Do Boulder winds change with climate?

Image by Zhang Fengsheng via Unsplash

Saturday, April 30, 2022

Mike Calderazzo was never afraid of grass fires.

Tremendous fires were occurring in wooded areas, with thick trees and thick undergrowth to feed them with hot, strong, unstoppable forces. Grass fires were burning rapidly, feasting on thin strips of dried vegetation.

Then came the Marshall Fire and its 100 mile per hour winds. He blew a fire across 6,000 acres, burning homes in places he never thought were at risk of wildfire.

“If you had asked me on Christmas Day, I would have said, ‘No, don’t worry about that,'” Calderazzo said.

“Now every grass fire is a little worrying.”

Boulder’s powerful winds and their potential to create powerful fires are certainly nothing new. But a seemingly very windy April and the seven (small) fires this month have many wondering whether, in addition to a drying and warming climate, the winds are also changing.

Calderazzo certainly thinks so. More windy days limit the time firefighters can conduct prescribed burns, he said, an important mitigation strategy.

Windy days come up frequently,” he said. “It seems to be a trend. We are going to see more windy days, rather than fewer.

Historic windstorms

When it comes to wind, there are a lot of things we don’t know. For starters, although instruments have been in place since the 1960s, reliable and consistent wind data only dates back to the 1990s.

Because the wind is cyclical, it limits the analysis we can do, said Dr. Julie Kay Lundquist, a member of the Department of Atmospheric and Oceanic Sciences at the University of Colorado and the National Renewable Energy Laboratory.

The main cycle we know is the annual cycle and El Niño every 5-7 years,” Lundquist said. “There are other cycles that are much longer than that: 10 years, 20 years, 70 years, and we don’t have very good records that go back that far. We can’t really untangle these long-term cycles.

Major wind events tend to be recorded in weather data and in the media. A 1974 National Oceanic and Atmospheric Administration article used newspaper coverage to analyze winds from 1869 to 1972. It found one to two windstorms each year, on average, of which about a third were associated with fire. .

“Boulder has always been a windy place,” said Dr. Gerald Meehl, senior scientist at the National Center for Atmospheric Research. The wind rushes through the mountains “like water over a dam” – a “mountain wave” that more often than not crashes over Boulder.

The 60s and 70s were particularly windy, Meehl said, with winds “regularly” above 120 mph. 1982 also saw a large wind event, with gusts of up to 137 mph affecting around 40% of buildings in the city.

The scarcity of damage in recent years does not mean that the winds are becoming weaker or less frequent. Building codes have become stricter, Meehl said, and mature trees help block structures from the strongest gusts.

A “remarkably windy” month of April

While more data is always nice, Ludquist said, “there’s a lot you can do with the data we have.”

She watched recently spring (January 1 to April 26) wind speeds from an NREL tower just east of Eldorado Canyon dating back to 2002. His conclusion? “This year is not going to be remarkable” in terms of top speed.

Focus on April alonethis month “was remarkably windy”, with the average wind speed higher than at any time in the past two decades (although previous Aprils had recorded higher peak speeds). Another analysis of total hours with winds above 20 miles per hour suggest this April was the windiest since at least 2012.

“The absolute strongest winds didn’t occur in April,” Lundquist summed up, “but in April there were tremendously strong winds.”

Meehl said the data suggests “large Boulder Chinook wind events have become less strong over time.” They can also occur later in the spring; historically they have been mostly confined to the winter months.

This summer, Meehl and others at NCAR will test their hypothesis that changing atmospheric conditions impact the severity of Chinook winds around Boulder, and whether those conditions have themselves been affected by climate change.

“We may be able to link it to climate change,” he said. “We don’t have the answers yet.”

“Increased risk no matter what”

Whether the winds change or not, other fire conditions do. The planet – and the northern Front Range in particular – is becoming increasingly hot and arid. The grasses and plants that populate the area are drying out, ready to ignite a wandering spark.

“The Boulder region’s long-term drying and warming, largely due to human-induced climate change, means fuels are more ready to burn,” Meehl said. “If you get a 100 mile per hour Chinook wind event, it might not be as strong as an event in the 60s or 70s, but when the winds get so strong and you have to fire and dry fuels, you are at increased risk no matter what.

Wind can also contribute to the drying out of vegetation.

Wind leads to a lot more evaporation,” said Dr. Adam Mahood, who studies fire ecology and plant communities at CU. “When you add a little bit of temperature, it makes the fire danger even worse.

For Calderazzo, this means that everyone should be on alert for fires, wherever they are.

“If you know there’s a red flag day, it’s like knowing a hurricane is coming,” he said. “Prepare. Just be ready.

Get disaster preparedness tips from the Boulder Office of Emergency Management

— Shay’s Castle, @shayshinecastle

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