NASA data helps pinpoint wildfire threats

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By studying shrublands prone to wildfire in southern California, scientists found that NASA earth observations accurately detected and mapped two key factors: plant moisture and fuel condition-or greenness-defined as the proportion of live to dead plant material. Moisture levels and fuel condition, combined with the weather, play a major role in the ignition, rate of spread, and intensity of wildfires.

"This represents an advance in our ability to predict wildfires using data from recently launched instruments," said lead author Dar Roberts, University of California-Santa Barbara. "We have come a long way in just the past 5 to 10 years and continue to gather much better data on the variables critical in wildfire development and spread."

To find out how well NASA satellites could detect these factors, researchers first sampled live fuel moisture, a critical measure for assessing fire danger, from several different plant species in sites across Los Angeles County, Calif. This ground-based data, collected by the Los Angeles County Fire Department over a five year period, were then compared to greenness and moisture measures from NASA's Moderate Resolution Imaging Spectrometer and Airborne Visible/Infrared Imaging Spectrometer. The space-based data were often closely linked to the field measurements, suggesting the instruments can be used to determine when conditions are favorable for wildfires.

"Improving the role of satellite data in wildfire prediction and monitoring through efforts like these is critical, since traditional field sampling is limited by high costs, and the number and frequency of sites you can sample," said Roberts. "This new data on the relative greenness of a landscape also allows us to see how conditions are changing compared to the past."

The satellite data worked best on landscapes where one plant type was dominant. The amount of vegetation cover in an area and its growth rate also influence the reliability of satellite data for wildfire prediction.

The study also found that in areas where branches and dead foliage often help spread fires, changes in the proportion of green vegetation to other plants may also indicate locations of potential fires, especially after moisture values fall below a critical level. The proportion of greenness determines the manner in which plants absorb and scatter sunlight and plays a major role in moisture retention.

Although scientists have long recognized the importance of moisture conditions in wildfire development, this research suggests that other variables may be just as significant. "While live fuel moisture values are critical in the development of wildfires, it's clearly not the last word. Even if vegetation is extremely dry, there are a number of other factors that influence whether a fire will develop and how quickly it spreads, including the ratio of live to dead foliage, plant type, seasonal precipitation, and weather conditions," said Roberts. "In Southern California, if a strong Santa Ana wind event occurs before our first major rainfall in the fall or winter, the risk for wildfire is significantly heightened."

As researchers continue to better understand wildfire development, they are also creating fire spread computer models that use wind speed and direction forecasts to determine where fires will travel. And in the near future, scientists will likely be able to map fire severity to get an indication of the overall impact of a wildfire on the landscape and environment, including the amount of carbon dioxide released into the atmosphere. As the data record from recent satellites continues to grow, scientists will also be able to better track historical changes that might modify fire danger to provide better information for decision makers.

NASA/Goddard Space Flight Center