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Anthony Westerling talks with and answers a few questions about this month's Fast Breaking Paper in the field of Geosciences.
Anthony Westerling, shown squatting in the middle of a burned over section from a large fire in the eastern Sierra Nevada. Photo was taken several years after the fire.

A podcast also is available for this commentary (podcast added July 1, 2008).
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Field: Geosciences
Article Title: Warming and earlier spring increase western US forest wildfire activity
Authors: Westerling, AL;Hidalgo, HG;Cayan, DR;Swetnam, TW
Journal: SCIENCE
Volume: 313
Issue: 5789
Page: 940-943
Year: AUG 18 2006
* Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA 92093 USA.
* Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA 92093 USA.
(addresses may have been truncated; see full article)

Why do you think your paper is highly cited?

I believe that this paper is highly cited for several reasons. It is the first to comprehensively establish that wildfire activity has increased across western US forests. It shows that the increase has been very large, in terms of the number of large forest wildfires and the total area burned in these fires, the increase in the length of the fire season, and the increase in the length of time individual fires continue burning.

Contrary to the conventional wisdom at that time, this paper showed that most of the increase in wildfire has occurred in forests where fuel loads are least affected by past fire suppression and land use practices.

And finally, this research is the first to conclusively link the increase in wildfire to trends toward warming and the appearance of earlier springs, implying that global warming will tend to increase wildfire in forest ecosystems where snow plays an important role in the area’s hydrology. Because of the nonlinear nature of the response in wildfire regimes in these forests to warming and earlier springs, they are very sensitive to climate change.

Does it describe a new discovery, methodology, or synthesis of knowledge?

I think all three describe this work. It is a synthesis of knowledge in that it relied on data sets that have been around for a while, but had not been looked at together in the right combination. In terms of methodology, some very simple but important innovations occurred in the way we defined the fire season and focused on the frequency of large fires.

Over 90% of reported fires are very small, and are not as responsive to climatic influences. The climate signal in the large fires, which are much more relevant in terms of their impact, tends to get lost in all the noise about the smaller fires. Also, the documentary record for large fires tends to be very much more accurate than is the case generally for all those small ignitions. So, in the past, researchers have tended to throw their hands up in dismay. By focusing on forest wildfires over 1,000 acres in size, we reduced the number of fire records that needed to be analyzed and checked for errors by two orders of magnitude.

It is a new discovery in that people had no idea about the scale of the changes in forest wildfire, nor did they realize that most of the increase was due to climate rather than the effects of fire suppression on fuels, nor that certain fire regimes are so sensitive to changes in temperature and the timing of spring.

Would you summarize the significance of your paper in layman’s terms?

In layman’s terms, this paper says that the warming observed in recent decades in western US forests is directly responsible for most of a very dramatic increase in forest wildfire observed in this region. That is true regardless of whether you think humans are or are not responsible for the warming itself. In addition, it says that any future increases in temperature due to human-caused climate change are going to result in more of these really big, intense fire seasons in western forests.

How did you become involved in this research, and were there any problems along the way?

I talked my way into a post-doctoral researcher position in the Climate Research Division at Scripps Institution of Oceanography while my wife was finishing up her Ph.D. in International Affairs. I had joint Ph.D.’s in Economics and International Affairs myself, so it was not always immediately obvious to everyone that I should be doing what was primarily natural science-oriented research in wildfire climatology.

I think it took two and half years to get the first paper I wrote in the field published. I got involved in wildfire research specifically on the advice of my mentor at Scripps, Dan Cayan, and once I started doing it I found I really loved it. I really enjoy the opportunity to learn from and collaborate with researchers in such a rich variety of fields: climatology, ecology, hydrology, paleofire, and land and resource management.

Where do you see your research leading in the future?

I am working on climate change impact assessments for wildfire in the western US, high resolution paleofire reconstructions for western forests, and high-resolution seasonal forecast models for fire management. All of these greatly benefit from the research presented in this paper. I am very interested in synergistic feedbacks between vegetation and wildfire and other disturbances and how those are affected by climate change.

Do you foresee any social or political implications for your research?

Yes. I think it brought home the message that climate change has the potential to have a substantial impact on life in the interior western US in the near term, and is not just a problem for people unfortunate enough to live somewhere else or a problem to be encountered at a time far into the future.

It also has important implications for forest management policy. If our wildfire problem was only exacerbated by the cumulative effects of fire suppression and land use changes on fuels, we could just rely on forest thinning and changes to suppression practices (letting more fires burn, etc.) to fix it.

But with climate driving much of the increase—particularly in forests where fire suppression doesn't have a big impact on fuel accumulation—the story gets more complex. Does it make sense to thin forests that haven’t been "thickened?" Would that decrease or increase the risks of fire and other disturbances there?

As efforts to mitigate climate change go forward, managing forests for carbon sequestration is going to become a big issue for policy and politics. How can we accomplish that if the frequency and intensity of large wildfires is going to increase because of climate change? Personally, I think the most effective policy to address risks to our forests in the long run will be to reduce net carbon emissions from industry, transport, and electricity generation.

Anthony Westerling
Assistant Professor of Environmental Engineering and Geography
Sierra Nevada Research Institute
University of California, Merced
Merced, CA, USA

A podcast also is available for this commentary (podcast added July 1, 2008).
Listen: MP3| WMA

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2008 : February 2008 - Fast Breaking Papers : Anthony Westerling
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