Moisture measured in trees, shrubs and grasses is lowest since records began in the 1970s
The record-setting heat across the western United States is helping to drive a dangerous side effect: Forests from Oregon to New Mexico are exceptionally dry and primed to ignite into wildfire.
Researchers across the West are measuring record levels of dryness in the sticks, leaves and wood samples they extract from forests and grasslands and analyze to determine their moisture level, according to an E&E News analysis of federal data.
Dryness makes forests and grasslands more likely to burn if they are ignited by a source such as a downed power line, a smoldering campfire or a lightning strike.
“It’s bone-dry in many parts of the West,” said University of Alberta fire scientist Mike Flannigan. “The dice are loaded. Things are ripe for a really active fire season.”
In the Carson National Forest in New Mexico, a wood fragment extracted from a pine tree on June 12 had a moisture level of 50%, according to federal records. The previous low moisture level on tree samples taken from the same spot in the month of June was 75%.
In the hills north of Phoenix, shrubs were measured with a moisture level of 39% on June 16. The previous low moisture level on shrub samples in the same spot in June was 54%.
E&E News analyzed 753 sites in the West where moisture readings have been taken for at least 10 years. In 76% of those sites, the average moisture level in June 2021 was below the average moisture level for all the previous June measurements.
The moisture readings go back to the late 1970s and are recorded in a National Fuel Moisture Database maintained by the Forest Service.
Moisture is calculated as a percentage of the dry weight of a piece of vegetation. Completely dry vegetation has 0% fuel moisture.
Moisture levels typically reach their lowest levels in the late summer and fall, which makes the current low readings alarming to experts.
“The fuels are at record-breaking low levels for June or even for the entire season,” Flannigan said.
Fire experts call forest trees, shrubs and grasses “fuel” because of their role in propelling wildfire. They monitor fuel moisture along with conditions such as humidity and lightning intensity to assess wildfire risk.
The conditions are particularly perilous in California, much of which “does not see any precipitation during July and August,” Flannigan said. “With the record-breaking fuel moisture levels, it could be that a greater number of lightning strikes will generate fires.”
The dry conditions have prompted the Forest Service to close several national forests in the West, particularly in Arizona, where a wildfire nearly the size of New York City has been burning since June 4. In numerous national forests that remain open, fire restrictions are in place prohibiting campfires, stove fires and smoking.
Dry conditions also have prompted officials to cancel Fourth of July fireworks shows and to bar individuals from setting off their own firecrackers.
Dry forests alone do not create wildfires, which need a spark to start and wind to spread. Many of the wildfires last year were caused by an unusually large spate of lightning strikes.
The dry conditions are a result of both short-term weather patterns such as the record heat wave in parts of the West and long-term climate trends including higher temperatures and less precipitation.
Wildfire has been particularly destructive in recent years. Last year, wildfire burned 10.1 million acres of land in the U.S., matching the record set in 2015.
In California, wildfires have killed 183 people and destroyed roughly 45,000 structures since 2017, according to the California Department of Forestry and Fire Protection.
“Record temperatures and very dry fuels continue to be reported in many states,” the National Interagency Fire Center said yesterday.
On June 22, the center raised its National Wildland Fire Preparedness Level to 4 out of 5, indicating that much of the country is experiencing wildfire and that areas are competing for firefighting resources.
Meanwhile, the U.S. Drought Monitor shows exceptional drought conditions across much of the West, particularly in Arizona, New Mexico, Nevada and Utah. In Nevada, 74% of the state’s population lives in an area facing the worst drought conditions.
The National Weather Service yesterday had excessive heat warnings in place in all of Washington state and Oregon and large swaths of California, Idaho and Nevada.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.
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(Sources: Scientific American)
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