18 April 2024

Drought alters post-fire recovery in the U.S.

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NASA satellite data reveal how drought has hampered recovery from wildfires in the western United States, resulting in the risk of creating permanent soil damage

by Matteo Cavallito

 

Fostered by climate change, drought is driving up the intensity and frequency of wildfires through the accumulation of combustible material such as dry branches and leaves. But quantifying the combined effect of the two phenomena on ecosystems has proven difficult. However, the use of NASA satellite data, some U.S. researchers suggest, could unravel these dynamics. Highlighting how drought affects the recovery of ecosystems from wildfires.

Recovery at risk even after less severe fires

In the study, published in the journal Nature Ecology & Environment, researchers from the U.S. Space Agency analyzed more than 1,500 wildfires in the western United States from 2014 to 2020 while also collecting data on drought conditions dating back to 1984. The data, the research says, “show that ecoregions dominated by grasslands and shrublands are more susceptible to drought, which amplifies fire-induced evapotranspiration decline and, subsequently, shifts water flux partitioning.”

In contrast, “severely burned forests recover from fire slowly or incompletely, but are less sensitive to dry extremes. We conclude that moisture limitation caused by droughts influences the dynamics of water balance recovery in post-fire years.”

“Many of the West’s grasslands experience low-severity fires,” said Shahryar Ahmad, co-author of the study and a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, quoted in a statement. “This study shows that even those blazes can trigger a slow recovery in these ecosystems if accompanied by a preceding drought.”
From wildfires and droughts, permanent soil damage as well

According to the authors, when ecosystems do not have enough time to recover before another drought or fire they can go through permanent changes in the types of plants that grow there. This increases the risk of erosion and landslides by altering the usual patterns of water runoff in streams and lakes. And this is where satellite technology comes in.

Leveraging data made available by the Landsat program, a partnership between NASA and the U.S. Geological Survey, the authors were able to examine trends in soil evapotranspiration before and after wildfires.

Monitoring this phenomenon allowed them to assess whether and how well different ecosystems had recovered after the fires. “Our results highlight the dominant control of drought on altering the resilience of vegetation to fires, with critical implications for terrestrial ecosystem stability in the face of anthropogenic climate change in the West,” the authors explain.

Two cubic kilometers of water are lost after a fire

To put it simply, a strenuous recovery can lead to potentially permanent changes. And not only in plant communities, but also in local and regional water dynamics. The researchers found that severe fires damage plants to such an extent that evapotranspiration is greatly reduced in subsequent years. Thus, instead of evaporating into the atmosphere, more water sinks into the ground and is likely to be lost through runoff.

“When more water becomes runoff, it means less could be available for ecosystem recovery or agriculture,” the statement says.

This is why, expecially because of climate change, “understanding these shifts is crucial for developing strategies to manage water resources more effectively and ensure water security for future generations.” Examining nearly 800 wildfires from 2016 to 2018, in particular, the researchers estimated that the ecoregions studied in the western United States lost an average of two cubic kilometers of water in the first year after a wildfire.