by Occupancy
as a Result of a Stone Canyon Dam Failure
Damage as a Percentage of the Total Structure
Occupancy
Type
1-10% 11-20% 21-30% 31-40% 41-50% >50%
Counts (%) Counts (%) Counts (%) Counts (%) Counts (%) Counts (%) Agriculture 0 0 0 0 0 0 0 0 0 0 0 0
Commercial 8 53 4 27 1 7 1 7 1 7 0 0
Education 0 0 0 0 0 0 0 0 0 0 0 0
Government 0 0 0 0 0 0 0 0 0 0 0 0
Industrial 8 80 2 20 0 0 0 0 0 0 0 0
Religion 0 0 0 0 0 0 0 0 0 0 0 0
Residential 33 14 79 33 53 22 30 13 20 8 23 10
Totals 49 85 43 31 21 23
Table 8-9: Expected Building Damage by Building Type
Damage as a Percentage of the Total Structure
Occupancy
Type
1-10% 11-20% 21-30% 31-40% 41-50% >50%
Counts (%) Counts (%) Counts (%) Counts (%) Counts (%) Counts (%) Concrete 7 70 3 30 0 0 0 0 0 0 0 0
Manufactured
Housing 0 0 0 0 0 0 0 0 0 0 0 0
Masonry 3 60 2 40 0 0 0 0 0 0 0 0
Steel 2 67 1 33 0 0 0 0 0 0 0 0
Wood 35 15 76 32 50 21 30 13 20 9 23 10

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The HazUS-derived total economic loss in Santa Monica estimated for the Stone Canyon dam failure scenario is $227.17 million, which represents about 31.5% of the total replacement value of the scenario buildings. Building-related losses can be divided into two categories: direct building losses and business interruption losses. Direct building losses are the estimated costs to repair or replace the damage caused to the building and its contents. Business interruption losses are the losses associated with the inability to operate a business because of the damage sustained during the flood.

Business interruption losses also include the temporary living expenses for those people displaced from their homes because of the flood.

HazUS estimates that the total building-related losses amount to $120.27 million. Forty-seven percent (47%) of the estimated losses are related to business interruption. The residential occupancies make up 26.84% of the total loss. Table 8-10 provides a summary of the losses associated with damage to the buildings in the impacted zone.

Table 8-10: Building-Related Economic Loss Estimates Resulting From a Catastrophic Stone Canyon Dam Failure Scenario
Millions of Dollars
Category Area Residential Commercial Industrial Others Total Building Loss
Building 32.43 14.56 4.71 0.69 52.38
Content 18.52 33.47 7.74 4.40 64.13
Inventory 0.00 2.60 1.15 0.02 3.76
Subtotal 50.94 50.63 13.60 5.10 120.27
Business Interruption
Income 0.04 39.28 0.55 1.23 41.10
Relocation 6.42 10.33 0.69 0.66 18.11
Rental Income 3.46 7.78 0.18 0.07 11.49
Wage 0.11 31.20 0.95 3.95 36.20
Subtotal 10.03 88.59 2.37 5.91 106.90
All Total 60.97 139.21 15.97 11.01 227.17
These results are comparable to the estimates calculated using Crisis Track® summarized in Table 8-11 below, given that, as discussed previously, the Crisis Track® software only considers the value of the structures using tax data, and does not include the loss of contents, inventory, or business interruption.

Table 8-11: Estimated Economic Losses to Residential and Commercial Buildings in Santa Monica Within the Stone Canyon Dam Inundation Zone Using Crisis Track® Software Damage
Category
Affected
(Green Tag)
Minor
(Green Tag)
Major
(Yellow Tag)
Destroyed
(Red Tag)
Total Cost $9,306,377.20 $23,265,943.00 $55,838,263.20 $93,063,722.00 Essential Facility Damage
Given that neither of the two hospitals in Santa Monica are located within the flood zone or the potential inundation zone, all of the hospital beds available in the city will be available for use by

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patients after either a 100-year or a dam inundation event. Significantly, however, in the case of the Stone Canyon dam failure, several regional hospitals, including several facilities on the UCLA Medical Center campus, are located within the anticipated inundation zone. It can be expected that the hospitals in Santa Monica would be asked to take on some of the extra patient load resulting from diversion of local patients, in addition to patients injured by the inundation event or the evacuation process itself. All other essential facilities in Santa Monica, including fire stations, emergency operation centers, and schools are expected to not be damaged and be fully operational after a Stone Canyon Dam failure. However, nearby inundation could limit access to the Santa Monica City Yards and the Fire Training Facility. Santa Monica would also be severely impacted by the evacuation and temporary or permanent relocation of several schools, fire stations, and LAPD’s police station in West Los Angeles.

Induced Flood Damage: Debris Generation
HazUS estimates the amount of debris that will be generated by a flood scenario. The model breaks debris into three general categories:
1) Finishes (dry wall, insulation, etc.),
2) Structural (wood, brick, etc.) and
3) Foundations (concrete slab, concrete block, rebar, etc.).

This distinction is made because of the different types of material handling equipment required to handle the debris.

The coastal flooding scenarios do not result in any significant amount of debris as a result of a 100- year flood event.

The HazUS model for the Stone Canyon dam failure estimates that a total of 2,250 tons of debris will be generated. Of this amount, “finishes” comprises 92% of the total, “structures” comprises 4% of the total, and “foundation” comprises the remaining 3%. If the debris tonnage is converted into an estimated number of truckloads, the model estimates that it will require 90 truckloads (@25tons/truck) to remove the debris generated by the inundation event.

Social Impact: Shelter Requirements
HazUS estimates the number of households that are expected to be displaced from their homes due to the flood and the associated potential evacuation. HazUS also estimates those displaced people that will require accommodations in temporary public shelters.

The model estimates that 2 households (or 6 people) will be displaced due to a 100-year flood.

Displacement includes households evacuated from within or very near to the flooded area. Of these, 0 people (out of a total population of 92,984) will seek temporary shelter in public shelters. Similarly, for a 500-year flood event, the model estimates 3 households (or 8 people) will be displaced due to the flood. Of these, 0 people will seek temporary shelter in public shelters. Significantly, the HazUS analysis also estimated that there would not be any injuries or loss of life as a result of the 100-year flood event.

The analysis for a Stone Canyon dam failure scenario estimates that 464 households (or 1,393 people) will be displaced due to the inundation. Of these, 59 people are anticipated to seek temporary shelter in public shelters. Since the flood waters from the hypothetically damaged reservoir are estimated to take at a minimum 60 minutes to reach the city of Santa Monica, the

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model assumed that all people within the potential inundation area would evacuate in advance, and as a result, that there would be no casualties. This is likely to be an incorrect assumption, but realistic estimates of the number of injuries and deaths are not available.

Business and Industry
Storm-flooding events impact businesses by damaging property and by interrupting business. Flood events can cut off customer access to a business as well as close a business for repairs. Roof leaks can impact the contents; in extreme cases, leaks can cause damage to sensitive electrical equipment, with the potential to cause the affected business thousands of dollars in material losses and potential loss of revenue. A quick response to the needs of businesses affected by flood events can help a community maintain economic vitality in the face of flood damage. Responses to business damages can include funding to assist owners in elevating or relocating flood-prone business structures, and loans to make building improvements, such as new roofs. Given that commercial structures are located within the 100-year flood zone, business-related losses associated with damage to the structures and their contents or inventory, and business interruption losses associated with lost wages, loss of income, and relocation and rental income losses would be anticipated.

The HazUS model indicates that commercial properties in Santa Monica within the flood zone will experience minor damage as a result of a 100-year flood event, with anticipated losses amounting to about $4.6 million. This estimate is thought to be low, with most of the losses captured in this estimate related to building and contents damage.

Public Infrastructure
Publicly owned facilities are a key component of daily life for Santa Monica residents. Damage to public water and sewer systems, transportation networks, flood control facilities, emergency facilities, and offices can hinder the ability of the government to deliver services.

A review of past storm damage shows that extensive flooding of streets is not common in Santa Monica. Similarly, as mentioned above, Santa Monica’s City Hall and other essential service buildings are not expected to be impacted by flooding associated with a 100-year flood, or as a result of localized flooding resulting from storm drain obstructions. Nevertheless, based on historical records, the economic losses associated with the cleanup and repair of the flooded areas can be substantial. It is thus important for the City and other responsible agencies to conduct regular inspections of culverts and storm drains to remove debris that may obstruct the flow of water during storms. This should reduce the potential for urban flooding in most areas The City’s water infrastructure at 26th Street and Olympic Boulevard is not anticipated to be inundated if Stone Canyon dam failed. Similarly, the City’s facilities near the intersection of Texas Avenue and Bundy Drive are also not within the dam inundation area.

FLOOD MITIGATION ACTION ITEMS
Based on the information presented in the sections above, flooding issues in Santa Monica are considered minor, with the HazUS coastal scenarios run for the city suggesting limited damage as a result of a 100-flood event, with losses estimated at between $4 million and $40 million. Recent regional storms have shown that minor damage to structures and businesses can cost thousands if not millions of dollars to repair, so these estimates are thought to be realistic. Moreover, in most

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cases, these loss estimates do not include lost revenue due to business interruption. Given that several of the structures in the 100-year flood zone in Santa Monica are public facilities that earn tax revenue for the City, damage to these structures would cost the City two-fold, consisting of both repair and/or replacement costs, and business interruption losses.

A HazUs analysis for Stone Canyon Dam estimates the total economic loss for the flood is $227.17 million, which represents 31.47 % of the total replacement value of the scenario buildings. The building losses for Stone Canyon Dam are broken into two categories: direct building losses and business interruption losses. The direct building losses are the estimated costs to repair or replace the damage caused to the building and its contents. The business interruption losses are the losses associated with the inability to operate a business because of the damage sustained during the flood.

Business interruption losses also include the temporary living expenses for those people displaced from their homes because of the flood. The total building-related losses are estimated at $120.27 million. 47% of the estimated losses were related to the business interruption of the region. The residential occupancies made up 26.84% of the total loss.

Flood mitigation activities listed here include current mitigation programs and activities that are being implemented by the city of Santa Monica, the County of Los Angeles, the U.S. Army Corps of Engineers, and other agencies and organizations.

The City of Santa Monica addresses its localized flooding problems as they arise, typically by deploying pumps to the impacted areas when a storm hits. However, these efforts have at times not been enough to prevent damage.

Main flood control services for the city of Santa Monica are provided by the City’s Public Works Department, with assistance as needed by the Los Angeles County Department of Public Works (LACDPW). Together with the U.S. Army Corps of Engineers, the LACDPW regulates flood levels by adjusting water flows upstream of flood-prone areas.

Because dam failure can have severe consequences, FEMA requires that all dam owners develop Emergency Action Plans (EAP) for warning, evacuation, and post-flood actions. Although there may be coordination with county officials in the development of the EAP, the responsibility for developing potential flood inundation maps and facilitation of emergency response is the responsibility of the dam owner. Dam owners are also required to prepare and submit emergency response plans to the State Office of Emergency Services, the lead State agency for the State dam inundation-mapping program. The flood inundation map prepared by Genterra Consultants, Inc. (2018) for Stone Canyon Dam, which is owned by the Los Angeles Department of Water & Power, was used for the dam inundation scenario described in this report. These documents, including dam inundation maps and emergency response plans are reviewed and updated at least annually to ensure that contact information is up to date. For additional information refer to the section on Inundation Due to Catastrophic Failure of Water Storage Structures.

Cities and counties are also required by State law to have in place emergency procedures for the evacuation and control of populated areas within the limits of dam inundation. In addition, legislation requires real estate disclosure upon sale or transfer of properties in the inundation area (AB 1195 Chapter 65, June 9, 1998; Natural Hazard Disclosure Statement).

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FLOOD RESOURCE DIRECTORY
The following resource directory lists resources and programs that can assist county communities and organizations. The resource directory provides contact information for county, regional, State and Federal programs that deal with natural hazards.

County Resources
Los Angeles County Public Works Department
900 S. Fremont Avenue, Alhambra, CA 91803
626-458-5100
https://dpw.lacounty.gov/
Sanitation District of Los Angeles County
1955 Workman Mill Road, Whittier, CA 90607
562-699-7411 x2301
https://www.lacsd.org/
State Resources
Governor’s Office of Emergency Services (Cal OES)
3650 Schriever Avenue, Mather, CA 95655
916-845-8911
www.caloes.ca.gov/
California Natural Resources Agency
715 P Street, Sacramento, CA 95814
916-653-5656
http://resources.ca.gov
California Department of Water Resources (DWR)
715 P Street, Sacramento, CA 95814
916-653-5791
https://water.ca.gov/
California Department of Conservation
715 P Street, Sacramento, CA 95814
916-322-1080
www.conservation.ca.gov
Federal Resources and Programs
Federal Emergency Management Agency (FEMA)
FEMA provides maps of flood hazard areas, various publications related to flood mitigation, funding for flood mitigation projects, and technical assistance. FEMA also operates the National Flood Insurance Program. FEMA's mission is to reduce loss of life and property and protect the nation’s critical infrastructure from all types of hazards through a comprehensive, risk-based, emergency management program of mitigation, preparedness, response and recovery.

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Federal Emergency Management Agency, Region IX
1111 Broadway, Suite 1200, Oakland, CA 94607
510-627-7100
www.fema.gov
Federal Emergency Management Agency (FEMA), Hazard Mitigation Planning California Governor’s Office of Emergency Services
3650 Shriever Avenue, Mather, California 95655
916-799-6499
www.fema.gov/emergency-managers/risk-management/hazard-mitigation-planning http://www.fema.gov/grants/mitigation/state-contacts
FEMA' s Community Status Book Report
This site provides information of California communities participating in the National Flood Program.
https://www.fema.gov/cis/CA.html
National Flood Insurance Program (NFIP)
In Southern California, many cities lie within flood zones as defined in FEMA Flood Maps. The City of Santa Monica is a community within a designated flood zone. As a result, flood insurance is available to citizens in the flood zone that adopt and implement NFIP building standards. The standards are applied to development that occurs within a delineated floodplain, a drainage hazard area, and properties within 250 feet of a floodplain boundary. These areas are depicted on federal Flood Insurance Rate Maps available through Los Angeles County.

P.O. Box 10055, Hyattsville, MD 20782-805
202-646-2500
https://www.fema.gov/flood-insurance
Other National Resources
Floodplain Management Association (FMA)
701 Pleasant Grove, Suite 180, Roseville, CA 95678
916-847-3778
https://floodplain.org/
The Association of State Floodplain Managers
The Association of State Floodplain Managers is an organization of professionals involved in floodplain management, flood hazard mitigation, the National Flood Insurance Program, and flood preparedness, warning, and recovery.
8301 Excelsior Drive, Madison, WI 53717
608-828-3000
http://www.floods.org

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National Weather Service
The National Weather Service provides flood watches, warnings, and informational statements. 520 North Elevar Street, Oxnard, CA 93030
805-988- 6610
https://www.weather.gov/lox
National Weather Service, Office of Water Prediction
The National Weather Service Office of Water Prediction offers information on floods and other aquatic disasters. This site offers current and historical data including an archive of past flood summaries, information on current hydrologic conditions, water supply outlooks, an Automated Local Flood Warning Systems Handbook, Natural Disaster Survey Reports, and other scientific publications on hydrology and flooding.

National Weather Service, Office of Hydrologic Development 1325 East West Highway, SSMC2
Silver Spring, MD 20910
https://www.weather.gov/owp
National Oceanic and Atmospheric Administration (NOAA)
1401 Constitution Avenue NW, Room 5128, Washington, DC 20230 202-482-6090
http://www.noaa.gov
NOAA's Mission: Science, Service, and Stewardship

1. To Understand and Predict Changes in Climate, Weather, and the Ocean and Coasts Science at NOAA is the systematic study of the structure and behavior of the ocean, atmosphere, and related ecosystems; integration of research and analysis; observations and monitoring; and environmental modeling. NOAA science includes discoveries and ever new understanding of the ocean and atmosphere, and the application of this understanding to such issues as the causes and consequences of climate change, the physical dynamics of high-impact weather events, the dynamics of complex ecosystems and biodiversity and the ability to model and predict the future states of these systems. Science provides the foundation and future promise of the service and stewardship elements of NOAA’s mission.

2. To Share That Knowledge and Information with Others
Service is the communication of NOAA’s research, data, information, and knowledge for use by the Nation’s businesses, communities, and people’s daily lives. NOAA services include climate predictions and projections; weather and water reports, forecasts, and warnings; nautical charts and navigational information; and the continuous delivery of a range of Earth observations and scientific data sets for use by public, private and academic sectors.

3. To Conserve and Manage Coastal and Marine Ecosystems and Resources Stewardship is NOAA’s direct use of its knowledge to protect people and the environment, as the Agency exercises its direct authority to regulate and sustain marine fisheries and their ecosystems, protect endangered marine and anadromous species, protect and restore habitats and ecosystems, conserve marine sanctuaries and other protected places, respond to environmental emergencies and aid in disaster recovery. The foundation of NOAA’s longstanding record of scientific, technical and organizational excellence is its people. NOAA’s diverse functions require an equally diverse set of skills and constantly evolving abilities in its workforce.

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National Resources Conservation Service (NRCS), US Department of Agriculture NRCS provides a suite of federal programs designed to assist state and local governments and landowners in mitigating the impacts of flood events. The Watershed Surveys and Planning Program and the Small Watershed Program provide technical and financial assistance to help participants solve natural resource and related economic problems on a watershed basis. The Wetlands Reserve Program and the Flood Risk Reduction Program provide financial incentives to landowners to put aside land that is either a wetland resource, or that experiences frequent flooding. The Emergency Watershed Protection Program (EWP) provides technical and financial assistance to clear debris from clogged waterways, restore vegetation, and stabilize riverbanks. The measures taken under EWP must be environmentally and economically sound and generally benefit more than one property. 3550 Harbor Blvd., Suite 2-202, Oxnard, CA 93035
202-720-7246
805-984-2358
http://www.nrcs.usda.gov/
U.S. Geological Services (USGS) Water Resources Division This agency provides current U.S. water news; extensive current (including real-time) and historical water data; numerous fact sheets and other publications; various technical resources; descriptions of ongoing water survey programs; local water information; and connections to other sources of water information.
12201 Sunrise Valley Drive, Reston, VA 20192
888-275-8747
http://ca.water.usgs.gov/
www.usgs.gov/mission-areas/water-resources
Bureau of Reclamation
The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. The Bureau provides leadership and technical expertise in water resources development and in the efficient use of water through initiatives including conservation, reuse, and research. It protects the public and the environment through the adequate maintenance and appropriate operation of Reclamation's facilities and manages Reclamation's facilities to fulfill water user contracts and protect and/or enhance conditions for fish, wildlife, land, and cultural resources.

Lower Colorado Basin Regional Office
500 Fir Street, Boulder City, NV 89005-2403
702-293-8411
http://www.usbr.gov/
U.S. Army Corps of Engineers
The Corps of Engineers administers a permit program to ensure that the nation’s waterways are used in the public interest. Any person, firm, or agency planning to work in waters of the United States must first obtain a permit from the Army Corps of Engineers. The Corps is responsible for the protection and development of the nation’s water resources, including navigation, flood control, energy production through hydropower management, water supply storage and recreation.

Los Angeles District
915 Wilshire Boulevard, Suite 1101, Los Angeles, CA 90017 213-452-3333
www.spl.usace.army.mil/

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American Public Works Association
1200 Main Street, Suite 1400, Kansas City, MO 64105-2100 816-472-6100
www.apwa.org
Publications
Refer to the papers and publications identified in the footnotes for recent sources of additional information.

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SECTION 9: LANDSLIDES
WHY ARE LANDSLIDES A THREAT TO THE CITY OF SANTA MONICA? Landslides are a serious geologic hazard in almost every state in the United States. Nationally, landslides cause 25 to 50 deaths each year0F
1 . The best estimate of direct and indirect costs of
landslide damage in the United States ranges between $1 and $2 billion annually. In California, landslides are a significant hazard, in part because of the region’s seismic activity, and in part because the region is underlain by weak soils and rocks that can fail when exposed along a slope, especially when saturated. Some landslides result in private property damage, whereas other landslides impact transportation corridors, fuel and energy conduits, and communication facilities.

As the numbers above show, landslides can also pose a serious threat to human life.

Physiographic Setting
The city of Santa Monica is located at the northwestern margin of the Los Angeles Basin and at the transition between the Peninsular Ranges and the Transverse Ranges physiographic provinces of southern California (see Figure 9-1). The Los Angeles Basin is part of the Peninsular Ranges, a region characterized by a northwest-trending structural grain aligned with the San Andreas fault and represented by a series of northwest-trending faults, mountain ranges and valleys stretching from the southern base of the Santa Monica and San Gabriel Mountains south to beyond the Mexican border.

Displacements on faults in this region are mainly of the right-lateral strike-slip and oblique-slip type, and where they have been most recently active, they have deformed the landscape and altered drainage patterns. Some of these faults include the Palos Verdes, Newport-Inglewood and ElsinoreWhittier faults, whereas the hills that formed in response to movement on these faults include the Palos Verdes Hills, the string of elevated hills and mesas from Beverly Hills to Newport Mesa along the Newport-Inglewood fault zone, and the Puente Hills along the Whittier fault.

Alternatively, the Santa Monica Mountains, along with the San Gabriel Mountains to the east, are part of the west-trending Transverse Ranges that form the northern boundary of the Los Angeles Basin. Bounded on the south by the fault system that is responsible for their uplift, these mountains form a topographic, geomorphic, geologic, and tectonic barrier in the region. The section of this fault system within the city of Santa Monica is the Santa Monica fault.

Although located near the rugged Santa Monica Mountains, the landscape within most of the city itself is relatively simple (see Figure 9-1). The northern portion of the city is underlain by a broad, gently south-sloping alluvial fan that emanated from the mountains to the north. On its western boundary, low-lying beaches serve as a buffer between the Pacific Ocean and coastal bluffs. As we will discuss further in this chapter, ongoing erosional processes are causing retreat of these bluff faces. Older marine, lake (lacustrine), playa or estuarine deposits, now elevated above the active floodplain, are present in the southern portion of the city.

Urban development of most of the city took place before mass grading practices became the norm, especially the section of Santa Monica between Montana Avenue on the north, Colorado Avenue on the south, the Pacific Ocean on the west and 26th Street on the east, as this section of the city was built in the late 1870s. Here, the original topography was generally preserved. Ground surface modifications are more prevalent in the southeastern, slightly newer portion of the city, generally

1 https://www.usgs.gov/faqs/how-many-deaths-result-landslides-each-year

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the result of both road grading and cut and fill associated with the leveling of building pads prior to construction. Grading was also likely employed to create the level pad that accommodates the Santa Monica airport runway. Ground surface elevations across the city vary from 0 to 10 feet above mean sea level (amsl) along the beach, to approximately 175 feet amsl at the eastern end of the airport and 340 to 370 feet amsl near the northeastern corner of the city, on Brentwood Knoll and near the intersection of 26th Street with La Mesa Drive. The coastal bluffs in the northwestern corner of the city rise approximately 50 to 150 feet above the beach below. Farther north, in the Pacific Palisades area, the bluffs are approximately 200 feet high.

Figure 9-1: Physiographic Map of Santa Monica and Surrounding Areas See full map with accompanying explanation in Appendix H, as Plate H-1.

Geologic Setting
The physical features described in the previous section are a reflection of the geologic and climatic processes that have impacted this region in the last few million years. Geologists rely on the principles of uniformitarianism that state that the “present is the key to the past.” Since the 1970s, however, geologists have also looked to the past to predict future geological trends or events. Thus, the geologic hazards that are likely to impact Santa Monica in the future are in great part defined by the geologic history of the area, and the age and characteristics of the sediments that occur at or near the ground surface. A geologic map and descriptions of the geologic units that occur at or near the ground surface in Santa Monica are included below on Figure 9-2.

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Figure 9-2: Geologic Map of Santa Monica and Vicinity with Unit Descriptions (for larger version of these figures refer to Appendix H, Plates H-13a and H-13b)

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This principle is the basis for the fault rupture studies required by the State Geologist across the Santa Monica fault and other faults in the region. Essentially, a fault that has moved at least once in the past 11,700 years is thought to have a relatively high probability of moving again in the future, and in response to this, the State mandates that new habitable structures not be placed across the trace of a Holocene-active fault. Similarly, areas that have experienced slope failures in the past are likely to experience slope failures again in the future, especially if the slopes have not been buttressed or strengthened. This section describes the geologic history of the area and the geologic units that occur at and near the ground surface as a means to identifying and addressing where slope failures could impact Santa Monica residents and visitors. As it is discussed further below, unlike fault rupture, which the State mandates to avoid, slope failures are typically addressed and corrected with appropriate engineering design.

The deposits that form the alluvial fan surface underlying the northern half of the city emanated from the Santa Monica Mountains. These deposits were transported to their current location by ancestral streams and/or gravity (as mudflows or slopewash) over thousands to tens of thousands of years, building an approximately 80- to 100-foot-thick section of sand, gravelly sand and silt at the base of the mountains. We know that the Santa Monica Mountains are the source for these sediments because the gravels, which occur in large amounts in the alluvial fan deposits, typically consist of clasts of bedrock types that crop out in these mountains. The rock type most often seen in the gravelly sections is Santa Monica slate, a dark bluish gray metamorphic rock, but lesser amounts of granitic, volcanic and sedimentary rocks eroded from the Topanga, Tuna Canyon and other formations are also present (Figure 9-2).

Deposition of the alluvial fan sediments occurred sporadically, with long periods of quiescence that allowed for the formation of soils at the surface, before being buried by new pulses of sedimentation.

These now-buried soils are typically clay-rich, forming distinct horizons that can be recognized in subsurface studies, and can be correlated across broad areas. Minor colluvial and sheetflow sediments were and continue to be transported and re-deposited during intense precipitation events.

For the most part, however, erosion and downslope movement of these soils now occurs only in a few areas where the soils are not covered by hardscape, and in areas of topographic relief, if the deposits are exposed in slopes.

Large-scale mudflows such as those that deposited the alluvial fan sediments that underlie the northern half of Santa Monica can no longer impact the city, as the alluvial fan surface is now elevated above the active zone of sedimentation and disconnected from the mountains to the north by the deep ravines of Santa Monica Creek and Rustic Creek canyons. These canyons were incised into the alluvial fan surface and underlying units during the last glacial maximum, which occurred approximately 25,000 to 19,000 years ago. At that time a significant portion of the water on the Earth’s surface was stored as ice, in glaciers, and as a result, sea level was approximately 410 feet (±125 meters) below current sea level (Ishiwa et al., 2019). Rivers draining the Santa Monica Mountains and other highlands surrounding the Los Angeles Basin carved deep channels to achieve equilibrium with this lower sea level. Then, once sea level began to rise, and for the next about 12,000 to 16,000 years, until about 7,000 to 3,000 years ago, many of these canyons were backfilled with sediment eroded off the adjacent highlands as these rivers adjusted to a new base level (Romans et al., 2009). Evidence for some of these now submarine canyons can still be observed in bathymetric maps of Santa Monica Bay, including Redondo Canyon, which connects to the modern shoreline, and Santa Monica Submarine Canyon, which has been buried in the continental shelf but can still be observed in the continental slope (Figure 9-3). Potential future mudflows emanating from the

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Santa Monica Mountains to the north would flow into the canyons of Santa Monica and Rustic creeks, and would not extend southward into the city.

Figure 9-3: Bathymetric Map of Santa Monica Bay Showing Offshore Canyons The offshore Santa Monica Submarine Canyon may be related to the drainage that formed the Ballona Gap. This term is now used for the channelized stream (Ballona Creek) that flows at the base of the Baldwin Hills, on their north side, but the gap covers the entire low-lying area between the Beverly Hills and the Baldwin Hills. Moreover, Ballona Creek is now a distributary of the greater Los Angeles River, but in centuries past, at times it would carry the Los Angeles River floodwaters out to sea. The last time this happened was between 1815 and 1825 (Grant and Sheppard, 1939 quoting Layne, 1935). Due to the high degree of urbanization, drainage within Santa Monica is now mostly managed via storm drains that capture runoff from precipitation events. Outside city limits, storm runoff is locally captured by a few key drainages, including Rustic Creek and Santa Monica Creek canyons on the north side, and the Ballona Creek channel to the south.

At depth below the alluvial fan deposits mentioned in the paragraphs above, is a thick sequence of non-marine and marine sediments. Under the Santa Monica area, these sediments extend to depths of between 5,000 and 12,000 feet, whereas in other areas of the Los Angeles basin, these sediments are locally more than 30,000 feet thick (Wright, 1991). Some of these marine deposits are exposed near the bottom of the coastal bluffs, where they sometimes act as planes of weakness for landslides.

This is discussed further below.

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DEFINITIONS
What is a Landslide?
In broad terms, landslides are downslope movements of landmasses, either as nearly intact bedrock blocks, or as jumbled mixtures of bedrock blocks, fragments, debris, and soil. Landslides are a type of “mass wasting” which denotes any down slope movement of soil and rock under the direct influence of gravity. The term “landslide” encompasses events such as rock falls, topples, slides, spreads, and flows, and in general, landslides can be broken down into two categories: 1) rapidly moving (mud or debris flows, rock falls, and rock topples), and 2) slow moving (earth flows and slumps). Movement of larger landmasses can range from rapid to very slow. Rapidly moving landslides or debris flows pose the greatest risk to human life, and people living in or traveling through areas prone to rapidly moving landslides are at increased risk of serious injury or worse.

Slow moving landslides can cause significant property damage, but are less likely to result in serious human injuries.

Geologists also describe the type of movement of a landslide as either: 1) translational (where movement occurs along a relatively planar dipping surface), 2) rotational (where sliding material moves along a curved surface) or 3) wedge (where movement occurs on a wedge-shaped block formed by intersecting planes of weakness, such as fractures, faults and bedding). The size of a landslide usually depends on the geology and the initial cause of the landslide. Landslides vary greatly in their volume of rock and soil, the length, width, and depth of the area affected, frequency of occurrence, and as mentioned above, speed of movement. Shallow slides (referred to as surficial slope failures) are generally about 15 feet or less in depth and involve the near surface soil, and possibly the underlying weathered bedrock. Deeper slides (referred to as gross slope failures) most often consist of bedrock blocks, either severely broken or relatively intact, depending on the bedrock structure and mode of failure.

What is a Debris Flow?
This type of failure is the most dangerous and destructive of all types of slope failure. A debris flow (also called mudflow, mudslide, and debris avalanche) is a rapidly moving slurry of water, mud, rock, vegetation and debris. Larger debris flows are capable of moving trees, large boulders, and even cars. This type of failure is especially dangerous as it can move at great speeds, is capable of crushing buildings, and can strike with very little warning. The development of debris flows is strongly tied to exceptional storm periods of prolonged rainfall, such as storms related to atmospheric rivers. Failure generally occurs during an intense rainfall event, following saturation of the soil by previous rains.

A debris flow most commonly originates as a soil slip in the rounded, soil-filled “hollow” at the head of a drainage swale or ravine. The rigid soil mass is deformed into a viscous fluid that moves down the drainage, incorporating into the flow additional soil and vegetation scoured from the channel.

Debris flows also occur on canyon walls, often in soil-filled swales that do not have topographic expression. The velocity of the flow depends on the viscosity, slope gradient, height of the slope, roughness and gradient of the channel, and the baffling effects of vegetation. Even relatively small amounts of debris can cause damage from inundation and/or impact (Ellen and Fleming, 1987; Reneau and Dietrich, 1987). Recognition of this hazard led FEMA to modify its National Flood Insurance Program to include inundation by “mudslides.”

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CONDITIONS CONDUCIVE TO SLOPE FAILURES
Landslides in the southern California region can be initiated by rainfall, earthquakes, changes in the depth to ground water or overall moisture content of the geologic materials, disturbance and change of a slope by human-made construction activities, changes in vegetation, or any combination of these causes. The potential for slope failure is also dependent on slope height, slope steepness, and shear strength and orientation of the underlying geologic unit(s). For example, water can increase the plasticity of weak clays lining joints or shears, forming planes of weakness along which a landmass can fail.

Failure of a slope occurs when the force that is pulling the slope downward (gravity) exceeds the strength of the earth materials that compose the slope. They can move slowly (millimeters per year), or can move quickly and disastrously, as is the case with debris flows. Debris flows can travel down a hillside at speeds up to 200 miles per hour (but more commonly, 30 – 50 miles per hour), depending on the slope angle, water content, and type of earth and debris in the flow. These flows are initiated by heavy, usually sustained, periods of rainfall, but sometimes can happen as a result of short bursts of concentrated rainfall in susceptible areas. Burned areas charred by wildfires are particularly susceptible to debris flows, as described further below.

For engineering of earth materials, these factors are combined in calculations to determine if a slope meets a minimum safety standard. The generally accepted standard is a factor of safety of 1.5 or greater (where 1.0 is equilibrium, and less than 1.0 is failure). Natural slopes, graded slopes, or graded/natural slope combinations must meet these minimum engineering standards where they impact planned homes, subdivisions, or other types of developments. Slopes adjacent to areas where the risk of economic losses from landsliding is small, such as parks and mountain roadways, are often allowed a lesser factor of safety. From an engineering perspective, landslides are generally unstable (may be subject to reactivation), and may be compressible, especially around the margins, which are typically highly disturbed and broken. The headscarp area above the landslide mass is also unstable, since it is typically oversteepened, cracked, and subject to additional failures.

Thus, locations at risk from landslides or debris flows include the following:
 On or close to steep hills
 Steep road-cuts or excavations
 Existing landslides or places of known historic landslides (such sites often have tilted power lines, trees tilted in various directions, cracks in the ground, and irregular-surfaced ground)  Steep areas where surface runoff is channeled, such as below culverts, V-shaped valleys, canyon bottoms, and steep stream channels
 Fan-shaped areas of sediment and boulder accumulation at the outlets of canyons  Canyon areas below hillside and mountains that have recently (within 1-6 years) been subjected to a wildland fire.

Some of the most common conditions leading to slope failures are described in more detail below.

Natural Conditions
Natural processes can cause landslides or re-activate historical and pre-historical landslide sites. The removal or undercutting of shoreline-supporting material along bodies of water by currents and waves produces countless small slides each year. Seismic tremors can trigger landslides on slopes

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historically known to have landslide movement. Earthquakes can also cause additional failure (lateral spreading) that can occur on gentle slopes above steep streams and riverbanks.

Weathering of geologic materials produces conditions conducive to landslides, while human activity often further exacerbates many landslide problems. Many landslides are difficult to mitigate, particularly in areas of large historic movement with weak underlying geologic materials.

Rock falls occur when blocks of material come loose on steep slopes. Weathering, erosion, or excavations, such as those along highways, can cause falls where the road has been cut through bedrock. Rock falls are fast moving, with the materials free falling or bouncing down the slope. In falls, material is detached from a steep slope or cliff. The volume of material involved is generally small, but large boulders or blocks of rock can cause significant damage.

As the list of historical landslides suggests, landslides are often triggered by periods of heavy rainfall.

Certain geologic formations are more susceptible to landslides than others. Human activities, including locating developments near steep slopes, can increase susceptibility to landslide events.

Landslides on steep slopes are more dangerous because movements can be rapid.

Wildland fires in hills covered with chaparral are often a precursor to debris flows in burned out canyons. The extreme heat of a wildfire can create a soil condition in which the earth becomes impervious to water by creating a waxy-like layer just below the ground surface. Since the water cannot be absorbed into the soil, it rapidly accumulates on slopes, often gathering loose particles of soil that combine to form a sheet of mud and debris. Debris flows can often originate upstream, miles away from a developed area, and approach the built environment at the mouth of a canyon at a high rate of speed and with little warning.

Impacts of Development and Redevelopment
Although landslides are a natural occurrence, human impacts can substantially affect the potential for landslide failures to occur. Grading and construction can decrease the stability of a hill slope by adding weight to the top of the slope, removing support at the base of the slope, and increasing water content. Grading for road construction and development can increase slope steepness. Other human activities effecting landslides include excavation, drainage and groundwater alterations, and changes in vegetation (as discussed further below). Proper planning and geotechnical engineering if applied judiciously, however, can be implemented to reduce the threat to people, property, and infrastructure posed by unstable slopes.

Slope excavation is common in the development of home sites or roads on sloping terrain. Grading these slopes sometimes results in slopes steeper than the pre-existing natural slopes. Since slope steepness is a major factor in landslides, these steeper slopes can be at an increased risk for landslides. The added weight of fill placed on slopes can also result in an increased landslide hazard.

Small landslides can be fairly common along roads, both along the road-cut and the road-fill sections. Landslides occurring below new construction sites are indicators of the potential impacts stemming from excavation. Alternatively, if unstable slope conditions are recognized and engineered for during grading, originally unstable or marginally stable slopes can be made safer.

Alterations to Drainage and Groundwater Systems
Water flowing through or above ground is often the trigger of landslides. Any activity that increases

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the amount of water flowing into landslide-prone slopes can increase landslide hazards. Broken or leaking water or sewer lines and seepage fields can be especially problematic, as can water retention facilities that direct water onto slopes. However, even lawn irrigation in landslide–prone locations can result in damaging landslides. Ineffective storm water management and excess runoff can also cause erosion and increase the risk of landslide hazards. Drainage can be affected naturally by the geology and topography of an area. Development that results in an increase in impervious surfaces (such as concrete- or asphalt-paved roads) impairs the ability of the land to absorb water and may redirect water to other areas. Channels, streams, ponding, and erosion on slopes all indicate potential slope problems.

Road and driveway drains, gutters, downspouts, and other constructed drainage facilities can concentrate and accelerate runoff flow. Ground saturation and concentrated velocity flow are major causes of slope problems and may trigger landslides.

Changes in Vegetation
Removing vegetation from very steep slopes can increase landslide hazards. Areas that experience wildfire and land clearing for development may have long periods of increased landslide hazard.

Also, certain types of non-native ground covers require extensive irrigation to remain green. As a result, clearing and replacement of native ground covers with non-native covers can lead to an increase in slope failures.

Watersheds that have been recently burned typically yield greater amounts of soil and debris than those that have not burned. Erosion rates during the first year after a fire are estimated to be 15 to 35 times greater than normal, and peak discharge rates range from 2 to 35 times higher. These rates drop abruptly in the second year, and return to normal after about 5 years (Tan, 1998).

In addition, debris flows in burned areas are unusual in that they can occur in response to small storms and do not require a long period of antecedent rainfall. These kinds of flows are common in small gullies and ravines during the first rains after a burn, and can become catastrophic when a severe burn is followed by an intense storm season (Wells, 1987). The United States Geological Survey (USGS), as part of its National Landslide Hazards Program1F 2 , has developed tools and
methodologies to identify and quantify slope stability hazards posed by burned watersheds. These tools include the installation of instruments in recently burned watersheds and canyons to collect data on rainfall, flow stage, soil moisture, and other parameters, and the development of mathematical models that use these data to predict the onset of landslides in an effort to develop real-time warning systems2F
3 .

HISTORICALLY AND LOCALLY SIGNIFICANT SOUTHERN CALIFORNIA

LANDSLIDES
Historically, there have been many landslides in the southern California area. Landslides recorded in the latter half of the 20th century alone caused losses of more than $5 billion (in 2000 dollars, approximately equivalent to $9 billion in 2023 dollars). Many of these landslides occurred after

2 https://www.usgs.gov/programs/landslide-hazards/what-we-do-landslide-hazards-program, accessed Dec. 2023 3 https://www.usgs.gov/programs/landslide-hazards/science/real-time-monitoring-potential-landslides, accessed Dec. 2023.

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particularly wet winters; others occurred in response to strong ground shaking during an earthquake.

Some of the costlier or most damaging landslides reported in the region and in the Santa Monica area are summarized below.
1956 Portuguese Bend Landslide, Palos Verdes
Cost: $14.6 million (2000 dollars; ~$26 million in 2023 dollars), on California Highway 14 in the Palos Verdes Hills. The Portuguese Bend landslide is a reactivated ancient slide that began its modern movement in August 1956, when displacement was noticed at its northeast margin.

Reactivation is blamed in part to human activity, including the extensive use of septic tanks and seepage pits for residential structures. Movement gradually extended downslope so that the entire eastern edge of the slide mass was moving within six weeks. By the summer of 1957, the entire mass was sliding towards the sea.
1969 Glendora, Los Angeles County
Cost: $26.9 million (2000 dollars; ~$50.3 million in 2024 dollars). The winter of 1969 was one of the wettest on record in the southern California area. The rain caused many of the streams draining the San Gabriel Mountains to overflow, resulting in debris flows that damaged 175 houses in the Glendora area alone.
1977-1978 Monterey Park, Baldwin Hills and Repetto Hills, Los Angeles County
Cost, >$14.6 million (2000 dollars; >~$27 million in 2024 dollars); 100 houses damaged due to debris flows; at least 3 people died; more than 300 evacuated from their apartment building and many more displaced from their homes in Culver City3F
4 .
1978 Bluebird Canyon, Orange County
Cost: $52.7 million (2000 dollars; ~$98.3 million in 2024 dollars); 60 houses destroyed or damaged.

On October 2, 1978, a portion of the Bluebird Canyon slope gave way, in great part due to the unusually heavy rains in March that may have contributed to initiation of the landslide. Although the 1978 slide area was approximately 3.5 acres, it is suspected to be a portion of a larger, ancient landslide.
1979 Big Rock, Los Angeles County
Cost: approximately $1.08 billion (2000 dollars; ~$2.02 billion in 2024 dollars); rockslide that caused damage to California Highway 1 (Pacific Coast Highway) in the Malibu area. High groundwater levels attributed to the use of septic tanks is considered a leading cause of this landslide. 1980 Southern California Landslides
Cost: $1.1 billion in damage (2000 dollars; ~$2.06 billion in 2024 dollars). Heavy winter rainfall in 1979-80 caused damage in six southern California counties. A sequence of five days of continuous rain that started on February 8 dropped more than 7 inches of water by February 14. Slope failures began to develop by February 15 and then very high-intensity rainfall occurred on February 16. As

4 https://www.nytimes.com/1978/03/05/archives/mudslides-kill-three-on-coast-as-hundreds-flee-homesdomestic.html, accessed Dec. 2023.

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much as 8 inches of rain fell in a 6-hour period in many locations. 1978-1979, 1980 San Diego County
San Diego County experienced major damage from storms in 1978, 1979, and 1979-80, as did neighboring areas of Los Angeles and Orange Counties. One hundred and twenty landslides were reported to have occurred in San Diego County during these two years. Rainfall for the rainy seasons of 1978-79 and 1979-80 was 14.82 and 15.61 inches respectively, compared to a 125-year average (1850-1975) of 9.71 inches. Significant landslides occurred in the Friars Formation, a geologic unit known to be slide-prone. [Of the nine landslides that caused damage in excess of $1 million (2000 dollars; ~$1.87 million in 2024 dollars) in the northern part of San Diego County, seven occurred in the Friars Formation, and two in the Santiago Formation.] 1983 San Clemente, Orange County
Cost: $65 million (2000 dollars; ~$121.5 million in 2024 dollars), California Highway 1. Litigation associated with this landslide ultimately cost approximately $43.7 million (2000 dollars; $81.7 million in 2024).
1983 Big Rock Mesa, Malibu, Los Angeles County
Cost: $706 million (2000 dollars; ~$1.32 billion in 2024 dollars) in legal claims; 13 houses condemned and 300 more threatened due to rockslide triggered by intense rainfall. 1994 Northridge Earthquake Landslides
As a result of the magnitude 6.7 Northridge earthquake, more than 11,000 landslides occurred over an area of 10,000 km2
. Most landslides occurred in the Santa Susana Mountains and in mountains north of the Santa Clara River Valley. The landslides destroyed dozens of homes, blocked roads, and damaged oil-field infrastructure. Several landslides were reported in the bluffs along PCH in Santa Monica, Pacific Palisades and Malibu4F
5 .
1995 Los Angeles and Ventura Counties Landslides
Cost – undetermined yet, but most likely in the billions, including litigation. Above-normal rainfall in March triggered damaging debris flows, deep-seated landslides, and flooding. Several deep-seated landslides were triggered by the storms, the most notable being the La Conchita landslide, which in combination with a local debris flow, destroyed or badly damaged 14 homes in the small town of La Conchita, about 20 km west of Ventura. There also was widespread debris-flow and flood damage to homes, commercial buildings, and roads and highways in areas along the Malibu coast that had been devastated by wildfire two years before.
2003-Present Del Mar Bluff Stabilization, San Diego County The Los Angeles-San Diego-San Luis Obispo (LOSSAN) rail corridor is the only rail connection between San Diego and the rest of the state and nation. The economy depends on this connection for both passenger and freight transport, but landslides, rapid erosion, and seismic activity have caused collapses along the Del Mar Bluffs. San Diego Association of Governments is working with the North County Transit District (NCTD) to stabilize the Del Mar Bluffs to maintain the integrity of

5 https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=ae120962f459434b8c904b456c82669d; accessed December 5, 2023.

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both the rail line and the surrounding area. Since 2003, the first four phases of the stabilization project have been completed and have identified the funding needed to complete the final two phases. In Phase 5, existing structures will be repaired and additional supports to stabilize the bluffs will be installed. Phase 5 began in 2024, is anticipated to last through 2026, and will cost approximately $88 million, funded through a combination of state, federal, and local sources. 2005 La Conchita Landslide, Ventura County
Cost – undetermined yet, but most likely in the billions, including litigation. On January 10, 2005 a landslide struck the sea-side community of La Conchita destroying 13 homes, severely damaging 23 others, and killing 10 people. The landslide occurred in an area known for prior landslide activity (more recently in 1995), and was the direct result of intense rainfall in the area, compounded by weak sediments and steep slopes. The landslide material failed almost simultaneously, and descended down the slope as a highly fluid, rapidly moving debris flow, with top speeds estimated at 30 feet per second (Jibson, 2005, 2006).
2005 Blue Bird Canyon Landslide, Laguna Beach, Orange County Cost – undetermined yet, but probably in the billions, in great part due to litigation. On June 1, a landslide began moving in the area, almost certainly in response to the extremely wet winter rains earlier that year, in January and February. This landslide occurred in the same general area as the 1978 landslides. Seventeen houses were destroyed, 11 were damaged, and another 23 were threatened. Fortunately, no one died or was seriously hurt. 2018 Montecito Landslide, Santa Barbara County
Cost – undetermined yet, but most likely in the billions. Early on the morning of January 9, 2018, mudflows struck Montecito, which had been affected by the 2017 Thomas Fire, and other areas of Santa Barbara County. An estimated 0.5 inches of rain fell within a five-minute period at approximately 3:30 a.m. causing mud and boulders from the Santa Ynez Mountains to flow down creeks and valleys into Montecito. The debris flows that impacted the lower areas of Montecito. were up to 15 feet high, included mud, boulders and tree branches, and moved at estimated speeds of up to 20 miles per hour. The mudflows resulted in 23 confirmed deaths, and more than 150 people were hospitalized with various injuries, including four in critical condition. The mudflows destroyed over 100 homes, damaged an additional 300, and blocked Highway 101 for months. 2021-2023 San Clemente Landslides, Orange County
On September 15, 2021, waves crashing over the rails damaged the train tracks in San Clemente.

The rail segment had to be shut down through October 3, 2021. Then, on September 29, 2022 the segment was again closed to passenger traffic due to soil movement; freight traffic continued at lowered speeds. Rocks were added after each incident to protect the slope from wave action and the passenger rail traffic stop continued as anchors were being placed into bedrock. The line fully reopened in April 2023, but rail service was soon halted again, this time two miles to the north.

Falling debris did not damage the tracks but ground movement continued from a landslide involving Casa Romantica on the bluff above. During the work closures, freight trains were able to resume at a speed of 10 miles per hour with officials onsite determining when it was safe to proceed. Full service resumed in late May 2023 but was halted indefinitely again in early June 2023. Orange County Transportation Authority (OCTA), which owns the section of track, declared an emergency on June 12, 2023 to speed up construction of a temporary barrier wall at the bottom of the slope.

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Service resumed on July 19, 2023.
2023 Rolling Hills Estates Landslide, Los Angeles County Cost – undetermined yet, but expected to be in the millions of dollars. Homes in a canyon were destroyed when the ground shifted on the northern side of Los Angeles County's Palos Verdes Peninsula. A landslide forced the evacuation of at least 12 homes in Rolling Hills Estates, where houses and garages cracked and crumbled in a canyon area. Deputies were sent to patrol the evacuated neighborhood, where about 16 people were displaced. 2023 Santa Monica Bluff Stabilization Emergency Work, Los Angeles County In July 2023, the City of Santa Monica mitigated an unstable portion of the Santa Monica Bluffs located just above the Pacific Coast Highway (PCH), between the California Incline and the northbound on-ramp to Moomat Ahiko Way. A portion of the bluff had a large crack that likely formed in response to the intense rains that occurred in the region in December 2022-January 2023.

The block of sediment that had separated from the main escarpment was proactively removed to ensure traffic safety and uninterrupted vehicle movement on PCH. The bluff removal was completed on July 26, 2023.

LANDSLIDE HAZARD ASSESSMENT FOR SANTA MONICA
Hazard Identification
Identifying hazardous locations is an essential step towards implementing more informed mitigation activities. Landslide deposits of Holocene and possibly latest Pleistocene age covering areas greater than about 12 acres (50,000 square meters) have been mapped north of the city of Santa Monica, on the landward side of PCH, within and north of the area covered by Figure 9-2 (the landslides mapped within the area covered by the map are shown in bright yellow). These large landslides in the Pacific Palisades and Malibu areas generally occur where siltstone and claystone beds in the marine units at the base of the cliffs dip out of slope. These failures are often translational slides that involve larger masses of material.

Smaller landslides and mudflows too small for the scale of Figure 9-2 have been reported along the coastal bluffs in Santa Monica proper as a result of both the 1994 Northridge earthquake and various intense rainfall events5F
6 , including the 1998 El Niño storms. Although not reported in the literature, slope failures are also likely to have occurred adjacent to the canyons that border the city on its northern side. These areas have steep slopes with gradients exceeding 40 degrees, and locally even nearly vertical (see red areas shown on Figure 9-4). These slopes are susceptible to both erosion and slope failure.

6 https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=ae120962f459434b8c904b456c82669d; accessed on December 5, 2023.

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Figure 9-4: Slope Distribution Map for Santa Monica and Adjoining Areas The smaller landslides that have occurred on the 50- to 150-foot-high, west- to southwest-facing coastal bluffs are typically generated from the horizontally bedded, Pleistocene, uncemented to slightly cemented sandy to gravelly alluvial fan materials that comprise most of the cliff face. Slope damage in these materials is often the result of increased pore water pressures following periods of heavy precipitation or over-irrigation. Blocks of these deposits locally separate from the larger mass and fail as block slides, or topples. If saturated as a result of intense winter rains, some sections may also fail as mudslides. Given the height of the bluffs and their exposure to the elements, localized slope failures of these materials can be expected to occur sporadically. As mentioned previously, in the historical landslide discussion, portions of the bluffs have also failed historically in response to strong ground shaking (see the entry for the 1994 Northridge earthquake). Areas susceptible to significant, potentially costly or damaging slope failures are shown in red on Figure 9-5.

The underlying marine deposits consist of bluish gray clay and fine sand. Coastal storms characterized by strong winds, high waves, and significant runoff can be locally damaging to the base of the bluffs, although in the Santa Monica area, PCH and the structures west of the road generally serve as a buffer between the waves and the bluffs. Landslide deposits, regardless of

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whether related to surficial or deep-seated failures, tend to be friable, susceptible to settlement and additional slippage, and thus do not make acceptable foundation materials.

Small surficial slope failures may also occur in other parts of the city with topographic relief. As discussed above, slope steepness has a strong influence on the development of flows, with most failures occurring on slopes with gradients of between about 20 and 56 degrees, and a large percentage of debris flows occurring on slopes between 20 and 36 degrees (Campbell, 1985; Morton et al., 2003). Slopes with gradients between 26 and 40 degrees are shown in yellow on Figure 9-4, and slopes with gradients between 10 and 26 degrees are shown in green. Based on this slope distribution map, there are several areas in Santa Monica where surficial slope failures in the form of flows, slips and soil creep could occur. These areas include slopes flanking the I-10 freeway, slopes flanking the southern and southwestern portions of the Santa Monica Airport, several slopes in the south side of the city between Ashland Avenue and Dewey Street, and slopes on the flanks of Brentwood Knoll. The slopes that may be susceptible to surficial failures are identified in light green on Figure 9-5.

Although several of these slopes are either hardscaped or landscaped, some sections expose soils at the surface, and if these deposits become very wet, they could experience slope creep or soil slips.

Surficial slope failures may also develop when concentrated runoff erodes the surficial deposits and creates rills on the slope faces that, if left unchecked, can eventually become soil flows, earth flows or debris flows. These areas, and small backyard slopes not shown on Figure 9-5, if not properly maintained, and especially if impacted by burrowing animals such as ground squirrels and voles, could experience small-scale failures following strong winter storms. This hazard can be mitigated, or at least managed, if the slopes are well maintained and surface runoff is diverted and not allowed to pool at the top of slopes.

Areas within and near the city of Santa Monica that could experience mudslides and debris flows include the canyons along and immediately north of the city, including Santa Monica Creek and Rustic Creek canyons. These areas may be particularly susceptible to this hazard if the areas upslope burn as a result of a wildland fire.

Santa Monica is for the most part built out, and new developments typically occur in previously built lots where the older structures are demolished and replaced with new buildings. These infill projects require that the soils be tested for their geotechnical properties, with geotechnical reports describing the analyses submitted to the City for approval before construction can begin. This, in addition to standard-of-practice construction practices, limits the likelihood of landslides occurring as a result of modifications to the terrain during construction.

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Figure 9-5: Areas in Santa Monica Susceptible to Slope Failure Vulnerability and Risk
A vulnerability assessment for landslides can help predict how different types of property or infrastructure and population groups will be affected by the hazard of unstable slopes. As mentioned in previous sections, some of the most important factors defining the hazard of slope instability include slope height, slope steepness, sheer strength, and orientation of weak layers in the underlying geologic units, as well as pore water pressures. The slope map for Santa Monica presented on Figure 9-4 is based on data obtained in 2002-2003, and is thus representative of areas in the city previously modified by grading. The slopes identified, together with historical data on previous slope failures, was used to develop Figure 9-5, which shows those areas in the city most likely to be impacted by slope failures. These data in turn can be used to assess the population and approximate total value of the properties and infrastructure at risk from future landslide occurrences.

As mentioned above, landslides have occurred and are likely to continue to occur along the bluff areas on the west side of Palisades Park, and further north, along Pacific Coast Highway in the Pacific

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Palisades and Malibu areas. In Santa Monica, the bluffs and the land immediately adjacent to the bluffs are part of Pacific Palisades Park and thus managed by the City. There is only one structure near the bluffs that could be impacted by slope failure. This structure is the City of Santa Monica Camera Obscura Art Lab, a facility that houses Santa Monica’s historical Camera Obscura artifact and serves as a community arts education center. The structure is located in Palisades Park near the intersection of Broadway and Ocean Avenue. Otherwise, at the bottom of the bluffs, the existing private properties are separated from the slope face by PCH, so damage to these structures is expected to be minor, if any.

Failures of the bluffs pose a hazard primarily to PCH and, if they occur suddenly, to motorists using PCH and the incline descending into and ascending from PCH. The probability of slope failure onto PCH is low, but the risk to limb and life is moderate to high given that this is a major route with significant traffic. Even if no one is physically harmed by a slope failure, sections of PCH would have to be closed to through-going traffic while cleanup of debris is ongoing. The resulting delays, detours, or right-out closures would pose significant socio-economic impacts to Santa Monica residents, and the residents of other communities served by this section of PCH. Significantly, however, a partnership between the California Department of Transportation and the City of Santa Monica facilitated the California Incline Bridge Replacement Project. This $17 million project was completed in September 2016 and included the construction of a new seismically upgraded vehicular bridge that includes a shared pedestrian/bicycle path. The construction project included the installation of 1,000 soil nails6F
7 to stabilize that section of the bluffs.

Moreover, given the potential impacts to the community and most importantly, the transportation network, the City monitors these slopes on an on-going basis, and over the years has implemented a variety of mitigation measures, such as the one discussed above, aimed at reducing the hazard of slope failure along the coastal bluffs in Pacific Palisades Park. These measures include capturing and re-directing surface runoff away from the bluff face to prevent erosion of the bluffs and limit infiltration of water into the underlying units. The area next to the bluffs with these special runoff considerations is shown on Figure 9-5. To supplement this effort, in 2010 the City retained a contractor who drilled horizontal subdrains (called hydraugers) into the bluff face; the drains capture groundwater that may collect at the boundary between highly permeable and less permeable geologic units, with the overall goal of reducing pore water pressures in the sediments that form the bluffs. In 2012, sections of the park were also re-graded to prevent surface water from flowing over the edge of the cliff and down the bluff face. If unstable slope sections are identified, the City conducts emergency work to remove the unstable section and stabilize the surrounding slopes. This was done most recently in July 2023, when a section of the bluff between the California Incline and Moomat Ahiko Way on-ramp to PCH was found to have destabilized, most likely in response to the 2022-2023 wet winter. As of late 2023, the City had just retained a geotechnical consultant to provide maintenance recommendations for the hydraugers that were installed in 2010.

The limited historical landslide damage elsewhere in Santa Monica is likely attributable to land development fundamentals that have been practice in southern California since the 1950s, including stricter hillside grading ordinances, sound project design that avoids severely hazardous areas, soil engineering practices that include detailed preliminary investigations and oversight during grading,

7 Soil nailing is a well-established remedial construction measure that uses relatively slender reinforcing elements (such as rebar) inserted into holes drilled into to slope and then grouted into place. Sometimes concrete or shotcrete is applied on the slope face. Alternatively, a mesh may be placed against the slope face, secured to the soil beneath the nail head plates.

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and effective agency review of hillside grading projects. Geotechnical review of all proposed new development and re-development projects should be continued.

Nevertheless, and although potential future slope failures in Santa Monica are anticipated to impact relatively small areas, the dollar loss could be high (in the tens of thousands to hundreds of thousands of dollars) if structures are damaged. Since insurance policies typically do not cover landslide damage and homeowners in the areas likely to be impacted by these localized soil slips are likely to not have flood insurance, slope failures can cause both an economic and emotional burden to property owners in the failure area. Moreover, even if a slope failure does not impact adjacent properties, the visual impact of a ruined slope can cause alarm among adjacent homeowners and can impact property values.

For these reasons, mitigation measures designed to prevent or reduce the impact of potential slope failures should be considered on an on-going basis. There are numerous methods for mitigating slope instability; selecting the most appropriate method for a given area should take into account the local geological conditions, safety needs, type and cost of construction repair, and aesthetics.

Any and all measures implemented to reduce the potential for erosion and slope failure need to be monitored regularly to ensure that they are performing as intended.

SUMMARY OF COMMUNITY LANDSLIDE ISSUES
What is Susceptible to Landslides?
The city’s hillsides are vulnerable to the types of slope instability mentioned above. Specifically, the steep-sided coastal bluffs and slopes along deeply incised drainages may be locally susceptible to slope instability in the form of block slides, topples and mudslides. This assessment is backed by historical data that show that if a landslide occurs along the coastal bluffs, communities served by PCH, including Santa Monica, would suffer immediate damages and loss of service. Specifically, the California Incline road leading to PCH is flanked by terrain that in the past has experienced landslide activity, and where the slope instability susceptibility is mapped as high. During an earthquake, or as a result of intense and/or protracted rainfall, the road could be impacted by slope failures. Less steep and lower slopes elsewhere in the city could locally experience surficial slope failures following intense or protracted rainfall events, especially if surface runoff is not managed correctly. The slope failures more likely to occur in these areas are of the soil slip, earth flow or debris flow variety.

Factors included in assessing landslide risk include population and property distribution in the hazard area, the frequency of landslide or debris flow occurrences, slope steepness, soil characteristics, and precipitation intensity. This type of analysis could generate estimates of the damages to the city due to a specific landslide or debris flow event, however, predicting the location, timing and size of a landslide is still not possible with the scientific methods currently available7F 8 .

Furthermore, there is little to no data regarding the economic costs of landslides in the United States that can be used to make valid predictions as to what a landslide event could cost in the future. The available data do suggest that the indirect costs associated with landslides, which include the closure of impacted transportation routes, are thought to exceed the direct costs by a factor of two or more8F 9 .

8 https://pubs.usgs.gov/of/2022/1075/ofr20221075.pdf, pg. 5, accessed on Dec. 10, 2023. 9 https://pubs.usgs.gov/of/2022/1075/ofr20221075.pdf, pg. 11, accessed on Dec. 10-14, 2023.

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A generalized review of the potentially unstable slope areas in the city, as shown on Figures 9-4 and 9-5, and comparison with the location of the City’s critical/essential facilities (Plate H-4) shows that most of the essential facilities in the city are not located in an area susceptible to slope instability.

The only exceptions are Fire Station 7, located at 1100 Pacific Coast Highway, and Mt. Olivette and Riviera reservoirs. These facilities may not be damaged by the potential slope failures, but access to or from these facilities may be obstructed. This in turn would impact emergency services from Fire Station 7, and water distribution services from the reservoirs. The economic and societal cost of these scenarios has the potential to be substantial, but currently unquantifiable. However, the City of Santa Monica has redundancies, with several additional fire stations and water storage reservoirs available to draw from in the short term.

Closures (which would require detours around the region) or limited access (with consequential delays) on PCH, have the potential to cause major disruption to emergency services, especially the mobilization of people in need of emergency services to the local hospitals. Therefore, inspection and repair of critical transportation facilities and routes is essential and should receive high priority.

Both PCH and the I-10 freeway are also designated as potential evacuation routes (Plate H-5), so slope failures along these roadways could have an impact on evacuations if the slope failures were the result of, or coincided with another natural disaster that prompted the evacuation of some portions of the city. An example of this kind of cascade scenario would be an earthquake on the offshore section of the Palos Verdes fault that causes a tsunami and slope damage along PCH, resulting in PCH being too damaged to serve as an evacuation route for people attempting to reach higher ground in advance of the tsunami. This low-probability but high-risk scenario has the potential to result in hundreds to thousands of injuries and deaths.

Future landslides along the coastal bluffs and other slopes in the city could affect not only the transportation system, but utility services and critical lifelines. Utilities, including potable water, wastewater, telecommunications, natural gas, and electric power are all essential to service community needs. Loss of electricity has the most widespread impact on other utilities and on the whole community. Natural gas pipes may also be at risk of breakage from landslide movements as small as an inch or two. Ideally, lifelines and utility services should remain operational during and following a natural hazard event. For this reason, slope areas showing signs of erosion should be mitigated before the next significant storm, to reduce the potential for damage to not only private property, but infrastructure and lifelines.

Landslide Mitigation Activities
Landslide mitigation activities include current mitigation programs and activities that have been implemented by the City, in addition to developers, residents, and State agencies (such as Caltrans).

All proposed development and redevelopment projects require a site-specific geotechnical evaluation of any slopes that may impact the future use of the property. This includes existing slopes that are to remain, and any proposed graded slopes. The investigation typically includes borings to collect geologic data and soil samples, laboratory testing to determine soil strength parameters, and engineering calculations. Numerous soil-engineering methods are available for stabilizing slopes that pose a threat to development. These methods include designed buttresses (replacing the weak portion of the slope with engineered fill); reducing the height of the slope; designing the slope at a flatter gradient; and adding reinforcements such as soil cement or layers of geogrid (a tough polymeric net-like material that is placed between the horizontal layers of fill). Most slope stabilization methods include a subdrain system to remove excessive ground water from the slope area, such as the system implemented by the City along the Pacific Palisades Park. If it is not feasible

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to mitigate the slope stability hazard, building setbacks are typically imposed.

There are numerous methods for mitigating block slides and topples. Choosing the best method depends on the geological conditions (i.e., slope height, steepness, fracture spacing, bedding orientation), safety, type and cost of construction repair, and aesthetics. A commonly used method is to regrade the slope, a mitigation measure that Santa Monica has also employed in the past along the coastal bluffs. This ranges from locally trimming hazardous overhangs, to completely reconfiguring the slope to a more stable condition, possibly with the addition of benches to catch small rocks. Another group of methods focuses on holding the fractured rock or sediments in place by draping the slope with wire mesh, or by installing tensioned rock bolts, tie-back walls, or even retaining walls. Shotcrete is often used on slope faces to prevent raveling in highly fractured rock, but its primary purpose is to offer surface protection only. A third type of mitigation includes catchment devices at the toe of the slope, such as ditches, walls, or combinations of both. Designing the width of the catchment structure requires analysis of how the rock or sediments will fall. For instance, the slope gradient and roughness of the slope determines if rocks will fall, bounce, or roll to the bottom. Rock slope stabilization may also include the addition of drains in order to reduce water pressure within the slope (Wyllie and Norrish, 1996).

For debris flows, assessment of this hazard for individual sites should focus on structures located or planned in vulnerable positions. This generally includes canyon areas; at the toes of steep, natural slopes; and at the mouth of small to large drainage channels. Mitigation of soil slips, earthflows, and debris flows is usually directed at containment (debris basins), or diversion (impact walls, deflection walls, diversion channels, and debris fences). A system of baffles may be added upstream to slow the velocity of a potential debris flow. Other methods include removal of the source material, placing subdrains in the source area to prevent pore water pressure buildup, or avoidance by restricting building to areas outside of the potential debris flow path.

There are a number of options for management of potential slope instability in developed hillsides.

1. Complete a detailed survey and assessment of existing developments in areas recognized to be vulnerable to potential slope failures (like the bluffs along Pacific Palisades Park).

2. Protect existing development and population where appropriate by physical controls such as drainage, slope-geometry modification, protective barriers, and retaining structures.

3. Implement monitoring or warning systems. For instance, in some recently burned watersheds, the USGS, in cooperation with the National Weather Service, installs and operates a system for real-time warnings for storm-related slope failures. Using a combination of tracking storm systems, measuring actual rainfall with a network of rain gauges, and comparing thresholds for the initiation of debris flows, they are able to issue Flash Flood/Debris Watches during the most intense storms, as necessary. This would be most appropriate for the canyons along Santa Monica Creek and Rustic Creek if the slopes above burned during a wildland fire.

4. Post warning signs in areas of potential slope instability.

5. Encourage homeowners to use landscaping methods that help stabilize the hillsides.

6. Incorporate recommendations for potential slope instability into geologic and soil engineering reports for additions and new grading.

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7. Educate the public about slope stability, including the importance of maintaining drainage devices. USGS Fact Sheet FS-071-009F
10 (May, 2000) and the CGS Note 3310F11 (November,
2001) provide public information on landslide and mudslide hazards.

LANDSLIDE RESOURCE DIRECTORY
City Resources
City of Santa Monica Community Development Department
1685 Main Street
Santa Monica, California 92660
Ph: 310-458-2275
County Resources
Los Angeles County Department of Regional Planning
320 West Temple Street
Los Angeles, CA 90012
Ph: 213-974-6411
State Resources
California Geological Survey, Southern California Regional Office 320 W. 4th Street, Suite 850
Los Angeles, CA 90013
Ph: 213-239-0877
California Geological Survey, Headquarters
801 K Street, MS 12-30
Sacramento, CA 95814
Ph: 916-445-1923
California Division of Forestry, Headquarters
1416 9th Street
PO Box 944246
Sacramento, CA 94244-2460
Ph: 916-653-5123
California Department of Water Resources
1416 9th Street
Sacramento, CA 95814
Ph: 916-653-6192
Flood Operations Center Ph: 800-952-5530

10 https://pubs.usgs.gov/publication/fs07100 11 https://www.conservation.ca.gov/cgs/Pages/Publications/Note_33.aspx

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Governor’s Office of Emergency Services (Cal OES)
3650 Schriever Avenue
Mather, CA 95655
Ph: 916-845-8510; Fax: 916-845-8511
www.caloes.ca.gov
California Department of Transportation (Cal Trans) – District 7 100 South Main Street
Los Angeles, CA 90012
Ph: 213-897-3656
Federal Resources and Programs
Federal Emergency Management Agency (FEMA) – Region IX
1111 Broadway, Suite 1200
Oakland, CA 94607-4052
Ph: 510-627-7100
Southern California Field Office Ph: 626-851-7900
Natural Resource Conservation Service (NRCS)
National Water and Climate Center
1201 NE Lloyd Boulevard, Suite 802
Portland, OR 97232-1274
Ph: 503-414-3031
US Geological Survey, National Landslide Information Center Mail Stop 966, Box 25046
Denver Federal Center
Denver, CO 80225
Ph: 800-654-4966 or 303-273-8588
National Oceanic and Atmospheric Administration
National Weather Service
San Diego Weather Forecast Office
11440 W. Bernardo Court, Suite 230
San Diego, CA 92127
Ph: 858-675-8700
Publications
(for References, Refer to Appendix I)
Godt, J.W., Wood, N.J., Pennaz, A.B., Dacey, C.M., Mirus, B.B, Schaefer, L.N., and Slaughter, S.L., 2022, National strategy for landslide loss reduction: U.S. Geological Survey Open-File Report 2022–1075, 36 p., https://doi.org/10.3133/ofr20221075 (available at https://pubs.usgs.gov/publication/ofr20221075).

Strategy document that describes goals and actions that can help reduce the United States’ risk

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from landslide hazards un equitable and effective ways. Publication also includes several additional recent references and links to websites on landslide hazards.

Olshansky, Robert B., 1996, Planning for Hillside Development: American Planning Association.

This document describes the history, purpose, and functions of hillside development and regulation and the role of planning, and provides excerpts from hillside plans, ordinances, and guidelines from communities throughout the US.

Olshansky, Robert B. and Rogers, J. David, 1987, Unstable Ground: Landslide Policy in the United States: Ecology Law Quarterly.

This report discusses the history and policy of landslide mitigation in the US.

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SECTION 10: WILDFIRES & URBAN FIRES
WHY ARE FIRES A THREAT TO THE CITY OF SANTA MONICA?
Although, historically, Santa Monica has not experienced a wildfire within its limits, the city is bordered to the north by natural areas that have burned in the past and could burn again in the future. Moreover, recent past wildfires in California, including the devastating January 2025 fires in the Los Angeles region, have shown that wildfires can easily spread into developed areas, especially when wildfires burn at or near the wildland-urban interface0F 1 (WUI), with ignited structures then
sustaining and transmitting the fire from one building to the next.

As will be discussed further in this section, one of the reasons wildfires have become more destructive and deadly in recent years is the expansion of the WUI, which exposes an increasingly larger number of people and property to this hazard. Moreover, the scale, frequency, and intensity of wildfires in California has increased in the last two decades and is expected to continue to increase due to climate change, with wildland fires in turn impacting and driving climate change.

Notably, the smoke from wildfires increases air pollution levels, emitting massive quantities of carbon dioxide and other substances into the atmosphere that add to the region’s greenhouse gas emissions (see Section 11), and can create a significant health risk in the impacted area and areas down-wind impacted by the fire-generated smoke and ash.

This section also discusses structure fires not associated with wildfires, and structure fires that develop following an earthquake. The section discusses these hazards in general terms first, and then provides an assessment, based on historical data and recent trends, of the likelihood of this hazard impacting the city of Santa Monica. Mitigation actions that the City has implemented over the years to reduce its fire hazard, and activities that could be implemented by the City and property owners are also addressed.

WILDFIRES
What are Wildfires?
Wildfires or wildland fires are fires that burn in natural areas, such as woodlands, forests, or grasslands. Wildland fire is a natural process and often a necessary part of the natural ecosystem in the western United States, including southern California. Many native plants require periodic burning to germinate and recycle nutrients that enrich the soils, and have a high oil content that makes them highly flammable. For example, some of the chaparral plants native to and common in the area, such as ceanothus, have heat-resistant seeds that sprout only after being exposed to fire.

Similarly, closed-cone coniferous trees have seed cones that only open after being exposed to heat.

The seeds themselves are protected by a thick coat of resin that insulates them. When the cones open, the seeds are released onto the ground, where they are more likely to sprout on rich, ashcovered soil that has been cleared of underbrush. Other native plants have fire-resistant roots that allow them to re-sprout quickly in recently burned areas.

These plant adaptations have developed over millennia in response to the region’s weather.

Specifically, the typically mild, wet winters characteristic of southern California’s Mediterranean climate result in an annual growth of grasses and plants that dry out during the hot summer months.

1 The area in between or consisting of a mix of urban and wildland zones.

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This dry vegetation then provides fuel for wildfires in the autumn, when the area is intermittently impacted by Santa Ana winds, the hot, dry winds that blow across the region predominantly in the late fall (see Section 11). These winds often fan and help spread wildland fires. It is important to note that wildfires in unpopulated areas are typically not considered a hazard unless the smoke and ash spread to populated areas, or the erosion following the fire silts up and impacts reservoirs used to store drinking water or generate hydroelectric power.

Wildfire Causes
Wildfires are typically caused either by lightning or by human actions. Lightning has been a significant cause of wildland fire in the western United States with approximately 44% of the wildfires in the region between 1992 and 2015 attributed to lightning strikes. Furthermore, these lightning-caused fires were responsible for 71% of the total area burned (Schartz and Penney, 20201F
2 ). These percentages vary, however, depending on several factors such as weather patterns, vegetation density, accessibility, and closeness to cities and towns. Thus, in California alone (rather than the entire western United States), for the period between 2010 and 2022, only about 14% of the wildland fires were caused by lightning, with human causes accounting for the remaining percentage. Moreover, in Los Angeles County, during this same time period, only 4% of the fires were caused by lightning, with humans being responsible for the remaining 96%. These data, compiled and graphed by Short (20222F
3 ) and published in the Wildfire Risk to Communities
webpage, are shown on Figure 10-1.

The more common human-caused fires are the result of a variety of accidental, intentional, or malicious activities. These include sparks from brush-clearing equipment and vehicles; improperly maintained or abandoned campfires; improperly disposed cigarettes; people (often children) misusing fire (such as matches or cigarette lighters); fireworks; firearms and explosives use; issues with power generation, transmission or distribution equipment; and arson (see categories on Figure 10-1). Downed or arcing power lines generally occur in response to strong winds, which is why electric utilities now often turn off power to high-risk areas during strong wind events (referred to as Public Safety Power Shutoffs, or PSPSs).

Figure 10-1 also shows that a large percentage of human-caused fires are categorized as undetermined, meaning that the post-fire investigation was inconclusive. Some of these fires may be the result of arson. Other causes that may be difficult to determine include the spontaneous combustion of oil-soaked rags, compost, manure piles, or baled hay; electrical charges from electrical fences surrounded by dry, flammable vegetation; refraction and magnification of sun rays by glass windows and mirrors; and embers associated with structural fires. Recently, a machinelearning model developed to predict the wildfire ignition cause based on physical, biological, social and management attributes of the fires was used to interpret the cause of more than 150,000 wildfires that occurred in the western United States between 1992 and 2020. The model attributed 21% of

2 Schwartz, J. and Penney, V., 2020, In the West, Lightning Grows as a Cause of Damaging Fires: The New York Times, article published Oct. 23, 2020; available from
https://www.nytimes.com/interactive/2020/10/23/climate/west-lightning-wildfires.html. 3 Short, K.C., 2022, Spatial wildfire occurrence data for the United States, 1992-2020 [FPA_FOD_20221014], 6th Edition: Forest Service Research Data Archive, Fort Collins, CO; available from https://doi.org/10.2737/RDS-2013- 0009.6.

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the fires to equipment and vehicle use, 20% to lightning, 18% to arson and incendiarism3F 4 , and 15%
to debris and open burning.4F
5 Figure 10-1: Wildfires Causes for the Period 2010-2020 in California (top) and in Los Angeles County (bottom) [From Short, 2022] As mentioned above, equipment and vehicle use are one of the leading causes of fires in California and Los Angeles County. A large number of fires are assigned to this category because this grouping includes a wide range of vehicles and equipment, from large construction rigs (bulldozers, tractors), to small equipment such as welders, grinders, chain saws and generators. Typically, these fires are the result of mechanical or electrical malfunction or failure of the equipment, but they can also be the result of misuse or carelessness, such as dragging chains or metal objects in rocky or hard terrain, causing sparks that then ignite vegetation. Vehicular collisions, flat tires, spillage of fuel during refueling operations, and driving vehicles across dry vegetation can also result in wildfires5F 6 .

Other significant causes of wildfires are burning piles of debris in the open (such as yard debris, open trash burning, and land clearing), and campground fires that are either improperly contained or improperly extinguished. An open fire can escape in a matter of minutes if not attended properly, if the area around the burn has not been cleared appropriately, and/or if fire suppression tools or equipment (such as shovels, water hoses or water pumps) are not available to immediately put out

4 Both arson and incendiarism refer to fires started intentionally, but arson refers to setting property on fire for the purpose of causing damage. Fires started by persons experiencing homelessness for the purposes of cooking and/or keeping warm likely fall under the incendiarism category. 5 Pourmohamad, Y., Abatzoglou, J.T., Fleishmna, E., Short, K.C., Shuman, J., AghaKouchak, A., et al. 2025, Inference of wildfire causes from their physical, biological, social and management attributes: Earth’s Future, Vol. 13, paper e2024EF005187, doi:10.1029/2024EF005187. 6
https://www.nifc.gov/fire-information/fire-prevention-education-mitigation/wildfire-investigation

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any flying embers. Open burns and campground fires should never be started in windy, dry conditions.

Arson is the fourth leading cause of wildland fires in California, and the third leading cause in Los Angeles County (Figure 10-1). Arson is the malicious or deliberate act of setting property or public lands on fire with the intent to cause damage or defraud. Under California Penal Code, arson is a crime punishable with imprisonment in jail. The arsonist may also be held responsible for all costs related to the suppression of the fire, damages incurred, and rehabilitation of the burnt land.6F 7 History of Wildfires Near Santa Monica and In Southern California As mentioned above, large fires have been part of the southern California landscape for millennia.

Based on oral histories, it is known that Indigenous peoples in California relied on fire to reduce fuel load and improve their ability to hunt and forage.7F
8 Stephens et al. (20078F9
) used ethnographic studies,
combined with dendrochronology analyses and other data on fire history, to estimate that before the 1800s, between about 4.5% and 12% of the state burned every year as a result of both lightninggenerated wildfires and fires set by Indigenous groups.

The first wildfire in the official historical record of wildfire statistics in Los Angeles County dates to September 1878. The fire reportedly burned the San Rafael Hills, a large section of the Verdugo Hills and into the Sierra Madre Mountains. The actual extent of the fire is unknown, and the data available suggest that there were several burns rather than one massive fire. Another series of burns that were erroneously grouped together and presented as the largest fire in Orange County’s history occurred in September 1889. These fires appear to have been confined to two main but separate areas, namely the foothills of the Santa Ana Mountains in what is now the city of Orange, and the Rancho Santa Margarita area in northern San Diego County.9F
10 In Los Angeles County, wildland fires typically occur in the undeveloped or slightly developed portions of the hills and mountains that surround the extensively developed basin. Areas in the County specifically known for their high to very high wildland fire susceptibility include Malibu, Calabasas, Glendale, Burbank, and the mountainous regions of La Cañada Flintridge, Altadena, Pasadena, and Sierra Madre. Wildland fires have also occurred historically in the Baldwin Hills and in Palos Verdes Hills, impacting the cities and communities therein.

Figure 10-2 shows those areas in the Santa Monica Mountains to the northwest, north and northeast of Santa Monica, and in the northwestern Baldwin Hills, to the east-southeast of the city, that have burned at least once between 1930 and March 2025, based on data available from the California Department of Forestry and Fire Protection (CAL FIRE10F 11). The figure shows areas that have burned

7 https://www.nifc.gov/fire-information/fire-prevention-education-mitigation/wildfire-investigation 8 e.g., Anderson, M.K., 2005, Tending the Wild: Native American Knowledge and the Management of California’s Natural Resources: University of California Press, Berkeley, California, 526p. 9 Stephens, S.L., Martin, R.E., and Clinton, N.E., 2007, Prehistoric fire area and emissions from California’s forests, woodlands, shrublands, and grasslands: Forest Ecology and Management, doi:10.1016/j.foreco.2007.06.005. 10 Goforth, B.R. and Minnich, R.A., 2007, Evidence, exaggeration, and error in historical accounts of chaparral wildfires in California: Ecological Applications, Vol. 17, No. 3, pp. 779-790. 11 http://frap.cdf.ca.gov/data/frapgisdata/select.asp; https://www.fire.ca.gov/what-we-do/fire-resource-assessmentprogram/gis-mapping-and-dataanalytics#:~:text=Unlocking%20Insights%20with%20GIS%20Mapping%20The%20Fire,the%20health%20of%2 0California%27s%20forests%20and%20rangelands.

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at least once during a 20-year period. Overlap of some of these burnt areas indicates that wildland fire has impacted some of the same areas more than once during the time period covered.

Significantly, Figure 10-2 shows that in nearly 100 years, no wildland fires have occurred in Santa Monica proper, although a few fires have been contained very close to the northern city boundary.

The most recent and impactful of these is the Palisades fire that occurred in January 2025. The area burned by this fire, and its location relative to Santa Monica, is shown by the area with horizontal red lines shown on Figure 10-2 below.

Figure 10-2: Historical (1930-2025) Wildfires Near Santa Monica (For a larger version of this figure refer to Plate H-16 in Appendix H) Based on the historical record, the risk of wildland fire in Santa Monica has traditionally been considered low to nil. However, hotter temperatures, drier conditions, and increased drought brought on by climate change have already increased the fire risk and lengthened the fire season in most areas of the United States, including southern California11F

12. The 2025 Palisades fire has shown
that a wildland fire in the Santa Monica Mountains during an intense drought period, especially if fanned by Santa Ana winds coming from the east to northeast, could encroach onto Santa Monica, placing the structures in the northern portion of the city in danger. This is discussed further in this section.

12 https://www.c2es.org/content/wildfires-and-climate-change/ accessed May 24, 2024; Khorshidi, M.S., Dennison, P.E., Nikoo, M.R., AghaKouchak, A., Luce, C.H., and Sadegh, M., 2020, Increasing concurrence of wildfire drivers tripled megafire critical danger days in Southern California between 1982 and 2018: Environmental Research Letters, Vol. 15, No. 10, Paper No. 104002, doi:10.1088/1748‐9326/abae9e.

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Table 10-1 lists the twenty most destructive fires in California to date, based on statistics collected and published by CAL FIRE. The table shows that 18 of the 20 most destructive fires in California occurred in the past 25 years (since the year 2000), with 15 of these having occurred since 2015.

These data highlight the fact that the fire risk in California has increased in the recent past as a result of both climate change and increased construction in the WUI.12F 13 Some of these fires, and others no
longer considered the most destructive but that effected change in the form of modifications to the fire and building codes, are described further in the sub-sections below. Also included in the subsections below are three of the largest fires that have occurred historically near Santa Monica.

Table 10-1: Top Twenty Most-Destructive Fires in California (as of April 3, 2025) Based on Total Number of Structures Destroyed
No. Fire Name (cause) Date County Acres Structures Deaths 1 Camp (powerlines) November
2018 Butte 153,336 18,804 85
2 Eaton (under
investigation, likely power
line)*
January
2025 Los Angeles 14,021 9,414 18
3 Palisades
(under investigation,
likely human related)*
January
2025 Los Angeles 23,448 6,837 12
4 Tubbs (electrical) October
2017 Napa & Sonoma 36,807 5,636 22
5 Tunnel – Oakland Hills
(rekindle)
October
1991 Alameda 1,600 2,900 25
6 Cedar
(human related)
October
2003 San Diego 273,246 2,820 15
7 North Complex (lightning) August
2020 Butte, Plumas & Yuba 318,935 2,352 15
8 Valley (electrical) September
2015 Lake, Napa & Sonoma 76,067 1,955 4
9 Witch (power line) October
2007 San Diego 197,990 1,650 2
10 Woolsey (electrical) November
2018 Ventura 96,949 1,643 3
11 Carr (human related) July 2018 Shasta & Trinity 229,651 1,614 8 12 Glass (undetermined) September
2020 Napa & Sonoma 67,484 1,520 0
13 LNU Lightning Complex
(lightning/arson)
August
2020
Napa, Solano,
Sonoma, Yolo, Lake &
Colusa
363,220 1,491 6
14 CZU Lightning Complex
(lightning)
August
2020
Santa Cruz & San
Mateo 86,509 1,490 1
15 Nuns (power line) October
2017 Sonoma 54,382 1,355 3

13 By some accounts, about 45% of new construction in California between 1990 and 2020 was at the WUI (https://silvis.forest.wisc.edu/data/wui-change/ as reported in https://calmatters.org/housing/2025/01/ca-wuihousingpolicy/#:~:text=Between%201990%20and%202020%2C%20nearly%2045%%20of,of%20all%20the%20land% 20in%20the%20state; both accessed May 12, 2025).

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No. Fire Name (cause) Date County Acres Structures Deaths 16 Dixie (power line) July 2021 Butte, Plumas, Lassen,
Shasta & Tehama 963,309 1,311 1
17 Thomas (power line) December
2017
Ventura & Santa
Barbara 281,893 1,063 2
18 Caldor
(human related?,
under investigation)
September
2021
Alpine, Amador &
El Dorado 221,774 1,003 1
19 Old (human related) October
2003 San Bernardino 91,281 1,003 6
20 Jones (undetermined) October
1999 Shasta 26,200 954 1
Sources: CAL FIRE website accessed in May 2024, February 2025, and April 2025: https://34c031f8-c9fd-4018-8c5a4159cdff6b0d-cdn-endpoint.azureedge.net/-/media/calfire-website/our-impact/firestatistics/top20_destruction.pdf?rev=adaea8332a014a7ebf11dc6fdb3f8e98&hash=EA9A8C492BD9FBAA0FB67C2FEA3F F52E
*CAL FIRE indicates that these numbers are preliminary, based on aerial assessments. Validated inspections are being conducted by Damage Assessment teams as of the writing of this report, so these totals may change slightly.

Topanga Canyon or Santa Monica Mountains Fire of 1938
This fire began on November 23rd and burned for a week. The area covered by this fire is shown in light purple on Figure 10-2. The fire began at the Trippet Ranch, about three miles from the mouth of Topanga Canyon, in the city of Los Angeles, when the ranch caretaker disposed of ashes thought to be inert onto the edge of the brush. Live coals in the ashes were fanned by high winds and because of the extremely low humidity at the time, the fire spread quickly. The Los Angeles Fire Department, upon realizing the severity of the fire, responded with dozens of engines and trucks, and hundreds of crew members13F

14. Except for many homes along the beach, most of the area burned was uninhabited. The fire department took measures to protect the homes exposed both along the beach lines, and along the southerly and easterly limits of the burn area. According to the after-fire report14F 15, the fire did not
cross Sunset Boulevard, but it did burn close to it at many points. As a result, only a handful of dwellings, stables, sheds, and garages were damaged. The total building loss, including contents, was reported as $19,228.25 (equivalent to about $428,000 in 2024 dollars).

The need for medical services at the scene of the fire was noticed almost immediately. In response, one of the city’s first aid ambulances was stationed at Pacific Palisades. The American Red Cross also responded very early on providing equipment and personnel to help with the firemen injured.

Although November 24th began a holiday weekend, the fire department received assistance from hundreds of volunteers, and assistance from many other government agencies, including the City of Los Angeles Department of Water and Power that provided a bus and several trucks to transport men and equipment to the front lines, in addition to bulldozers. In the post-fire analysis, the Chief Engineer, Mr. R.J. Scott, recommended that the “large water supply main be continued from its present terminus on Mulholland Highway, … and that laterals be run from this main along each existing and contemplated fire road.” He also recommended building additional roads through the

14 http://www.lafire.com/famous_fires/1938-1123_1938BrushFire/112338_BrushFire.htm, accessed on May 27, 2024. 15 Ibid

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region; the regular upkeep of the existing firebreaks; and acquisition of caterpillars, bulldozers, and large trucks to transport men and equipment.

Bel Air, Brentwood and Santa Ynez Fires of 1961
The first of these fires began on November 6th, 1961 on the north slope of the Santa Monica Mountains, and fanned by strong southerly and westerly Santa Ana winds burned to the top of the mountains and then south, eventually jumping across Mulholland Drive and into Stone Canyon. A second, short-lived fire was started by arson in Benedict Canyon; followed by a third fire south of Mulholland Drive near Topanga Canyon that burned in a southeasterly direction15F

16. This third fire is
referred to as the Santa Ynez fire. Vegetation in the region was tinder dry as a result of several years of drought. The area covered by these fires is shown in the darker green on Figure 10-2.

At the time in the Bel Air-Brentwood area, shingle and shake roofs were predominant. That, together with the dry conditions, hot temperatures, strong wind conditions, narrow winding roads, and difficult terrain, combined to create a disastrous brush fire. The Bel Air-Brentwood fire burned more than 6,000 acres, a small number compared to most of the other fires in Table 10-1, but it destroyed 484 residences and damaged another 21 buildings. Fortunately, no lives were lost, and there were no major injuries. The total building loss was not provided in the sources reviewed, but the cost of the houses destroyed was estimated to range between $35,000 and $700,000 apiece ($367,000 to $7.3 million in 2024 dollars). The Santa Ynez fire burned 8,560 acres of brush lands and destroyed nine buildings16F

17. The post-fire analysis17F
18 of the Bel Air-Brentwood fires found that 75% of the buildings destroyed had wood roof coverings, with the combustible roofs being a major point of ignition. The investigation also found that although less than 3% of the buildings in the area were stilted or cantilevered on steep slopes, 44.5% of buildings with this structural feature suffered substantial damage. Large, unprotected eaves and exposed floors in these structures allowed the fire to impact the buildings.

More than 45% of the houses located on hilltops were destroyed, and about 70% of the ruined homes were located within 50 feet of natural vegetation, with inadequate clearance around the structures.

Los Angeles Fires of 1978
On October 23, 1978, at least ten wildfires started in different areas of southern California. Because the region was experiencing strong Santa Ana winds, many of these fires spread quickly, burning thousands of acres. These fires included: 1) a fire in Mandeville Canyon that is described in more detail below, 2) four brush fires in San Dimas, 3) a fire in Chino that spread into Carbon Canyon in Orange County (which may be related to a fire that reportedly began in the Elsinore-Perris region), 4) a fire in Agoura also described further below, 5) a fire in Agua Dulce, 6) a fire in Glendale, and 7) a brush fire north of Sierra Madre that impacted mostly the San Gabriel Mountains.

The Mandeville Canyon fire was first reported at 9:41 AM on October 23rd; emergency officials declared it a major emergency within the first hour due to its fast spread. The fire reportedly began near the intersection of Sepulveda Boulevard and Mulholland Drive, and quickly spread west

16 https://www.lafire.com/famous_fires/1961-1106_BelAirFire/1961-1106_LAFD-Report_BelAirFire.htm, accessed May 27, 2024. 17 Ibid 18 Ibid

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through Kenter, Mandeville, Sullivan, Rustic, Temescal and Santa Ynez Canyons, reaching the Pacific Coast Highway (PCH) in about two hours, prompting the evacuation of sections of Pacific Palisades and Malibu (light green area on Figure 10-2 north of Santa Monica). The ensuing heavy traffic load on Sunset Boulevard impacted emergency vehicles response.18F 19 This fire reportedly
burned an estimated 6,130 acres, destroyed 30 homes and damaged another 18 in Pacific Palisades.19F
20 In Pacific Palisades the fire reportedly also destroyed the St. Matthew’s Episcopal Church built in 1941, and the mill building. At the Boy Scout Camp in upper Rustic Canyon, the ranger’s house was destroyed, together with several other buildings, but the Main Lodge survived. Other significant buildings that were destroyed include a guest house at the Presbyterian Conference grounds, the Josepho and Murphy Ranches, and the Will Rogers get-away cabin.20F 21 The cause of the
Mandeville fire was power lines that were downed by the strong winds. The City of Los Angeles was deemed liable and ultimately paid $8.5 million to 22 Mandeville Canyon residents and eight insurance companies.21F
22 The Agoura fire, referred to as the Agoura-Malibu fire, or the Agoura-Malibu firestorm, was started around noon on October 23rd by a 15-year-old who used a lit cigarette wrapped in a matchbook as an incendiary device. The fire was first reported in Agoura at 12:11 PM, and by 2:30 PM, it had reached Broad Beach in Malibu. The fire continued to burn through the canyons in the Santa Monica Mountains for four days, with the total burned area estimated at 25,000 acres. Agoura residents evacuated to a shopping center next to the 101 Freeway in Agoura Hills. The juvenile that started the fire was arrested and sentenced to jail until his 21st birthday, confined in the California Youth Authority.22F
23 The Mandeville Canyon and Agoura-Malibu fires combined appear to have destroyed 230 homes and damaged at least another 254 structures, resulted in three civilian fatalities, and approximately 50 civilian injuries. Damage was estimated at $71.4 million (approximately equivalent to $343.5 million in 2024).

Tunnel Fire of 1991 (Oakland Firestorm)
This is still the fifth worst fire in California, according to the statistics presented on Table 10-1. This large suburban fire at the WUI occurred in the hillsides of northeastern Oakland and southeastern Berkeley on October 19-22, 1991. Firefighters responded to a grass fire northeast of the intersection of State Routes 24 and 13 on October 19th that by the end of the day was thought to be under control.

However, on the morning of the 20th a single ember blew into a tree; the tree caught fire, and the flames fanned by strong wind gusts moved quickly to the southwest. Burning embers carried by the winds ignited fires ahead of the original burn, eventually igniting hundreds of structures.

Firefighting efforts were hampered by several factors including: high heat and strong wind gusts that caused the fire to spread quickly; damage to power lines that serviced 17 of the pumping stations in the Oakland water system resulted in several emptied reservoirs to go unfilled; compatibility issues with the equipment used by responding fire departments from other counties not matching the fire hydrant outlets; antiquated communications equipment; narrow, winding roads crowded with

19 https://www.circlingthenews.com/the-1978-blaze-destroyed-25-homes-and-st-matthews-church/, accessed on May 7, 2025. 20 Ibid 21 Ibid. 22 https://www.newspapers.com/article/the-los-angeles-times-la-must-pay-85/94877101/ accessed May 8, 2025. 23 https://en.wikipedia.org/wiki/1978_Agoura-Malibu_firestorm accessed May 8, 2025.

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parked cars, many in front of fire hydrants; thick, dry vegetation; and widespread occurrence of wood shake or wood shingle roofs.23F
24 The fire burned only about 1,600 acres, but destroyed about 2,900 structures, including 2,843 single-family dwellings and 433 apartment and condominium units, damaged another 193 singlefamily dwellings, killed 25 people and injured 150 others. Losses associated with the fire were estimated at $1.537 billion ($3.54 billion in 2024 dollars). In response to this fire, the California Fire Code was modified to include regulations regarding defensible space around buildings. The California Building Code now also requires fire-resistant construction materials for all new structures at the WUI. The lessons learned from this fire also created the foundation for the “Incident Command System,” the process of organizing and managing multi-jurisdictional emergencies that is still utilized today.24F
25 Laguna Fire of 1993
The Laguna or Laguna Canyon fire occurred on October 27-31, 1994 in Orange County. As with the other fires summarized here, abundant flammable, dry vegetation following several years of drought, strong Santa Ana winds, and extensive development at the WUI combined to create the perfect conditions for a small vegetation fire to intensify quickly, spreading through the canyons at a rate of about 100 acres per minute, and at one point burning four structures every minute. The flames reportedly were routinely 40 to 50 feet high, and at times more than 200 feet high. The fire spread so quickly that the fire department’s objectives soon switched from structure defense to saving lives and protecting downtown Laguna Beach. The entire population of Laguna Beach, approximately 24,500 people, were under evacuation orders.

The fire burned more than 16,000 acres and destroyed 441 structures. Amazingly, no fatalities and only eight injuries were reported. Total losses in property damage were estimated at $528 million ($1.14 billion in 2024 dollars). Following the fire, because six of the 22 reservoirs in the area were completely drained by the firefighting efforts, the water district built two new reservoirs, and also purchased additional backup generators and pumps. The City of Laguna Beach strengthened building codes, requiring that all new homes have automatic sprinkler systems and fire-retardant roof coverings, and expanded a vegetation management program that uses goats year-round.25F 26 Southern California Fires of 2003, Including Cedar Fire The fall of 2003 marked one of the most destructive wildfire seasons in California history (in terms of acreage burned). In a ten-day period, 12 separate fires raged across southern California in Los Angeles, Riverside, San Bernardino, San Diego and Ventura counties. This fire season followed five years of unusually dry conditions in southern California, with rainfall totals gaged at between 50 and 75% of normal levels.

The massive “Cedar” fire in San Diego County alone consumed 3,241 structures (2,800 homes) and burned more than 270,000 acres.26F
27 It still ranks in the upper six most-destructive wildland fires in

24 http://www.sfmuseum.org/oakfire/overview.html and https://en.wikipedia.org/wiki/Oakland_firestorm_of_1991, accessed May 27, 2024. 25 Cole, D., 2000, The Incident Command System: A 25-Year Evaluation by California Practitioners; available at https://apps.usfa.fema.gov/pdf/efop/efo31023.pdf. 26 https://en.wikipedia.org/wiki/Laguna_Fire_(1993), accessed May 27, 2004. 27 https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5297020.pdf, accessed May 27, 2024.

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the state (see Table 10-1). The fire was started on October 25th by a hunter lost in the Cleveland National Forest who lit a fire to signal for help, with the fire quickly spreading out of control.

Between midnight and 3:00 AM on the 26th, the fire had spread from 5,500 acres to 62,000 acres, burning a southwesterly path toward the city of San Diego at a rate of between 3,600 and 6,000 acres per hour. The fire killed 12 people in Wildcat Canyon and Muth Valley, and destroyed 39 homes on the Barona Indian Reservation. On the 26th, at 5:00 AM, the fire reached Poway, destroying 54 homes and 16 businesses, and continued westward impacting several communities in north and east San Diego. By noon, hundreds of homes in the Scripps Ranch community were burning. On the 27th, the fire burned hundreds of additional homes in several bedroom communities near San Diego before the winds changed direction, causing the fire to advance to the east. The fire reached the communities of Cuyamaca and Julian in the early hours of the 28th, destroying more than 500 homes in its path. On the 29th, the fire reached the Riverwood Estates, a community near Santa Ysabel where a group of firefighters were trapped and overrun by the fire. One firefighter died and three others were injured. Containment was achieved on November 3rd, but it took until December 5th before the fire was completely under control. In total, 15 people died; at least ten of those died in their cars as they were trying to flee the flames. Losses related to this fire were estimated at $1.3 billion27F
28 (approximately $2.21 billion in 2024 dollars).

Tubbs Fire of 2017
As of April 2025, the Tubbs fire ranks as the fourth most-destructive fire in California history. The fire began on October 8, 2017 north of Calistoga, and within hours, fanned by winds 20 to 70 miles per hour, had travelled more than 12 miles into densely populated areas of the town of Santa Rosa.

The fire then leaped across Highway 101 and destroyed more than 1,300 homes in the Coffey Park subdivision. On October 10th, winds changed direction and on the 11th, the entire town of Calistoga was evacuated. The fire was not fully contained until October 31st. The fire, which is now known to have been caused by a private electrical system, burned more than 36,800 acres, destroyed more than 5,600 homes, and killed 22 people. Tens of thousands of people were evacuated in and around Santa Rosa. This was one of more than a dozen wildfires that were burning in northern California at the same time. In total, these fires destroyed more than 7,000 structures, burned about 160,000 acres, and killed more than 40 people.28F
29 The fire damage in Santa Rosa alone was estimated at $1.2 billion ($1.54 billion in 2024 dollars), with an estimated 5% of its housing stock destroyed.29F 30 The Tubbs fire also destroyed several
commercial structures, including the Fountaingrove Inn, the Fountaingrove Round Barn, a Hilton hotel, a Kmart store, the Redwood Adventist Academy, the Fountaingrove campus of Keysight Technologies, and the Santa Rosa Community Health’s Vista Campus. Several medical centers had to be evacuated, including the Kaiser Permanente and Sutter Health facilities in Santa Rosa.

The fire destroyed an entire subdivision in Fountaingrove that was surrounded by a 100-foot wide fire break, and where the homes were built with fire-resistant siding, roofing and deck materials, including the use of protected eaves to keep windblown embers from entering the structures.30F 31 The
deathly toll of the Tubbs fire was attributed to hurricane-force winds, above-normal rainfall earlier

28 https://en.wikipedia.org/wiki/Cedar_Fire, accessed May 27-28, 2024. 29 https://theconversation.com/why-were-californias-wine-country-fires-so-destructive-86043, accessed May 28, 2024. 30 https://en.wikipedia.org/wiki/Tubbs_Fire#, accessed May 28, 2024. 31 Ibid

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in the year that resulted in increased grass growth, which in turn made the fire very intense, and increased population at the WUI, with a high density of homes in the area.31F 32 Camp Fire of 2018
The most-damaging and most-deadly fire to date in California’s history began on November 8th, 2018 when a poorly maintained electric transmission line was downed by strong winds, causing a brush fire by Camp Creek Road, near Pulga, in northern California. The conditions at that time included a heavy cover of unusually dry vegetation due to a wet spring, followed by drought in the fall, and low humidity (10%) associated with hot, dry gusty winds locally called Jarbo winds (similar to the Santa Ana winds in southern California). The area impacted had last burned in 2008, and could only be accessed via winding roads with sharp curves, steep adjacent slopes and inadequate shoulders.32F
33 Because high winds and low humidity had been forecasted, Pacific Gas & Electric (PG&E) had notified customers in the area that they would probably shut down electric power. However, the line that failed could only be de-energized manually, and that had not been done the morning that the fire began. The fire was noticed by PG&E Rock Creek Powerhouse personnel soon after it began, but the mountain road near where the fire began was too narrow for fire engines to navigate, and it was too early in the morning and too windy for air resources to be deployed. The fire quickly grew, and by 7 AM had reached the community of Concow. By 8 AM, the fire had reached the town of Paradise; 95% of the structures in both of these communities were lost in the first six hours after the fire began, before evacuation orders were issued. Loss of 17 cell towers and a series of failures in the emergency alert system meant that 25-94% of the emergency alerts issued in the first few hours failed to reach the residents in the impacted areas. Other communities impacted include Pulga, Magalia, Centerville, Butte Valley, Chico, Forest Ranch, Helltown, Inskip, Oroville, and Stirling City.33F
34 Full containment of the fire was announced on November 25th, with a total burn area of nearly 154,000 acres. The total number of destroyed structures is officially set at 18,804; most of these were homes, but the list also includes five public schools in Paradise, a large shopping center, several restaurants and numerous small businesses, churches, and part of the Feather River hospital.

The fire killed 85 civilians and injured 17. The injury count includes five firefighters. A large number of deaths (70) occurred inside or immediately outside victim’s homes, and seven people died trapped in their vehicles while trying to evacuate.34F
35 The total cost of this fire is still being determined. In addition to the property loss, cleanup of the fire debris is considered the largest hazardous cleanup effort in California history (although this could be surpassed by the costs of cleaning up the Eaton and Palisades fires). Contaminants related to the burned structures and burned plastic pipes soaked into the ground and contaminated surface waters with high levels of heavy metals, dioxins, and benzene, to mention a few. The large number of insurance claims caused the Merced Property and Casualty Company, a small insurer, to become

32 https://theconversation.com/why-were-californias-wine-country-fires-so-destructive-86043, accessed May 28, 2024. 33 https://en.wikipedia.org/wiki/Camp_Fire_(2018), accessed May 27-28, 2024. 34 Ibid 35 Ibid and https://34c031f8-c9fd-4018-8c5a-4159cdff6b0d-cdn-endpoint.azureedge.net/-/media/calfirewebsite/our-impact/fire-statistics/top-20-destructive-cawildfires.pdf?rev=3f619258cab84b34b680ce521d615525&hash=6C6AD8F9377A31117DF437BBDBE68F07

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insolvent. Anticipating liabilities in the billions of dollars as a result of the 2015 Butte fire, the 2017 North Bay fires (which include the Tubbs fire), and the 2018 Camp fire, PG&E filed for bankruptcy protection and reorganization. The utilities company has since settled, paying $1 billion to state and local governments, $11 billion to insurance carriers and investment funds, and $13.5 billion for other claims handled through the PG&E Fire Victim Trust.35F 36 Woolsey Fire of 2018
The Woolsey fire ignited on November 8th, 2018, the same day that the Camp fire ignited in northern California (see entry above). The wildfire started in Woolsey Canyon, in the Santa Susana Mountains above Simi Valley, near the boundary between Los Angeles and Ventura counties, on Boeing-owned property of the Santa Susana Field Laboratory. Other smaller wildfires that began the same day in southern California impacted response to this one, as described further below.

Southern California Edison reported an outage in their Big Rock 16 kV circuit about 2 minutes before a brush fire at the same location was first reported. Because Ventura County first-responder resources were assigned to both the Borderline Bar and Grill shooting that had occurred the evening prior, and to the Hill fire that was burning nearby, it took almost 20 minutes for the first firefighters to respond to the area where the Wooley fire was burning. Staff with a private firefighting company contracted by Boeing to protect their Field Laboratory were also delayed because their engine broke down. 36F
37 Strong Santa Ana winds fanned the fire, spreading it quickly toward the south; the fire crossed the 101 Freeway near Calabasas, and into the Agoura Hills and Santa Monica Mountains during the night and the early morning hours of November 9th. Due to the strong winds, aerial suppression could only begin at about 5 AM on November 9th. However, the fire continued to spread through the mountains south of the 101 Freeway, reaching PCH in Malibu that afternoon. The fire also spread west to areas of Thousand Oaks and Westlake Village, and east-southeast, to the West Hills neighborhood of Los Angeles. Firefighting units from CAL FIRE and the United States Forest Service were deployed to fight the fire, with an estimated 3,242 firefighters assigned to this blaze by November 10th. By then the fire had burned more than 70,000 acres, forcing the evacuation of nearly 300,000 residents, including total evacuation of Bell Canyon, Malibu, Agoura Hills, the community of Malibou Lake, and Oak Park. Strong winds in the early morning hours of November 14th caused the fire to flare in the rugged mountains at the western end of the Santa Monica Mountains, in a slightly populated area with scattered homes. The fire was declared fully contained at 6:11 PM on November 21st
.

The Woolsey fire destroyed 1,643 structures, including about 1,600 houses, and damaged another 364 structures.37F
38 Several filming locations and historical sites were impacted by the fire, with the Santa Monica Mountains National Recreation Area (SMMNRA) sustaining significant damage.

Specifically, about 88% of National Park Service lands within the SMMNRA burned38F 39, forcing the
closure of many trails in the park for many months to allow the area to recover. In total, 96,949 acres of land burned. Two people died inside their vehicle on Mullholland Highway, and another body was found in Agoura Hills. Charred human remains found in Malibu on January 22, 2019

36 Ibid. 37 https://en.wikipedia.org/wiki/Woolsey_Fire, accessed April 25, 2025. 38 Ibid 39 https://www.nps.gov/samo/learn/management/2018-woolsey-fire.htm, accessed April 25, 2025.

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suggest a fourth victim. Two of the 13 mountain lions fitted with radio collars in the Santa Monica Mountains also died as a result of the Woolsey fire. The damage caused by this fire was estimated at $6 billion in 2018 dollars (approximately equivalent to $7.5 billion in 2024).

City of Santa Monica staff assisted with the evacuation of the Santa Monica Mountains on November 9th. Santa Monica’s main focus was to support evacuations along PCH, closing entry points into Santa Monica that could slow-down the evacuation traffic. City of Malibu staff evacuated civic buildings in downtown Malibu, and on November 10th, the Malibu Emergency Operations Center (EOC) was relocated to the Santa Monica EOC and remained there for almost three weeks. Santa Monica personnel supported Malibu’s EOC, especially in public communications and emergency management roles. Santa Monica High School’s gymnasium was activated as a shelter and also hosted the event’s community meeting for persons impacted by the fire.

Franklin (Malibu) Fire of 2024
This wildfire began at 10:50 PM on December 9th, 2024 along Malibu Canyon Road, in Malibu Creek State Park and over the next day burned approximately 2,600 acres, fanned by Santa Ana winds. The fire burned and destroyed at least 20 buildings, and damaged 28 others39F 40, forced
thousands of Malibu residents to evacuate, and extended into the campus of Pepperdine University, where students sheltered in place. Ultimately, the fire burned 4,037 acres, and was finally contained in the evening of December 18th. As of this writing, its cause was under investigation. Although windy, helicopters with night-vision capabilities were able to fly most of the night during the first night, directing crews to the most critical areas. Two large air tankers were brought in the next morning to help with the firefighting operations. The winds died down by the afternoon of the 10th, allowing fire fighters to use more planes and helicopters to fight the blaze. On the ground, approximately 2,000 fire fighters were assigned to this event. The American Red Cross set up a shelter in Santa Monica, at the Child Development Services building on Ocean Park Boulevard. The shelter hosted approximately 7 persons and their pets during the event. The Franklin fire was declared 100% contained on December 18 at 8:00 PM.

Palisades Fire of 2025
The Palisades fire is currently considered the third most-damaging historical fire in California based on the number of structures destroyed. The fire was first reported just before 10:30 AM on Tuesday, January 7, 2025 in the mountains behind Pacific Palisades. When the fire was first reported it probably covered about 10 acres, but within 20 minutes it is estimated it had grown to 200 acres, and by around 2 PM it covered more than 700 acres. An hour later, it had nearly doubled to 1,262 acres, and by 12:29 AM on January 8th, CAL FIRE reported the fire had grown to 2,921 acres. The fire continued to grow at an accelerated rate through the day, with CAL FIRE reporting at 11:10 PM that evening that the fire had grown to 17,234 acres. On January 8, 2025, a spot fire on the southern edge of the fire destroyed several homes approximately 2,000 feet from the Santa Monica/Los Angeles border, with the fire quickly spreading from structure to structure.

By the morning of January 9th, the fire authorities reported that more than 5,300 structures had been destroyed and nearly 20,000 acres had burned. The fire continued burning throughout the day but at a much lower pace, with a status report issued by CAL FIRE at 7:39 AM on January 10th indicating that the fire had grown to 20,438 acres. At 8:00 AM it was reported that the fire was about 8%

40 https://en.wikipedia.org/wiki/Franklin_Fire, accessed April 25, 2025.

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contained. At 2:33 PM a new status report indicated that the area impacted was 21,317 acres, with containment still at 8%. CAL FIRE reported at 8:00 AM on January 11th that the fire had grown another 1,000 acres overnight, and by 4:37 PM that afternoon, the burned area had been updated to 23,654 acres, with the fire burning towards Mandeville Canyon, Encino, Tarzana, and the western portion of Bel Air. After the 11th, the fire did not grow any more, but it took fire fighters nearly 20 more days before the fire was considered fully contained. 100% containment was reported on January 31st
.

The cause of the fire is still under investigation, but its fast growth was the result of the strong Santa Ana winds, moderate drought conditions in the area due to a lack of any measurable precipitation for at least the prior eight months, and dense brush resulting from decades-long effective fire suppression efforts that meant a large part of the wildland area that ultimately burned had not burned since the 1940s. As a result of these conditions, the National Weather Service had issued a rare “potentially dangerous situation” Red Flag Warning the day before, effective from noon on Tuesday, January 7th through 4:00 PM on Wednesday, January 8th.40F 41 As a result of this warning, Caltrans had
closed several roads in the fire-warning area, CAL FIRE had positioned several firefighting assets around southern California, and the Los Angeles Department of Water & Power had topped off their three 1-million-gallon water tanks in the area. Filling up the water tanks unfortunately proved to be insufficient, with an estimated 20% of the fire hydrants in the higher-elevation areas of Pacific Palisades running out of water.41F
42 The 117-million-gallon Santa Ynez reservoir in Pacific Palisades was being repaired and out of commission when the fire started. Had this reservoir been online, it is anticipated that the water therein could have temporarily helped to fight the fires, although many specialists indicate that the water infrastructure is not designed to fight these regionally extensive fires42F
43 and the impact that this reservoir could have had would have been relatively minor. The Red Flag Warnings were extended through January 23rd.

The damage caused by the Palisades fire is still being assessed, with a total cost not likely to be known for several years. Building safety assessments of the area burned indicates that 6,837 structures were destroyed, and another 973 structures were damaged. The total death toll is currently at 12 people; four injuries were also reported, with one of those being a firefighter. Most of Pacific Palisades north of Sunset Boulevard burned, including several architecturally significant residences, at least three churches, the Palisades branch of the Los Angeles Public Library, and several elementary schools. Several buildings that were part of the Palisades Charter High School were also destroyed, but the administration and main classroom buildings survived. The building housing the Getty Villa was not damaged thanks to museum staff actively patrolling the grounds throughout the night with fire extinguishers on hand, dousing embers that landed onsite. Several structures at the Will Rogers State Historic Park and Topanga State Park were also destroyed. Smoke from the Palisades fire and several other fires that were burning at the same time in the region impacted air quality in a large portion of the Los Angeles basin. Residents were advised to wear masks and sensitive individuals were encouraged to stay inside as much as possible.

The Palisades fire prompted wildfire evacuation orders for the city of Santa Monica, the first in the city’s history. Given the strong winds and wind direction, firefighters were concerned that the

41 https://www.dailynews.com/2025/01/06/santa-ana-winds-could-gust-60-90-mph-in-some-southern-californiaareas-boosting-fire-danger/, accessed June 18, 2025. 42 https://en.wikipedia.org/wiki/Palisades_Fire, accessed April 25-28, 2025. 43 https://www.nbcnews.com/news/us-news/reservoir-pacific-palisades-was-commission-fire-started-rcna187217, accessed April 28, 2025.

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Palisades fire could reach the northern part of the city, either through Sullivan/Rustic Canyon, or from fire in Mandeville Canyon burning south and west through Santa Monica Canyon. At the same time, several brushfires that had ignited along the Santa Monica bluffs and off the I-10 Freeway, within Santa Monica city limits, were straining the firefighting resources in the city. As a result, at 7:24 PM on January 7th, the City of Santa Monica implemented a mandatory evacuation order for the most northerly parts of the city, from San Vicente Boulevard north to the city limits, extending from the Pacific Ocean to 26th Street. At the same time, an evacuation warning was issued for the area between San Vicente Boulevard and Montana Avenue, from 11th Street to 26th Street, and for the area between San Vicente Boulevard and Montana Avenue, between PCH and 11th Street (see Table 10-2). The areas under evacuation orders and evacuation warnings were expanded on January 8th after several homes on Chautauqua Boulevard, in Pacific Palisades and 0.4 miles north of Santa Monica city limits, ignited and were ultimately destroyed. Specifically, on January 8th, the evacuation orders were expanded to include the area between San Vicente Boulevard and Montana Avenue from 11th Street to PCH, while an evacuation warning was issued for the area between Montana Avenue and Wilshire Boulevard, from 10th Street to PCH. As the days progressed, some of the areas under evacuation orders were downgraded to evacuation warnings. The last evacuation warnings were cancelled on January 18th at 12:00 PM.

Table 10-2: Zones in Santa Monica Under Evacuation Orders and Evacuation Warnings During the Palisades Fires of January 2025
Geographic Area
Dates and Times*
When Evacuation Orders
Were In Effect
Dates and Times*
When Evacuation
Warnings Were In Effect
From San Vicente Blvd north to the City limits,
from the Pacific Ocean to 26th St
01/07/2025, 19:24 to
01/13/2025, 8:00
01/13/2025, 8:00 to
01/18/2025, 12:00
Between San Vicente Blvd and Montana Ave,
from PCH to 11th St
01/082025, 14:30 to
01/10/2025, 15:22
01/07/2025, 19:24 to
01/08/2025, 14:30 and
01/10/2025, 15:22 to
01/13/2025, 08:00
Between San Vicente Blvd and Montana Ave,
from 11th St to 26th St NA 01/07/2025, 19:24 to 01/13/2025, 0:800 Between Montana Ave and Wilshire Blvd,
from PCH to 10th St NA 01/08/2025, 14:30 to 01/10/2025, 15:22 *Times are based on a 24-hour clock.

Evacuation decisions were directed by the Santa Monica Police Department (SMPD) in close coordination with the Santa Monica EOC, the CAL FIRE Incident Management Team 2, and the Los Angeles County EOC. SMPD was primarily responsible for the evacuation orders with door-to-door notifications to residences and businesses, and implementing traffic closure points to prohibit reentry. The City’s Department of Transportation deployed buses and bus operators to evacuees in need of transportation from the evacuation zones to the American Red Cross emergency shelter. At the start of the fire, the SMPD also implemented traffic closure procedures to facilitate evacuation traffic from Malibu and Pacific Palisades through Santa Monica, and prevent evacuation traffic bottlenecks. The SMPD also redirected traffic from the westbound I-10 Freeway into Santa Monica thereby prohibiting access into the burn zone from PCH, and closed several streets to prevent access into the Los Angeles burn zone from various coastal and northern access roads. On January 8th, Santa Monica officials issued a curfew order for all evacuation areas in the city, to prevent looting of evacuated Santa Monica properties and mitigate security concerns in Pacific Palisades and Malibu.

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Eaton Fire of 2025
The Eaton fire began in the early evening of January 7, 2025, the same day as the Palisades fire. The fire was first reported on a hillside above and to the east of Eaton Canyon Wash, across the wash from the intersection of Altadena Drive and Canyon Close Road in northeastern Pasadena, near high-tension power lines. Strong Santa Ana winds were blowing in the region, and the fire spread very quickly to the south-southwest, such that within 10 minutes of having started, the fire had spread 10 acres, and less than 10 minutes later, flying embers were setting on fire structures that were nearly 1 mile away. Night-flying helicopters from the Los Angeles County Fire Department were on the scene less than 20 minutes after the fire was first reported, but, given the strong winds, were not able to drop water on the blaze. Two of the helicopters had to leave the area while a third managed to stay in the vicinity and conveyed information on the fire spread to ground crews.43F 44 The fire grew overnight; a little past midnight the fire had expanded to more than 1,000 acres, and by early morning on January 8th, it had grown to more than 2,200 acres. Between 6:30 and 10:30 AM on the 8th, it grew to more than 10,600 acres with zero containment. Over the next few days the fire continued to grow, albeit at a slower rate, and firefighters started to make inroads. On January 12th the fire was 27% contained, on the 16th it was 55% contained, and on the 18th it was 73% contained. Full containment was reported on January 31st .44F
45 Ultimately, the Eaton fire burned an estimated 14,021 acres, decimating the community of Altadena, and damaging portions of the cities of Pasadena and Sierra Madre. With 9,414 structures destroyed and 1,074 structures damaged, the Eaton fire is now considered the second-most destructive, and fifth deadliest historical fire in California (see Table 10-1). On April 3rd, the Los Angeles County Office of the Medical Examiner reported that remains found in Altadena were human, bringing the death toll from the Eaton fire to 18. As of the writing of this report, the cause of the fire is still under investigation, with reports from residents near where the fire started suggesting that the fire was caused by faulty power lines owned by Southern California Edison that were not de-energized in response to the red flag warnings that had been issued for the region by the National Weather Service.

Wildfire Characteristics
The wildland fire hazard of an area is typically based on the combined input of several parameters.

These conditions are briefly described below:
• Fuel loading: i.e., the density and type of vegetation, with native chaparral vegetation; thicket stands that have not been cleared or have not burned in decades; and dry, flammable vegetation surrounding structures all posing a high fire hazard. In the WUI, fuel includes not only natural vegetation, but irrigated or cultivated vegetation in parks and landscaped areas, structures (such as homes and commercial structures), infrastructure (bridges, utilities), and other features (such as fences, decks, propane tanks, etc.).45F 46 • Topography: i.e., slope, which influences the movement of air and thus the fire direction, with steeper slopes having a higher rate of wildfire spread.

44 https://en.wikipedia.org/wiki/Eaton_Fire, accessed April 25- May 6, 2025. 45 Ibid. 46 https://lci.ca.gov/docs/20220817-Complete_WUI_Planning_Guide.pdf, accessed May 5-6, 2025.

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• Weather: the southern California Mediterranean climate, with less than 30 inches of yearly precipitation; hot dry summers; and high, hot, dry winds in the fall, create a high fire risk. • Drought conditions: periods of unusual low precipitation may result in large geographic areas with abundant dry or dead vegetation that is more likely to burn, and reduced storage in water reservoirs may limit the availability of water to fight fires. • Dwelling density and development: Isolated structures built at the end of narrow roads, surrounded by vegetation, are difficult to evacuate and protect during a wildland fire.

Similarly, densely packed structures, especially if surrounded by dense vegetation and above-ground power lines, may spread a wildfire and hinder firefighting efforts. • Wildfire history: As indicated by the data on Figure 10-1, areas that have burned in the past have a higher probability of burning again. Areas with thick underbrush that has not burned in a long time have a higher fire hazard.
• Existing mitigation measures: local mitigation measures in place (such as an extensive network of fire hydrants, fire-rated46F
47 construction, fuel modification zones, etc.) can help reduce the fire rating of an area.

There are three categories of interface fire: The classic WUI occurs where well-defined urban and suburban development presses up against open expanses of wildland areas; the mixed WUI characterized by isolated homes, subdivisions and small communities situated predominantly in wildland settings; and the occluded WUI where islands of wildland vegetation occur inside a largely urbanized area.

As described in the historical fires section above, certain conditions are often present when significant WUI fires have occurred. The most common conditions include: hot, dry and windy weather; a large fuel load (dense stands of dry vegetation); steep terrain with limited or no vehicular access; lack or limited water to fight the fire; communication issues that hinder evacuation efforts and/or cooperation efforts between responding units; or multiple fires at the same time that overwhelm the available firefighting resources. Once a fire has started, several conditions influence its behavior, including fuel, topography, weather, and degree of development (dwelling density and accessibility), building construction (with emphasis on the use of fire-retardant construction materials and combustible roofs), and the availability of local mitigation measures and resources (such as nearby fire stations, fire hydrants, roads, fuel modification zones, fire sprinklers in structures, etc.). The most significant of these conditions are discussed further below. • The Interface: A challenge southern California faces regarding its wildfire hazard is the result of the increasing number of houses being built at the WUI. Every year the growing population has expanded farther and farther into the hills and mountains, including forest lands. The increased number of structures at the interface means an increase in threats to life and property from fires, often pushing existing fire protection systems beyond original or current design and capability. Property owners in the interface are often not aware of the threats they face, nor their responsibilities in managing this hazard. Therefore, many owners do little

47 Fire-rated construction materials or assemblies have been specifically designed and tested to withstand fire for a given period of time, usually measured in minutes or hours. The rating indicates how long the material can maintain its structural integrity when exposed to fire, heat and smoke.

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to manage or offset the fire hazards on their own properties. Furthermore, human activities increase the incidence of fire ignition and potential damage. • Fuel: Fuel is the material that feeds a fire and is a key factor in wildfire behavior. Fuel is classified by volume and by type. Volume is described in terms of "fuel loading," or the amount of available vegetative fuel. The type of fuel also influences wildfire. Southern California has two distinct areas of risk for wildland fire: 1) The foothills and lower mountain areas most often covered with scrub brush or chaparral, and 2) the forested terrain at higher elevations, in the mountains.

Chaparral is a primary fuel of southern California wildfires. In southern California, chaparral habitat ranges in elevation from near sea level to over 5,000 feet. Chaparral communities experience long dry summers and receive most of their annual precipitation from winter rains. Some chaparral communities have evolved so that they require fire to spawn regeneration. Many species invite fire through the production of plant materials with large surface-to-volume ratios, volatile oils and periodic die-back of vegetation. These species have further adapted to display special reproductive mechanisms following fire. For example, several species produce vast quantities of seeds which lie dormant until fire triggers germination. The parent plant which produces these seeds defends itself from fire with a thick layer of bark that allows enough of the plant to survive so that the plant can crown sprout following the blaze. In general, chaparral community plants have adapted to fire through the following methods: a) fire induced flowering, b) bud production and sprouting subsequent to fire, c) in-soil seed storage and fire-stimulated germination, and d) on-plant seed storage and fire-stimulated dispersal.

Forest fires pose a higher risk to the WUI, as exemplified by the 2003 fires in San Bernardino and San Diego counties. The magnitude of those fires was the result of three primary factors:
1) severe drought, locally accompanied by a series of storms that produced thousands of lightning strikes and windy conditions; 2) an infestation of bark beetles that had killed thousands of mature trees in the region; and 3) the effects of wildfire suppression over the previous century that had led to buildup of brush and small-diameter trees in the forests.

This last factor is discussed further below.

Modern forests are generally significantly denser than they were in past centuries, especially prior to the arrival of European settlers. Thus, Lewis and Clark, on their exploration of the American Northwest in the early 1800s, reported that forests were relatively open, with an estimated 20 to 25 mature trees per acre. Forest density was likely controlled by lightningstarted fires that would sweep through, clearing out the underbrush and small trees, in addition to brush clearing conducted by Indigenous people to manage their surroundings and promote hunting, the production of food, reduce pests, support ceremonial practices, and other similar purposes.47F
48 Today’s forests typically have 300 to 400 mature trees to an acre, along with thick underbrush.48F
49 This density makes trees susceptible to disease, and less

48 Knight, C.A., Anderson, L., Bunting, M.J., Champagne, M., Clayburn, R.M., Crawford, J.N., KlimaszewskiPatterson, A., Knapp, E.E., Lake, F.K., Mensing, S.A., Wahl, D., Wanket, J., Watts-Tobin, A., Potts, M.D. and Battles, J.J., 2022, Land management explains major trends in forest structure and composition over the last millennium in California’s Klamath Mountains: Proceedings of the National Academy of Sciences (PNAS), Vol. 119, No. 2, e2116264119, doi:10.1073/pnas.2116264119. 49 According to Yablonski, B., 2022, The Big Burn of 1910 and the choking of America’s forests: Decades of fire suppression fuel catastrophic fires today: PERC Reports, Vol. 41, No. 1 (available at https://www.perc.org/wpcontent/uploads/2023/04/PR-SUM22-220608-WEB-spreads-1.pdf), in California, prior to White settlement, most forest types had about 64 trees per acre, whereas today most forests have about 300 trees per acre.

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drought- and fire-resistant. The thick under-story causes forest fires to burn intensely, which destroys the mature trees, so that damaged forests take decades to recover, rather than a few years. Unfortunately, this change is the result of the well-intentioned but misguided forest management programs that began in the early 1900s, in part as a result of the Big Burn of 1910, a devastating forest fire that burned about three million acres in western Montana and northern Idaho.49F
50 Essentially, these programs required that forest fires be avoided at all costs, with the use of prescribed fires and cultural burning prohibited, and policy requiring that all forest fires be suppressed as soon as possible, usually by 10 AM the day after the fire was first reported.50F
51 After nearly a century of these fire suppression efforts, “dog-hair" thickets have accumulated, which enable high intensity fires to flare and spread rapidly. • Topography: Topography influences the movement of air, thereby directing a fire course.

For example, if the percentage of uphill slope doubles, the rate of spread in wildfire will likely double. Gulches and canyons can funnel air and act as chimneys, which intensify fire behavior and cause the fire to spread faster. Solar heating of dry, south-facing slopes produces up-slope drafts that can complicate fire behavior. Unfortunately, hillsides with hazardous topographic characteristics are also desirable residential areas in many communities. This underscores the need for wildfire hazard mitigation and increased education and outreach to homeowners living in interface areas. • Weather: Weather patterns combined with certain geographic locations can create a favorable climate for wildfire activity. Areas where annual precipitation is less than 30 inches per year, such as southern California, are extremely fire susceptible. High-risk areas in southern California share a hot, dry season in late summer and early fall when high temperatures and low humidity favor fire activity. Santa Ana winds, which are heated by compression as they flow southwestward from Utah to southern California (see Section 11), create a particularly high risk, as they can rapidly spread what might otherwise be a small fire.

Recent concerns about the effects of climate change, particularly drought, are contributing to concerns about wildfire vulnerability. The term drought is applied to a period in which an unusual scarcity of rain causes a serious hydrological imbalance. Unusually dry winters, or significantly less rainfall than normal, can lead to relatively drier conditions and leave reservoirs and water tables lower. Drought leads to problems with irrigation and may contribute to additional fires, or additional difficulties in fighting fires. This is covered in greater detail in Section 11.

The Santa Monica Mountains area typically has mild, wet winters that lead to an annual growth of grasses and plants. This vegetation dries out during the hot summer months and is exposed to Santa Ana wind conditions in the fall. During Santa Ana conditions, winds in excess of 40 miles per hour (mph) are typical; gusts in excess of 100 mph may occur locally.

Santa Ana winds are generally consistent in their direction, but when combined with winds generated from burning vegetation, the wind direction generally becomes extremely erratic.

This can stress firefighting resources and reduce firefighting success. • Urban Development: As mentioned previously, growth and development in scrubland and forested areas is increasing the number of human-made structures in the interface areas of

50 Ibid. 51 https://wildfiretaskforce.org/wp-content/uploads/2022/05/californias-strategic-plan-for-expanding-the-use-ofbeneficial-fire.pdf, accessed May 12, 2025.

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southern California. Wildfire has an effect on development, yet development can also influence wildfire. The newer, larger homes being built in the WUI, with large exterior surface areas, provide more opportunities for embers and flames to ignite the structure, whereas the surrounding large lots are potentially more challenging to maintain as adequate defensible space. Owners often prefer homes that are private, have scenic views, are nestled in vegetation and use “natural” construction materials. A private setting may be far from public roads, or hidden behind a narrow, curving driveway. These conditions, however, make evacuation and firefighting difficult. The scenic views found along mountain ridges can also mean areas of dangerous topography. Natural vegetation contributes to scenic beauty, but it may also provide a ready trail of fuel leading a fire directly to the combustible fuels of the home itself.

Wildfire Hazard Identification
In California, wildfire hazard mapping, wildfire protection, and wildfire suppression are managed and conducted by three separate fire authorities in regions referred to as Federal, State and Local Responsibility Areas.51F
52 Each one of these is described further below.

The Federal and State governments have each developed their own methodologies to quantify the severity of the fire hazard in a region. These methodologies were generally developed in response to specific fires that caused significant loss of life and/or property damage. Early methods characterized the fire hazard of a region based on a weighted factor that typically considered fuel, weather and topography. More recent systems rely on the use of Geographic Information System (GIS) technology to integrate these factors to map the hazards, predict fire behavior and evaluate the impact that wildland fire would have on the surrounding communities and watersheds. Ranges of the wildfire hazard are further determined by the ease of fire ignition due to natural or human conditions and the difficulty of fire suppression. The wildfire hazard is also magnified by several factors related to fire suppression/control such as the surrounding fuel load, weather, topography and property characteristics.

Federal Responsibility Areas (FRAs)
Federal Responsibility Areas (FRAs) are lands in California that are typically owned or controlled by federal agencies where the US Forest Service, with no oversight from the State, manages all fire suppression and protection. These lands include, but are not limited to those controlled by the Bureau of Land Management (BLM), the Forest Service, and the National Park Service. Although the Federal government is responsible for these lands, given that Federal and State lands often adjoin each other, FRAs are often managed through cooperative agreements between Federal and State agencies in an effort to provide effective fire suppression and protection to both Federal and State lands.

Technical, financial, and resource guidance in support of wildland fire management across Federal lands in the United States is provided by the National Fire Plan (NFP). The NFP was authorized by the U.S. Congress in the year 2000 in response to the wildfires of that year. The NFP is a cooperative effort of the US Department of Agriculture’s Forest Service, the Department of the Interior, and the

52 Miller, R.K., Field, C.B., and Mach, K.J., 2020, Factors influencing adoption and rejection of fire hazard severity zone maps in California: International Journal of Disaster Risk Reduction, Vol. 50, doi:10.1016/j.ijdrr.2020.101686.

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National Association of State Foresters, and addresses firefighting, rehabilitation, hazardous fuel reduction, community assistance, and accountability.52F 53 Consistent with those objectives, the NFP emphasizes steps necessary to: 1) assure that firefighting resources and personnel are available to respond to wildfires that threaten lives and property; 2) reduce hazardous fuels as a means to decrease the likelihood of large, damaging fires occurring, especially near the WUI, 3) conduct emergency stabilization and rehabilitation of landscapes and communities impacted by a wildfire, and 4) actively participate in the intergovernmental Wildland Fire Leadership Council, a committee dedicated to the consistent implementation of wildland fire policies, goals, and management activities.53F
54 The NFP encourages the use of hazardous fuel
reduction treatment techniques (including prescribed fire alone, mechanical treatment alone, mechanical treatment plus prescribed fire, and other/wildland fire use, such as allowing lightningcaused fires to burn) to reduce the impact of wildland fire in FRAs and FRA-adjacent communities within the WUI. Another Federal wildland fire initiative that helps to reduce the risk posed by wildfires is the Healthy Forests Initiative (HFI) which, supported by several administrative reforms enacted in 2002 and 2003, allow Federal agencies to streamline the process of conducting fuel reduction activities in FRAs.

State Responsibility Areas (SRAs)
State Responsibility Areas (SRAs) include State lands, unincorporated communities and private property covered wholly or in part by timber, brush, undergrowth or grass. Wildfire hazard management of these lands is accomplished through laws and requirements enacted by the State through the California Government Code, with CAL FIRE being the agency responsible for firefighting in SRAs.

Legislative mandates passed in 1981 (Senate Bill 81, Ayala, 1981) and 1982 (Senate Bill 1916, Ayala, 1982; codified in Public Resources Code 4201-4204), that became effective on July 1, 1986, first required the State Fire Marshall to develop and implement a system to classify lands within SRAs according to their fire hazards into Fire Hazard Severity Zones (FHSZs). This program was developed in response to the Panorama fire in San Bernardino County in 1980. Areas are rated as having a moderate, high or very high fire severity based primarily on fuel types, their probability of burning and expected fire behavior. Specifically, areas are assigned a hazard score that considers fire history, vegetation, predicted flame length, ember production and movement, topography (terrain) and typical fire weather. These ratings do not take into consideration mitigation measures that may have been implemented, such as fire retardant construction or fuel reduction efforts, and the ranking categories are not an estimate of structural loss or potential risk.

The State mandates wildfire-resistant standards in fire-hazard zoned areas, including a defensible space buffer, fire-resistant materials for all new construction and major retrofits in accordance with Chapter 7A of the California Government Code, and access restriction if a disaster is ongoing. Local jurisdictions may impose more stringent requirements. 54F 55 Mandatory and recommended mitigation
strategies that can be implemented by property owners to reduce their wildfire hazard are discussed in more detail later in this section.

53 https://www.forestsandrangelands.gov/resources/overview/, accessed May 13, 2025. 54 Ibid, and https://www.forestsandrangelands.gov/leadership, both accessed May 13, 2025. 55 https://readyforwildfire.org/fire-safety-laws/, accessed May 9, 2025.

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Local Responsibility Areas (LRAs)
Local Responsibility Areas (LRAs) are incorporated communities where local governments oversee fire protection. In LRAs, City governments establish or adopt local ordinances, often modeled after the California Building and Fire Codes, and enforce land use planning, zoning and building permits designed to reduce the wildfire hazard in their jurisdiction.

The identification of areas or properties within LRAs at high risk of being impacted by a wildfire was first mandated by the Bates Bill (Assembly Bill 337, September 29, 1992). This legislation was a direct result of the great loss of lives and homes in the Oakland Hills Tunnel Fire of 1991 (see Table 10-1). Briefly, CAL FIRE in cooperation with local fire authorities was tasked to identify Very High Fire Hazard Severity Zones (VHFHSZs) in Local Responsibility Areas (LRAs). To accomplish this, CAL FIRE formed a working group comprised of state and local representatives that devised a point system that considers fuel (vegetation), slope, weather, and dwelling density. To qualify as a VHFHSZ, an area has to score ten or more points in the grading scale.

Once the boundaries of a VHFHSZ have been delineated, CAL FIRE notifies the local fire authorities that are responsible for fire prevention and suppression within that area. Local agencies must adopt at a minimum the maps as identified by the State Fire Marshal. California Fire Code (CFC) 4904.3.2 allows the local agency to have discretion to expand those areas, but local fire authorities cannot reduce or remove the VHFHSZs identified and designated as such by the State. This means that a local agency may include other areas in their jurisdiction not identified by the State as VHFHSZs into their local maps, provided that they have substantial evidence to support their findings.

Properties within VHFHSZs are required to comply with a variety of building requirements and vegetation management practices spelled out in the California Fire Code.

Mapped Wildfire Hazard Zones Near and In Santa Monica
There are no Federal Responsibility and State Responsibility Areas (FRAs and SRAs) near Santa Monica. The closest SRA to Santa Monica is in the Santa Monica Mountains area north of Malibu, stretching west from Tuna Canyon Park to Point Mugu State Park, and including a large portion of the Santa Monica Mountains National Recreation Area. Within the larger SRA there are several pockets and larger areas that are managed by the Federal government and are thus FRAs. The SRAs and FRAs closest to Santa Monica as of December 2024 are shown on Figure 10-3.

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Figure 10-3: Federal Responsibility Areas (FRAs) in light green and State Responsibility Areas (SRAs) in yellow to the north and northwest of Santa Monica as of December 31, 2024 (note that these areas continue to the north and west, outside of the boundaries of this figure; City of Santa Monica boundaries, in turquoise, are approximate) Source: Modified from
https://experience.arcgis.com/experience/bd8234bfe71548b087b11210a0d7d45e?id=468717e399fa4238ad 86861638765ce1, accessed May 9, 2025.

Most of Santa Monica has relatively gentle topography and is highly urbanized. Moreover, Santa Monica does not press against open wildland areas in the southern flanks of the Santa Monica Mountains, and the vegetated areas within the city are for the most part landscaped and irrigated, although the 2025 Palisades and Eaton fires showed that urban landscapes can burn and transmit fire. There are at least three canyons in the southern flanks of the Santa Monica Mountains that could convey a wildfire to the northern city boundaries. These are the Mandeville, Sullivan and Rustic canyons. Wildfires in Mandeville and Sullivan canyons could burn down to Santa Monica Canyon, along the northern city boundary. Although less likely given their extensive development, there are other canyons farther to the northeast of the city that if ignited, could convey a WUI fire to the northeastern portion of Santa Monica in the area of the Brentwood Country Club, and then onto the vegetated corridor that extends from Montana Avenue to Centinela Avenue.

Although these areas have not burned historically, there is a small but significant possibility that these areas could burn in the future, a condition that has recently been recognized by CAL FIRE (see below). Thus, enhanced onsite protection for structures and people in or adjacent to these areas is recommended, including educating property owners about their responsibility in maintaining their properties and adhering to construction standards that make their houses more fire-resistant. The bluffs of Pacific Palisades are also locally covered with vegetation that could be ignited by embers blown in from the north-northeast, or as a result of human activities, such as illegal encampments by unhoused individuals (small vegetation fires have occurred here before).

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Prior to 2025, the city of Santa Monica was not identified as having a wildfire hazard, with the nearest VHFHSZ bordering the city on its northern side. Following the January 2025 Palisades fire, CAL FIRE has issued a new map that places the northern portion of Santa Monica within a VHFHSZ.

Narrow strips to the south of the VHFHSZ are also now considered as having a high and moderate fire hazard. The City of Santa Monica Fire Department has recommended that City Council adopt this new fire hazard map issued by the State with no changes. The newly issued fire hazard zones are shown on Figure 10-4 (also included as Plate H-17 in Appendix H). Fire hazard mitigations that are now required in these areas are discussed further in the following sections of this report.

As briefly mentioned before, climate change is expected to increase the likelihood of wildland fires in the mountains and hills surrounding the Los Angeles basin. A study conducted in the Santa Monica Mountains National Recreation Area found that in 2020, invasive, non-native, highly flammable annual grasses and herbaceous plants amounted to 34% of the vegetation cover in the area (Stork et al., 2023). This is significant because in the Santa Monica Mountains, this type of vegetation directly correlates with higher property losses based on analysis of wildland fires that occurred there between 2001 and 2010 (Syphard et al., 2012). Furthermore, simulations conducted by Dong et al. (2022) suggest that the number of annual large fire days in southern California will increase from about 36 days in 1970-1999 to about 58 days under the moderate RCP 4.5 scenario, and about 71 days under the RCP 8.5 scenario55F

56. These numbers, the authors indicate, reflect “both
an intensification of conditions during the traditional summer fire season and a lengthening of the large fire season in spring and fall.”
Overall, burned areas in southern California are projected to increase over 60% for Santa-Ana-wind based fires and over 75% for non-Santa Ana-wind fires (Hall et al., 2018). In Los Angeles County, the San Gabriel Mountains have the highest degree of wildfire risk and are projected to experience an increase in wildfire burn area of approximately 40% and 50% in 2050 and 2080, respectively, under the RCP 8.5 scenario. In the watershed immediately to the north and northwest of Santa Monica, which is defined by the western half of the south-facing slopes of the Santa Monica Mountains, these numbers are approximately 19% and 11% respectively, compared to the 1961- 1990 baseline period.

56 Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 are two of the four scenarios used by the Intergovernmental Panel on Climate Change to model future climate change based on different greenhouse gas emission trajectories. RCP 4.5 is an intermediate scenario, and RCP 8.5 is a business-as-usual, worst-case scenario. For additional information, refer to Section 11.

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STRUCTURE FIRES
Definition and Recent Statistics
Structure fires are fires that affect the structural components of a building or structure, including residential, commercial, and industrial buildings, and infrastructure such as bridges. A structure fire can be confined to a single room, a portion of a building, or can engulf the entire structure, and can involve any and all parts of a structure, such as the walls, roof, or floors.

A 2021 report by FEMA56F
57 that evaluated the incidence of building fires in the United States indicated that an estimated 368,500 residential57F
58 building fires occurred in the country from 2017 to 2019, with these fires accounting for an estimated 2,770 deaths, 11,650 injuries, and property losses of about $8.1 billion. Another similar analysis of fires in the United States (Hall, 2024)58F 59 found that an
estimated 470,000 fires occurred throughout the country in 2023, resulting in 3,070 civilian deaths, 11,790 civilian injuries, and about $14.7 billion in property losses. Note that the statistics for 2023 alone are higher than those for 2017-2019 combined. Of the structure fires reported in 2023, about 352,000 were residential fires, accounting for nearly 75% of the total. Furthermore, residential structure fires in 2023 accounted for more than 95% of civilian deaths, more than 86% of civilian injuries, and more than 77% of property losses reported. The numbers provided are thought to underestimate the total number of fires that occurred in buildings given that many fires confined to their point of origin, such as a fire in a cooking pot or in an oven, go unreported.

Hall (2024)59F
60 also reviewed fire statistics in the United States for the years between 1980 and 2023 inclusive and found that the number of civilian deaths and injuries based on total population have decreased over the past 43 years. Specifically, in 1980, 28.6 civilians out of every 1 million died in structure fires compared to 11.0 civilians in 2023 (Figure 10-5[A]). Similarly, the number of fires per year accounting for the overall increase in population has also decreased from 13.1 total fires per 1,000 people in 1980 to 4.1 total fires per 1,000 people in 2023, and home fires have decreased from 3.2 per 1,000 people in 1980 to 1.0 in 2023 (Figure 10-5[B]).

However, when looking at the number of deaths per number of home fires reported, there actually has been an increase in deaths over the years, with 7.1 deaths reported for every 1,000 home fires reported in 1980 compared to 8.7 deaths for every 1,000 home fires reported in 2023 (see Figure 10-5[C]). It is noteworthy that the number of deaths associated with apartment fires has decreased over time, with this thought to be related to increased regulations and higher oversight by fire departments of multi-family residential structures (such as monitored fire detection systems in apartment complexes that lead to fire department response when a fire alarm is triggered). The cost of structure fires has also increased over the years, even when adjusted for inflation. Thus, the average loss per structure fire in 1980 was about $5,200 ($19,100 in 2023 dollars), whereas in 2023, the average loss per structure fire amounted to $31,200 (see Figure 10-5[D]; these figures exclude the Twin Tower losses on 9/11/2001). These figures show that although there have been

57 https://www.usfa.fema.gov/downloads/pdf/statistics/v21i2.pdf, accessed May 13, 2025 58 The term residential in the FEMA report includes single-family homes, two-family homes, multi-family buildings, manufactured housing, hotels, motels, dormitories, assisted living facilities and halfway houses. It does not include prisons, nursing homes, juvenile care facilities, or hospitals. 59 Hall, S., 2024, Fire loss in the United States: NFPA Research article available from https://www.nfpa.org/education-and-research/research/nfpa-research/fire-statistical-reports/fire-loss-in-the-unitedstates, accessed May 13-14, 2025. 60 Ibid.

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improvements in reducing the number and impacts of structure fires, these still pose a significant hazard and that more can be done to reduce the losses associated with structure fires.

Figure 10-5: Various Statistics for Fire Losses in the United States, 1980-2023 [A]: Civilian Fire Deaths Per Million Population [B]: Fires per 1,000 population by year [C]: Deaths per 1,000 Reported Home Fires by
Year and Occupancy [D]: Average loss per structure fire Source: Hall (2024)
Causes of Structure Fires
According to FEMA (2021)60F
61, cooking is the leading cause of residential building fires, accounting for more than 41% of all home fires. Although most cooking fires are small and confined to their point of origin, a still significant percentage of non-confined residential fires also start in cooking areas and kitchens. Table 10-3 lists the main causes of residential building fires in the U.S. for the period between 2017 and 2019. In residential buildings, the next most common areas where fires start are bedrooms (12%), family rooms or living rooms (6%), garages and carports (5%), vacant spaces and attics (5%), laundry areas (5%), and exterior wall surfaces (5%). Cooking is also the main cause of structure fires in non-residential buildings, such as assembly places, eating and drinking establishments, educational and institutional facilities, stores, offices, detached garages, industrial, manufacturing, and storage facilities.61F
62 In non-residential buildings, fires most often occur in kitchen areas, outside areas, storage buildings, and vehicle storage areas.62F 63 61 https://www.usfa.fema.gov/downloads/pdf/statistics/v21i2.pdf, accessed May 13-5, 2025 62 https://www.iccsafe.org/building-safety-journal/bsj-dives/non-residential-building-fires-report/, accessed May 15, 2025. 63
Ibid.

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In both residential and non-residential settings, the most significant factors contributing to ignition that lead to non-confined fires include the misuse of materials or products (such as combustible materials placed too close to a heat source; abandoned or discarded matches, cigarettes or other combustible materials), failure or malfunction of an electrical or mechanical system, operational deficiencies (such as unattended equipment), and inability to control the spread of what began as a small, confined fire. Characteristics common to the large, non-confined fires reported in the sources referred to for these statistics in both residential and non-residential structures is that a large percentage of the impacted buildings did not have fire alarms and were not fitted with automatic extinguishing systems.

Table 10-3: Causes of Residential Building Fires in the U.S. (2017-2019), Organized from Highest to Lowest Percentages
Cause Percentage Cause Percentage
Cooking 41.4 Unknown 18.5
Heating 7.6 Unintentional,
careless actions 6.1
Electrical malfunction 5.4 Intentional 3.5
Open flame 3.5 Other heat source 2.7
Appliances 2.4 Equipment missoperation, failure 1.9
Smoking 1.7 Exposure 1.5
Natural 1.4 Under investigation 1.1
Other equipment 1.0 Playing with heat
source

0.3 Factors that Impact Structure Fire Risk in a Community Fire departments quantify and classify structural fire risks to determine where a fire resulting in large losses of life or property is more likely to occur using criteria such as the following:
• Type of occupancy, that is residential, commercial, manufacturing, etc. • density, such as high-occupancy vs low-occupancy, and thus the risk and potential for loss of life presented by the occupancy type and occupancy load, including mobility of the occupants
• building size, height, including number of floors (stories) above ground level), and location • age of the building
• estimated dollar value or historical value of the occupancy • construction type and access
• unique hazards presented by the occupancy, such as the types of combustibles therein, hazardous materials, previous fire history
• needed fire flow versus available fire flow
• proximity to other buildings (called exposure separation), and • built-in protections, such as fire-resistant construction materials, built in fire alarms and fire protection systems such as fire sprinklers

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Occupancies that, given a combination of the characteristics listed above are recognized as likely to strain the fire department’s response capability, are called “target hazards.” Target hazards encompass all structural inventories in the community that have a maximum and significant fire risk, as described further below. Typically, fire departments identify the major target hazards in their service area and then perform intensive pre-fire planning, inspections and training to address the specific fire problems in that particular type of occupancy (for example, training to respond to fires in facilities that handle hazardous materials is significantly different than training to respond to a fire in a high-occupancy facility such as a mall, auditorium or night club).

Residential occupancy is typically, the most common target hazard due to the life-loss potential, 24- hour occupancy, and risk and frequency of events; however, the consequences of residential fires can be high or low, depending on the age of the structure, location, size, and occupancy load, among other factors. For example, in newer residential areas where construction includes fireresistant materials in addition to internal fire sprinkler and fire alarm systems, most building fires can be confined to the room or unit of origin, especially if the fire department responds promptly. In older residential areas where the building materials may not be fire-rated, there is a higher probability of a building fire spreading from the room of ignition to other rooms or units in the structure, and even spreading into adjacent structures, unless there is ample distance between structures, there are no strong winds, and the fire department is able to respond in a timely manner.

In medium- to high-density residential and commercial areas, narrow spaces in between structures may limit emergency access and/or evacuation of the structure during a fire. Access by emergency services personnel, including firefighters and medical response teams with gurneys, can be hindered if projections such as bay windows and roof awnings extend into the setback between structures, or if non-structural items, such as garbage cans or sheds are kept there. High-density occupancies may include multi-story buildings with multiple housing units or offices, enclosed shopping centers with large, open rooms that house highly flammable materials like clothing and paper goods (such as a large retail store at a mall), and large entertainment venues like movie theaters, night clubs and concert halls. High-density locales may also often be associated with heavy traffic conditions and limited parking areas for emergency response vehicles, both of which can impact response times.

Four classifications of risk are typically considered, as follows:
• High Probability/High Consequences (Maximum Risk) such as multi-family dwellings and residential buildings (especially older ones) that require a large amount of water and fire suppression personnel to contain the fire, have the potential for a high loss of life, are irreplaceable or would have a major financial or social impact on the community if lost, or have hazardous materials occupancies (see Section 12). Some of the high probability/high consequence targets that fire departments are most concerned about are high-rise buildings due to the specialized firefighting equipment needed, the limited routes of access into and out of a building, and the potential for great loss of life. • Low Probability/High Consequences (High Risk) are buildings of substantial size that have the potential for loss of life and property, and if lost to fire would have a significant impact on the community (in the form of reduced or eliminated critical services, lost jobs and/or tax revenue), but that have built-in fire protection systems and fire alarms. Examples include hospitals and medical facilities, schools, child-care centers and nursing homes, mid-size

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shopping malls, industrial occupancies that do not use or store hazardous materials, and large office complexes.
• High Probability/Low Consequences (Moderate Risk) are buildings of moderate size that can present a potential for loss of life and property, but that loss would be generally limited to the immediate occupants of the structure. Examples include smaller apartment buildings, small office buildings, older single-family residential homes built with non-fire rated construction materials and mobile homes.
• Low Probability/Low Consequences (Low Risk) are buildings that have limited exposure and are built of fire-retardant materials, include fire alarms and automatic fire suppression systems, and have a low potential of spreading to other structures. Fires in these structures have a high probability of being confined to the room of origin, and would pose a limited financial impact on the owners and the community. Examples include detached singlefamily dwellings and small structures not normally occupied by people.

Structure fire response requires numerous critical tasks to be performed simultaneously. The number of firefighters required to perform the tasks varies based upon the risk. Thus, the number of firefighters needed at a maximum or high-risk occupancy, such as a shopping mall or large industrial occupancy, would be significantly higher than for a fire in a lower-risk occupancy. Given the large number of firefighters that are required to respond to a high-risk, high-consequence fire, fire departments, such as the Santa Monica Fire Department, routinely rely on automatic and mutual aid agreements to address the fire-suppression needs of their community.

Fires After an Earthquake
Large fires following an earthquake in an urban region, although rare, have the potential to cause great losses. Two of the largest peace-time urban fires in history, the 1906 San Francisco, and 1923 Tokyo, Japan fires were caused by earthquakes. The conflagration in San Francisco after the 1906 earthquake was the single largest urban fire, and the single largest earthquake loss, in U.S. history.

Three days of fires consumed more than 28,000 buildings within a 4.6-square-mile area.63F 64 The cost
was (and is) staggering: $250 million in 1906 dollars, or about $8.7 billion in 2024 dollars.

More recently, the 1989 Loma Prieta earthquake, the 1994 Northridge earthquake, and the 1995 Kobe, Japan earthquake all demonstrate the current, real possibility of a fire-following-an earthquake developing into a conflagration. The Loma Prieta earthquake caused 41 fires64F 65, whereas the Kobe
earthquake is estimated to have caused 300 separate fires that damaged an area approximately equivalent to 70 U.S. city blocks65F
66 and contributed to more than 600 deaths. The moderately sized, M6.7 Northridge earthquake caused several structural fires, many the result of broken gas mains: the earthquake caused 15,021 natural gas leaks that resulted in three street fires, 51 structure fires (23 of these caused total ruin of the buildings) and the destruction by fire of 172 mobile homes. In one incident, the earthquake severed a 22-inch gas transmission line and a motorist ignited the gas while attempting to restart his stalled vehicle. Response to this fire was impeded by the earthquake’s rupture of a water main; five nearby homes were destroyed. Elsewhere, one mobile home fire started

64 Scawthorn, C., 1987, Fire Following Earthquake—Estimates of the Conflagration Risk to Insured Property in Greater Los Angeles and San Francisco: report prepared for the All-Industry Research Advisory Council, Oak Park, IL. Scawthorn, C., O’Rourke, T.D., and Blackburn, F.T., 2006, The 1906 San Francisco earthquake and fire—Enduring lessons for fire protection and water supply: Earthquake Spectra, Vol. 22, No. S2, pp. S135-S158. 65 https://www.iitk.ac.in/nicee/wcee/article/10_vol10_5983.pdf, accessed June 19, 2025. 66 https://www.nist.gov/el/earthquake-kobe-japan-1995, accessed June 19, 2025.

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when a downed power line ignited a ruptured transmission line. In many of the destroyed mobile homes, fires erupted when inadequate bracing allowed the homes to slip off their foundations, severing gas lines and igniting fires. There was a much greater incidence of mobile home fires (49.1 per thousand) than other structure fires (1.1 per thousand).

The damages from the 1994 earthquake echoed the findings of a study published in 1988 by the California Division of Mines and Geology (Toppozada and others, 198866F 67). The 1988 study
identified projected damages in the Los Angeles area as a result of an earthquake on the NewportInglewood fault. The earthquake scenario estimated that thousands of gas leaks would result from damage to pipelines, valves and service connections. That study prompted the Southern California Gas Company to start replacing their distribution pipelines with flexible plastic polyethylene pipe, and to develop ways to isolate and shut off sections of supply lines when breaks are severe.

Nevertheless, as a result of the 1994 Northridge earthquake, the Southern California Gas Company reported 35 breaks in its natural gas transmission lines and 717 breaks in distribution lines. About 74 percent of its 752 leaks were corrosion related. Furthermore, in the aftermath of the earthquake, 122,886 gas meters were closed by customers or emergency personnel. Thankfully, most of the leaks were small and could be repaired at the time of service restoration, but the costs and time associated with these repairs were considerable.

The major urban conflagrations in 1906 San Francisco and 1995 Kobe, Japan, among others, were in part the result of closely built, congested areas of attached buildings with no fire sprinklers, no adequate fire separations, no fire code enforcement, and narrow streets. In the past, fire apparatus and water supplies were also inadequate in many large cities, and many fire departments were comprised of volunteers. Many of these conditions no longer apply to the cities of today. However, the recent historical data show that fires after earthquakes continue to be a threat. Khorasani and Garlock (201767F
68) reported that at least 20 earthquakes between 1906 and 2014, including the earthquakes mentioned above, and ranging in size between magnitudes 5 and 9, resulted in firefollowing-earthquake losses. Scawthorn (198768F 69) and Cousins and Smith (200469F70) also found that
the number of ignitions increases with an increase in earthquake intensity.

Earthquake-induced fires have the potential to result in a worst-case fire-suppression scenario for a community as a result of a series of events that can combine to create what is referred to as a “cascade effect.” Specifically, damage to the electrical and gas systems can cause multiple, simultaneous fire ignitions distributed over a broad geographic area. Fallen electrical and gas appliances or equipment inside structures, especially if surrounded by flammable materials, can also start fires. Many of these interior fires may normally be put out quickly by the building occupants, but if the structure has been evacuated in response to the earthquake’s ground shaking, the fire may go unnoticed until it has spread to the point where a fire department response is necessary.

67 Toppozada, T.R., and others, 1988, Planning Scenario for a Major Earthquake on the Newport-Inglewood Fault (Los Angeles and Orange Counties): California Division of Mines and Geology Special Publication No. 99. 68 Khorasani, N.E. and Garlock, M.E.M., 2017, Overview of fire following earthquake: historical events and community responses: International Journal of Disaster Resilience in the Built Environment, Vol. 8, No. 2, pp. 158- 174; doi:10.1108/IJDRBE-02-2015-0005. 69 Scawthorn, C., 1987, Fire Following Earthquake—Estimates of the Conflagration Risk to Insured Property in Greater Los Angeles and San Francisco: report prepared for the All-Industry Research Advisory Council, Oak Park, IL. 70 Cousins, W.J., and Smith, W.D., 2004, Estimated losses due to post-earthquake fire in three New Zealand cities:

Proceedings of the Annual Technical Conference, 19-21 March 2004, Rotorua, New Zealand Society for Earthquake Engineering, Paper No. 028.

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Notification to the fire department of an ongoing structural fire may be delayed because of disruptions to the communications network, and if the firefighters are occupied in search and rescue operations, their ability to respond to these fires may be impaired or delayed due to limited resources and personnel. Damage to fire stations, and streets blocked by fallen debris or facades may also hinder the timely response by the fire department. Significantly, if the water distribution system has been damaged, reduced or non-existent water volume and pressure would further limit the fire suppression efforts (Juliá et al., 202170F
71). Finally, if earthquake-induced fires occur during Santa Ana wind conditions, the results can be far worse.

VULNERABILITY AND RISK ASSESSMENT
What is Susceptible to Wildfires in Santa Monica
Southern California neighborhoods at or near the WUI are characterized by a diverse mixture of housing structures, development patterns, ornamental and natural vegetation, and natural fuels. In the event of a wildfire, this diverse mixture of vegetation, structures and development patterns, compounded by the local topography and weather at that specific time, can result in an unwieldy and unpredictable fire. Factors important in fighting such fires include access, firebreaks, proximity of water sources, distance from a fire station, and available firefighting personnel and equipment. A review of past WUI fires has shown that many structures are destroyed or damaged for one or more of the following reasons:
• Combustible roofing material
• Wood construction
• Structures with no defensible space
• Fire department with poor access to structures
• Subdivisions located in heavy natural fuel types
• Structures located on steep slopes covered with flammable vegetation • Limited water supply and
• Winds over 30 miles per hour
As discussed previously, the northern portion of the city of Santa Monica is now considered to have a wildfire hazard, with the newly defined moderate, high, and very high fire hazard severity zones in the city shown on Figure 10-4 (and Plate H-17). These hazard zones were defined by CAL FIRE based on an analysis of factors such as:
• fire history (i.e., the recent, nearby Palisades fire that burned to within a few hundred feet of the northern city boundary),
• existing and future potential fuel conditions (such as densely vegetated slopes along Santa Monica canyon, the coastal bluffs and the I-10 embankments), • terrain and slope (houses on the north side of San Vicente Boulevard and streets north and west of San Vicente Boulevard that are at the top of the north-facing slope that forms the

71 Juliá, P.B., Ferreira, T.M., and Rodrigues, H., 2021, Post-earthquake fire risk assessment of historic urban areas: A scenario-based analysis applied to the Historic City Centre of Leiria, Portugal: International Journal of Disaster Risk Reduction, Vol. 60, doi:10.1016/j.ijdrr.2021.102287.

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south side of Santa Monica Canyon),
• structural density (i.e., distance between structures allowing fire to jump from one structure to another)
• fire occurrence and weather (i.e., hot, dry and windy conditions, and whether or not the area is experiencing a drought, with these conditions likely to become more common as a result of climate change), and
• possible ignition sources, including the possibility of Santa Ana winds transporting embers from adjacent burning areas to the northern portion of the city, and brushfires ignited within Santa Monica proper, along the coastal bluffs and other vegetated areas, that could then spread to developed areas.

It is important to note that the hazard zones mapped by CAL FIRE do not take into consideration mitigation measures that may be in place or could be implemented to reduce the hazard, including hardening of structures and fuel reduction efforts. The risk posed by a wildfire is the potential damage that a fire can do to the area based on factors such as those described above, taking into consideration the modifications that have been made, including the use of fire-resistant building materials and design, the implementation of fuel reduction projects, and the establishment of defensible spaces around existing structures.71F
72 Road access is a major issue for all emergency service providers. In many single-family residential neighborhoods, including several of the residential streets in Santa Monica, there is limited space for emergency vehicle turnarounds, hindering emergency workers’ access to the houses at risk. This is especially true in streets with parking lanes on both sides. Narrow winding roads with inadequate turn-around space are also particularly challenging as fire trucks are too long to maneuver in these roads. Fires at the WUI tend to move quickly, with most of the damage or losses generally occurring in the first few hours after the fire starts (refer to the descriptions of the 1978 Los Angeles and 2025 Eaton fires at the top of this section). Therefore, access to fire-impacted areas for the purposes of emergency response is critical. This requires streets that meet minimum access and egress requirements so that they can be traversed by fire apparatus.

As the 2025 Los Angeles area fires illustrated, the water supply system that feeds fire hydrants is not designed to fight a regional fire where multiple ignitions are being battled at the same time. Areas at higher elevations may be serviced by water that is pumped up to the higher elevations. In the event of a fire, and especially if the electric system has been powered down, it may be impossible to pump additional water to the reservoirs at or above the fire line. Emergency water storage is also critical, especially when battling large wildland fires. Leaks and breaks in the water distribution system, including leaking irrigation lines and open valves in destroyed homes72F 73, and residents using
firehoses to battle embers on their property, also reduced the amount of water available to the firefighters. A seven-day emergency storage supply in the reservoirs is recommended, especially in areas likely to be impacted by fires after earthquakes, due to the anticipated damage to the main water distribution system as a result of ground failure due to fault rupture, liquefaction, or landsliding.

A vulnerability assessment of the interface areas of the city at risk from wildfire requires knowledge about the population and total value of the property at risk, and an estimate of the area that would

72 https://osfm.fire.ca.gov/what-we-do/community-wildfire-preparedness-and-mitigation/fire-hazard-severity-zones, accessed May 13, 2025. 73 SMFD reported that this was a challenge during the 2025 Palisades fire.

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be impacted by the fire. Unlike an earthquake, which has the potential to impact the entire region, wildfires at the WUI are often contained thanks to the heroic efforts of the local fire department, generally with help from other local, regional, State, and Federal agencies. Thus, estimates of the potential loss are approximate at best. However, using the software Crisis Track and considering the areas in Santa Monica now identified as having a very high fire hazard, we estimate that property losses as a result of a wildfire just in that small northern portion of the city would range between $60 million and almost $600 million. A fire within the very high fire hazard zone would impact 1,715 structures. Given that nearly 99% of these structures are residential, a fire therein would result in the temporary or permanent displacement of thousands of residents.

Structure Fires
Recent historical records (for the years 2016 to 2019 inclusive) from the Santa Monica Fire Department show that fires comprise a small percentage (<2%) of the incidents that the Santa Monica Fire Department responds to on an annual basis, with structure fires accounting for about

0.53% of the total calls (Citygate Associates, 2020). For example, in 2019 alone, out of the 17,051 emergency calls that the fire department responded to, approximately 220 were for fires. Of these, 71 were reported as structure fires. All of these structure fires, except for five, occurred in the central portion of the city bounded by Montana Avenue on the north and Ocean Park Boulevard on the south. The five exceptions were structure fires reported in the southwestern portion of the city, south of Ocean Park Boulevard and generally west of Highland Avenue.73F 74 The fire occurrences in the city are generally reflective of the age of the structures in Santa Monica.

Most (85%) of the City’s housing stock was built more than 30 years ago, and thus built to older building standards and with non-fire resistive construction materials. Moreover, many buildings date from before the 1930s in the older sections of the city, including Ocean Park, the Third Street neighborhood, and the area between Montana Avenue on the north, Colorado Avenue on the south, the Pacific Ocean on the west and 26th Street on the east. Many of the oldest buildings in the city that predate the early 1930s are unreinforced masonry buildings that are susceptible to collapse during a fire, posing a significant risk to fire department responders. Even if retrofitted, the retrofits may not keep the structure from collapsing during a fire.

Single-family detached structures make up about 31% of the housing stock in Santa Monica; the remaining housing units include courtyard apartments, condominiums and large mixed-use residential complexes. Single-family units predominate in the northern and southern portions of the city, and multi-family units are concentrated along the central portion of the city.74F 75 Significantly, the
residential population density in the city ranges from about 1,500 people per square mile to more than 20,000 people per square mile, with an average of 11,067 people per square mile (based on 2022 Census data). This makes Santa Monica the 108-most densely populated incorporated area in the United States.75F
76 Moreover, some of the more densely populated areas have a high concentration of residents that are 65 years old and older. In addition to residential units, Santa Monica has approximately 4,325 other buildings used for commercial, industrial, education, religious and government purposes. These buildings house approximately 11,000 non-residential occupancies,

74 Citygate Associates, 2020, Community Risk Assessment / Standards of Cover Analysis, City of Santa Monica, CA, Volume 2 of 2: Map Atlas. 75 City of Santa Monica 2021-2029 Housing Element, Final Draft dated September 2022. 76 https://en.wikipedia.org/wiki/List_of_United_States_cities_by_population_density, accessed May 14, 2025.

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including offices, professional services, retailers, dining and entertainment-based businesses, healthcare facilities, schools, and government facilities.76F 77 The large commercial and
technological/industrial base in Santa Monica means that there is also a potential for chemical fires to occur in some areas of the city, which directly and indirectly can also impact nearby residential areas. The generation, use, or storage of chemicals at these facilities is conducted under the oversight of the local Certified Unified Program Agency (CUPA), who conducts compliance inspections on an annual basis to confirm that all of these substances are being handled appropriately. For more information on this refer to Section 12.

High Probability/High Consequences (Maximum Risk) target hazards in the city of Santa Monica include condominium and apartment buildings; large-occupancy buildings of historical significance like the Charmont Apartments, the Georgian Hotel, the Sovereign Hotel and the Hotel Casa del Mar; and large shopping centers and malls like the Santa Monica Place.

Low Probability/High Consequences (High Risk) buildings in Santa Monica include the two main hospitals (UCLA Santa Monica Medical Center and Providence Saint John’s Health Center), other medical facilities, schools, child-care centers and nursing homes, mid-size shopping malls, industrial occupancies that do not use or store hazardous materials, and large office complexes. The City’s Standards of Cover Study prepared by Citygate Associates (2020) identified 2,150 buildings in Santa Monica with a maximum or high fire risk.

High Probability/Low Consequences (Moderate Risk) buildings in Santa Monica include smaller apartment buildings, small office buildings, older single-family residential homes built with non-fire rated construction materials and mobile homes.

Low Probability/Low Consequences (Low Risk) buildings in Santa Monica include detached singlefamily dwellings built to recent building and fire codes, and small structures not normally occupied by people.

Significantly, in Santa Monica these risk categories often co-exist in the same area. For example, residential buildings often adjoin and/or are intermixed with commercial buildings, such as the residences immediately north and south of the businesses along Montana Avenue and Wilshire Boulevard. There are also the mixed-use buildings that typically house commercial businesses at ground level, and have residential units in the floors above. While this type of development has several environmental and social advantages in that it may reduce dependency on automobiles which in turn reduces traffic and improves air quality, and promotes economic investment and a sense of community, there are specific fire hazards associated with this type of development that need to be considered. This is especially true if the businesses on the ground floor include restaurants, bakeries, or engage in other commercial activities that involve the use of stoves or ovens, or the storage of flammable materials. As a result of infill development in the city, multi-family structures often occur next to single-family detached residences.

Given that several risk categories occur within the same geographic area, it is appropriate for the Santa Monica Fire Department to have several fire stations spread out across the city, with Fire Stations 1, 2 and 3 located in and servicing some of the most densely populated areas that include

77 Citygate Associates, 2020, Community Risk Assessment / Standards of Cover Analysis, City of Santa Monica, CA, Volume 1 of 2: Technical Report.

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all of these fire risk categories (see Figures 3-1 and 10-4 for the location of the fire stations in the city). Citygate Associates (2020) determined that all planning areas in the city, except for planning zone 5, which covers the area around the airport, have a moderate building fire risk. Planning zone 5 is considered to have a low building fire risk.

The high value of real-estate in Santa Monica means that a structure fire in the city, even if the fire impacts only a portion of the building, has the potential to result in tens to hundreds of thousands of dollars in property damage. Structure fires also displace households, or, if in a commercial or industrial building, can result in business interruptions, and economic losses. Structure fires can impact insurance premiums and availability, and property tax revenue losses.

Fires After an Earthquake
As discussed in greater detail in Section 6 – Earthquakes, there are some sections of Santa Monica where, due to ground failure as a result of either fault rupture or liquefaction, breaks in the gas mains and the water distribution system could lead to a significant fire-after-earthquake situation.

Specifically, the Santa Monica fault is mapped as extending through the northern portions of the city, whereas liquefaction-susceptible areas have been mapped along the coastline and in the far east-central portion of the city near the Interstate 10 (I-10) freeway. Refer to Figures 6-13 and 6-14 (and Plates H-4 and H-5 in Appendix H) for information regarding those areas of the city susceptible to surface fault rupture and liquefaction, respectively. Surface rupture, with the resultant breakage of gas transmission and distribution pipelines, and water mains, is expected to occur if the Santa Monica fault ruptures, causing an earthquake centered in Santa Monica. Liquefaction could occur not only in response to an earthquake on the Santa Monica fault, but also in response to earthquakes on the Newport-Inglewood, Palos Verdes, or other nearby faults.

Loss-estimation scenarios were conducted for the city of Santa Monica using HAZUS. Specifics of this analysis are discussed in detail in Section 6 – Earthquakes. Three different fire-after-earthquake scenarios were considered for the city. The results of these loss estimations indicate that Santa Monica could experience between three (3) and five (5) ignitions immediately following an earthquake, with the San Andreas and Newport-Inglewood fault earthquake scenarios triggering three ignitions, and the Santa Monica fault earthquake scenario triggering five ignitions (see Table 10-4). The burnt area resulting from these ignitions will vary depending on wind conditions.

The models estimated that between 0.12 and 0.35 percent of the total area covered by the city (equivalent to between 0.01 and 0.03 square miles) would be burnt by the fires following the earthquake. If Santa Ana wind conditions are present at the time of the earthquake, the burnt areas can be expected to be significantly larger.

The fires triggered by an earthquake on the San Andreas and Newport-Inglewood faults are anticipated to displace approximately 78 to 80 people, whereas the fires resulting from an earthquake on the Santa Monica fault are expected to displace about 407 people. Property losses as a result of these fires are estimated to range between about $20 million and $80 million. These values are for low wind conditions. If winds stronger than 30 miles per hour are blowing through the region at the time of the earthquake, the burnt area, number of people displaced, and property losses would be higher than those shown on Table 10-4. The significant loss that could be caused by earthquake-induced structure fires stress the importance for local firefighting resources to prioritize target hazard surveys post-earthquake to promptly identify and extinguish structure fires.

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Table 10-4: Fires Following an Earthquake
Earthquake Scenario No. of
Ignitions
Approximate
Burn Area
(% of city)
No. of
Displaced
Individuals
Building Value
Destroyed
(Millions of $)
Santa Monica 5 0.35 407 80
Newport-Inglewood 3 0.12 80 21
San Andreas 3 0.12 78 20
Social Vulnerability to Fires
Humans exposed to fire are at risk of injury, in the form of life-threatening burns, or death, and, as discussed above, fires can result in the destruction of property and infrastructure, which can lead to the displacement of people and even entire communities. Social vulnerability to fire refers to the susceptibility of individuals and communities to experience adverse impacts as a result of a fire. The factors that influence how an individual, family, and/or community prepare for, respond to, and recover from a fire include socioeconomic, demographic and infrastructural elements. Infrastructural factors are aspects of the built environment, such as the proximity of buildings and infrastructure to the WUI, the condition of the electrical infrastructure (such as above ground electric lines susceptible to strong wind events that can cause the lines to spark or fall, causing a fire), and the availability of adequate access roads and water supply to fight a fire.

Given that wildland fires do not recognize jurisdictional boundaries, can occur in areas vegetated with light fuels such as grasses and ornamental plants, and generally spread uphill, it is appropriate to consider the possibility that a wildland fire approaching Santa Monica from the north could extend into the residential areas facing Santa Monica Canyon, in the now identified VHFHSZ shown on Figure 10-4. These conditions, combined with strong winds from the north (prevalent in the Santa Monica region between October and February), could help transport embers from the fire front into other parts of the city. Although less likely, if a vegetation fire occurred in one of the City parks or the I-10 Freeway embankments, typically the result of homeless encampment activities, the fire could also spread to nearby structures.

The risk posed by a wildfire spreading into the northern or northeastern portion of the city, or a vegetation fire occurring in a city park and spreading to nearby areas was recognized in mapping by the Wildfire Risk to Communities website (https://wildfirerisk.org). This is a project of the U.S.

Department of Agriculture (USDA) Forest Service under the direction of Congress, and through a partnership with the Rocky Mountain Research Station’s Missoula Fire Sciences Laboratory, Pyrologix, and Headwaters Economics, a nonprofit research group, that helps communities understand their relative wildfire risk and socioeconomic vulnerability. Screen captures of Santa Monica’s relative wildfire risk, wildfire exposure, risk to houses, and impact to potentially vulnerable populations are presented on Figure 10-6. These findings as they pertain to the city of Santa Monica in comparison to the nation as a whole are discussed further below0F

78. 78 Based on data from wildfirerisk.org for Santa Monica, California accessed on May 19, 2025.

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The wildfire likelihood in Santa Monica, based on analyses by wildfirerisk.org, is now considered to be, on average, greater than 92% of the communities nationwide. Wildfire likelihood at the community level is the average annual probability of a wildfire occurring where housing units occur.

Similarly, homes in Santa Monica are considered to have, on average, a greater wildfire risk than 94% of the communities nationwide. This is a measure of the relative consequence of wildfire to residential structures everywhere on the landscape, whether a home actually exists there or not.

Wildfirerisk.org estimates that about 80 buildings in Santa Monica (amounting to less than 1% of the total building stock) are at direct exposure and may be ignited by adjacent vegetation, flying embers and nearby structures. An estimated additional 992 buildings (amounting to about 5% of the total buildings in the city) are in the indirect exposure zone and may be ignited by embers or hometo-home ignition. Thus, despite the relatively high wildfire likelihood north of Santa Monica (Figure 10-5), homes and other structures in Santa Monica have generally a low risk of being directly exposed to wildfires. This assessment is consistent with the findings of a 2023 study by Modaresi Rad et al.78F
79 that evaluated the social vulnerability of communities and people exposed to wildlife in the Western United States between 2000 and 2021. That study found that although the number of people in the West Coast exposed to wildfire has increased exponentially over the past decade, Californians exposed to wildfire generally have a low vulnerability because highly vulnerable people in the State more often live in large metropolitan areas that are not exposed to wildfire. Figure 10-5 shows that the wildfire likelihood, wildfire exposure and the wildfire risk to homes is not the same across Santa Monica, but rather concentrated along the northern and northeastern city boundaries.

The actual ability of a home to survive a fire is dependent on a variety of conditions including the home’s age, construction materials, whether or not the home is surrounded by flammable vegetation, and whether the home is owner- or non-owner occupied. More than 62% of the homes in Santa Monica were built before 1980, with a median year of structure build of 1966. This means that many of the homes in the city may not incorporate wildfire-resistant construction materials.

According to U.S. Census data79F
80, the owner-occupied housing unit rate in Santa Monica for the period between 2019 and 2023 is estimated at 28.8%, and data from the U.S. Department of Finance from 2023, as reported in the Santa Monica Daily Press80F 81, shows that an estimated 10% of the
housing stock in the city at that time was vacant.81F
82 A high percentage of non-owner-occupied
properties, seasonal homes and vacant homes may limit the scope of maintenance efforts, such as removal of dry flammable vegetation around the structure, that help reduce the home’s wildfire exposure. In addition, “the presence of many non-owner-occupied homes may also make it difficult for community leaders to reach homeowners whose support is needed for the passage of land use planning tools, such as landscape ordinances or building codes, that reduce the risk from wildfires.”82F
83 79 Modaresi Rad, A., Abatzoglou, J.T., Fleishman, E., Mockrin, M.H., Radeloff, V.C., Pourmohamad, Y., Cattau, M., Johnson, J.M., Higuera, P., Nauslar, N.J., Sadegh, M., 2023, Social vulnerability of the people exposed to wildfires in U.S. West Coast states: Science Advances, Vol. 9, No. 38, doi:10.1126/sciadv.adh4615. 80 https://www.census.gov/quickfacts/fact/table/santamonicacitycalifornia/BZA110222, accessed May 19, 2025. 81 https://smdp.com/news/population-decrease-and-housing-increase-drive-local-vacancy-rate-to-10percent/, accessed May 19, 2025 82 This number may be lower in 2025 in response to the Palisades fire, as the fire created a surge in demand for temporary housing, with displaced residents looking for alternative living arrangements. Specific statistics were not available. 83 Profile of Wildfire Risk report for Santa Monica, California downloaded from the wildfirerisk.org website on September 27, 2023.

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Wildfires, even if not occurring in the immediately adjacent region, can pose severe health hazards to sensitive populations. Thus, wildfires in the Santa Monica Mountains and surrounding areas, including the San Gabriel Mountains to the northeast, can indirectly expose Santa Monica residents and visitors to a variety of impacts. Specifically, smoke from wildfires can negatively impact local air quality, causing respiratory illnesses and eye inflammation. Smoke contains large amounts of air pollutants including volatile and semi-volatile organic materials and nitrogen oxides that form ozone and organic particulate matter (PM). For example, in November 2018, in response to the Camp Fire in Northern California, the daily air quality index (AQI) levels of PM smaller than 2.5 micrometers in diameter (PM 2.5) and ozone doubled to quadrupled across most of California. 83F 84 The smoke
produced by the Camp Fire also contained large concentrations of lead, zinc, and other metals.84F 85 Similarly, the 2025 Palisades and Eaton fires generated significant levels of air pollution across large portions of the Los Angeles basin.

Children, the elderly, and people with pre-existing conditions, such as asthma and heart conditions, are at higher risk from the impacts of smoke. Ash from wildfires may also include toxic, potentially carcinogenic substances. Inhaling these pollutants can cause respiratory, cardiovascular, and cerebrovascular issues ranging from asthma to heart disease, which disproportionally impact populations over 65 and those with underlying chronic illnesses, in addition to post-traumatic stress disorder and mental health issues. These impacts have also been shown to have long-term consequences, including shorter height in children born to mothers exposed to fire smoke, low birthweight and neurological issues in infants, and overall poorer health and early death for impacted adults85F
8686F87.

Several census tracts in Santa Monica have a significant percentage of populations that are disproportionally vulnerable to wildfire risk due to underlying health conditions, age, income levels, no access to a vehicle, and/or disabilities (see Figure 10-5; the blue-colored areas in the social vulnerability maps capture those census tracts where two, or all three, of the social vulnerability conditions highlighted prevail). Essentially, these populations are more likely to be affected by wildfire disasters because they lack the resources to prepare for, respond to, and recover from a wildfire. Low income is considered the strongest predictor for compromised health and ability to recover from a disaster. Low-income residents are generally disproportionally impacted by wildfires because they lack the financial resources and time to take proactive measures in advance of a wildfire, are less likely to be able to evacuate or relocate, experience more acute emotional stress, are more likely to be overlooked by emergency response services, and are less likely to have adequate property insurance so they bear a greater burden from property damage following a wildfire. People without access to a car are less likely to evacuate or access emergency response centers.

Populations with disabilities, especially those with mobility issues and medical conditions, are likely to have a reduced ability to respond to natural disasters, including wildfires. Older populations and young children are particularly sensitive to health problems related to wildfire smoke. Older

84 https://www.getawair.com/blog/how-the-2018-camp-fire-impacted-air-quality, accessed on June 19, 2024. 85 https://ww2.arb.ca.gov/news/new-analysis-shows-spikes-metal-contaminants-including-lead-2018-camp-firewildfire-smoke; accessed on June 18-19, 2024. 86 https://journalistsresource.org/health/wildfires-longterm-impact-on-health/ accessed on November 12, 2023. 87 Grant, E. and Runkle, J., 2022, Long-term health effects of wildfire exposure: A scoping review: The Journal of Climate Change and Health, Vol. 6, 100110
(https://www.sciencedirect.com/science/article/pii/S2667278221001073), accessed Nov. 12, 2023.

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populations are more likely to have pre-existing medical conditions or compromised mobility that can limit or hinder their ability to respond to a wildfire. Older populations and children are both particularly susceptible to air pollution, such as particulates, associated with wildfire smoke. Based on a nationwide comparison, several census tracts in Santa Monica are considered to have a high percentage of vulnerable populations.

Such vulnerable communities may be less able to receive notice of nearby fires, vacate, or protect themselves and their belongings from direct and indirect fire effects. These populations may also be more exposed to unhealthy levels of wildfire smoke. For example, houses without air conditioning units or air purifiers may experience lower air quality inside their homes. Finally, because the population in the Western US is expected to increase and get older, and fires are expected to become more common, larger, and more destructive, the number of people exposed to wildfire will increase.

This in turn means that an increasing number of vulnerable people will be impacted by the hazard of wildfire.

Ash can irritate the skin of both humans and animals, and affect the leaves of healthy vegetation.

Wildfire debris, ash and sediment can also change the chemistry of ponds and other bodies of water, killing aquatic life and the animals that depend on them. The Palisades Fire presented new challenges to coastal communities as wildfire debris was deposited into the Santa Monica Bay from oceanfront homes that burned in the fire and storm drains from inland burn zones. This prompted the temporary closure of ocean waters for recreational use and a robust, multi-jurisdictional effort to test ocean waters, sand and wildfire sediment to evaluate safety. Large wildfires release large quantities of carbon dioxide and other greenhouse gases into the atmosphere, which in turn impact and exacerbate climate change. To avoid the flames and smoke, wild animals may migrate into more densely populated areas where they are forced to come in contact with humans. Vehicular collisions with some of these animals may occur. The reduced vegetation cover results in loss of habitat for many animal species.

Fires usually last only a few hours or days, but their effects can last much longer, especially in the case of intense fires that develop in areas where large amounts of dry, combustible vegetation have been allowed to accumulate. The lack of vegetation cover following a wildfire typically results in soil erosion. If wildland fires are followed by a period of intense rainfall, debris flows off the recently burned hillsides can develop (see Section 9). Flood control facilities may be severely taxed by the increased flow from the denuded hillsides and the resulting debris that washes down. This in turn can impact water quality and water supply to downstream watersheds. If flood control structures are overwhelmed, widespread damage can ensue in areas down gradient from these failed structures.

Other effects of wildfires and structure fires in general are financial and social. Homeowners who lose their house to a fire may not be able to recover financially and emotionally for years to come.

Businesses that burn impact both the business owner, employees, and client base that are dependent on that business’s services. Even businesses not directly in the fire zone are impacted, with a clientele that is displaced. Tourism may also be significantly impacted for the region surrounding the wildfire, due to environmental concerns and the closure of popular recreational and tourist activities.

Transportation routes that are necessary for commerce may be closed or impacted even during recovery phases, as crews work to rebuild infrastructure and damaged properties, and clear debris.

For example, PCH in the Santa Monica-Malibu region was closed from January 7, 2025 to May 23, 2025 as a result of the Palisades fire. Wildfires have a significant impact on the insurance industry, typically resulting in increased premiums, policy changes, and even denial of future coverage for

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homeowners in high-risk areas. In addition, buildings that are destroyed by fire are usually eligible for re-assessment, which reduces income to local governments from property taxes.

Wildfires near Santa Monica can also stress fire and emergency management services across Los Angeles County, and disrupt regional transportation and utility systems. Wildfires can cause major community-wide disturbances, like evacuations, power outages, economic losses, road and school closures, and disruptions to recreational activities. The 2025 Palisades fire destroyed several elementary schools and damaged the high-school in Pacific Palisades. Several elementary schools and Palisades Charter High School have relocated to Santa Monica, made possible through the City’s emergency order relaxing permitting requirements for schools. This enabled schools to quickly convert non-traditional spaces, such as a vacant department store or office space, into temporary school environments. As discussed above, many of the displaced households sought alternate temporary (or permanent) housing elsewhere, including in Santa Monica. This raised rental and realestate prices, with price gouging reported in some areas. Rebuilding efforts are impacted by the increased costs of materials and labor, and in insurance premiums, all of which impact economically and socially disadvantaged populations more.

FIRE HAZARD MITIGATION ACTIVITIES
Hazard mitigation programs in wildfire hazard areas typically include:
• fire prevention,
• vegetation management,
• construction requirements, and
• public awareness.

There are both State and local legal requirements designed to mitigate the hazard of fires. These requirements are discussed below under each of the four major groups of hazard mitigation programs. There are also specific activities that property owners and local communities can do to further reduce their hazard, although not required by law. Some of these activities are also described further below.

Fire Prevention
Fire prevention aims to reduce the incidence and extent of fire by preventing wildfires from occurring in the first place. In the 20th century, a variety of fire prevention programs were developed and implemented by Federal, State, and local agencies. These programs typically included education, engineering, patrolling, code enforcement, and signing (Greenlee and Sapsis, 199687F 88). In the latter
half of the 20th century, for example, Smokey Bear was one of the best-known characters in the U.S., attesting to the success of the public education programs aimed at fire prevention at the time.

Quantitative studies conducted in the 1990s showed that fire losses arising from human fires, especially those caused by children, had dropped substantially, in some cases by as much as 80 percent.88F
89 Therefore, fire prevention is a well-understood program with a high degree of success.

However, as discussed previously, by preventing wildfires from occurring, fuel loads in forests and

88 Greenlee, J.M., and Sapsis, D.B., 1996, Prefire effectiveness in fire management: A summary and a review of the state-of-knowledge. Fairfield, WA: International Association of Wildland Fire. 89 Ibid.

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natural areas increased, which in turn increased the potential for high intensity wildfires and resultant damage to both the natural environment and adjacent communities in the WUI. Therefore, it is now recognized that fire education and prevention need to be complemented with several other programs that help reduce the losses resulting from wildfires.

Vegetation Management
Experience and research have shown that vegetation management is an effective means of reducing the wildland fire hazard. Hazard reduction and fuel modification are the two methods that communities and property owners most often employ to reduce the risk of fire at the WUI. Both methodologies use the principle of reducing the amount of combustible fuel available, which reduces the amount of heat, associated flame lengths, and the intensity of the fire that would threaten adjacent structures. In forested areas, prescribed fire may also be used for vegetation management.

Hazard reduction includes requirements for the maintenance of existing trees, shrubs, and ground cover to reduce the amount of fuel on those sides of any structure that face the WUI. These requirements include: clearing all dead or dying foliage; planting fire-resistive vegetation; keeping clearances between tree stands, bushes and shrubs, and between trees and structures; irrigating ground covers; storing firewood and combustible materials away from habitable structures; using fire-resistant roofing and construction materials; cleaning vegetation debris from roofs and rain gutters; and using spark arresters on chimneys.

Fuel modification involves the removal of vegetation around a structure, typically a distance of at a minimum 30 feet, and the planting of native, drought-tolerant and fire-resistant vegetation beyond that. The types and density of approved plants varies depending on distance from the structure being protected.

The purpose of these methods is to reduce the hazard of wildfire by establishing a defensible space around buildings or structures. Defensible space is defined as an area, either natural or man-made, where plant materials and natural fuels have been treated, cleared, or modified to slow the rate and intensity of an advancing wildfire, and to create an area for firefighters to suppress the fire and save the structure. These standards require property owners in the WUI to conduct maintenance, modifying or removing non-fire-resistive vegetation around their structures to reduce the fire danger.

In VHFHSZs such as that now mapped in the northern portion of Santa Monica, State law requires a 100-foot defensible space. Specifically, State law states that “a person who owns, leases, controls, operates, or maintains a building or structure in, upon, or adjoining a mountainous area, forestcovered lands, shrub-covered lands, grass-covered lands, or land that is covered in flammable material, shall maintain 100 feet of Defensible Space.”89F 90 Even before the northern portion of Santa Monica was zoned as having a high or very high fire hazard, property owners in the City were required to mitigate the fire hazard in their properties by implementing vegetation management practices that include the abatement of uncontrolled or high weeds, brush, or other plant material that if dry can create a fire hazard. Specifically, the Santa Monica Municipal Code (Chapter 7, Section 7.44) defines weeds to include brush or plants “which

90 https://readyforwildfire.org/wp-content/uploads/2024/07/Defensible-Space-and-the-Law-Factsheet-Revisions-Jan2024.pdf. Specific requirements can be found in ublic Resource Code (PRC) § 4291, 14 California Code of Regulations (CCR) § 1299.03, Board of Forestry (BOF) General Guidelines, California Fire Code (CFC) § 505.1, and California Building Code (CBC) § 2113.9.2.

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attain such growth as to become, when dry, a fire menace to adjacent improved property,” … and “dry grass, stubble, brush or other flammable material which endangers the public safety by creating a fire hazard…” These weeds are considered a public nuisance. Moreover, the City’s Director of Public Works has the authority to give the property owner of record a notice to abate the hazard by properly disposing the weeds located on their property. The notice is served via registered mail addressed to the owner or agent to the last known address. A copy of the notice is also posted on the property. The owner or agent has five days, not counting the day the notice was posted, to completely dispose of the weeds described in the notice. If the responsible individual does not abate the hazard during that time period, the City may take further action, with the Director of Public Works authorized to retain a contractor to dispose of the weeds. The cost of the weed abatement, including incidental expenses, is made a lien upon the property.

Prescribed fires are deliberately set by CAL FIRE and the U.S. Forest Service under carefully controlled and monitored conditions for the purpose of removing brush and other undergrowth that can fuel uncontrolled fires. Prescribed burning is used to alter, maintain or restore vegetative communities, achieve desired resource conditions, and protect life and property that would be degraded by wildland fire. Prescribed fire is only accomplished through managed ignition and should be supported by planning documents and appropriate environmental analyses.

Construction Requirements
Building construction standards for such items as roof coverings, fire doors, and fire-resistant materials help protect structures from external fires and contain internal fires for longer periods, limiting the spread of fire to adjacent structures. Fire-resistant materials can help reduce the impact of not only wildfires, but also structure fires. Many of these are legal requirements spelled out in the California Building Code (CBC) and the California Fire Code (CFC), including CBC § 2113.9.2 and Chapter 7A, and CFC § 505.1.

The portion of a structure most susceptible to ignition from a wildland fire is the roof, due to the deposition of burning cinders or brands. Burning brands or embers are often deposited far in advance of the actual fire by winds. Roofs can also be ignited by direct contact with burning trees and large shrubs. The danger of combustible wood roofs, such as wooden shingles and shakes, has been known to firefighting professionals since 1923, when California’s first major urban fire disaster occurred in Berkeley. It was not until 1988, however, that California was able to pass legislation calling for, at a minimum, Class C roofing in fire hazard areas. Then, in the early 1990s, there were several other major fires, including the Paint fire of 1990 in Santa Barbara, the 1991 Tunnel fire in Oakland/Berkeley, and the 1993 Laguna Beach fire, whose severe losses were attributed in great measure to the large percentage of combustible roofs in the affected areas. In 1994-1996, new roofing materials standards were approved by California for VHFHSZs. Today, the roofing standards for new habitable structures in VHFHSZs, SRAs, and in the WUI are spelled out in Chapter 7A of the California Building Code. Section 8.12.070 of the 2022 Santa Monica Building Code spells out roofing standards for all new structures and new roofs in the city.

To help consumers determine the fire resistance of the roofing materials they may be considering, roofing materials are rated as to their fire resistance into three categories that are based on the results of test fire conditions that these materials are subjected to under rigorous laboratory conditions, in accordance with test method ASTM-E-108 developed by the American Society of Testing Materials.

The rating classification provides information regarding the capacity of the roofing material to resist

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a fire that develops outside the building on which the roofing material is installed, taking into consideration wind conditions. The three ratings are as follows:

Class A: Roof coverings that are effective against severe fire test exposures.

Class B: Roof coverings that are effective against moderate fire test exposures.

Under such fire exposures, roof coverings of these classes:
o Are not readily flammable;
o Afford a high degree of fire protection to the roof deck; o Do not slip from position; and
o Do not produce flying brands.

Class C: Roof coverings that are effective against light fire exposures. Under such exposures, roof coverings of this class:
o Are not readily flammable;
o Afford a measurable degree of fire protection to the roof deck; o Do not slip from position; and
o Do not produce flying brands.

Non-Rated Roof coverings have not been tested for protection against fire exposure. Under such exposures, non-rated roof coverings:
o May be readily flammable;
o May offer little or no protection to the roof deck, allowing fire to penetrate into attic space and the entire building; and
o May pose a serious fire brand hazard, producing brands that could ignite other structures a considerable distance away.

The City of Santa Monica enforces a Class A or Class B roofing material requirement for all new structures and new roofs. Specifically, “the use of non-fire retardant wood shingles or non-fire retardant shakes for new or replacement roofing is prohibited. Class A or B assemblies and roof coverings shall be listed and tested in accordance with ASTM E108 or UL 790.”90F 91 Attic ventilation openings are also a concern regarding the fire survivability of a structure. Attics require significant amounts of cross-ventilation to prevent the degradation of wood rafters and ceiling joists. This ventilation is typically provided by openings to the outside of the structure, but these opening can provide pathways for burning brands and flames to be deposited within the attic.

Therefore, it is important that all ventilation openings be properly screened to prevent this.

Additional prevention measures that can be taken to reduce the potential for ignition of attic spaces is to “use non-combustible exterior siding materials and to site trees and shrubs far enough away from the walls of the house to prevent flame travel into the attic even if a tree or shrub does torch” (Fisher, 1995).

The type of exterior wall construction used can also help a structure survive a fire. Ideally, exterior walls should be made of non-combustible materials such as stucco or masonry. During a wildfire, the dangerous active burning at a given location typically lasts about 5 to 10 minutes (Fisher, 1995),

91 Section 8.12.070 of the Santa Monica Building Code (2022 edition adopted 10/25/22 under Ord. No. 2727CCS § 4).

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so if the exterior walls are made of non-combustible or fire-resistant materials, the structure has a better chance of surviving.

Similarly, the type of windows used in a structure can help reduce the potential for fire to impact a structure. Single-pane, annealed glass windows are known for not performing well during fires; thermal radiation and direct contact with flames cause these windows to break because the glass under the window frame is protected and remains cooler than the glass in the center of the window.

This differential thermal expansion of the glass causes the window to break. Larger windows are more susceptible to breakage when exposed to high heat than smaller windows. Multiple-pane windows, and tempered glass windows perform much better than single-pane windows91F

92. Fisher
(1995) reported that in Australia, researchers noticed that the use of metal screens helps protect windows from thermal radiation. Insect screens made of bronze, fiberglass and aluminum all reportedly improve the performance of glass subjected to radiant exposure, but not to direct, flame contact exposure92F

93. The City of Santa Monica Building and Safety Division enforces requirements of the Building Code with respect to exterior wall construction and window material requirements, and the City’s Fire Department reviews buildings for compliance with the Fire Code.

Public Awareness
Fire prevention can include limiting access to fire hazard areas during certain times of the year. The wildfire susceptibility of an area changes throughout the year, and from one year to the next, in response to local variations in precipitation, temperature, vegetation growth, and other conditions.

When the fire danger in an area is deemed to be of special concern, local authorities can rely on increased media coverage and public announcements to educate the local population about being fire safe. These announcements are typically triggered by the National Weather Service (NWS), the Federal agency that monitors lightning, wind and humidity conditions.

If the NWS determines that the current or expected meteorological conditions are likely to contribute to extreme fire danger or fire behavior, the NWS issues Fire Weather Watches or Red Flag Warnings for the area impacted, as appropriate. These conditions and criteria93F 94 as they pertain to southern
California west of the San Gabriel and San Bernardino Mountains (and thus the Santa Monica area) include:
• Dry lightning: This is a lightning event that is not accompanied by sufficiently wet fuels that have been identified as critically dry. Significant precipitation is defined as ranging from 0.05 inches for grass or brush, to 0.15 inches for closed-canopy timer and heavy fuels. Watches and warnings are issued when dry lightning is expected to be widespread. As described previously, lightning only causes a small percentage of the wildfires in Los Angeles County. • Wind and humidity: Watches and warning are issued if relative humidity is less or equal to 15%, with sustained winds equal to or greater than 25 miles per hour (mph) and/or frequent gusts equal to or greater than 35 mph with an expected duration of 6 hours or more, or if relative humidity is less than or equal to 10% for an expected duration of 10 hours or more regardless of wind presence.

92 https://ucanr.edu/sites/Wildfire/Side_of_House/Windows/, accessed October 4, 2023. 93 https://ucanr.edu/sites/Wildfire/Side_of_House/Windows/, accessed October 4, 2023. 94 94 https://www.weather.gov/gjt/firewxcriteria, accessed October 4, 2023.

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A Fire Weather Watch alerts land managers, fire suppression agencies and the public that upcoming weather conditions (consisting of a combination of surface relative humidity, sustained surface wind, and fuel moisture levels94F
95) could cause wildfires or extreme fire behavior. It means that critical fire weather conditions are possible but are not imminent or occurring. Appropriate response to a Fire Weather Watch is to prepare fire response equipment and personnel.

A Red Flag Warning is issued when the conditions are right for extreme wildfire events. Red Flag Warnings are issued when fire conditions are ongoing or expected to develop shortly. Appropriate response to a Red Flag Warning is for local, affected fire agencies and land managers to take action, and for everyone to avoid or be extremely careful with open flames. Residents in and near VHFHSZs should prepare to evacuate with little notice in the event of a wildfire developing in their neighborhood. An enhanced version of a Red Flag Warning referred to as an Extreme Red Flag Warning was first issued by the NWS on October 29, 2019 in the southern California region as a result of very strong Santa Ana winds. This warning means that, due to a combination of strong, prolonged winds, very low humidity, and very dry fuels, there is a heightened potential for fire growth and extremely dangerous fire behavior.

In addition, NWS will utilize the phrase “Potentially Dangerous Situation (PDS)” to heighten the public’s awareness and urgency in action during Red Flag Warning events. This designation is used for many types of weather events, highlighting extreme and potentially life-threatening conditions.

PDS Red Flag Warning events were declared in December 2024 when the Franklin Fire occurred and in January 2025 before the Palisades and Eaton fires.

Prior to issuing a Fire Watch or Red Flag Warning, the NWS will confer with local fire and emergency management agencies to discuss fuel conditions and local concerns. This is intended to assist local agencies in allocating or moving resources to the affected areas in anticipation of increased fire activity. However, ultimate responsibility to issue a fire watch or warning rests with the NWS forecaster.95F
96 Utility companies such as Southern California Edison (SCE) use these forecasts and their own modeling to assess the potential impact to their electric distribution system, especially electric lines and circuits. If their analysis indicates that circuits might be impacted by the extreme fire conditions, including strong winds, dry vegetation, and low humidity, the utility may temporarily shut off the power to reduce the risk of wildfire caused by downed or damaged utility equipment.

This is called a Public Safety Power Shutoff (PSPS). No PSPSs have been implemented by SCE in Santa Monica since October 2021.96F
97 Local authorities can rely on increased media coverage and public announcements regarding fire watches and red flag warnings to educate the local population about being fire safe. For example, to reduce the potential for wildfires during fire season, hazardous fire areas can be closed to public access during at least part of the year. Typically, the fire season in southern California begins in May and lasts until the first rains in November, but local counties or jurisdictions can opt to start the fire season earlier and end it later.

95 See https://www.weather.gov/lwx/warningsdefined for additional information. 96 https://gacc.nifc.gov/oscc/predictive/weather/myfiles/Watches_and_Warnings_for_California.htm, accessed May 2025. 97
https://capuc.maps.arcgis.com/apps/dashboards/ecd21b1c204f47da8b1fcc4c5c3b7d3a, accessed October 2025.

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Use of signage during high and extreme fire conditions along the roads adjoining the VHFHSZ mapped within the city, can help reduce the fire hazard by alerting and educating motorists, residents and visitors alike, about the potential fire hazard in the area. Santa Monica Office of Emergency Management will issue social media alerts of Red Flag Warning conditions. Their fire preparedness website provides guidance on actions to take to prepare for wildfires and potential local evacuations. It recommends residents have an evacuation checklist and kit ready. It also suggests that all residents who are planning to visit the Santa Monica Mountains or other mountains in the region first check if there are any wildfire-related restrictions or guidelines in place. It is best to cancel the hike or trip if a wildfire is burning nearby.97F 98 Restricted public access to hiking trails in and around the city of Santa Monica during the fire season may help reduce the opportunity for human-caused wildfires in the area. Continued use of signs during high and extreme fire conditions along the freeways and roads that cut through the wildland areas in the city and adjacent areas can also help reduce the fire hazard by alerting and educating motorists and residents.

Fire protection in the WUI relies heavily on landowners taking measures personally to protect their properties. Property owners are more likely to take the initiative if they are informed of the risk.

Therefore, public education and awareness should play a greater role in the areas identified as having a wildfire hazard, with property owners encouraged to exercise care to reduce the risk of fire in their property. Some of the tasks that property owners and residents can take on are listed below.

This list is not all-inclusive, but provides a starting point and framework to work from. • Mow and irrigate your lawn regularly, but do not mow during the hottest time of the day • Dispose of cuttings and debris promptly, according to local regulations • Store firewood away from structures
• Be sure the irrigation system is well maintained
• Use care when refueling garden equipment and maintain it regularly • Store and use flammable liquids properly
• Dispose of smoking materials carefully
• Do not light fireworks. All fireworks are illegal in Santa Monica, except for aerial public fireworks display approved by City Council, the use of fireworks for special effects in entertainment productions as authorized by State law, and the use or transportation of fireworks by State or Federal authorities (Section 8.40.020 of the Municipal Code). • Become familiar with local regulations regarding vegetation clearings, disposal of debris, and fire safety requirements for equipment
• Follow manufacturers’ instructions when using fertilizers and pesticides • When building, selecting or maintaining a home, consider the slope of the terrain. Be sure to build on the most level portion of the lot, since fire spreads rapidly on slopes, even minor ones.
• Use construction materials that are fire-resistant or non-combustible whenever possible, in accordance with local requirements and the California Building and Fire Codes

98 https://www.santamonica.gov/how-to-prepare-for-wildfires-in-santa-monica, accessed May 2025.

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• For roof construction, the City of Santa Monica requires a minimum Class B rating. Nonfire-retardant wood shingles or non-fire-retardant shakes for new or replacement roofing are prohibited (Santa Monica 2022 Building Code Section 8.12.070). • Constructing a fire-resistant sub-roof can add protection. • On exterior wall cladding, fire-resistive materials such as stucco or masonry are much better than vinyl, which can soften and melt.
• Install an approved automatic fire sprinkler system and/or install portable fire extinguishers. The City of Santa Monica has specific requirements for sprinklers and the installation of portable fire extinguishers.
• Display the assigned address number so that it is visible from the street and alley upon which the address is based. The City of Santa Monica requires that the numbers in the signs be a minimum of 6 inches high for commercial structures, and 4 inches high for interior suites, offices, and rooms in commercial structures, and in one- and two-family dwellings. The numbers need to have a minimum stroke width of 0.5 inches, and contrast with their background (Santa Monica 2022 Building Code Section 8.40.020). • So that everyone has a way out, provide at least two ground level doors for safety exits and at least two means of escape (doors or windows) in each room • Keep gutters, eaves, and roof clear of leaves and other debris • Occasionally inspect your home, looking for deterioration, such as breaks and spaces between roof tiles, warping wood, or cracks and crevices in the structure • If an all-wood fence is attached to your home, a masonry or metal protective barrier between the fence and house is recommended
• Use non-flammable metal when constructing a trellis and cover it with high-moisture, non-flammable vegetation
• Prevent combustible materials and debris from accumulating beneath patio decks or elevated porches. Screen, or box in, areas that lie below ground level with wire mesh • For properties along the northern and northeastern edges of the city and properties facing steep slopes, make sure that elevated wooden decks are not located at the top of a hill where it will be in the direct line of a fire moving up slope • Install automatic seismic shut-off valves for the main gas line to your house. Information for approved devices, as well as installation procedures, is available from the Southern California Gas Company.

In California, properties located in fire hazard areas need to be disclosed in real estate transactions; that is, real-estate sellers are required to inform prospective buyers whether or not the property is located within an area that could be impacted by a wildland fire [California Civil Code Section 1103(c)(6)]. This disclosure requirement applies to properties within a State Responsibility Area.

As of July 1, 2021, California Assembly Bill 38 (AB 38) states that the seller of a residential property located in a High and Very High Fire Hazard Severity Zone (HFHSV or VHFHSZ must submit documentation of compliance with the locally adopted defensible space requirements prior to the close of escrow, or enter into an agreement with the buyer pursuant to the buyer obtaining documentation of compliance. The bill also states that on or after January 1, 2021, the seller of any real property located in a high or very high fire hazard severity zone is to provide a prescribed disclosure notice to the buyer, if the home was constructed before January 1, 2020, of information

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relating to fire hardening improvements on the property and a list of specified features that may make the home vulnerable to wildfire and flying embers and which features, if any, that exist on the home of which the seller is aware. These requirements apply to properties in Santa Monica located in the newly designated HFHSZ and VHFHSZ.

WILDFIRE RESOURCE DIRECTORY
Local Resources
Santa Monica Fire Department
The Santa Monica Fire Department is responsible for fire suppression, pre-hospital emergency medical services, hazardous materials release oversight and response, and fire and life safety community outreach services for the City of Santa Monica. The Fire Department responds to a variety of medical and rescue calls, vegetation and structure fires, vehicle accidents, public assistance, and false alarms. Organized fire suppression services in the area date back to 1875, when the Crawford Hook and Ladder Company was formed by six local residents. Then, in March 1889, less than three years after the city was incorporated, the Santa Monica Hose and Ladder Company was founded.

This was the beginning of the Santa Monica Fire Department as it is known today.

Firefighting and emergency response resources in Santa Monica are provided from the five fire stations listed in Table 10-5 below. The locations of these fire stations are shown on Figures 10-4, 3-1 and Plates H-3 and H-17 in Appendix H. Combined, these fire stations are manned by 105 emergency response (suppression and rescue) personnel, with a combined minimum daily staffing for the five stations of 35 personnel. Resources and staffing assigned to each of these fire stations are summarized in Table 10-5 also.

The Santa Monica Fire Department administrative offices, with 14 budgeted personnel, and an allhazards fire prevention division, also with 14 budgeted personnel, are housed at the City’s Public Safety Facility at 333 Olympic Drive. Staffing includes a Fire Prevention Coordinator, who oversees public education programs. The Fire Department also has an accredited fire academy located at 2500 Michigan Avenue that is staffed by 3 budgeted personnel. The general telephone number for the Santa Monica Fire Department is (310) 458-8652. For emergencies, dial 911.

Based on data provided by Citygate Associates (2020) the five fire stations in the city of Santa Monica respond to approximately 17,000 incidents a year. Note that about 70% of the responses are for medical and rescue emergency calls. This is typical of most communities. In Santa Monica, “all response personnel are trained to either the Emergency Medical Technician (EMT) level, capable of providing Basic Life Support (BLS) pre-hospital emergency medical care, or EMT Paramedic level, capable of providing Advanced Life Support (ALS) pre-hospital emergency medical care.”98F 99 Medical
emergencies are handled by the closest available engine company. Therefore, on average, each fire station responds to nearly 2,400 calls a year, although this case load is not equally distributed among all five fire stations. Specifically, Fire Stations 1, 2 and 3 are located in and service some of the most densely populated areas. Citygate Associates (2020) determined that all planning areas in the city, except for planning zone 5, which covers the area around the airport, have a moderate building fire risk. Planning zone 5 is considered to have a low building fire risk.

99 Citygate Associates, 2020, Community Risk Assessment / Standards of Cover Analysis, City of Santa Monica, CA, Volume 1 of 2: Technical Report.

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Table 10-5: Santa Monica Fire Department Stations, Resources and Minimum Daily Staffing Station No.;
Address Year Built Assigned Resourcesδ Minimum Daily Staffing 1; 1337 7th Street 2020
Engine 1
Engine 6
Truck 1
Rescue Utility 1
Community Response Unit 1 (ambulance)
Battalion 1
Battalion 2 (reserve)
Rescue Ambulance 1 (Reserve)
15 2; 222 Hollister
Avenue 2003
Engine 2
USAR 2
USAR Utility 2
Rescue Ambulance 2 (reserve)
4 3; 1302 19th Street 1971
Engine3
Engine 4
Engine 8 (reserve)
8 5; 2450 Ashland
Avenue 1980
Engine 5
Aircraft Rescue 5
ARFF Utility 5
HazMat Unit 5
Engine 9 (reserve)
Truck 2 (reserve)
Rescue Ambulance 5 (reserve)
4 7;
1100 Palisades
Beach Road
(Pacific Coast
Hwy.)
2019
Engine 7
Beach Medical Vehicle 7
Utility 7 4
δ Staffed resources are in bold; other resources, including reserves, are staffed as needed by on-duty station personnel or recalled off-duty personnel
Sources: City of Santa Monica Fire Department, with data extracted from Citygate Associates, LLC (2020) and https://fire.fandom.com/wiki/Santa_Monica_Fire_Department (accessed on August-September 2023).

The Insurance Services Office (ISO) provides rating and statistical information for the insurance industry in the United States. To do so, ISO evaluates a community’s fire protection needs and services, and assigns each community evaluated a Public Protection Classification (PPC) rating. The rating is developed as a cumulative point system, based on the community’s fire-suppression delivery system, including fire dispatch (operators, alarm dispatch circuits, telephone lines available), fire department (equipment available, personnel, training, distribution of companies, etc.), and water supply (adequacy, condition, number and installation of fire hydrants). Insurance rates are based upon this rating. The worst rating is a Class 10. The best is a Class 1. Santa Monica has maintained a Class 1 ISO rating since 2012.

Automatic and Mutual Aid Agreements
Firefighting agencies often team up and work together during emergencies. These teaming arrangements are handled through automatic and mutual aid agreements, which obligate fire

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departments to help each other under pre-defined circumstances. Automatic aid agreements obligate the nearest fire company to respond to a fire regardless of the jurisdiction. Mutual aid agreements obligate fire department resources to respond outside of their district upon request for assistance.

The California Disaster and Civil Defense Master Mutual Aid Agreement (California Government Code Section 8555-8561) states: “Each party that is signatory to the agreement shall prepare operational plans to use within their jurisdiction, and outside their area.” These plans include fire and non-fire emergencies related to natural, technological, and war contingencies. The State of California, all State agencies, all political subdivisions, and all fire districts signed this agreement in 1950.

Santa Monica is part of the Los Angeles County Operational area, and more specifically, a member of Disaster Management Area A. The Operational Area is part of the Standardized Emergency Management System (SEMS), further described below, that promotes effective disaster management, response and cooperation across jurisdictional boundaries. Other jurisdictions, in addition to Santa Monica, that are members of Operational Area A include Beverly Hills, Culver City and West Hollywood. As a result of being part of the same Operational Area group, all of these jurisdictions have mutual aid agreements that allow them to obtain additional emergency resources, as needed, from non-affected members in the group. On February 13, 2024, Santa Monica City Council approved an Automatic Mutual Aid Agreement with Los Angeles Fire Department.

Numerous other agencies are available to assist the City if needed. Locally, these include the City’s Office of Emergency Management, the City’s Police Department and the California Highway patrol.

The City’s Office of Emergency Management oversees the City’s police and fire dispatch operations, emergency alerting capabilities, as well as manages the City’s multi-department Emergency Operations Center that coordinates large-scale emergency response operations. The City’s Police Department and/or California Highway patrol, depending on the location of the incident, would facilitate evacuations and prevent people from traveling to the evacuated areas to watch their operations, as this can hinder fire suppression and emergency response efforts.

Several other State and Federal agencies have roles in fire hazard mitigation, response and recovery, depending on the type of incident and its location. These agencies include the Los Angeles County Fire Department, the Los Angeles County Chief Executive Office, the California Division of Forestry and Fire Protection, the Office of the State Fire Marshal, the California Governor’s Office of Emergency Services, FEMA, and several agencies under the U.S. Department of the Interior including the Bureau of Land Management and Office of Aviation Services, the National Weather Service, and, in extreme cases, the Department of Defense. In forest areas (and therefore not applicable to Santa Monica), other agencies that may be involved include the Fish and Wildlife Service, National Park Service, US Forest Service, National Association of State Foresters, and the Department of Agriculture. Private companies and individuals may also be asked to provide assistance in some cases. Contact information for several of these local, State and Federal agency resources are provided at the end of this section.

Standardized Emergency Management System (SEMS)
The SEMS law refers to the Standardized Emergency Management System described by the Petris Bill (Senate Bill 1841; California Government Code Section 8607, made effective January 1, 1993) that was introduced by Senator Petris following the 1991 Oakland fires. The intent of the SEMS law

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is to improve the coordination of State and local emergency response in California. It requires all jurisdictions within the State of California to participate in the establishment of a standardized statewide emergency management system.

When a major incident occurs, the first few moments are absolutely critical in terms of reducing loss of life and property. First responders must be sufficiently trained to understand the nature and the gravity of the event to minimize the confusion that inevitably follows catastrophic situations. The first responder must then put into motion relevant mitigation plans to further reduce the potential for loss of lives and property damage, and to communicate with the public. According to the State’s Standardized Emergency Management System, local agencies have primary authority regarding rescue and treatment of casualties, and making decisions regarding protective actions for the community. This on-scene authority rests with the local emergency services organization and the incident commander.

Depending on the type of incident, several different agencies and disciplines may be called in to assist with emergency response. Agencies and disciplines that can be expected to be part of an emergency response team include medical, health, fire and rescue, police, public works, emergency management, and coroner. The challenge is to accomplish the work at hand in the most effective manner, maintaining open lines of communication between the different responding agencies to share and disseminate information, and to coordinate efforts.

Emergency response in every jurisdiction in the State of California is handled in accordance with SEMS, with individual City agencies and personnel taking on their responsibilities as defined by the City’s Emergency Plan. This document describes the different levels of emergencies, the local emergency management organization, and the specific responsibilities of each participating agency, government office, and City staff.

The framework of the SEMS system is the following:
• Incident Command System – a standard response system for all hazards that is based on a concept originally developed in the 1970s for response to wildland fires • Multi-Agency Coordination System – coordinated effort between various agencies and disciplines, allowing for effective decision-making, sharing of resources, and prioritizing of incidents
• Master Mutual Aid Agreement and related systems – agreement between cities, counties and the State to provide services, personnel and facilities when local resources are inadequate to handle and emergency
• Operational Area Concept – coordination of resources and information at the county level, including political subdivisions within the county; and • Operational Area Satellite Information System - a satellite-based communications system with a high-frequency radio backup that permits the transfer of information between agencies using the system.

The SEMS law requires the following:
• Jurisdictions must attend training sessions for the emergency management system.

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• All agencies must use the system to be eligible for funding for response costs under disaster assistance programs.
• All agencies must complete after-action reports within 120 days of each declared disaster.

Santa Monica Office of Emergency Management
333 Olympic Drive, Santa Monica, CA 90401
(310) 458-2263
Email: [email protected]
https://www.santamonica.gov/departments/city-managers-office/office-of-emergency-management As mentioned briefly before, Santa Monica’s Office of Emergency Management oversees the City’s police and fire dispatch operations, emergency alerting capabilities, as well as manages the City’s multi-department Emergency Operations Center that coordinates large-scale emergency response operations. These services are provided by two divisions within the Office of Emergency Management, as follows: 1) Emergency Services and Preparedness, and 2) Public Safety Communications.

Emergency Services and Preparedness administers the implementation of extensive disaster planning, training and proactive community-based preparedness programs to ensure that the City is a disaster-resilient community. This division also oversees the operation of the City’s Emergency Operation Center (EOC), which provides a central command center for all City departments and external response stakeholders to collaboratively manage, plan, prevent, and recover from all events (planned and unplanned) and emergencies in the city.

Public Safety Communications provides joint communication services to the City’s Police and Fire Departments, including answering 911 and non-emergency phone calls, dispatching public safety resources, and providing emergency medical dispatch services and 911 education to the public.

Santa Monica Police Department
333 Olympic Drive, Santa Monica, CA 90401
(310) 458-8495
https://www.santamonica.gov/departments/police
Southern California Edison (SCE)
SCE may temporarily shut off power to an area or region to reduce the risk of a wildfire caused by failure of their equipment during dangerous fire weather conditions such as strong winds. Such a shutoff is referred to as a Public Safety Power Shutoff (PSPS). Residents can sign up to receive notifications of a potential PSPS. For additional information regarding PSPSs, refer to the links below. 2244 Walnut Grove Ave, Rosemead, CA 91770
(1-800) 655-4555
https://www.sce.com/outages-safety/outage-preparedness/outage-types/public-safety-powershutoff-psps/psps-faqs; https://www.sce.com/

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County Resources
Los Angeles County Fire Department
(323).881-2411
https://fire.lacounty.gov/
Los Angeles County Chief Executive Office
Manages the Los Angeles County’s Operational Area and Disaster Management Areas 500 W. Temple St., Room 358, Los Angeles, CA, 90012
(213) 974-1311
https://ceo.lacounty.gov/;
https://data.lacounty.gov/datasets/lacounty::disaster-management-areas/about State Resources
California Division of Forestry & Fire Protection and
Office of the State Fire Marshal (OSFM)
715 P Street
PO Box 944246
Sacramento California 94244-2460
(916) 653-5123
https://www.fire.ca.gov/
https://osfm.fire.ca.gov/
California Governor’s Office of Emergency Services (Cal-OES) https://www.caloes.ca.gov/
California FireSafe Council (CFSC)
Non-profit organization that supports communities across the State in wildfire preparedness and resiliency through grant funding, programmatic support, and technical assistance. They provide resources and support for community-led wildfire resiliency efforts. Their activities include outreach and education; landscape, community and parcel level mitigation activities; and planning and community hardening.
7301 I Street, No. 236
Sacramento, CA 95814
(916) 648-3600
https://cafiresafecouncil.org/
Federal Resources and Programs
The role of the federal land managing agencies in the WUI is reducing fuel hazards on the lands they administer; cooperating in prevention and education programs; providing technical and financial assistance; and developing agreements, partnerships and relationships with property owners, local protection agencies, states and other stakeholders. These relationships focus on activities before a wildfire occurs, which render structures and communities safer and better able to survive a fire occurrence.

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Federal Emergency Management Agency (FEMA)
FEMA is directly responsible for providing fire suppression assistance grants and, in certain cases, major disaster assistance and hazard mitigation grants in response to fires. FEMA coordinates across federal agencies to help state, local, tribal and territorial partners respond to wildfires nationwide.

Federal support for fire management assistance through FEMA includes personnel, technical assistance and financial investments that help communities mitigate and respond to wildfires. Some of mitigation opportunities accessed through FEMA include the Hazard Mitigation Grant Program (HMGP), the Building Resilient Infrastructures and Communities (BRIC) program, and Fire Management Assistance Grants.
https://www.fema.gov/disaster/wildfire-actions
U.S. Department of the Interior
Large umbrella organization under which there are several bureaus that have roles in the management of public lands, the suppression and management of wildfires in national lands, and other similar issues. These bureaus include the Bureau of Land Management, the National Park Service, the Bureau of Safety and Environmental Enforcement, Office of Aviation Services, and the U.S. Fish and Wildlife Service.
https://www.doi.gov/
National Weather Service
The National Weather Service is the service line office within the Federal National Oceanic and Atmospheric Administration (NOAA) that provides weather, water and climate data, forecasts, warnings, and impact-based decision support services for the protection of life and property and enhancement of the national economy. This includes real-time mapping of fire weather watches and red fire warnings.
https://www.weather.gov/
https://www.weather.gov/fire/
Other National Resources
National Fire Protection Association (NFPA)
This is a U.S.-based international nonprofit organization devoted to eliminating death, injury, property damage, and economic loss due to fire, electrical, and related hazards. The NFPA website provides information on a variety of subjects including wildfires, industrial and chemical hazards, electrical hazards, home fire safety, and community risk reduction.

Public Fire Protection Division
1 Batterymarch Park, Quincy, MA 02169-7471
(800) 344-3555 and (1-617) 770-3000
https://www.nfpa.org/
National Interagency Fire Center (NIFC)
The NIFC in Boise, Idaho is the nation’s support center for wildland firefighting. NIFC is home to the national wildland fire management programs of the Department of the Interior’s Bureau of Land Management, National Park Service, U.S. Fish and Wildlife Service, and Bureau of Indian Affairs, and the U.S. Department of Agriculture’s Forest Service, in addition to the National Association of

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State Foresters, the U.S. Fire Administration, the National Weather Service, and the Department of Defense. The NIFC and its partners compile information about the current wildfire situation and statistics that encompass lands managed by federal, state, local, tribal, and private agencies, and summarize the current fire situation nationwide on a daily to weekly basis. The NIFC’s website provides information on ongoing wildfires, in addition to a variety of research and educational resources.
3833 S. Development Ave., Boise, Idaho 83705
(208) 387-5512
https://www.nifc.gov/
United States Fire Administration (USFA)
As an entity of the U.S. Department of Homeland Security’s Federal Emergency Management Agency (FEMA), the mission of the USFA is to support and strengthen fire and emergency medical services (EMS) and stakeholders to prepare for, prevent, mitigate and respond to all hazards through leadership, advocacy, coordination and support.

USFA, Planning Branch, Mitigation Directorate
16825 S. Seton Ave.

Emmitsburg, MD 21727
(301) 447-1035
https://www.usfa.fema.gov/
Additional Resources
Firewise USA
A program of the NFPA designed for communities and people who live in wildfire prone areas, that can also be of use to local planners and decision makers. The site offers online wildfire protection information and checklists, as well as listings of other publications, videos and conferences. (617) 770-3000
http://www.firewise.org/,
https://www.nfpa.org/Education-and-Research/Wildfire/Firewise-USA Insurance Services Office (ISO)
The Insurance Services Office (ISO), now a subsidiary of Verisk Analytics, developed a program used by the insurance industry to identify those areas where the potential loss due to wildfire is greatest. Their FireLine software uses satellite-imagery interpretation to evaluate the factors of fuel types, slope and roads (access) to develop risk ratings for communities. Most insurance companies that provide insurance services to homeowners in California now use this system. Their Community Hazard Mitigation group works with local fire and building departments, water agencies, and municipalities, and ranks their firefighting capabilities, as discussed above. https://www.isomitigation.com/
Publications
Refer to the footnotes of this document for a variety of publications that address wildland fire, structure fires, and fires after earthquakes.

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SECTION 11: CLIMATE CHANGE &

SEVERE WEATHER HAZARDS

WHY DO CLIMATE CHANGE AND SEVERE WEATHER POSE A THREAT TO THE CITY OF SANTA MONICA?
Climate change has caused rapid and widespread changes in the atmosphere, oceans, and the planet as a whole; the result, in great part, of human activities, especially the emissions of greenhouse gases (AR6 Synthesis Report and Headline Statements from the International Panel on Climate Change, 20230F
1 ). The impacts of climate change (Figure 11-1), which are being felt in California and around the world, include higher temperatures and more common extreme heat events, more severe wildfires, more frequent and intense droughts, flooding due to extreme precipitation events, and coastal flooding and erosion from sea level rise (Ehlers, 2022). These changes in climate impact human health (Figure 11-2), including injuries, illnesses, and deaths related to extreme heat and natural disaster events (floods and wildfires); air pollution from wildfire smoke; reduced water quality due to runoff from extreme precipitation events and sea-water intrusion into aquifers; impacts on food and water supplies from droughts; and increasing prevalence of certain diseases (Ehlers, 2022).

Figure 11-1: Impacts of Climate Change on California
Source: Ehlers (2022)

1 https://www.ipcc.ch/report/ar6/syr/resources/spm-headline-statements, accessed August 22, 2024.

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Figure 11-2: Health Impacts of Climate Change
Source: Ehlers (2022), who adapted the figure from one issued by the Centers for Disease Control and Prevention and Senate Office of Research.

According to statistics compiled and reported by the National Oceanic and Atmospheric Administration (NOAA), between 1980 and September 10, 2024 (the most recent date for which data were available), California experienced 46 climate/weather events that exceeded $1 billion in costs each. These events include droughts, floods, freezes, severe storms, and wildfires, with droughts and wildfires accounting for nearly 72% of the total losses. Table 11-1 below summarizes these data.

Table 11-1: Summary of Natural Hazard Events in California (1980-Sept. 2024) Costing >$1 Billion
Disaster Type No. of
Events Events/Year % Frequency Total Cost($ Billion) % of Total Costs Drought 14 0.3 30.4 10.0-20.0 10.7
Flooding 6 0.1 13.0 10.0-20.0 12.4
Freeze 3 0.1 6.5 10.0-20.0 10.0
Severe Storm 4 0.1 8.7 2.0-5.0 2.3
Wildfire 19 0.4 41.3 50.0-100.0 64.7
All Disasters 46 1.0 100.0 100.0-200.0 100.0
Source: National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI) U.S. Billion-Dollar Weather and Climate Disasters (2024)1F 2 .
2 https://www.ncei.noaa.gov/access/billions/, DOI: 10.25921/stkw-7w73 accessed in August and September 2024.

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Table 11-1 above illustrates the economic cost that severe weather and climate change has had on California in the past four decades. The annual average for the entire 44 years (1980-2023 inclusive) is 1.0 events, whereas the annual average for the most recent complete five years (2019-2023 inclusive) is 1.8 events. The annual average number of events, and the costs per event, are expected to continue to rise as the effects of climate change become more pronounced. The 44 events listed on Table 11-1 are responsible for a reported 1,495 fatalities, although this number likely includes deaths in adjacent states that were also impacted by some of these disasters. The highest number of fatalities is associated with heat waves during droughts, followed closely by wildfires.

This chapter discusses the impacts of climate change and the climate change-related weather hazards the city of Santa Monica is likely to face in the coming decades, including impacts from:

1. extreme heat

2. drought

3. sea level rise, and

4. extreme windstorms
The hazards of extreme precipitation and wildfire, which are also becoming increasingly more common and damaging due to climate change, are discussed in detail in Sections 8 and 10, respectively, of this report. Each of the hazards in the list above is discussed individually in the following sub-sections, providing definitions for specific terms as appropriate, followed by a discussion on the climate change-related vulnerabilities anticipated for the city of Santa Monica.

This section is modeled after a similar chapter prepared for the Technical Background Report to the City’s Safety Element Update (2024). For information on the sources used, the reader is encouraged to review Chapter 5 in the Technical Background Report and the publications and sources referenced in this section. Please note that scientific and planning documents related to the impacts of climate change are being published at an astonishing rate and while we aimed to be as up-todate as possible in this report, given the pace of scientific inquiry into this subject, sections of this report may already be slightly obsolete at printing time.

SNAPSHOT OF SANTA MONICA’S CLIMATE AND WEATHER BASED ON

HISTORICAL DATA, AND ELEMENTS IMPACTING FUTURE FORECASTS The city of Santa Monica is located within the western coastal portion of Los Angeles County, and within the South Coast Air Basin. The regional climate2F 3 is considered semi-arid and is characterized
by warm summers, mild winters, infrequent seasonal rainfall, moderate daytime onshore breezes, and moderate humidity. Annual temperatures typically range from 49°F to 76°F and rarely go below 43°F or above 84°F. The annual average rainfall in the city is approximately 12 inches, with the majority occurring between December and March.3F
4 The average monthly wind speeds in the city
generally range from 5 miles per hour (mph) to 9 mph, with the highest wind speeds occurring along the coast and during the spring and summer months.4F
5 Winds in the city generally blow in a
southwest direction year-round, and tend to decrease in average speed moving inland. The city is

3 Climate is the average weather over a long period of time, such as 30 years, whereas weather is the hourly or daily state of the atmosphere at a given place with respect to heat, humidity, sunshine, wind, rain, etc. 4 NOAA National Weather Service; https://www.weather.gov/wrh/Climate?wfo=lox, accessed December 2022. 5 Wind and weather statistics for Santa Monica Pier and Santa Monica Airport from Windfinder.com, accessed in 2022.

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bounded by the Pacific Ocean to the west and as a result, experiences a marine microclimate. For additional information on the climate in Santa Monica please also refer to Section 2.

Climate change projections and the impacts that climate change will have on the weather of the southern California region, including Santa Monica, are forecasts and as such have inherent uncertainties. Computer models that attempt to predict future weather patterns are based on complex data that are in a state of flux. Essentially, climate change is driven by greenhouse gas (GHG) emissions and changes in the level of emissions released into the atmosphere in the near term versus the distant future will play a role in determining the severity of potential future climate change effects. These uncertainties in GHG emissions depend in part on factors such as population levels, economic activities, government policies, and personal behavior. Climate change models also consider factors such as water vapor, carbon dioxide, heat, and the Earth’s rotation to calculate the interactions between the ocean, the atmosphere and land. The models are currently limited by the availability of climate data and computing power; as these factors improve, models are expected to improve, yielding higher-resolution results in less time, and better forecasts.5F 6 The climate change projections presented in the following sub-sections are based on greenhouse gas concentration trajectories called Representative Concentration Pathways (RCPs) adopted by the Intergovernmental Panel on Climate Change (IPCC, 2022a). Representative concentration pathways are different scenarios for the future severity of climate change. Four scenarios are commonly used by the global scientific community: RCP 2.6, RCP 4.5, RCP 6, and RCP 8.5.6F 7 The higher the RCP
number, the more severe future climate change conditions are projected to be. Each RCP is briefly described below.
• RCP 2.6 – Stringent Mitigation/Low Emissions Scenario: This scenario represents aggressive emissions reduction that assumes global greenhouse gas emissions will peak in 2020, with emissions of carbon dioxide (CO2) from human activities reducing to zero around 2075. RCP

2.6 most closely corresponds to the ambitious goals of the United Nations Framework Convention on Climate Change 2015 Paris Agreement. The RCP 2.6 pathway delivers a temperature increase of about 1.6˚C by 2100, relative to pre-industrial temperatures. • RCP 4.5 and RCP 6.0 – Intermediate/Medium Emissions Scenarios: These scenarios represent a mitigation scenario where global greenhouse gas emissions peak by 2040 and 2060, respectively, then decrease for the rest of the century. The RCP 4.5 and 6.0 pathways lead to temperature increases of about 2.45˚C and 2.85˚C, respectively, by 2100, relative to pre-industrial temperatures.
• RCP 8.5 – High Emissions Scenario: This scenario represents a “business-as-usual” scenario where global greenhouse gas emissions continue to rise throughout the 21st century. The RCP 8.5 pathway leads to a temperature increase of about 4.3˚C relative to pre-industrial temperatures by the year 2100. The California Office of Planning and Research (OPR) recommends that agencies use RCP 8.5, the high emissions scenario, when considering impacts through 2050 because there are minimal differences between the low and high emissions scenarios through the first half of the century.

6 For a more in-depth discussion on climate models, refer to https://www.climatehubs.usda.gov/hubs/northwest/topic/basics-global-climate-models. 7 The RCP numbers (2.6, 4.5…8.5) refer to the range of radiative forcing values in the year 2100 that affect global warming and climate change. Radiative forcing is the change in the net radiative flux [energy measured in watts per square meter (W m− 2)] at the tropopause or top of atmosphere due to a change in an external driver of climate change such as a change in the concentration of carbon dioxide or changes in solar energy output.

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Vulnerabilities to climate change are also dependent on a variety of geographic, social, economic and governmental factors. As a result, every community is likely to have a different response to the effects of climate change. Climate change vulnerability is defined by the IPCC as the susceptibility of a population, system, or resource to the negative effects of climate change and other stressors, and includes three components: exposure, sensitivity, and adaptive capacity. Each of these components is defined below:
• Exposure is the amount and rate of change that a population or system experiences from the direct (e.g., temperature, precipitation changes) or indirect (e.g., habitat shifts due to changing vegetation composition) impacts of climate change; • Sensitivity refers to characteristics of a population or system that are dependent on specific environmental conditions, and the degree to which it will likely be affected by climate change (e.g., temperature or hydrological requirements); and • Adaptive capacity is the ability of a species (including humans) to cope and persist under changing conditions through local or regional acclimation, dispersal or migration, adaptation (e.g., behavioral shifts), and/or evolution.

Findings regarding Santa Monica’s vulnerability to climate-related hazards, as described in this report, are based on a review and consolidation of the vulnerability and risk assessments obtained from a variety of governmental resources and web-based tools, including data obtained from the Federal Emergency Management Agency (FEMA) and other Federal organizations, the State of California, Los Angeles County, and the City of Santa Monica. Some of these sources provide information and rankings specific to Santa Monica’s vulnerabilities to climate change, and natural hazards in general, whereas other sources provide a regional, County-specific assessment but do not zero-in to a city or census-tract level of detail.

EXTREME HEAT
Extreme heat occurs when temperatures rise significantly above the average high for a particular region. Therefore, “extreme heat” is a relative term—temperatures of 100 degrees are normal in locations like the Coachella Valley, but almost unprecedented in coastal regions of Los Angeles County. The coastal regions in Los Angeles County (LA County) historically experience 95thpercentile daily maximum temperatures of about 85°F, while inland regions historically experience 95th-percentile daily maximum temperatures of about 100°F.7F 8 The two highest recorded
temperatures to date in Santa Monica were 103°F, recorded on September 27th, 2010, and 101°F, recorded on September 4, 2022 and on October 24, 2017. Comparatively, in the inland San Fernando Valley a notable heat event occurred in September 2020, where maximum temperatures spiked to an all-time high of 121°F. It is also worth mentioning that many of the record-high monthly temperatures in Santa Monica occurred within the past 15 years (Table 11-2).

8 Los Angeles County (2021), LA County Climate Vulnerability Assessment.

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Table 11-2: Record Monthly Temperatures (°F) and Years of Record in Santa Monica Temp Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual High 88
2018
90 2022
94 2015
95 2009
94 2014
92 1957
92 2018
95 1983
103
2010
101
2017
100
1966
89 1979
103
2010
Low 26
1913
32 1903
28 1907
33 1917
39 1915
41 1908
42 1906
47 1919
40 1907
37 1919
32 1919
30 1916
26 1913
Based on data recorded between 1900 and 2023 as follows: 1900-1938, Santa Monica weather station near the intersection of 11th Street and Olympic Boulevard; 1939-2000, Santa Monica Pier; 2001-2023, Santa Monica Municipal Airport.

Source: https://www.extremeweatherwatch.com/cities/santa-monica, with data from the NOAA National Climate Data Center accessed on September 1, 2023.

An extreme heat event is defined as two or more days and nights of unusually high heat for the region. An extreme heat day is defined as a day in a year when the daily maximum exceeds the 98th historical percentile value of historical daily maximum temperatures, based on data from 1961 to 1990, between April and October. In Santa Monica, annual temperatures typically range from 49°F to 76°F and are rarely below 43°F or above 84°F.8F
9 If the maximum temperature in Santa Monica is
greater than 86.7°F, that day is considered an extreme heat day in the city.

Between 1961 and 1990, the observed historical data for the city indicates an average of two (2) extreme heat days per year, with some years experiencing zero extreme heat days, and others seeing more than the average. In September 2022, Santa Monica experienced a heat wave, with temperatures ranging between 87°F and 101°F, that lasted nine (9) consecutive days.9F 10 In 2024,
between September 5th and September 9th, the city hit highs of at least 87°F that prompted an excessive heat warning. A high of 100°F was recorded on September 6th; this temperature has only been recorded in Santa Monica eight times in its recorded history.10F 11 Looking forward in time, extreme heat is predicted to intensify in Santa Monica. While the historical 30-year annual average maximum temperature in Santa Monica is 69.1°F11F 12, under the worst-case
climate change scenario (RCP 8.5), Santa Monica is projected to experience an annual average maximum temperature increase of 3.7°F (to 72.8°F) by mid-century (2035-2064), and a 6.8°F increase (to 75.9°F) by end-century (2070-2099). In contrast, the medium emission scenario (RCP

4.5) projects an average maximum temperature increase of 2.9°F (to 72°F) by mid-century, and 3.9°F (to 73°F) by end-century (Figure 11-3, upper panel).

9 Weather Spark, Climate and Average Weather Year-Round in Santa Monica; https://weatherspark.com/y/1727/Average-Weather-in-Santa-Monica-California-United-States-Year-Round, accessed in December 2022. 10 https://www.extremeweatherwatch.com/cities/santa-monica/year-2022. 11 https://smdp.com/2024/09/12/heat-wave-dying-down-after-rare-100-degree-high/, accessed on September 16, 2024. 12 Cal-Adapt Local Climate Change Snapshot for Santa Monica California, cal-adapt.org.

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Figure 11-3: Projections of Maximum Temperatures and Extreme Heat Days in Santa Monica (1950-2100) under RCP 4.5 (teal) and 8.5 (violet) Source: Cal-Adapt Local Climate Change Snapshot for Santa Monica California. cal-adapt.org.

Similarly, the annual number of extreme heat days in Santa Monica is also projected to increase (Figure 11-3, lower panel). Compared to the historical average of two (2) extreme heat days per year, the city’s extreme heat days are projected to increase to an average of eight (8) days per year by mid-century (2035-2064), and an average of 21 days per year by end-century (2070-2100) under the RCP 8.5 scenario. Compared to the RCP 8.5 scenario, the RCP 4.5 scenario is projected to result in an average of seven (7) extreme heat days by mid-century and an average of nine (9) extreme heat days by the end of the century. These numbers highlight the importance of managing GHG emissions, as the number of extreme heat days by end-century is projected to increase at a significantly higher rate under the RCP 8.5 scenario compared to the RCP 4.5 scenario.

It is also important to note the spatial differences in global warming in southern California (California’s Fourth Climate Change Assessment). Specifically, coastal regions are projected to experience relatively lower amounts of warming due to the ocean’s buffering effect, while interior regions are expected to experience the highest amounts of warming, up to 10°F in the late 21st century under RCP 8.5 (Hall et al., 2018).

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Social Vulnerability to Extreme Heat
Extreme heat is dangerous to all living creatures on Earth. For human populations, direct exposure to extreme heat can cause heat cramps, heat exhaustion, heat stroke, and quicken dehydration.

Extreme heat is the leading cause of weather-related deaths in the United States and in California, as discussed previously. Hot and sunny days can also increase the production of ground-level ozone, a harmful pollutant that is the main component of smog, which can damage the respiratory system and is particularly harmful for those with asthma and other respiratory conditions.

Abnormally high temperatures can also harm non-human animals and plants that are not adapted to these conditions, increase wildfire conditions by drying out plant material, and contribute to drought conditions. Thus, extreme heat can also indirectly affect humans by causing wildfires, limiting water, and affecting food production. Specifically, extreme heat directly impacts crops due to intense ultraviolet light, which can stress the plants, resulting in stunted development and plant mortality. This in turn causes lower quality produce, and overall reduced crop yields with significant implications for food security (see the sub-section on drought below).

Heat waves, which are extended periods of extreme temperatures, can be particularly dangerous by exacerbating drought and wildfires, and compromising air quality. Extreme heat also increases electricity demand for cooling, and can simultaneously lower the ability of transmission lines to carry power, possibly leading to electricity reliability issues like rolling blackouts during heat waves.

For example, about 15,200 electricity customers in the Los Angeles areas of Lincoln Heights and Highland Park were without power at the height of the heat wave in September 2024.12F 13 Like many other effects of climate change, the adverse impacts of extreme heat are felt most acutely by vulnerable populations, including older adults, children, and those with pre-existing health conditions such as asthma and cardiovascular disease. Combining these characteristics with additional factors, such as poverty, occupation (outdoor workers), language barriers and housing insecurity, can put these individuals at a disproportionately high risk of heat-related illness and death (Basu and Malig, 2011). Unhoused populations, those with inadequate shelter, or those without access to air conditioning, are particularly vulnerable to life-threatening heat.

In its heat wave planning and response activities, the City of Santa Monica utilizes the National Weather Services HeatRisk tool to better identify when forecast conditions pose heat-related risks to heat-sensitive populations or the general public. HeatRisk is an experimental tool that combines Centers for Disease Control and Prevention’s (CDC) health-based temperature thresholds with National Weather Service’s local temperature parameters and climatology. HeatRisk takes into consideration how unusual the heat is for the time of year, the duration of the heat wave (both daytime and nighttime temperatures are considered), and if the temperatures pose an elevated risk of heat-related impacts based on CDC data.

The California Heat Assessment Tool (CHAT) was developed to help state and local public health officials understand how heat vulnerability will change with increasing temperatures due to climate change. Development of the tool was funded by the California Natural Resources Agency as part of development of the state's Fourth Climate Change Assessment. The tool helps users identify heat vulnerable areas based upon changes in high heat days under different climate scenarios and social, health and environmental vulnerability factors. The study defines "Heat Health Events" (HHEs) as

13 https://smdp.com/2024/09/12/heat-wave-dying-down-after-rare-100-degree-high/, accessed on September 16, 2024.

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heat events that cause negative public health impacts. The tool helps users determine how climate change will affect the severity, duration, and shifts in timing of HHEs under different emissions scenarios. Projected HHEs for Santa Monica through the year 2090 using CHAT are presented in Table 11-3 below.

Table 11-3: Santa Monica Projected Heat Health Eventsβ
Time Period
2011-2030 2031-2050 2051-2070 2071-2090
Annual Number of Heat Health
EventsΩ 2.2 4.45 6.25 6.75
Average Max Temperature (˚F) 84.46 83.58 83.45 83.05
Average Min Temperature (˚F) 68.92 69.59 70.12 69.85
Average Event Duration 3.77 4.37 4.88 5.25
Average Max Relative Humidity (%) 83.09 82.26 80.69 84.03 Average Min Relative Humidity (%) 45.39 46.81 47.34 50.08 Annual Frequency Relative Change
(%) 127.59 360.34 546.55 598.28
Duration Relative Change (%) 35.07 56.49 74.72 88.03
β Data represent RCP 8.5, the months of June, July, and August; and the 95th percentile. Ω Heat Health Event (HHE) is any event that results in negative public health impacts, regardless of the absolute temperature. Each local area has a unique HHE specific to its climate and the historical sensitivity of people in that area to past heat events.

Source: California Heat Assessment Tool, 2024.

The primary indicators of social sensitivity and lower adaptive capacity to extreme heat in Los Angeles County are higher percentages of children and older adults, pre-existing health conditions such as asthma and cardiovascular disease, outdoor workplace conditions, no health insurance, mobile homes/homes that lack adequate thermal envelopes, households without vehicle access or transit access, and low-income households.

Santa Monica’s social vulnerability to extreme heat is considered low according to the Los Angeles County Climate Vulnerability Assessment (LACCVA, Los Angeles County, 2021), and is projected to be one of the lowest in the County under RCP 8.5 conditions mid-century. This is primarily due to the City’s low overall social sensitivity score, meaning the general population is less susceptible to the negative impacts of extreme heat events. Nevertheless, there are vulnerable populations within the city, such as older adults and people with health conditions, unhoused individuals, households without air conditioning, and households without access to vehicle access, that should be considered when developing climate-hazard mitigation goals and policies. The lower overall temperatures in Santa Monica during a regional heat wave as a result of its geographic location are also expected to result in an increase in day-time visitors, with inland residents flocking to the beach to cool off. This will result in extra strain on traffic patterns and would impact access by the local residents to the same limited resources being utilized by a larger number of people.

The impacts of extreme heat on utility infrastructure can result in significant damage, repair costs, and service interruptions that can be catastrophic to human health. Some types of infrastructure, including power lines and roadways, face greater stresses during high temperatures, as the heat makes the materials used to build these structures unstable, which in turn makes failure more likely.

The 2019 Santa Monica Climate Action and Adaptation Plan (CAAP) ranks the City’s water and

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Based on the LACCVA and CAAP vulnerability assessments, the following bullet points summarize the primary issues Santa Monica is likely to face due to extreme heat and rising temperatures. Note that extreme heat can also exacerbate drought and wildfire conditions; those hazards and their potential impacts on the city of Santa Monica are discussed separately in this report (drought is discussed in this section and wildfires are discussed in Section 10). • Impacts to the health of vulnerable populations, including the elderly, children, homeless, and those with chronic illnesses
• Impacts to the health and safety of workers, especially for those working outdoors for long hours
• Power outages during extreme heat events due to regional energy supply-demand imbalances
• Reduced water supply and quality regionally
• Uncomfortable and potentially unsafe conditions for occupants of buildings without air conditioning
• Inadequate power for cooling equipment at residential care, continuing care and nursing facilities
• Instability and potential failure of critical infrastructure, including power lines and roadways • Faster wear and tear of pavement, increasing safety hazards and maintenance costs Extreme Heat Mitigation Actions and Resources
There are a variety of policies and action items that communities can undertake to reduce the impacts of extreme heat on their population and infrastructure. The City of Santa Monica, in its 2019 CAAP, has identified and is already undertaking several action items designed to do this.

First and foremost, California and Santa Monica have both undertaken an aggressive plan to reduce GHG emissions. The City’s goal is to reduce GHG emissions by 80% below 1990 levels by 2030.

As of 2022, Santa Monica had achieved a 48% reduction in emissions from 1990 levels, with vehicle transportation and building electricity usage showing the largest decreases in carbon emissions.13F 14 To reach its goals, the City has implemented and will continue to implement a series of programs, initiatives and strategies. These programs currently include: 1) reducing the use of fossil fuels to heat and cook in residential and commercial buildings, and 2) increasing the use of electric vehicles (EVs). As part of this last effort, the City has adopted a new code requiring new multi-family buildings to provide a larger number of EV charging stations. The City will also restrict the sale of gasoline cars by 2035.

Other actions aimed specifically at managing extreme heat events include identifying suitable locations for neighborhood resilience hubs and cooling centers at City-owned and non-City-owned sites from where disaster assistance and supplies can be made available to impacted individuals14F

15. 14 https://www.santamonica.gov/blog/sustainable-and-connected-community-the-2022-santa-monica-greenhousegas-emissions-inventory; accessed June 17, 2024. 15 Climate-Ready Community Action Items 2 (Expand the Community Resilience Network) and 4 (Prepare for Extreme Heat) in Santa Monica’s 2019 CAAP.

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2025 Climate Change & Severe Weather Hazards Page 11-11 For example, during the most recent heat wave in September 2024, City of Santa Monica airconditioned libraries and park facilities were opened for multiple days to provide relief from the heat, and City staff highlighted heat-related health information and the availability of pools and splash pads at Annenberg Community Beach House, Santa Monica Swim Center, Virginia Avenue Park and Tongva Park. City personnel distributed emergency water at these cooling locations, especially for those seeking relief from the heat, including unhoused populations and seniors. The City and County of Los Angeles also opened several cooling centers.15F 16 City departments closely
monitored heat conditions and distributed heat safety information to its many outdoor workers.

Given the long-term impacts of climate change, the City is also considering programs to prepare residents to respond to climate change. This includes continuing the development of community outreach and engagement materials. Currently the City provides general information about extreme heat safety on one of several emergency preparedness websites with links to general resources, including the National Integrated Heat Health Information System. Other action items that the City may consider deploying during heat waves include ensuring that temporary shade structures are available for community events, that coastal access is maintained for those seeking relief from the heat, and that City facilities have the capacity to provide air conditioning for residents, visitors and workers.

Other long-term action items listed in the City’s CAAP (2019) include adopting standards for asphalt and roof surfaces that will help reduce the local heat-island effect; develop outreach and educational materials on passive cooling strategies such as shade trees and insulation; and increase tree canopy in vulnerable neighborhoods. The City is also promoting fossil-fuel-free HVAC systems, such as pump technologies, for buildings installing or replacing air conditioners16F

17. Longer-term action items
include developing building design guidelines for climate-resilient buildings, and adopting and implementing these standards for new and substantially renovated buildings17F

18. The City of Santa Monica is also partnering with local utilities, regional agencies and local jurisdictions to assess the vulnerability of its energy infrastructure. Other action items include the deployment of local resilient energy systems, including solar, energy storage, combined heat and power, and fuel cells for new projects and existing facilities. These actions are meant to prepare the community for the impacts of future heat waves, wildfires, and other similar hazards. Residents and local businesses are also encouraged to install resilient energy systems18F