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 in California. Scientists estimate that the summer and autumn seasons were often filled with smokey skies of burning forests. This could be because forest cover was generally more widespread in the past, resulting in larger fires. Fires were also seen as mostly healthy for forests, as newer growth would sprout more easily after fires.

One of the first major recorded California 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 that also affected how fires were suppressed in California. Fire suppression strategies already began to be evident in places such as Yosemite, General Grant, and Sequoia national parks by the 1880s. 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. This devastation over a relatively low populated area resulted in a major policy move by authorities. The 1889 Santiago Canyon Fire reinforced, in the mind of authorities, to apply more 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, rather than let them burn partially or completely out. 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. This led to many older trees or even dead trees occupying large forest areas in many Western states, including in California.

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. Better fire suppression led to many fires being generally small, but that may have contributed to larger fires decades later as forests continued to grow older with minimal fire damage. Later, the Bel Air 1961 fire (Figure 2), about 16,900 acres burned, and Laguna fire in 1970, about 175,000 acres, 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. Fires had been relatively small for most of the first half of the 20th century, and trees had by then become generally older. In fact, almost no new giant sequoia had been growing by the mid-20th century, as noted by ecologists. With these new results, the Wilderness Act of 1964 and Leopold Report both now encouraged wildfires to be left alone and to be allowed to burn. This may have initially enabled larger fires to develop during this time, as less suppression occurred. However, often fires would still be put out because they were deemed to be near built-up areas, leading to frequent fire suppression as fires expanded outside of rural areas. 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 places, 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, however, fires were still relatively small.

Figure 2. The Bel Air fire of 1961 witnessed a more destructive fire that also saw it reaching parts of wealthy Bel Air and Hollywood.

Recent Wildfires

What has changed is that since 2000 the scale of wildfires has now become far larger, even approaching some of the scales witnessed in pre-1800 data. 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 2020 the worst since historical records began. The August Complex fire, burning between San Francisco and Oregon, has consumed more than 1 million acres alone. Most large fires were under 100,000 acres previously. 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. Climate change, undoubtedly as most scientists have concluded, is a key factor in this, as trees become dry, the rainy season is diminished, and tree mortality from insects that kill trees and that thrive in warmer temperatures increase. 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 general policy shifts. This has meant that as forests do not burn as much from a year-to-year basis, at least in the recent past, 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 more often less than estimates for annual fires and their size for the pre-1800 era.

Summary

Wildfires over the last twenty years are becoming larger and more financially and materially devastating. There are multiple reasons for this, but historical trends show that prior to 1800 fires may have still been generally larger than today. It is possible larger fires occurred because there was far less built-up area, with many more trees. While fire size generally declined over the 20th century, increasing urbanization has also led to more damage to property. Over the late 20th century, and particularly over the last two decades, the spatial extent of fires has substantially increased as older growth forests have been left to thrive and climate change has contributed to more devastating fires. One improvement has been that safety has improved due to early warning detection becoming better in recent decades.