A new study using NASA satellite data reveals how drought affects the recovery of western ecosystems from fire, a result that could provide meaningful information for conservation efforts.
The West has been witnessing a trend of increasing number and intensity of wildland fires. Historically a natural part of the region's ecology, fires have been exacerbated by climate change—including more frequent and intense droughts—and past efforts to suppress fires, which can lead to the accumulation of combustible material like fallen branches and leaves. But quantifying how fire and drought jointly affect ecosystems has proven difficult.
In the new study, researchers analyzed over 1,500 fires from 2014 to 2020 across the West, and also gathered data on drought conditions dating back to 1984. They found that droughts make it harder for grasslands and shrublands, such as those in Nevada and Utah, to recover after fires—even the less severe blazes. Forests, if not burned too badly, rebound better than grasslands and shrublands because some forest roots can tap into water deeper in the ground. The team reported its findings in Nature Ecology & Evolution.
"Many of the West's grasslands experience low-severity fires," said Shahryar Ahmad, lead author of the study and a research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This study shows that even those blazes can trigger a slow recovery in these ecosystems if accompanied by a preceding drought."
If ecosystems don't have enough time to bounce back before another drought or fire, that could lead to permanent changes in the types of plants growing there. That, in turn, can increase the risk of soil erosion and landslides, and alter the usual patterns of water running off into streams and lakes.
"Once a fire is contained, that's when the remediation efforts happen," said Everett Hinkley, the national remote sensing program manager for the U.S. Forest Service, who wasn't involved in the new research. "Understanding how a particular ecosystem and land cover type is going to respond after the fire informs what actions you need to take to restore the landscape."
Without such restoration, changes in land cover can cascade to potentially affect agriculture, tourism, and other community livelihoods. To track the recovery of the different ecosystems, the researchers examined changes in evapotranspiration (ET)—the transfer of water to the atmosphere through evaporation from soil and open water and transpiration from plants—before and after the fires. Monitoring evapotranspiration helped the team identify whether different ecosystems, such as forests and grasslands, completely recovered after a fire, or if the recovery was delayed or disrupted.
That evapotranspiration data came from OpenET, a tool that calculates evapotranspiration at the scale of a quarter-acre across the western United States. It does so using models that harness publicly available data from the Landsat program, a partnership between NASA and the U.S. Geological Survey, along with other NASA and NOAA satellites.
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