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The hottest summer days in California’s Sierra Nevada have greatly increased the risk of wildfires igniting or spreading, and the risks will increase as the planet continues to warm, scientists said Wednesday.
Examining daily temperatures and data from nearly 450 Sierra Nevada fires from 2001 to 2020, and projecting the analysis into the future, the research found that the number of fires could increase by about 20 percent or more through the 2040s, and that the total area of fires burned could increase by about 25 percent or more.
The findings “show how short-lived events like heat waves affect fires,” he said. California Irvine and lead author of a book paper describing work in the journal Science Advances. “We were able to measure that.”
As for forecasts for the next twenty years, he said, “The days are getting warmer and therefore the risk of fires into the future increases.”
In the western United States, wildfires are increasing in size and intensity, and wildfire seasons are getting longer. California, in particular, has suffered in recent years, including last summer when the Sierra Nevada experienced several major fires. One, the Dixie Fire, burned nearly one million acres and was the largest fire in the state’s history.
Recent research has suggested that the heat and dryness associated with global warming are the main causes of the increase in larger and more powerful fires.
The new study’s findings are generally in line with previous research, but there is an important difference. Most previous studies looked at temperature and other data collected on monthly to annual time scales. The new research looked at daily data.
“What makes this novel is that we’re trying to determine the role of temperature extremes in individual histories,” said Jim Randerson, senior author of the paper and professor of earth systems science at UC Irvine.
Researchers found that a 1 degree Celsius (1.8 degree Fahrenheit) increase in average summer temperature over the past 20 years increases the risk of fires that start on a given day — whether by human activities or being struck by lightning — by 19 to 22 percent. and increased the burned area by 22 to 25 percent.
Dr. Randerson gave an example of why extremely hot weather can cause fires that spread more and more easily.
“On a normal day, say 80 degrees Fahrenheit, and you accidentally create a spark and there’s an ignition, you could probably step on it or local fire departments can come and put it out,” he said. The vegetation still contains a significant amount of moisture, so the heat from the fire must evaporate first. This slows the spread of flames.
But on a 100 degree day, Dr. Randerson said the vegetation is so dry that there is little moisture to evaporate, a fire spread and grows rapidly.
“You’ll experience rapid expansion,” he said, “and eventually a fire so big that it could last for weeks and weeks.”
John Abatzoglou, who studies the impact of climate change on wildfires at the University of California, Merced, said the study “adds to the growing scientific literature of the potential for climate-induced fires in western forests.”
Not involved in the study, Dr. “The observed and predicted increase in temperatures combines pre-existing conditions, namely fuel accumulation in our forest, to increase fire risk,” said Abatzoglou.
The researchers used meteorological data averaged for the region and fire data from two sources: California’s Department of Forestry and Fire Protectionconcisely recording when fires started and sensors on two NASA satellites can measure the spread of fire on a daily basis.
While studying at Irvine and earning her BA in 2018, she worked full time there with Dr. For Ms. Gutierrez, who works in Randerson’s lab, this meant dealing with a data deluge that lasted for months.
But exploring the link between daily extreme temperatures and wildfires was well worth it, he said.
“We decided this was a question we needed to ask,” Ms Gutierrez said. “And yes, the amount of data we have to process is a bit frustrating, but that’s an important question.”
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