Scripps Researchers Unveil the First Comprehensive Wildfire Forecast for the Western United States


Using statistical methods developed in climate forecasting research, scientists at Scripps Institution of Oceanography at the University of California, San Diego, have constructed the first comprehensive forecast for wildfires in the western United States.

The devastating 2000 wildfire season, reported to be one of the worst in the past half-century, included more than 90,000 wildfires and 7 million acres burned, inflicted $1.6 billion in damage, and required more than 30,000 fire-suppression personnel. Although the new Scripps forecast predicts a much milder wildfire season for 2001, the experimental analysis may become valuable in aiding fire-suppression preparation and response.

"This promises to be a valuable tool for scheduling fire management," said Anthony Westerling, the lead developer of the forecast, which is administered through the Scripps-based California Applications Program. "The western United States has been pooling its resources together for fire suppression. A lot of important decisions are made early in the year about prepositioning 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."

Important to this forecast development was the assembly of more than 20 years’ worth of fire information recorded by the U.S. Forest Service, the Bureau of Land Management, and the National Park Service. Dan Cayan, director of the California Applications Program, hopes to develop a closer working relationship with California’s Department of Forestry and Fire Protection so that the new "Western Wildfire Season Forecast" can be tailored to assist the agency in fire protection and resource management.

The basis for the unique forecast is its statistical consideration of past seasons’ moisture deficit or excess beyond the weather conditions at the time of the fire season.

Rather than relying on forecasts of the summer weather during the fire season, the main feature of the new wildfire forecast is a calculation of the amount of vegetation available to burn during the fire season, also called the fire "fuel" availability.

"This forecasting model is based on our understanding of fuels that are available for fires to burn," said Westerling. "We looked at the correlations between the Palmer Drought Severity Index–which summarizes moisture characteristics in 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."

For example, in California fires are more likely to occur during a year following a dry winter immediately preceding, and a wet winter two years prior. Wildfire fuel builds up because of the productive wet winter two years prior and dries out during the following arid winter, so the prospects for wildfire are increased. In the drier Great Basin area, moisture conditions, and hence fuel production, in the winter and spring a year before the fire season are most important. Westerling notes that fuels will always be dry enough to burn there and it’s just a matter of enough fuel becoming available.

The 2001 Western Wildfire Season Forecast is based on data from January and March of 2001; January, March, May, and August of 2000; and May of 1999. The forecast covers the western United States from the West Coast through the Rocky Mountains.

In the 2001 forecast model, Westerling and his colleagues show a much less severe wildfire season compared with 2000. The fire severity has tapered off after two years of dry conditions. In other words, the model suggests that the fuel is dry, but there’s less fuel to burn.

Westerling notes that the experimental forecast does not indicate detailed information, such as how a specific fire will behave and how much it will burn (this is not possible a season or more in advance).

However, with proper funding and improved data collection, future versions of the forecast could include more detailed biological-climate information so that more precise forecasts may be made across the West according to specific ecological and climate conditions.

The researchers also are exploring whether it is possible to forecast smaller time frames, such as the early and late portions of the fire season, and whether the lead time can be increased.

Contributors to the forecast research include Timothy Brown (Desert Research Institute), Cayan (Climate Research Division, Scripps Institution of Oceanography and U.S. Geological Survey), Michael Dettinger (U.S. Geological Survey), and Alexander Gershunov (Scripps Institution).

The research was supported by the National Oceanic and Atmospheric Administration Office of Global Programs through the California Applications Program and the Experimental Climate Prediction Center; and the Department of Energy Accelerated Climate Prediction Initiative.

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