Chinooks and Santa Ana winds: How Calgary prepares for wildfire risk driven by warm winds

As destructive wildfires continue to plague southern California, they're being propelled by a phenomenon that's familiar to Albertans.

The wildfires that have devastated the Los Angeles area this month have been fuelled by dry vegetation in drought conditions, and fanned by powerful, warm Santa Ana winds.

The downslope flow of these warm winds is a condition similar to what Albertans see from chinooks. And the potential for a chinook to exacerbate the spread of a wildfire is closely monitored by the Calgary Fire Department (CFD).

Fire Chief Steve Dongworth and his team prepare especially for chinooks hitting in the spring, when the snow has melted and dry vegetation potentially lies in the path of a fire.

"We know that the risk is higher in Calgary. We stand up extra resources if the conditions are right," said Dongworth, who's currently in Orange County, Cal., for a Metropolitan Fire Chiefs Association board meeting.

"The temperature that we believe Calgary's going to get to, the relative humidity of the fuels on the ground, as well as the wind — all of those things give us a picture of how likely it is that we would have a fire that would spread rapidly."

The Santa Ana winds blow from dry areas inland toward the coast. The winds come from dry desert regions in Nevada, Utah, Idaho and Oregon, and become more dry as they pass down the mountains. Chinooks, meanwhile, are the warm winds that come down the east side of the Rocky Mountains, blowing into areas like Calgary that border the mountains.

The CFD prepares for similar fire risks where wildland and urban areas intersect, both on Calgary's periphery in communities close to forested areas, and in city parks like Fish Creek Provincial Park and Nose Hill Park. The department has a district chief assigned to look at the city's fire risk in these areas.

The CFD is trained to fight fires in a wildland environment, Dongworth said. This can involve watching for where embers could land, to have assets ready to respond quickly. Strong, warm winds can carry embers far, and even if they don't ignite structures directly, they can do so by landing near those structures.

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The key difference between the fire in California and the conditions in Calgary, Dongworth notes, is drought. Despite heavier rain in recent winters, Dongworth points to drought conditions over several years in California that have left vegetation very dry.

Coupled with 160 km/h winds last week, this has made for a disastrous combination in California. If the wind moves faster, it spreads fire more quickly.

The CFD trains for this risk in Calgary, especially as a warming climate leads to less snow each winter. But Dongworth wouldn't expect Alberta's conditions to fuel a fire to the same magnitude as what's being seen in the United States.

"What they saw last week in L.A. was fires burning downslope, and massive embers from structures actually, not just from vegetation, being blown by those Santa Ana winds a mile or two away, just spreading fire much more quickly than anyone could possibly keep pace with," Dongworth said.

He noted the powerful winds also grounded some of the fire department's aerial assets needed to put out the flames.

Calgary's preparation to combat wildfires is helped by mutual aid agreements with nearby communities like Tsuut'ina Nation and Rocky View County to move resources more quickly when fire units need support.

The similarities that Albertans see between chinooks and Santa Ana winds are because the same physics are at play, said Natalie Hasell, a warning preparedness meteorologist with Environment and Climate Change Canada.

The downslope movement of the wind creates compression warming. Air that's forced down experiences greater pressure and warms up. Both winds are quite dry, too, Hasell said, making areas more prone to drought.

"Unfortunately for the scenario we're seeing now in Los Angeles, if there are fires, these winds can spread them and violently so," Hasell said. "It's a very devastating combination of factors going on in Los Angeles."

The Santa Ana winds, which drive most wildfires in southern California, come through gaps in mountain passes. The gaps funnel those winds and make them particularly strong. While Alberta sees similar winds, Hasell noted the province doesn't experience the same frequency or intensity as what California sees.