By NED ROZELL
July 08, 2010
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 patterns.
Image courtesy U.S. Geological Survey and Geographic Information Network of Alaska.
"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 scenario: 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 clouds.
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 were not located upwind.
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 during winter.
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.
Publish A Letter in SitNews Read Letters/Opinions