Historically, wildfires are a naturally occuring phenomenon critical to maintaining the health of forests throughout the western U.S. Through the natural cycles, wildfires consume old vegetation and convert it into nutrient-rich soil. They also trigger the germination of fire-adapted plant species, producing diverse forests that thrive on the power of wildfire. 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 severe. This has altered the natural wildfire regime completely.
The Utah Forest Institute is characterizing these "new" wildfire regimes in the state of Utah.
We are quantifying the "fire normals" (analogous to "climate normals") for fires in Utah as a whole and within Utah's major vegetation types more specifically. The initial goal is to quantify >95% of the land burned from 1984 to present and monitor the land burned on an ongoing basis through field-calibrated remote-sensed techniques. We will leverage the federal program, Monitoring Trends in Burn Severity, and add to it the land burned for smaller wildfires. The primary objectives include:
• Determine the number, area burned, and burn severity of wildfires.
• Determine the spatial pattern of burn severity within wildfires.
• Calibrate the remote-sensed technique with ground data (e.g. vegetation type, ecosystem age, pre-fire ecosystem condition, disturbance history, management history, and soil type.
• Generate a publically available dataset of Utah wildfires with their burn severity attributes and products - otherwise known as the Utah Fire Atlas.
The Utah Fire Atlas will not only increase the scientific understanding of wildfire in Utah but also spur the Institute's evolution into becoming a hub of resources and cutting-edge knowledge to engage with and provide scientific support to our collaborative parners, and guide collaborative decision-making in fire and forest health informed by best available science.
The team of undergraduate technicians use remote-sensed imagery and geospatial statistics to caluclate multiple indices of burn severity. In short, the technicians gather Landsat imagery 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 and its ancillary data are the main product o the Utah Forest Insitiute 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.
To ensure the accuracy of our remotely-sensed analyses of burn severity, we began collecting data on "on-the-ground" estimates of burn severity in the summer of 2020. A crew of Field Technicians visited multiple 2019 fires and installed hundreds of Composite Burn Index (CBI) plots. The data collected in the CBI plots average conditions of many factors (e.g., species change, amount of vegetative material untouched, scorched, toched, and consumed) across multiple strata (e.g., forest floor, understorty vegetation, overstory vegetation) to derive a severity value for a plot. The method is a corollary to the way the sensors on Landsat satellites average all features of multispectral brightness within a pixel. We then compare the CBI data to the remotely-sensed data to ultimately demonstrate the efficacy of our work. However, many hundreds of data points more are needed to do so robustly. As such, we will continue to send crews of Field Technicians out to recently burned forests to continue collecting these vital data.
Click here to learn more about the 2019 fires that our crew sampled and how the CBI data compared to the remotely-sensed data.