'Double-hazard' zones for wildfire in the West

Date:
February 7, 2022
Source:
Stanford University
Summary:
Rapidly growing communities in the American West's forests and
shrublands are nestled in zones where local soil and plant traits
amplify the effect of climate change on wildfire hazards and lead
to bigger burns.



FULL STORY ==========================================================================
Some plants and patches of Earth withstand heat and dry spells better
than others. A new Stanford University study shows those different coping mechanisms are closely linked to wildfire burn areas, posing increasing
risks in an era of climate change.


==========================================================================
The results, published Feb. 7 in Nature Ecology and Evolution, show
swaths of forest and shrublands in most Western states likely face
greater fire risks than previously predicted because of the way local ecosystems use water. Under the same parched conditions, more acreage
tends to burn in these zones because of differences in at least a dozen
plant and soil traits.

The study's authors set out to test an often-repeated hypothesis that
climate change is increasing wildfire hazard uniformly in the West. "I
asked, is that true everywhere, all the time, for all the different
kinds of vegetation? Our research shows it is not," said lead author
Krishna Rao, a PhD student in Earth system science.

'Double-hazard' zones The study arrives as the Biden administration
prepares to launch a 10-year, multibillion-dollar effort to expand forest thinning and prescribed burns in 11 Western states.

Previous research has shown that climate change is driving up what
scientists call the vapor pressure deficit, which is an indicator of how
much moisture the air can suck out of soil and plants. Vapor pressure
deficit has increased over the past 40 years across most of the American
West, largely because warmer air can hold more water. This is a primary mechanism by which global warming is elevating wildfire hazards.



==========================================================================
The new analysis, which comes from the lab of Stanford ecohydrologist
Alexandra Konings, suggests vapor pressure deficit is rising fastest in
areas where plants are especially prone to drying out. The combination of highly sensitive, tinder-dry plants and a faster-than-average increase in atmospheric dryness creates what the authors call "double-hazard" zones.

The 18 newly identified double-hazard zones lie within regions that have
seen a disproportionately rapid rise in burn area with every uptick in
vapor pressure deficit over the past two decades. Ranging in size from
a few hundred to nearly 50,000 square miles, they're concentrated in
eastern Oregon, Nevada's Great Basin, central Arizona's Mogollon Rim
and California's southern Sierra Nevada, where recent wildfires have
destroyed thousands of giant sequoia trees that had survived fires for
hundreds of years.

According to the authors, the results suggest the distribution of
vegetation across the West -- that is, the arrangement of scrub,
alpine meadows, sagebrush, coniferous forest and other plant communities
from the Pacific Coast to the western fringe of the Great Plains -- has "amplified the effect of climate change on wildfire hazard" in the region, specifically, the amount of acreage burned.

"California and other Western states are working hard to figure out how
to adapt to the changing wildfire risk landscape, including long-term
decisions around issues such as land use, vegetation management, disaster planning and insurance," said study co-author Noah Diffenbaugh, the Kara J Foundation Professor and Kimmelman Family Senior Fellow at Stanford and a senior fellow at Stanford Woods Institute for the Environment. "There's a wealth of information in this analysis to support decisions about how to
more effectively manage the risks of living in the West in the context
of a changing climate." Plant-water sensitivity Plant physiologists
and ecologists, not to mention farmers and home gardeners, have long
understood that plants rarely act in unison. "Each plant is different,
each species is different and the geography of a place defines how a
plant's moisture level responds to different environmental conditions,"
Rao explained.



==========================================================================
But models for calculating wildfire risk at landscape scale generally
don't account for the diversity of drought responses, "in part because
it's really difficult," said Konings, who is the study's senior author
and an assistant professor of Earth system science at Stanford's School
of Earth, Energy & Environmental Sciences (Stanford Earth). "It's very labor-intensive to measure how much an ecosystem is drying out, and it's difficult to predict without those direct measurements because it depends
on what kind of soil you have, the topography and what kinds of plants."
To solve this problem, the scientists used satellite data to create
a new metric they call plant-water sensitivity. It combines plant and
soil hydraulic traits that affect the moisture content of vegetation,
such as how much water the soil can hold, how easily water moves through
the soil when saturated and root depth.

The authors used artificial intelligence, statistical analysis and
microwave remote sensing data to show that this measure of local
vulnerability to drying out in the face of limited rainfall and an arid atmosphere is tightly linked to increases in wildfire burn area with
a drying climate in forests and shrublands. In grasslands, they found
annual burned area did not increase much with vapor pressure deficit, suggesting that other factors such as fuel availability, ignitions,
the plants' growth stage and strong winds may play a bigger role. They
then used census data to track the population rise in vulnerable regions.

Disproportionate growth The underlying causes for catastrophic wildfires
that have scorched so much of the American West in recent years are
complex, including not only climate change but also decades of fire
suppression and growing populations along the periphery of undeveloped wilderness -- a transition zone sometimes called the wildland-urban
interface or WUI.

In California alone, more than 11 million of the state's 40 million
residents live in the WUI, which encompasses not only densely forested
areas like Paradise, a northern California town destroyed in the deadly
2018 Camp Fire - - but also parts of the wooded coastal foothills around Silicon Valley, the brush-and-grass covered hills around Santa Barbara
and Los Angeles, and neighborhoods in the Oakland hills, just a few
miles east of the San Francisco Bay.

Throughout the WUI, in Western states and beyond, people provide the vast majority of ignitions for fires that then torch the abundant vegetation
and threaten human lives and structures. Simply having more people
and homes nestled among flammable trees, chaparral and grasses add to
wildfire risks.

The new research underscores how unevenly climate change is amplifying
those risks. It also shows that communities within the WUI are booming
in the very places where ecosystems are most sensitive to drought, having
added an estimated 1.5 million people between 1990 and 2010. Populations
in parts of the WUI with high plant-water sensitivity have grown 50
percent faster than the West's wildland-urban interface overall, the
study finds.

According to Konings, "This redoubles the need to be thinking about what
we can do to reduce wildfire impacts in the WUI in general, including
for this subgroup of people who are in the most vulnerable locations."
special promotion Explore the latest scientific research on sleep and
dreams in this free online course from New Scientist -- Sign_up_now_>>> ========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Josie Garthwaite. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Map_and_charts_showing_plant_water_sensitivity_and_developments ========================================================================== Journal Reference:
1. Krishna Rao, A. Park Williams, Noah S. Diffenbaugh, Marta Yebra,
Alexandra G. Konings. Plant-water sensitivity regulates
wildfire vulnerability. Nature Ecology & Evolution, 2022; DOI:
10.1038/s41559-021- 01654-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220207155659.htm

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