Staff portrait for Peter Cowan.
By ,
Director of Conservation Science

Last year, the U.S. Government released its Fourth National Climate Assessment, assessing the impacts and risks our nation faces from climate change. Among its findings were that the frequency of large fires in the United States is increasing, and more worrying is that areas that haven’t historically experienced as much fire are becoming fire-prone.

This news won’t come as much of a surprise to most Californians, who over the last two years have experienced the worst fires in recorded state history. Last year, the Camp Fire destroyed the town of Paradise, taking nearly three times more lives and homes than any previous fire. And this was on the heels of the Ranch Fire, the largest fire in California history surpassing a mark set only the year before by the Thomas Fire.

With this many catastrophic fires taking places within the state in the past two years, many people are beginning to wonder if this is the “new normal,” as Governor Jerry Brown stated earlier this year. Many of us in the scientific community are trying to understand what changes are causing these patterns in wildfire.

What does the future hold for fire in California and how can we best prepare for it?

To help find answers to these questions and hopefully alleviate some uncertainty, this is the first in a series of posts where I will help decipher wildfire trends within California. The scope of this analysis will encompass the state as a whole to provide context for the changes we’re likely to experience here on the Peninsula and in the South Bay, where POST’s work is focused.

Let’s start with the fundamentals. What are the factors driving these catastrophic wildfires within the state, how have they changed in recent years and what does the future hold?

Fire in California - POST
Strong east winds have helped fuel and spread many of the large fires that have occurred in the past few years, like the deadly Camp Fire pictured here toward the top of the frame. Photo: NASA (Joshua Stevens), 2018 (CC)


The weather when a fire starts has a dramatic impact on how quickly a wildfire can spread and the containment options available to firefighters. A variety of factors play into this, but wind is arguably the most significant. Many of the recent fires in the state ignited during strong, east winds blowing toward the coast from the Great Basin. Not only does this wind dry out the vegetation (fuel for the fire), it gives embers something to ride and spread a growing fire.

How climate change might impact the state’s wind patterns is still unknown, but another trend is emerging with longer periods of dry weather as winter rains arrive later and end earlier. It’s hot and dry for a longer period of time now which is making much of the state more susceptible to wildfire for a greater part of the year. These changes in seasonal precipitation are something scientists predict will persist and strengthen in the future.

Fire in California - POST
The recent drought, in addition to a beetle infestation, has left the state with 129 million dead trees, primarily in the Sierras. This huge availability of fuel is part of the reason we’ve experienced such intense wildfire in recent years. Photo: U.S. Geological Survey, 2016 (CC)


Vegetation, the fuel that feeds wildfires, has been a focus of many conversations recently and the subject of misconceptions in the aftermath of major fires. Fuels across the state have experienced major changes over the last century as climate change has generally caused them to be drier. The recent drought, in addition to a beetle infestation, left the state with 129 million dead trees, primarily in the Sierras.

The natural ecosystems in many parts of California need fire to rejuvenate and be healthy. Over much of the last century, however, we pursued a strategy of immediate fire suppression, rather than letting them run their natural course (when safe to do so). Obviously, suppression is necessary to protect lives and property, but it has contributed to an unhealthy amount of fuel accumulation, increasing the threat if a fire were to occur today. Fortunately, as land managers, supporting the health of the landscape’s vegetation is something we can actively work toward.

Fire in California - POST
In the past decades, more people in the West have moved into the “wildland urban interface,” the area bordering the state’s open spaces. Since most fires are started by people, this has increased the number of ignition sources for wildfire and, unfortunately, put more property in harm’s way when fires do start.  Photo: U.S. Geological Survey, 2016 (CC)


You might be surprised to hear that the majority of wildfires within the state are started by people, either intentionally or accidentally. Over the past few decades, the number of people living adjacent to or near the state’s open spaces has exploded. Common nomenclature for this borderland between our wild and urban landscapes is the “wildland urban interface” (WUI), a mixing zone of natural and manmade spaces. The simple truth is that this has increased the number of ignition sources for wildfires and subsequently helped increase the frequency of fire in the state.


This is a good place for us to leave things for now—an introduction to this unsurprisingly complex subject. There’s still so much for us to study and understand. How does past land management and fire suppression intersect with our changing climate and patterns of housing expansion in rural areas to influence the future of fire in the state?  Just what does the future hold for fire in California and what does it mean for us here on the Peninsula and in the South Bay?

Stay tuned for more articles on this subject as we work to find some clarity regarding this complex phenomenon and the future of fire here in the Golden State.


About the author:

Dr. Peter Cowan is an ecologist fascinated by how species interactions, climate and humans shape nature. A Stanford and Berkeley graduate, he has concentrated on conservation throughout California for the past three years. After completing his dissertation on the evolution of chaparral and other fire-prone plant communities, he worked on science policy in Sacramento and Washington DC before returning to the Peninsula. He joined POST as Director of Conservation Science in early 2018.

Photo credits:
Banner image: FEMA photo/Andrea Booher, 2007 (CC)

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