[env-trinity] A Fiery Legacy

[Patrick Truman]

A Fiery Legacy: USGS Assesses 26 Years of Wildland Fires
By Rebecca L. Johnson, SAIC, contractor to the U.S. Geological Survey
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Photo by BLM-Idaho.
The USGS-USDA Monitoring Trends in Burn Severity project is mapping and analyzing the destructive impact of major U.S.wildfires from 1984 to 2010. The project is part of a Wildland Fire Leadership Council strategy to monitor the effectiveness of the National Fire Plan and the Healthy Forests Initiative.
Start with soaring summertime temperatures. Add a profusion of parched landscapes. Season liberally with violent storms. And you have the perfect recipe for potentially disastrous wildland fires.  

Jeff Eidenshink at the U.S. Geological Survey's Center for Earth Resources Observation and Science knows that recipe well. But while most of us merely wonder or worry about where the next fire will strike, Eidenshink is part of a scientific effort to assess the occurrence and effects of wildland fires in the United States over time. The Monitoring Trends in Burn Severity project is a six-year collaboration between USGS and the USDA Forest Service to map and analyze the destructive impact, or burn severity, of large wildfires over a 26-year period. (The MTBS project defines large fires as those that affect more than 1,000 acres in the western United States or 500 acres in the East.) This project is part of the Wildland Fire Leadership Council's overall strategy to monitor the effectiveness of the National Fire Plan and the Healthy Forests Restoration Act. 


In the past, consistent geospatial information on the effects of large U.S. wildfires was nonexistent. Researchers and land managers had no scientifically sound baseline for burn severity, no clear and comprehensive data set to identify trends in the frequency of wildland fires or the shifts in the post-fire characteristics of burned lands. 


But the MTBS project is changing that. For the next several years, the project will be creating an invaluable data legacy of wildland fires and their impacts across the nation. "Burn severity maps and analyses will help answer many fundamental questions about wildland fires, including how fires relate to possible climate change," Eidenshink says.

Eidenshink and his colleagues at EROS and the Forest Service's Remote Sensing Applications Center are developing data on U.S. wildfires by using a powerful mathematical tool, the "differenced Normalized Burn Ratio algorithm."  The methodology to map burn severity was developed by colleagues from USGS and the National Park Service. The group has begun mapping the burn severity of the thousands of major U.S. wildland fires from 1984 to 2010 and is carrying out the project in two concurrent time phases: historic and current. 

They are mapping by region fires from 1984 to 2003 (historic fires). At the same time, they are mapping fires across the country from 2004 to 2010 (current fires). Mapping is now underway for historic fires in the Pacific Northwest and California. Mapping for current fires from 2004 culminated this past spring. During 2004, 347 major wildland fires raged across 7,781,049 acres nationwide. 

This extraordinary project contains an essential ingredient: Landsat images. These readily available, low-cost images provide the longest consistent record of relatively high spatial and spectral resolution data for mapping burn severity. In fact by employing Normalized Burn Ratio algorithms, the project's computer programs can automatically extract a great deal of fundamental burn-severity information from Landsat images. However, creating burn-severity maps, requires the skills of highly trained analysts. These specialists interpret the raw data in light of their own experience with fire behavior and its effects in a given ecological setting. It is a time-consuming process. 


"Once an analyst has the appropriate pre- and post-fire imagery in hand," says Eidenshink, "a single assessment can take several hours, depending upon the size of the fire and the complexity of the interplay of land-cover and burn-severity variations." 


The mapping team will have to invest an enormous amount of time and effort to analyze all of the major wildfires from 1984 to 2010. But the 26-year span of the project is critical. Severe periodic droughts, increased fuel loads, and a higher frequency of uncharacteristic fires since 2000 have made it essential for trend analyses to span a significant period of time. These lengthier analyses will help the mapping team better account for variability in factors potentially affecting fire severity, including climate.  

The maps and analyses from the MTBS project are accessible to anyone at  http://svinetfc4.fs.fed.us/mtbs/, but local, state and national researchers and land and resource managers are the site's primary audience. Online project information will help this group to evaluate trends in burn severity and to develop and assess the effectiveness of their land-management decisions. It will also provide them with an essential baseline from which they can monitor the recovery and health of fire-affected landscapes over time - a recipe for success.

To learn how scientists create burn-severity maps, go to:

http://eros.usgs.gov/images/mtbs_process.jpg
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