The risk of wildfires spreading or igniting in California’s Sierra Nevada is greatly increased by the scorching summer temperatures. Scientists also warned Wednesday that global warming will only accelerate the problem.
The research, which analyzed daily temperatures and data from almost 450 Sierra Nevada fires between 2001 and 2020, and projected the future analysis, found that there could be an increase in fires by around 20% or more by 2040s and that the area burned could increase by 25% or more.
The findings “show how short events like heat waves impact fires,” said Aurora A. Gutierrez, a researcher at the University of California Irvine and the lead author of a paper describing the work in the journal Science Advances. “We were able to quantify that.”
As for the projections over the next two decades, she said, “We are getting hotter days and that’s why the risk of fires is increasing into the future.”
Wildfires in the West are becoming more intense and larger, with wildfire seasons getting longer. California has been particularly affected in recent years, with several large fires in the Sierra Nevada. One, the Dixie Fire, burned nearly a million acres and was the largest single fire in the state’s history.
Recent research has shown that global warming and heat are the main reasons for the increase of bigger and more powerful fires.
While the findings of the new study are in line with earlier research, there is a significant difference. Most studies that looked at temperature and other data over a longer time period (e.g., monthly or annual) focused on temperature. The new research focused on daily data.
“What makes this novel is that we were trying to identify the role of individual temperature extremes on individual dates,” said Jim Randerson, the senior author on the paper and a UC Irvine professor of earth systems science.
Over the past 20 years, the researchers found, a 1 degree Celsius (1.8 degree Fahrenheit) increase in mean summer temperature increased the risk of a fire starting on a given day — either by human activity or a lightning strike — by 19 to 22 percent, and increased the burned area by 22 to 25 percent.
Dr. Randerson shared an example of how extreme heat can lead to more, and faster spreading, fires.
“If it’s a normal day, say 80 degrees Fahrenheit, and you accidentally create a spark and there’s an ignition, you can probably stomp on it, or local fire agencies can come and put it out,” he said. The vegetation still has significant moisture, so the heat from a fire must first evaporate it. This slows down the spread of flames.
Dr. Randerson stated that the vegetation becomes so dry on 100-degree days, with little moisture to evaporate, that a flame spreads quickly and grows.
“You get rapid expansion,” he said, “and eventually a fire so big it can last for weeks and weeks.”
John Abatzoglou, who studies the influence of climate change on wildfires at the University of California, Merced, said the work “adds to the growing scientific literature of climate-driven fire potential in forests of the West.”
“The observed and projected upward march in temperatures is compounding pre-existing conditions, namely fuel accumulation in our forest, to escalate fire risk,” said Dr. Abatzoglou, who was not involved in the study.
The researchers used meteorological data, averaged over the region, and fire data from two sources: California’s Department of Forestry and Fire Protection, which records with precision when fires begin, and sensors on two NASA satellites that can measure fire spread on a daily basis.
For Ms. Gutierrez, who worked in Dr. Randerson’s laboratory while an undergraduate at Irvine and full time there after receiving her undergraduate degree in 2018, that meant wrangling a deluge of data over many months.
She said that it was worth the effort to find out the connection between wildfires and extreme temperatures each day.
“We decided this is a question we need to ask,” Ms. Gutierrez said. “And yes, it’s a bit tedious with the amount of data we’re having to process, but it’s an important question.”
Source: NY Times