The fires in Los Angeles in January were some of the most destructive in history, but not unprecedented. The region has been prone to fire throughout its history, and the ecosystem has become dependent on them for long-term health. However, this issue is not limited to Southern California.
We are not immune to fires
With its Mediterranean climate and regions of chaparral, forests, and deserts with dry summers and relatively wet winters, most of California is a fire-dependent ecosystem that has only recently become subject to urban development. Furthermore, the introduction of non-native plant species, such as Eucalyptus trees and French Broom, has exacerbated the hazards even more. Are we in San Francisco at risk of similar events, and if so, are we prepared?
The natural environment of San Francisco looks quite different today. Historically, the western part of the city was composed of sand dunes. The San Miguel Hills (today referred to as Mount Sutro, Mount Davidson, and Twin Peaks) were chaparral, a shrubland environment consisting of coyote brush, California sage, and various species of lupine. Marshland was dominant on the eastern shores. You would have had difficulty finding many trees except for the occasional coast live oak and redwood in the sheltered valleys. You can still see remnants of these environments in various locations (Presidio, Lake Merced, Twin Peaks, Mount Davidson, and Glen Canyon).
Regardless, many of San Francisco’s natural areas depended on infrequent but consistent fires for health. With a climate that we are only beginning to understand, characterized by its short- and long-term cycles of cooling, heating, and drought, we are prone to severe fire weather, even in highly urbanized San Francisco.
It is often claimed that our city’s climate is too cold and damp for wildfire, but this is not always the case. In reality, we are also prone to the low-humidity, high-temperature, high-speed winds known in Southern California as Santa Ana winds. Locally, however, they are referred to as Diablo Winds.
Whatever the name or location, they form when air from elevated, inland locations flows to the ocean, compresses, warms, and dries out as it flows westward. This can lead to inland locations having similar temperatures to coastal locations. They occur any time of the year, but are most common in late summer and fall.
Unknown to most people, they appear here yearly but vary in severity. When they do occur, they rapidly dry out grasses, shrubs, and trees to the point where the probability of fire becomes high. One of the best examples of this happening in recent memory is the Tunnel Fire, more commonly known as the Oakland Hills fire, in 1991.
Several risk factors could make urban wildland fires possible here: the overgrown stands of eucalyptus; repeated cycles of drought and excessive rainfall; and power lines.
The weather during the Oakland Hills fire was hot, dry, and windy. Temperatures were in the low 90s even at the coast with a powerful northeast wind contributing to extreme fire behavior. The Oakland Hills fire was one of Northern California’s most significant fire events. This led to several changes, including the more widespread adoption of the Incident Command System, revisions to communication policies, updates to fire codes, and the standardization of fire hydrants throughout California.
The Oakland Hills fire was not unprecedented. Similar fires occurred in 1923 and 1970.The weather was a major contributor to the fire, but lesser known, yet equally significant, were the vegetation density, difficult access, the lack of interoperability between fire departments, and the flammable fuels involved, such as Eucalyptus trees.
Eucalyptus: the aromatic threat
Eucalyptus trees have a long history in California and the Bay Area. They were planted because they are a fast-growing source of wood; however, they are not suitable for lumber. The wood warps when drying, splits easily, and is difficult to cut. They were also used to indicate property boundaries, which can be seen today. The portion of Mount Davidson covered by trees indicates the land that Adolph Sutro owned in the 1800s.
The same eucalyptus oil that has therapeutic properties also makes the trees very flammable. When burned, the heat output is very high, likely contributing to the rapid fire spread in the Oakland Hills in 1991.
On San Francisco’s West Side, we have large stands of eucalyptus, many of which are approaching the end of their 150-year lifespan. As a result, there is an increasing risk of trees dying and falling over, in addition to the fire hazard.
Large stands of eucalyptus border homes and neighborhoods, the most significant of which are homes on Dalewood Way, Kensington Way, and Crestmont Drive. This is combined with plants of various sizes that add to the combustibility of the vegetation. These plants are classified in firefighting as one-, 10-, and 100-hour fire fuels and ladder fuels. The hour of fuels indicates the diameter of fuels and how fast they dry.
Grasses fall within the one-hour fuel category, small shrubs fall within the 10-hour category, larger shrubs and small trees within the 100-hour category, and larger trees within the 1,000-hour category. Ladder fuels are climbing plants that can carry fire from the ground to tree-top level. These are present in our eucalyptus stands and include other invasive species that promote the spread of fire.
Several risk factors could make urban wildland fires possible here: the overgrown stands of eucalyptus trees with ladder fuels and ignitable small-diameter fuels; the repeated cycles of drought and excessive rainfall, which stress trees; and power lines, which on a windy day can fall into vegetation. Climate change could be a factor. However, our understanding of the climate here in California is only just beginning, so it is difficult to ascertain the full extent of the impact.
Climate data dates back to the 1860s, but it is not as reliable, accurate, precise, or plentiful as it is now. Temperatures in the 100s are possible and likely in San Francisco in the future, as they have occurred several times in the last decade. Annual rainfall is periodic and fluctuates between high and low amounts, and it is uncommon to have consecutive years of average rainfall.
Response
If fires occur here in San Francisco due to an earthquake, weather, or both (remember that the October 1989 earthquake occurred during a mild heatwave with light east winds and temperatures in the mid-70s to lower 80s), what will the response look like?
We will rely on mutual aid responses from other agencies in the state and the country to assist our resources, which will be overwhelmed. Resources from as far away as Los Angeles and further will help with the response. The San Francisco Fire Department has deployed front-line engines to fires in Southern California, so it is likely they will also send resources here. Mutual aid response resources will likely report to a staging area (for example, the Cow Palace), get an assignment, and go to work. However, San Francisco has a few challenges for other departments.
[On Thursday: the importance of common fire infrastructure, and the good news.]
The author is a former wildland firefighter with extensive experience in wildland/urban interface operations who has been deployed to numerous large-scale fires around the United States, as well as having served with volunteer fire departments in Southern California. The author is currently a state fire marshal-certified fire instructor who has instructed in fire academies statewide, with extensive knowledge in fire engine pump operations, hydraulics, and disaster operations.