Thursday, July 6, 2006

Climate Change Fuels Western Wildfires

Science today published what is bound to be an incredibly controversial study by Westerling concluding that increased forest wildfire activity in the West, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons, is primarily due to climate change, not land use management:

...while land use history is an important factor for
wildfire risks in specific forest types (e.g. some ponderosa
pine and mixed conifer forests), the broad-scale increase in
wildfire frequency across the western United States has been
driven primarily by sensitivity of fire regimes to recent
changes in climate over a relatively large area.
The overall importance of climate in wildfire activity
underscores the urgency of ecological restoration and fuels
management to reduce wildfire hazards to human
communities and to mitigate ecological impacts of climate
change in forests that have undergone substantial alterations
due to past land uses. At the same time, however, large
increases in wildfire driven by increased temperatures and
earlier spring snowmelts in forests where land use history had
little impact on fire risks indicates that ecological restoration
and fuels management alone will not be sufficient to reverse
current wildfire trends.
    These results have important regional and global
implications. Whether the changes observed in western
hydro-climate and wildfire are the result of greenhouse gasinduced global warming, or only an unusual natural
fluctuation, is presently unclear. Regardless of past trends,
virtually all climate model projections indicate that warmer
springs and summers will occur over the region in coming
decades. These trends will reinforce the tendency toward
early spring snowmelt  and longer fire seasons. This
will accentuate conditions favorable to the occurrence of
large wildfires, amplifying the vulnerability the region has
experienced since the mid-1980s. The Intergovernmental
Panel on Climate Change’s consensus range of 1.5C to 5.8C
projected global surface temperature warming by the end of
the 21st Century is considerably larger than the recent
warming of less than 0.9ºC observed in spring and summer
during recent decades over the western region.
If the average length and intensity of summer drought
increases in the Northern Rockies and mountains elsewhere in
the western U.S., an increased frequency of large wildfires
will lead to changes in forest composition and reduced tree
densities, thus affecting carbon pools. Current estimates
indicate that western US forests are responsible for 20-40%
of total U.S. carbon sequestration. If wildfire trends
continue, at least initially this biomass burning will result in
carbon release, suggesting that the forests of the western U.S.
may become a source of increased atmospheric carbon
dioxide rather than a sink, even under a relatively modest
temperature increase scenario. Moreover, a recent
study shows that warmer, longer growing seasons lead to
reduced CO2 uptake in high elevation forests, particularly
during droughts. Hence, the projected regional warming
and consequent increase in wildfire activity in the western
U.S. is likely to magnify the threats to human communities
and ecosystems, and significantly increase the management
challenges in restoring forests and reducing greenhouse gas
emissions.  Wildfire conclusions

Science also has a podcast with Dr. Westerling (the Westerling piece can be found from :50 - 8:00 of the 32 minute podcast)

Science Abstract

Warming and Earlier Spring Increases Western U.S. Forest Wildfire Activity

Anthony Leroy Westerling 1*, Hugo G. Hidalgo 2, Daniel R. Cayan 3, Thomas W. Swetnam 4

Western United States forest wildfire activity is widely thought to have increased in recent decades, but surprisingly, the extent of recent changes has never been systematically documented. Nor has it been established to what degree climate may be driving regional changes in wildfire. Much of the public and scientific discussion of changes in western United States wildfire has focused rather on the effects of 19th and 20th century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it to hydro-climatic and land-surface data. Here, we show that large wildfire activity increased suddenly and dramatically in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks, and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks, and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.

http://lawprofessors.typepad.com/environmental_law/2006/07/science_today_p.html

Air Quality, Climate Change, Forests/Timber, Governance/Management, North America, Sustainability, US | Permalink

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