Dramatic Increase in Western U.S. Wildfires Linked to Climate Change

Posted Oct. 25, 2017

MP3 Interview with Leroy Westerling, co-director of the Sierra Nevada Research Institute at the University of California, conducted by Scott Harris


The early October wildfires that swept six northern California counties, including Napa, Lake, Sonoma, Mendocino, Butte and Solano, constitute the deadliest fires in California history. Officials reported that multiple blazes across the state killed 42 people and hospitalized nearly 200 others. The wildfires destroyed at least 8,400 homes and other structures – burning more than 200,000 acres, roughly the size of New York City.

An estimated 5,000 firefighters continue to battle 10 different fires across northern California. Altogether 100,000 people were displaced by the fires, leaving thousands of evacuees not knowing if they’ll be able to find new homes in the region in the months and years ahead. All told, this year’s California fires caused the largest loss of life due to fire in the U.S., since Minnesota’s Cloquet fire in 1918.

Since the 1970s and early 1980s, the number of large wildfires has increased more than 500 percent in federally managed forests across the western U.S. Questions are now being raised by many about why there’s been such a dramatic rise in wildfires in recent years. According to scientists, the answer is climate change, in combination with other factors. Between The Lines’ Scott Harris spoke with Leroy Westerling, co-director of the Sierra Nevada Research Institute at the University of California at Merced. Here, he explains how climate change has increased the frequency and destructive power of wildfires - and will make the future incidence of these fires ever more dangerous.

LEROY WESTERLING: So, across the western United States there has been a very dramatic increase overall in wildfires since the 1970s. Every decade since then has seen more fires, more large fires, more area burned in those fires, more high severity fires in places that didn't used to get high severity fire that frequently.

The thing to keep in mind is that there is a lot of diversity in the ecosystems and fire in those ecosystems within the West – so some places are much more sensitive to changes in temperature than others are. These fires that we're talking about in California most recently – Sonoma and Napa Counties in particular – are burning at a different kind of vegetation. It's lower elevation, doesn't snow there, it's much warmer and drier in the summer. And so the temperatures that we've had are compounding this. But there's a lot more going on than just the temperatures.

This last winter was a very wet winter, and that gave us a lot of extra fuel, but it was also very hot temperatures in the spring and into the summer and so those fields dried out and were available to burn the same year that they grew. At the same time, we had a record drought in California for several years. Fuels were really super dry, there was more fuel than usual on the landscape and we had these winds. And we always have plenty of ignition. And that gave us this really combustible situation and then a lot of homes have been built in these subdivisions that are right up against dense chaparral, shrub land, fuels, grasses and things like that as well.

That mix of homes and really dense fuels and then the really dry conditions give you a really risky situation all the way around.

BETWEEN THE LINES: I would ask you, Leroy, to comment on something you had written. You had written that these very destructive wildfires we're seeing are not a natural occurrence. And you link them with climate change. How do we know it's climate change that's feeding this pattern of ever-increasing and more severe fires?

LEROY WESTERLING: The important thing to keep in mind around the western U.S. and globally, is that when we're looking at fire, we're not thinking of fire as a way to prove that climate change is happening. We know climate change is happening because we know about the basic physics of what we're doing to the atmosphere. We know how we've changed the content of the atmosphere, increasing concentrations of greenhouse gases. There would be no life on earth, earth would not be warm enough to support the ecosystems we have without the greenhouse effect. What we've done is intensify that. The temperature of the earth is catching up and that's affecting ecosystems. It's that energy imbalance that we've introduced by changing the atmosphere; it's affected the climate system, as a whole, warming up earth, and there are a lot of feedbacks.

And fire is one of those feedbacks. Fire allows us to see the impacts very abruptly of climate change on the landscape. So as you warm things up gradually over time, you still get very abrupt changes in the landscape in sort of steps. From fire, from insect infestations, from drought die-back and things like that. So these are natural processes, but they're sort of like a natural way the system responds as it's transformed by climate change.

BETWEEN THE LINES: We have a government in Washington right now, both the Congress and in the White House in the Trump administration, a lot of climate deniers in charge of key agencies that have a lot to do with fighting fires and providing resources to prepare for the next set of fires next season. How is the climate change denial in our government hobbling and placing obstacles for those who are really concerned about it and trying to do their best to combat these fires before they start?

LEROY WESTERLING: With the current administration, it's hard to see how they are responsive to the science that would tell you what you to do where and when to get the results that you want to get. So, we had a lot of trepidation that the policies are going to be enacted to manage the landscape that don't take account of the science that tells us what their effects are going to be.

We've had these problems in the past and if we do it again at this time, this moment in our history, we're just going to be compounding the risks that we face and the difficulty that we’re going to have in the future to manage these landscapes in a way that provides the services we want for them.

For more information, visit Leroy Westerling's web page at ulmo.ucmerced.edu.

Related Links:

Subscribe and get Between The Lines' Weekly Summary in your inbox!