[Vision2020] Western U.S. Forest Wildfire Activity

[Ted Moffett]

All-

Regarding the ongoing Southern California fires, and the very important
issue of Western US fire potential (especially in Idaho) and causes in
general, the following fact and science based sources are critical.

Read about the record drought and heat waves for Southern California (both
this year), coupled with the findings from the research on Western USA
fires, in the Science magazine article below, co-authored by the scientist,
Thomas Swetnam (University of Arizona), who I referenced at the start of
this thread, who was interviewed on CBS 60 Minutes last weekend on the
subject of wild land fire, with astonishing timing, given the explosion in
the Southern California fires that occurred immediately after:

http://www.terradaily.com/reports/Western_US_States_Swelter_Under_Record_Heatwave_999.html

*Parched California has driest 'rainy season' on record*

Los Angeles (AFP) July 1 - Los Angeles suffered through the driest rainy
season on record in 2007, marking the least amount of precipitation here in
the 130 years

http://www.noaanews.noaa.gov/stories2007/s2838.htm

In Los Angeles, the lack of rainfall led to the driest water-year to date
for the city since records began in 1877. From July 1, 2006, through the end
of March, downtown Los Angeles had received only 2.47 inches of rain, almost
one foot below the normal amount of rainfall for the period.

In the West, where mountain snowpack is relied upon to supply water needs
throughout the region, below-average rain and snowfall have become
increasingly common. In only two of the past nine years has snowpack on
April 1 been at or above the long-term average in at least half the region.
--------------

For those who wish to skip most of the Science magazine article, here is a
critical finding of their research, indicating human land use is not the
cause of the documented increase (note not the cause of the "increase," not
that humans do not start fires) in Western USA fires in recent decades:

http://www.sciencemag.org/cgi/content/full/313/5789/940

We compiled a comprehensive database of large wildfires in western United
States forests since 1970 and compared it with hydroclimatic and
land-surface data. Here, we show that large wildfire activity increased
suddenly and markedly 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.
--------------------

I will excerpt a few more paragraphs from this article:


*Science* 18 August 2006:
Vol. 313. no. 5789, pp. 940 - 943
DOI: 10.1126/science.1128834
 Prev <http://www.sciencemag.org/cgi/content/short/313/5789/936> | Table of
Contents <http://www.sciencemag.org/content/vol313/issue5789/index.dtl> |
Next <http://www.sciencemag.org/cgi/content/short/313/5789/944>
Research Articles Warming and Earlier Spring Increase Western U.S. Forest
Wildfire Activity *A. L.
Westerling,1,2*<http://www.sciencemag.org/cgi/content/full/313/5789/940#COR1>
H.
G. Hidalgo,1 D. R. Cayan,1,3 T. W. Swetnam4 *

http://www.sciencemag.org/cgi/content/full/313/5789/940

We compiled a comprehensive database of large wildfires in western United
States forests since 1970 and compared it with hydroclimatic and
land-surface data. Here, we show that large wildfire activity increased
suddenly and markedly 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.
------

Snow carries over a substantial portion of the winter precipitation that
falls in western mountains, releasing it more gradually in late spring and
early summer, providing an important contribution to spring and summer soil
moisture (*35*<http://www.sciencemag.org/cgi/content/full/313/5789/940#REF35>).
An earlier snowmelt can lead to an earlier, longer dry season, providing
greater opportunities for large fires due both to the longer period in which
ignitions could potentially occur and to the greater drying of soils and
vegetation. Consequently, it is not surprising that the incidence of
wildfires is strongly associated with snowmelt timing.

Changes in spring and summer temperatures associated with an early spring
snowmelt come in the context of a marked trend over the period of analysis.
Regionally averaged spring and summer temperatures for 1987 to 2003 were
0.87°C higher than those for 1970 to 1986. Spring and summer temperatures for
1987 to 2003 were the warmest since the start of the record in 1895, with 6
years in the 90th percentile—the most for any 17-year period since the start
of the record in 1895 through 2003—whereas only 1 year in the preceding 17
years ranked in the 90th percentile. Likewise, 73% of early years since 1970
occurred in 1987 to 2003 (Fig.
1<http://www.sciencemag.org/cgi/content/full/313/5789/940#FIG1>
).

--------

If the average length and intensity of summer drought increases in the
Northern Rockies and mountains elsewhere in the western United States, 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 U.S. forests are responsible for 20 to 40%
of total U.S. carbon sequestration
(*38*<http://www.sciencemag.org/cgi/content/full/313/5789/940#REF38>,
*39* <http://www.sciencemag.org/cgi/content/full/313/5789/940#REF39>). If
wildfire trends continue, at least initially, this biomass burning will
result in carbon release, suggesting that the forests of the western United
States may become a source of increased atmospheric carbon dioxide rather
than a sink, even under a relatively modest temperature-increase scenario (*
38* <http://www.sciencemag.org/cgi/content/full/313/5789/940#REF38>,
*39*<http://www.sciencemag.org/cgi/content/full/313/5789/940#REF39>).
Moreover, a recent study has shown that warmer, longer growing seasons lead
to reduced CO2 uptake in high-elevation forests, particularly during
droughts (*40*<http://www.sciencemag.org/cgi/content/full/313/5789/940#REF40>).
Hence, the projected regional warming and consequent increase in wildfire
activity in the western United States is likely to magnify the threats to
human communities and ecosystems, and substantially increase the management
challenges in restoring forests and reducing greenhouse gas emissions.

------

Vision2020 Post: Ted Moffett
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