What is the history of wildfires in California?

Wildfires are not only natural but they help keep forests healthy and help renewed growth. However, wildfires, appear to have become more intense in recent history, particularly in places such as California, where the weather is often dry in many parts of the state. Looking at the history of wildfires, reasons as to why they have become more destructive become clear.

Early Record of California Wildfires

The archaeological and ecological record in California reveal a long history of wildfires in the state of California. In a study looking at pre-1800 wildfires, almost 1.8 million hectares were estimated to burn annually in California. This is about the level that has burned as of early October 2020. Scientists estimate that the summer and autumn seasons were often filled with smokey skies of burning forests.

One of the first major recorded wildfires occurred in 1889; this fire is sometimes called the Great Fire of 1889 or the Santiago Canyon Fire. The fire mainly occurred in what are today's Orange, Riverside, and San Diego counties. Until 2018, this may have been the largest single wildfire event in California's recorded history, with over 300,000 acres burned. It started in September 24 and continued to September 30th. The fire was preceded by a very dry season, with only 0.4 inches of rain during the rainy season and strong Santa Ana winds were recorded that year. Other fires occurred that year, including in San Diego, but were far smaller. The 1871 Peshtigo Fire (Figure 1), which occurred in Wisconsin, influenced policy regarding wildfires in the late 19th century. Fire suppression strategies already began to be evident in places such as Yosemiti, General Grant, and Sequoia national parks. The Peshtigo fire covered 1.2 million acres and became the most deadly wildfire in US history, with 1500-2500 people killed in relatively rural areas of northeast Wisconsin. The 1889 Santiago Canyon Fire also led to more intense fire suppression strategies to avoid loss of life and property. This meant that as soon as fires started, policy was to put out the fires as quickly as possible. Overall, these fire suppression strategies may have contributed to some of the larger fires that occurred much later, including in the 21st century, as it meant that forest growth was not renewed as quickly as would have been likely.

Figure 1. Sketch of the 1871 Peshtigo Fire that has been considered influential in fire suppression policy, including in California's forests, that may have contributed to larger fires in future decades.

Twentieth Century Wildfires

In the early 20th century, recorded fires were relatively small in scale but became destructive as the infrastructure and towns in California became built-up. The Berkley Fire of 1923 and Griffith Park Fire in 1933 are two examples of fires that were only about 10s of acres, although in the case of the Griffith Park Fire about 29 people died. This period saw that policy around fire suppression became more established, with the US Forest Service stating that wildfires were to be put out by 10 AM after the day a fire began. Later, the Bel Air 1961 fire and Laguna fire in 1970 were larger, indicating that fires began to get larger by the mid-20th century and later. By this time, increasingly scientists realized forest with large trees were not growing new trees as there were few large fires. In fact, almost no new giant sequoia had been growing by the mid-20th century. The Wilderness Act of 1964 and Leopold Report both encouraged fires, particularly naturally occurring ones, to be allowed to burn. This may have initially enabled larger fires to develop during this time. However, often fires would still be put out because they were deemed to be near built-up areas, leading to frequent fire suppression. The policy allowing fires to sometimes burn out by themselves, with the exception when fires were near built areas, became a common practice for fire suppression strategies for most of the rest of the 20th century. However, the policy was not evenly practiced. Additionally, forest management often did not involve removing old or dead trees, creating, in some place, a large number of potentially highly combustible trees. Perhaps the most devastating fires over the next few decades were the Panorama Fire in 1980, which burned 28,800 acres and killed 4 people, and Oakland firestorm in 1991, which burned about 1500 acres and killed 25 people. Once again, fires threatening built areas made these fires devastating rather than the fact they were very large fires. By historical standards, fires were still relatively small.

Recent Wildfires

What has changed is that since 2000, the scale of wildfires has now become far larger. In 2000, about 300,000 acres burned in total in the state of California. By 2018, the total was almost 2 million acres. In 2018, the Camp Fire was the most deadly wildfire in California's history, with 150,000 acres burned and 85 fatalities. It burned over 18,000 buildings and was the most expensive natural disaster in 2018, largely destroying the towns of Paradise and Concow. To date, the 2020 wildfires have consumed about 4 million acres, about the size of Connecticut, making this year the worst since historical records began. The August Complex fire, burning between San Francisco and Oregon, has consumed more than 1 million acres alone. The most likely factors causing this trend is the fact the fire seasons is now historically longer than it was over the 20th century, when fires were relatively small. Additionally, many trees have also died over multi-year droughts, causing a larger fire hazard as dead trees are not cleared or left standing in forests. Fires have generally become less deadly, as warning systems have improved, although increased urbanization has also meant that fires can be more destructive, at least financially, than they have been historically. Overall, about 800,000 acres burn annually on average over the last 20 years. Additionally, fire suppression, while diminished from earlier in the 20th century, has still continued despite generally policy shifts. This has meant that as forests do not burn as much from a year-to-year basis, fires are likely to be larger when they do burn, as there is more likely to be old growth and even dead trees left standing. This also appears to play some role in the large scale of recent fires. However, interestingly, the scale of fires is still generally less than estimates for annual fires and their size for the pre-1800 era.