Scientists Improve Wildfire Forecasts for Western United States

National Geographic News
July 18, 2001

Borrowing statistical methods long used by climate forecasters, scientists in California have developed a modeling tool to help officials better predict the wildfires that devastate large parts of the western United States every year.

In an initial study of the application, they produced the first comprehensive forecast for wildfires in the western United States. The results showed that this year's fire season is likely to be much milder than in 2000. The wildfire season generally extends from May to October.

Last year the region suffered the worst season of destructive land and forest fires in the past half-century, according to official reports. As many as 90,000 outbreaks of fire burned 7 million acres, causing U.S. $1.6 billion in damage. Thirty thousand firefighters were called on to combat the blazes.

The scientists say that after further refinements, the new analytic technique should be highly useful in fire-fighting preparation and response.

"This promises to be a valuable tool for scheduling fire management," said Anthony Westerling of the University of California's Scripps Institution of Oceanography in San Diego, who led the team that developed the new forecasting model.

"The western United States has been pooling its resources together for fire suppression," he said. "A lot of important decisions are made early in the year about pre-positioning equipment and personnel. Anything we can do to provide a forecast of where fires are likely to occur is going to save a lot of money, time, and effort."

The Fuel Factor

Traditional methods of wildfire prediction have been based on forecasts of the summer weather during an impending fire season.

The new approach takes into account a much more extensive set of factors and conditions, viewed over much longer periods. The data come from records compiled over the past 20 years by the U.S. Forest Service, the Bureau of Land Management, and the National Park Service.

Westerling said the forecasting model "is based on our understanding of fuels that are available for fires to burn." That entails calculating the amount of vegetation that's likely to exist in an impending wildfire season, based on weather conditions in the preceding years.

The scientists look at correlations between levels of drought—an indicator of the moisture content of soil and vegetation—and acres burned, or fire frequency. "The previous climate tells us how much fuel has been produced, and how moist that fuel is going into the fire season, so that's what's driving this forecast," Westerling said.

In California, for example, fires are more likely to occur after a two-year cycle of a wet winter followed by a dry winter. This happens because a high-moisture winter increases vegetation, and as that vegetation dries out in the subsequent winter it makes conditions ripe for the spread of wildfires.

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