Utah Forest Institute
Wildfires

Historically, wildfires are a naturally occuring phenomenon critical to maintaining the health of forests throughout the western United States. Through their natural cycles, wildfires consume old vegetation and convert it into nutrient-rich soil. They also trigger the germination of fire-adpated plant species, producing diverse forests that thrive on the power of fire. However, the natural cycles of wildfire have been disrupted by modern attempts to control it. As a result, forests have become densely populated with maladapted plant species and have accumulated large stocks of dead vegetation. Combined with a warming climate and drier conditions, wildfires have become more frequent and more severe. This has altered the natural fire regime completely.

The Utah Forest Institute is characterizing the "new" fire regime in the state of Utah. There will always be fire in the western United States. What the United States - generally - and Utah - more specifically - needs is better post-fire outcomes, and that requires an understanding of areas where management can make a difference. The main product coming from the Utah Forest Institute - the Utah Fire Atlas - will help move discussions of fire in Utah to a more quantitative footing.

Photo Credit: Etta Crowley
Objectives

The Utah Forest Institute is quantifying the "fire normals" (analogous to "climate normals") for fires in Utah as a whole and within Utah's major vegetation types. The goal is to quantify >95% of the area burned from 1984 to present and monitor the area burned on an ongoing basis. The Institute will leverage the federal program, Monitoring Trends in Burn Severity, and add to it the area burned for smaller fires, as well as calibrate the satellite data for Utah forest types and conditions. The primary objectives include:

  • Determine the number, area burned, and burn severity of fires >40 ha in Utah.
  • Determine the proportion of area within fire perimeters that burned at high severity (>75% basal area mortality) and the spatial pattern of high severity patches.
  • Determine the proportion of area within fire perimeters that did not burn or burned at very low severity (i.e. fire regufia) and the spatial pattern of fire refugia.
  • Calibrate satellite measurements with Utah forest ground data such as forest type, forest age, pre-fire forest condition (i.e. beetle kill), as well as soil type and amount of pre-fire vegetation cover.
  • Make the Utah Fire Atlas publically available for land managers, policy makers, and interested citzens.

Photo Credit: Etta Crowley
Methodology

The team of technicians at the Utah Forest Institute use remote-sensed imagery and geospatial statistics to calculate multiple indices of burn severity. In short, the technicians gather Landsat data from before and after a particular fire, and analyze the images in both ArcMap and R with a standardized and consistent methodology. The result is a map of the extent and severity of Utah wildfires at a 30 meter resolution dating back to 1984. This map is the main product of the Utah Forest Institute and is referred to as the Utah Fire Atlas.

The burn severity indices that the technicians calculate are the Normalized Burn Ratio, delta Normalized Burn Ratio, and Relativized delta Normalized Burn Ratio.

Below are three images of the 2014 Greek Peak fire near Enterprise, UT. The image on the left is a pre-fire Landsat image displaying the normal amount of vegetation greeness for the time of year the image was acquired by the Landsat satellite. The image in the middle is a post-fire Landsat image displaying the reduction in vegetation greennes due to the fire. The image on the right is a delta Normalized Burn Ratio. The red indicates greater than 75% basal area mortality; yellow indicates between 25% and 75% basal area mortality; light green indicates less than 25% basal area mortality; and green indicates basal area mortality less than what the satellite can detect.

Beginning in the summer of 2020, a crew of field technicians will vist recent wildfires and install composite burn index plots to collect vegetation and mortality data to calculate ground-derived burn severity indices. The ground-derived burn severity indices will be used to calibrate the satellite-derived burn severity indices to ensure the accurateness of the Utah Fire Atlas.