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California wildfires burn at higher altitudes


Just hours before the Caldor fire threatened to wipe out the resort town of South Lake Tahoe, the massive fire accomplished a staggering feat: burning from one side of the Sierra to the other.

It traversed ridges and valleys, foothills and ridges – and also at elevations of 8,000 feet or more.

Ash and smoke descended on the Tahoe Basin and sent thousands to flee its soot-darkened shores as the blaze skirted a towering granite ridge that many believed to be a buffer against the flames. But the fire continued to climb higher, leaping from tree to tree and spewing wind-whipped embers that landed, in some cases, over a mile away.

Experts said the fire’s extreme behavior was part of a worrying trend driven by the state’s global warming, in which rapid snowmelt and critical drought are propelling wildfires to ever higher altitudes. lofty, scorching terrain that was previously too wet to burn and threatening countless residents.

“What we are seeing is that these high altitude fuels which were not generally capable of carrying fire, are now capable of carrying fire,” said John Abatzoglou, associate professor of climatology at UC Merced. and co-author of a recent study. on forest fires at higher altitudes. “This allows these fires to effectively reach new heights. ”

The study, published in June in the Proceedings of the National Academy of Sciences, found that global warming in recent decades has exposed an additional 31,400 square miles of U.S. forests to fires at higher elevations.

He also revealed that between 1984 and 2017, fires in the Sierra Nevada increased by more than 1,400 feet in elevation, surpassing some previously reliable moisture barriers.

Of the 15 ecological regions studied by the researchers, the Sierra Nevada was among the three that experienced the greatest advances upstream, along with the Southern and Middle Rockies.

“We see in the Sierra Nevada that fires have increased in terms of area burned over the past 40 years,” Abatzoglou said. “What’s new here is that we are documenting a further change in the elevation bands where these fires are occurring.”

Before 2000, it was rare for a forest in the Sierra Nevada to burn above 8,200 feet, Abatzoglou said. In the years that followed, there were eight times as many forest areas burned at this altitude. The Caldor Blaze and the Dixie Blaze – the second largest wildland fire on record in the state – have passed that elevation threshold.

One of the most extreme examples, the 2020 Cameron Peak fire in Colorado, soared to over 12,000 feet above sea level and crossed the Continental Divide.

On average, the fires have spread 826 feet higher in the mountains over the past several decades, exposing an additional 31,400 square miles of forests to the fire.

(MR Alizadeh)

This extreme behavior may partly explain why the Caldor fire may have blown up the granite ridge overlooking the Tahoe Basin, Abatzoglou said, noting that the dried out fuels and hot conditions provide more “real estate” for the fire. progresses to higher altitudes and reduces physical barriers. , like more humid forests that would resist burning.

It also helps explain how the Caldor and Dixie Fires became the first two fires to burn across the Sierra.

“Twice in our history, and they happen both this month,” said California Department of Forestry and Fire Protection chief Thom Porter. “We have to be really aware that there are fires in California that we have never seen before.”

Mark Schwartz, professor emeritus at UC Davis, noted that the Dixie fire quickly spread as it reached its crest and descended on the eastern side of the Sierra. It also burned in Lassen Volcanic National Park, where it reached elevations of 8,500 feet or more.

“As the fire spreads to higher elevations, we are at a higher risk of fires that move up and over the crest of the mountain ranges and then down again on the other side,” said Schwartz, who co -writes a 2015 study on the rising rise of forest fires in the Sierra Nevada.

Some of the peaks and ridges near South Lake Tahoe are well over 8,000 feet and are sparsely populated with fir trees. But the dried vegetation is ready to ignite, allowing some fires to rise higher and send more embers into the air.

“It’s dangerous,” said Schwartz, “because wildfire control has often relied on containment at lower elevations, leaving fires running out of fuel and fires at higher elevations.”

Several factors could be contributing to this change, but the researchers said the main cause is the warming trend that is exacerbating drought and drying out of vegetation statewide. The vast majority of high-altitude fires in California are started by lightning – which is more likely to start a fire when it hits arid vegetation.

“There is a good relationship between the heat and dryness of the vegetation in the wider Sierra, and the height to which these fires can spread in these mountain systems,” said Abatzoglou.

Higher elevations usually have snow packs that last until June. When these melt, they provide an additional stream of water which keeps the vegetation moist. But with warmer temperatures and continued drought, much of that moisture is gone.

On April 1, when California’s snowpack is generally at its peak, the California Department of Water Resources only recorded 59% of its average depth. Rains in the northern and central Sierra were even lower, at 50% of average, which matched 2021 for the third driest water year on record.

Mojtaba Sadegh, assistant professor of civil engineering at Boise State University and another of the fire study authors, said the region’s snowpack is entering a dangerous cycle with high altitude fires .

“These high altitude mountains are water towers for us,” Sadegh said. “Most of our water in the West comes from this snowpack.”

When a fire burns trees at high altitudes, it removes part of the canopy shading the snowpack and opens it to more melting sunlight, he explained. This same process also changes the reflectance of the surface, exposing darker soil and evaporating more water.

It’s a cycle that can change both the quantity and the quality of water supplied to the state’s reservoirs, he said.

And although warming is the main driver of change, studies from 2015 and 2021 noted that a century of fire suppression in California allowed a build-up of vegetation to build up in forests, especially at low and low. medium altitude. When the fire arrives it has more fuel to carry the flames and potentially over ridges and mountains.

It’s something firefighters have observed as they battle the state’s increasingly unpredictable fires, said Robert Foxworthy, spokesperson for Cal Fire. Foxworthy said there had been a “huge deficit” in the snowpack this year, as well as massively parched vegetation.

The dry fuel conditions “lead to these longer lasting fires and burn at higher elevations that we have not seen in the past,” he said.

And while not all fires rise to such altitudes, extremely high fires are often difficult to fight. Many high altitude fires occur in remote areas, and some of the small towns in these areas offer little infrastructure and few roads for access or evacuation. Firefighters have to walk further and higher, often with only the supplies they can carry.

“We have very rarely [8,000-] or an elevation of 9,000 feet and be nice and flat, ”Foxworthy said. “It’s generally quite rough and steep terrain, so obviously that’s going to pose challenges as this terrain is more difficult to work.”

And it’s not just firefighters who are affected by the transition to higher altitude fires. Fires are also dangerous for the people who live below them; the fires can remove trees that help anchor themselves against avalanches, the researchers said.

Experts are increasingly concerned about the implications of these elevation advances, especially as officials warn that this year’s fire season – and those to come – could result in even more extreme behavior.

Schwartz, of UC Davis, said letting fires spread upstream has been a sensible approach in the past and has helped protect people and homes at lower elevations. But that becomes a less safe measure as the state gets hotter and drier, increasing the risk of fires “overflowing” the mountains.

“We can expect to see more of this type of fire behavior in the future,” said Schwartz, “and this dramatically increases the workload of containing a forest fire from a distance, which is hard enough. . “