ISU Headlines

ISU-BLM project plots fire danger for southeast Idaho landowners

Posted July 23, 2007

Land managers, planners and fire agencies are using a Web site developed by Idaho State University and the Bureau of Land Management to help determine the fire danger where wild and urban lands meet in nine southeast Idaho counties.    

The Web site – http://giscenter-ims.isu.edu/website/wui/viewer.htm – displays results of the ISU-BLM Wildland/Urban Interface Fire Projects, which features fire information for Bannock, Bingham, Teton, Clark, Power, Oneida, Caribou, Bear Lake and Fremont counties. The information was developed at the ISU GIS (Geographic Information Systems) Center in Pocatello. A similar wildfire assessment for Bonneville County will be completed this fall.

“We have a Web site that features maps allowing users to zoom in and find the fire susceptibility rating for their areas,” noted Keith Weber, Director of the ISU GIS Center.

The online map is shaded: areas shaded in the darkest red represent spots with the greatest fire danger and those in lighter shades display lesser danger.

“We’ve been working with the BLM for years and completed our first project together in 1999 that detailed susceptibility to wildfire at areas where wild lands and urban areas meet,” Weber said. “The concern of this project is not wildland fires in general, but more so those fires that burn on wildland immediately adjacent to where people live. As cities sprawl out, more people are moving into more highly susceptible fire areas.”

Overall fire susceptibility is calculated by combining eight individual factors including the fuel load of an area, its slope, vegetation type, structure density, topography and other factors. These factors are combined and then plotted as the color-coded map shown on the Web site.

“We have students collecting data and using satellite imagery to create a fuel load map for the entire county.  These maps are about 90 percent accurate,” Weber said. “We take the fuel load models and integrate them with topographic models.”

He said a number of factors combine to determine an area’s fire susceptibility. For example, wildfires burn much faster on steep slopes, and those steep areas are hard for firefighters to contend with. Beyond certain steepness firefighters cannot use vehicles to fight fires and must go on foot or have fire suppressants dropped from aircraft.  The “aspect direction,” or direction a slope faces, is also important. South-facing slopes tend to dry out most quickly and can carry large amounts of fine fuels such as cheatgrass. The data displayed on the site has been and is being used by land management agencies to help determine fuel-load reduction prescriptions for areas with a lot of fuel and high susceptibility. Individual landowners are also using the information collected to take steps to protect their own property from wildfire.

Weber made some interesting observations about wildfire danger in southeast Idaho, including:

• Although higher elevations with Douglas fir trees and other timber feature have much more fuel, they are less likely to burn because of their elevation and moisture content. Also, fewer people live at the higher elevations where fir trees are found.

• Cheatgrass is extending its range in southern Idaho, causing problems for land managers on two fronts. Cheatgrass grows early and quickly. It dries out fast and is easily ignited. Fires are now starting in the cheatgrass and being carried into juniper and pine tree stands. Overall, cheatgrass is much more susceptible to wildfire and much less affected by it than native grasses.

•  Juniper trees are extending their range in southern Idaho, going down to lower elevations. The colonizing juniper trees are providing more fuel for wildfires at lower elevations.

• Although lightning strikes much more frequently at higher elevations, it is actually a much greater fire danger at lower elevations because of the differing vegetation and associated dryness. The window, generally, for lightning to cause wildfires at high elevations in southern Idaho is 10 to 14 days, while at lower elevations on the Snake River Plain, especially with the expansion of cheatgrass, the window for lightning causing wildfires is as long as 90 days.

For additional information on the ISU-BLM Wildland/Urban Interface Projects visit http://giscenter-ims.isu.edu/website/wui/viewer.htm or http://giscenter.isu.edu/. For questions on how to use or interpret the map on the ISU-BLM Web site, e-mail giscenter@isu.edu.