Wildfire Concepts Wildfire









In Yellowstone’s forests above 2,000 feet, hundreds of years may go by before enough fuel has accumulated to support a fire that can burn through an entire stand of trees (Franke 2000).  Although it has been estimated that the fire return interval for the region is between 200-300 years, researchers looking further into the past have found no evidence for such a conclusion (see figures below). 

An analysis of the charcoal deposits in several Yellowstone lakes led Millspaugh, Whitlock and Bartein (2000) to determine that fire frequency has been closely correlated to the intensity of summer drought for at least the last 17,000 years (see figure at right).  Long-term fluctuations in the solar radiation that reaches Earth during the summer have caused gradual climate shifts by altering atmospheric circulation (Millspaugh, Whitlock and Bartlein 2000).

Based on a sediment core from Cygnet Lake on Yellowstone’s central plateau, the researchers determined that fires occurred most frequently (15 per 1,000 years) in the early Holocene period about 10,000 years ago.  After that, fire frequency declined to no more than 2 or 3 fires per 1,000 years on the central plateau.

 Figure and text from Millspaugh, Whitlock and Bartlein 2000.

Prehistoric Period from 1690 – 1886.  Complete suppression from 1886-1972.  Natural fire policy from 1972-1988.Figure above shows the percent of the area within Romme and Despain's (1989a) study area that burned in 20-year increments from 1690-1988. Adapted from Romme and Despain (1989a).

When the last fires were declared out in November 1988, over 25,000 firefighters had fought the GYA fires including a high of 9,600 at one time, and nearly $120 million was spent on suppression (Franke 2000).  Only two fire related deaths occurred throughout the suppression attempt, both occurring outside the park and away from the flames.

The previous six summers were wetter than average so the first fires in June (ignited by lightning) were allowed to burn according to the natural fire policy in effect at Yellowstone National Park (YNP).  However, by July 15th no rain had fallen and the fires had covered about 8600 acres.  By July 21st, 17,000 acres had burned and full suppression was attempted.  The suppression effort seemed to help little, with over 400,000 by August 21st (see figure at right).

Research conducted after the fires revealed that weather was the main factor in determining the size of the fires, and the rate of spread (Franke 2000).  High winds, associated with cold fronts moving through the area, gusted to nearly 100mph.  Combined with temperatures reaching above 90°F and drought conditions of 7% moisture in decaying surface material (15-20% is normal), the fires were unpredictably large and fast.

This map shows the fires’ progress throughout the summer in four stages.  The first stage shows the scope of the fires on July 22, when firefighting efforts began on all fires.  August 20th was Black Saturday, when high winds fanned fires to new dimensions.  The outside line shows the final fire perimeter.  From Ekey 1989.

During one twenty-four hour period, August 20th or “Black Saturday,” the fires burned over 15,000 acres, leaping over the firelines that the hundreds of firefighters had put in (Carey and Carey 1989).  By September, when the smoke had cleared a bit, it was apparent that over 1 million acres in the GYA and about 720,000 acres in YNP were burned.

These great fires made up what Yellowstone officials called “the most significant political, ecological, and economic event in the park’s 116- year history” (Carey and Carey 1989).  The attempt to subdue these fires has been called the largest, most technologically sophisticated fire-fighting effort in US history (Varley and Schullery). Eventually this effort included more than 25,000 firefighters, dozens of helicopters, retardant-dropping bombers, fire trucks, and other vehicles, and the participation of the Wyoming National Guard and the US Air Force, Army, and Marines (Varley and Schullery).  The total cost was estimated at about $120 million (Franke 2000).