Even in drought-stricken California, not all regions are equally vulnerable to wildfires. A recent study that used data from NASA’s ECOSTRESS mission found relationships between wildfire intensity and water stress in plants measured months before the fire.
The correlations weren’t just because dry plants burned faster than hydrated plants; some areas with enough vegetation burned more severely, possibly because the fires had more fuel to burn.
The study, led by scientists at NASA’s Jet Propulsion Laboratory in Southern California, is based on data on plant water use collected by the ECOsystem and Spaceborne Thermal Radiometer Experiment on Space Station, or ECOSTRESS.
What did the study find?
When plants are short of water, the instrument measures their temperature as they warm up. The researchers focused on data collected during parts of 2019 and early 2020 in six regions – three in the mountains of southern California and three in the Sierra Nevada – which were later scorched by wildfires. forest for this study.
Other research found that the wildfire season in the western United States begins earlier in the year and grows longer and more severe.
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In California, a state with 33 million acres of forest – much of it managed by federal, state and local agencies – detailed information on the relationship between wildfires and water availability for vegetation could help fire officials determine not only if an area is likely to catch fire, but also the severity of the damage if so.
“We are in an intense mega-drought – the worst in 1,200 years – and this is creating conditions for more catastrophic fires,” said Christine Lee, co-author of the study at JPL.
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Researchers have found that the rate at which plants release water through “transpiration” – a process known as evapotranspiration – as well as how efficiently they use water for photosynthesis, can help predict whether subsequent forest fires are more or less intense.
Both indicators show whether a plant community is getting enough water or is stressed due to a lack of water.
Plant stress monitoring
Plants, like humans, struggle to function in extreme heat. In the same way that transpiration keeps humans cool, plants regulate their temperature through evapotranspiration.
Evapotranspiration combines the rate at which plants lose water as it evaporates from the soil with transpiration, which occurs when they release water through the stomata of their leaves. To avoid losing too much water, plants begin to close their stomata when they become too dry.
“As a result, they start to warm up because they don’t have the ‘sweat’ advantage anymore,” Lee said.
What is ECOSTRESS?
“With ECOSTRESS, we can observe these very fine temperature changes, which are used to understand changes in evapotranspiration and water use efficiency.”
Slower evapotranspiration and lower efficiency, in general, indicate that plants are suffering from water stress. Higher values indicate that the plants are getting enough water.
ECOSTRESS monitors evapotranspiration with a high-resolution thermal radiometer capable of measuring the temperature of patches of the Earth’s surface as small as 130 by 230 feet (40 by 70 meters).
High or low stress
Researchers found that water stress variables, along with elevation, were dominant predictors of burn severity in areas affected by three Southern California wildfires in 2020: the Bobcat Fire in Angeles National Forest, as well as the 2020 Apple and El Dorado fires. San Bernardino National Forest.
According to Pascolini-Campbell, the main vegetation type in an area determined whether higher or lower stress predicted more severe burning. Stressed pine forests, for example, tended to burn more severely, implying that drier conditions made the trees more flammable.
Meanwhile, in grasslands, lower stress was associated with more burn damage, suggesting that vigorous vegetation growth produced more fuel, leading to more intense fires.
NASA studies forest fires
The research comes as NASA steps up efforts to use its technology, expertise and resources to study wildfires. NASA announced the creation of NASA Wildland FireSense in May, an initiative to bring together experts from various disciplines, along with advanced technologies and analytical tools, to develop approaches that can inform and guide decision makers in managing disasters. fires.
The importance of tools like ECOSTRESS, which is expected to run through September 2023, will increase as climate change increases the risk of wildfires in the western United States, Pascolini-Campbell explained.
“This is a high priority region for using these types of studies to see which areas are most vulnerable,” she added.
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