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Discussions over the causes of this year’s fire season have mostly centered
on the need for earlier and more frequent prescribed burns. To help establish
the best times for burning, scientists from the University of Arizona are
looking to climate: El Niño and La Niña.
With two consecutive years of La Niña, more than 6.9 million
acres of American forests went up in flames this summer. Over the past
five years, the El Niño Southern Oscillation (ENSO) has primed western
forests to ignite, says dendrochronologist Thomas Swetnam of the University
of Arizona. Similar weather phenomena may have contributed to the Yellowstone
Park fires of 1988, he says. |
This image was captured late
in the afternoon on Aug. 6, 2000, from a bridge over the East
Fork of the Bitterroot River
just north of Sula, Mont. These elk sought refuge in the river
bottom during what may have
been the most extreme day of fire activity near the Bitterroot
in more than 70 years. Photo
by John McColgan, BLM Alaska Fire Service. |
“In both the tree-ring record and during the 20th century we’re seeing
synchronized forest fires at regional to continental scales,” Swetnam says.
He believes the driving factors creating these fire catastrophes are fire
suppression over the past century and ENSO climate effects. He has been
working on linking seasonal disasters with longer climate cycles for over
a decade, but, he says, “climate relationships with fire are just now being
recognized.”
Still, it may be some time before fire managers turn to the climate
phenomena for strategy advice. Don Smurthwaite of the National Interagency
Fire Center says that while long-range forecasting is interesting, the
“long-range” for fire managers is 24 hours to a week. General trend forecasting,
however, does help Smurthwaite to pre-position fire fighters in regions
where fires are expected to be the worst.
But, Swetnam says, it is easy now to look online and use the forecasts
to help fire managers prepare for high-risk seasons at least a year in
advance. Scientists at the National Oceanic and Atmospheric Administration
(NOAA) can detect the onset of an extreme summer El Niño event,
such as in 1997, as early as January or February. Years of extreme El Niño
generally bring about wet conditions to the Southwest, perfect for prescribed
burns, Swetnam says. Although it is hit or miss if a desiccating
La Niña event follows the next summer, the preparation can’t hurt,
he says. Should a strong La Niña follow closely after an extreme
El Niño — be prepared, he says.
Using tree-ring records going back 300 years, Swetnam studied fire scars
in several thousand pines and giant sequoias. He compared those records
with the climate history told in the ring width patterns of pines and Douglas
firs. He found that fire damage correlated strongly with extreme conditions
of a wet El Niño followed within three years by a dry La Niña.
In the Pacific Northwest, where El Niño and La Niña tend
to have opposite precipitation and temperature effects than in the Southwest,
Swetnam warns that fire risks are higher during the dry El Niño
years following a La Niña. In average years of mild climate flux,
the relationship to fire scars is weak.
U.S. Geological Survey research biologist Dave Peterson agrees that
climatic data in tree-ring records and the sedimentary record clearly connect
weather patterns with fires, but adds that on a local level it is difficult
to place the blame on ENSO. He contends that the fires were a result of
many different factors, including ENSO and fire exclusion.
Agricultural activity, road-building and clear-cutting have also made
the forests more susceptible to fires, he says.
While using climate forecasts, forest restoration and prescription burns
might help, “we just need some decisions,” Peterson says. “We need to develop
an integrated plan with federal, regional, and state agencies, municipalities
and the public and then enact it. Our initial efforts have to be phenomenal.”
Meg Rudolph
Geotimes contributing writer
