Burned Alaska may cause more
By Ned Rozell
November 30, 2006
The blackened scars that Alaska fires leave on the landscape
may result in more lightning, more rain in some areas just downwind
of the scars, and less rain farther away, according to two scientists.
Nicole Mölders and Gerhard Kramm, both of the Geophysical
Institute at the University of Alaska Fairbanks, study how changes
in landscapes affect the weather. After Alaska's fire season
in 2004, when smoke befouled much of the air Alaskans breathed
and a collective area the size of Vermont burned, the scientists
wondered how all that charred country would affect local weather
A fire scar in the
making near Venetie, Alaska on June 24, 2004.
Image courtesy U.S. Geological Survey and Geographic Information
The researchers used MM5, a computer model based at Penn State
University and the National Center for Atmospheric Research,
to simulate conditions on the ground and in the air above it.
They compared the surface of Alaska before and after Alaska's
record fire season, in which 6.72 million acres burned. The model
told them that fire scars larger than 250,000 acres-about the
space taken up by the five boroughs of New York City-have an
impact on weather close to the fire scar.
"There's more rain locally, in the lee side of the scar
and then less precipitation farther out," Mölders said.
"It's a far-reaching impact." She and Kramm also said
fire scars might be responsible for flash floods in areas close
to them, and fire scars might also help generate lighting strikes.
"Formation of thunderstorms is more likely (around large
fire scars) than in the unburned forest," Kramm said.
Burned areas may be weather-makers because hot fires destroy
trees, shrubs, moss, and other plants that cool the soil and
the surrounding air. Satellite sensors have shown higher summer
temperatures in a fire scar in Canada up to 15 years after the
burn, Mölders said.
Mölders said fire scars might create the following weather-altering
The warm soil in a burned area
heats up the air above it, and that hot, dry air rises. Moist
air from unburned areas rushes in to fill the void, and that
moist air also rises. That air cools as it rises, reaches a saturation
point and condenses into a cloud that lifts higher than surrounding
That cloud, now loaded with moisture, reaches a level where graupel,
ice pellets that resemble tiny hailstones, forms. As graupel
particles rise, electrical charges occur within the cloud and
increase the possibility of lightning strikes.
The cloud moves downwind and releases its moisture as rain adjacent
to the fire scar. After the cloud dumps its load, areas farther
away don't receive any rain where they possibly would have if
a fire scar was not located
Though the model tells the researchers that large fire scars
affect summer weather, fire scars seem to cool the landscape
after the snow falls. A group of scientists, including UAF's
Terry Chapin, studied areas around Delta Junction that burned
three, 15, and about 80 years ago. Looking at the sun's radiation
absorbed all year, rather than just summer, they found that the
burn-scar sites absorbed less heat year-round, mostly because
snow covered more of the ground surface of recently burned sites
Mölders and Kramm want to use a new weather research and
forecasting computer model to combine the effects of burn scars
in summer with local weather. They hope to develop forecasts
that might help firefighters and pilots of small aircraft that
operate around fire scars.
This column is provided
as a public service by the Geophysical
Contact the Editor
University of Alaska Fairbanks, in cooperation with the UAF
community. Ned Rozell [email@example.com]
is a science writer at the institute.
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