Increasingly frequent wildfires linked to human-caused climate change


Date:
November 5, 2021
Source:
University of California - Los Angeles
Summary:
A new study strengthens the case that climate change has been
the main cause of the growing amount of land in the western
U.S. destroyed by large wildfires. And researchers say the trend
is likely to worsen.



FULL STORY ========================================================================== [Forest fire (stock | Credit: (c) Lumppini / stock.adobe.com] Forest fire (stock image).

Credit: (c) Lumppini / stock.adobe.com [Forest fire (stock | Credit:
(c) Lumppini / stock.adobe.com] Forest fire (stock image).

Credit: (c) Lumppini / stock.adobe.com Close Research by scientists
from UCLA and Lawrence Livermore National Laboratory strengthens the
case that climate change has been the main cause of the growing amount
of land in the western U.S. that has been destroyed by large wildfires
over the past two decades.


==========================================================================
Rong Fu, a UCLA professor of atmospheric and oceanic sciences and the
study's corresponding author, said the trend is likely to worsen in the
years ahead. "I am afraid that the record fire seasons in recent years
are only the beginning of what will come, due to climate change, and our society is not prepared for the rapid increase of weather contributing
to wildfires in the American West." The dramatic increase in destruction caused by wildfires is borne out by U.S.

Geological Survey data. In the 17 years from 1984 to 2000, the average
burned area in 11 western states was 1.69 million acres per year. For the
next 17 years, through 2018, the average burned area was approximately
3.35 million acres per year. And in 2020, according to a National
Interagency Coordination Center report, the amount of land burned by
wildfires in the West reached 8.8 million acres -- an area larger than
the state of Maryland.

But the factors that have caused that massive increase have been the
subject of debate: How much of the trend was caused by human-induced
climate change and how much could be explained by changing weather
patterns, natural climate variation, forest management, earlier springtime snowmelt and reduced summer rain? For the study, published in the Nov. 9 edition of the journal Proceedings of the National Academy of Sciences,
the researchers applied artificial intelligence to climate and fire data
in order to estimate the roles that climate change and other factors
play in determining the key climate variable tied to wildfire risk:
vapor pressure deficit.

Vapor pressure deficit measures the amount of moisture the air can hold
when it is saturated minus the amount of moisture in the air. When vapor pressure deficit, or VPD, is higher, the air can draw more moisture
from soil and plants. Large wildfire-burned areas, especially those not
located near urban areas, tend to have high vapor pressure deficits,
conditions that are associated with warm, dry air.



==========================================================================
The study found that the 68% of the increase in vapor pressure
deficit across the western U.S. between 1979 and 2020 was likely due
to human-caused global warming. The remaining 32% change, the authors concluded, was likely caused by naturally occurring changes in weather patterns.

The findings suggest that human-induced climate change is the main cause
for increasing fire weather in the western United States.

"And our estimates of the human-induced influence on the increase in
fire weather risk are likely to be conservative," said Fu, director of
UCLA's Joint Institute for Regional Earth System Science and Engineering,
a collaboration with NASA's Jet Propulsion Laboratory.

The researchers analyzed the so-called August Complex wildfire of 2020,
which burned more than a million acres in Northern California. They
concluded that human-induced warming likely explains 50% of the
unprecedentedly high VPD in the region during the month the fire began.

Fu said she expects wildfires to continue to become more intense and more frequent in the western states overall, even though wetter and cooler conditions could offer brief respites. And areas where vast swaths of
plant life have already been lost to fires, drought, heatwaves and the
building of roads likely would not see increases in wildfires despite
the increase of the vapor pressure deficit.

"Our results suggest that the western United States appears to have
passed a critical threshold -- that human-induced warming is now more responsible for the increase of vapor pressure deficit than natural
variations in atmospheric circulation," Fu said. "Our analysis shows
this change has occurred since the beginning of the 21st century, much
earlier than we anticipated." The paper's lead author is Yizhou Zhuang,
a UCLA postdoctoral scholar; co- authors are Alex Hall, a UCLA professor
of atmospheric and oceanic sciences and director of the UCLA Center
for Climate Science; Benjamin Santer, a former atmospheric scientist
at Lawrence Livermore National Laboratory; and Robert Dickinson, a UCLA distinguished professor in residence of atmospheric and oceanic sciences.

The research was funded by the National Oceanic and Atmospheric
Administration and the University of California.

========================================================================== Story Source: Materials provided by
University_of_California_-_Los_Angeles. Original written by Stuart
Wolpert. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yizhou Zhuang, Rong Fu, Benjamin D. Santer, Robert E. Dickinson,
Alex
Hall. Quantifying contributions of natural variability and
anthropogenic forcings on increased fire weather risk over the
western United States.

Proceedings of the National Academy of Sciences, 2021; 118 (45):
e2111875118 DOI: 10.1073/pnas.2111875118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211105114305.htm

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