Anthony Westerling talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of
A podcast also is available for this
commentary (podcast added July 1, 2008).
Field: Geosciences Article Title: Warming and earlier spring increase
western US forest wildfire activity
AL;Hidalgo, HG;Cayan, DR;Swetnam, TW
Year: AUG 18 2006
* Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA
* Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA
(addresses may have been truncated; see full
Why do you think your paper is highly
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.
"...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
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.
This scatter plot of annual
number of large (> 200 ha) forest wildfires versus
average spring and summer temperature for the western
United States shows the nonlinear relationship between
temperature and large forest wildfire frequency. Fires
are from Forest Service, Park Service, and Bureau of
Indian Affairs management units reporting 1972 - 2004,
for fires reported as igniting in forested areas only.
Temperature data from see Jones, P.D.
and Moberg, A., 2003: Hemispheric and large-scale
surface air temperature variations: An extensive
revision and an update to 2001. J. Climate 16,
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
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
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
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.
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).
Note: links to external sites will open in a new browser
window. Thomson Scientific and ScienceWatch.com does not endorse