origin, images, intensity… Is the Oak Fire a megafire?

FIRE. The “Oak Fire” that has been ravaging California for five days does not seem ready to go out. It has already burned 7,200 hectares of forest and is coming dangerously close to Yosemite National Park. We take stock.

[Mis à jour le 27 juillet 2022 à 16h15] “From the start, we gave everything we had,” assured the Los Angeles Times Mike Van Loben Sels, the local manager of the Cal Fire firefighting agency. To fight against the fire that has devoured California since its outbreak in the small town of Midpines on Friday July 22, 2,500 firefighters are working tirelessly, supported by 300 trucks and 17 helicopters. Favored by “extreme drought”, winds and rising temperatures, it has already burned at least 7,2000 hectares of forest.

The situation is very hard for the more than 3000 evacuated inhabitants. The fire has already destroyed 41 properties, damaged dozens of others and threatens several thousand. Oak Fire has an “unprecedented” behavior, alerted this morning the firefighters who are fighting boldly against flames more than 30 meters high. Sending sparks more than 1 mile (1.6 km) around, it continues to progress, destroying hopes of a return to a normal situation by California. Thanks to the many resources deployed, the fire is still partially controlled: on the evening of July 26, the firefighters announced that Oak Fire “was 26% contained”, compared to 16% the day before. We take stock of the origin of the fire, between human responsibility and global warming, but also on the risk of fire in Yosemite National Park.

Although the causes of the fire that broke out on July 22 in Mariposa County, California, on the outskirts of Yosemite National Park have not yet been identified, experts agree to qualify it as the largest wildfire. Californian of the season. For the time being, the authorities do not know if the origin of the fire is criminal. Only one thing is certain: the extreme temperatures recorded in the region did not help the firefighters to contain the flames.

The American West is currently experiencing an unprecedented heat wave with temperatures that rose to 38°C in this region of California on July 23. The level of humidity in the air also reached levels close to record levels: 8 to 9% humidity was recorded on July 24, while normal is generally between 30 and 50% in this area at this time. of the year.

Aided in its progress by particularly arid terrain, it still threatens thousands of homes in small rural communities in Mariposa County. As a result, California Governor Gavin Newson declared a state of emergency. Particularly vigorous, the fire “advances very quickly” and the “reaction window” to evacuate people is “limited”, as explained on CNN Jon Heggie, a Californian firefighter official.

Evacuations continue in California. “More than 6,000 people, mostly living in small high-altitude communities, had to evacuate,” a California fire department spokesman reported on July 23, quoted by the Los Angeles Times newspaper. For the inhabitants of these damaged houses, the situation is sometimes difficult to bear. “It was scary when we left, because we were getting ashes on us and we had such a vision of this cloud (of smoke). It looked like it was over our house and coming towards us very quickly”, explained in particular a woman who had to leave her house this weekend during a testimony broadcast on the local television channel KCRA 3. For her husband, currently a refugee in a school in Mariposa transformed into a center for emergency reception, everything went very quickly: “We were starting to gather our things. I went up the hill to look and I thought + Oh my God +, it (the fire) was coming quickly”.

Oak Fire has not finished impressing or terrorizing Californians. One testimony in particular was relayed: that of David Lee, an evacuee who confided in the newspaper Santa Cruz Sentinel: “The flames reached up to 30 meters high”. This 55-year-old man was among the first people evacuated on July 22. He had to leave his house and all his belongings, which he thinks are now engulfed in the fire. “It was heading straight for us. This fire is by far the fastest I have ever seen,” he told reporters.

While California fire chief John Heggie called the ongoing blaze near Yosemite Park a “megafire,” technically the flames aren’t yet large enough to use that term. In fact, according to Cal Fire, the American firefighting agency, the flames have already destroyed some 7,200 hectares of forest and 41 houses (according to the point made on the evening of July 26). In addition, American firefighters have already managed to contain 25% of the flames, against 16% the day before, July 25, and this in large part thanks to increased humidity. They are therefore able to control a certain proportion of the circumference of the area affected by the fire. However, fires are only considered megafires when the affected area extends over more than 10,000 hectares and they are totally out of control.

If the causes of the start of the fire are under examination, the climatologists are formal: it is fed by dead trees and dry bushes, plagues which tend to multiply in this region victim of chronic drought. John Heggie, the head of the California fire department, believes that it is a “direct result of climate change”: “You can’t have ten years of drought in California and expect things not to change”, has he declared. In fact, the Oak Fire, while very impressive, is really just one of the countless scars of the heat waves that hit America this month. According to a map from the National Weather Service (NWS), a very large part of the country, including California, all of the south, and then much of the east coast, experienced temperatures of 37°C to 43°C. With this scorching heat, difficult to extinguish the flames.

This finding is shared by Jonathan Pierce, a spokesman for the California fire department who believes that low humidity and high temperatures are currently fueling the fire. He also referred to the high “tree mortality” in Mariposa County, where the many “standing dead trees” leave potentially flammable items on the ground. The lengthening of the fire season therefore produces weather conditions that are particularly favorable to flames.

What is the human role in starting the fires in California?

It’s not for lack of warning. “Scientists have been predicting these extraordinary and catastrophic events for decades now, lamented this Sunday July 24 on the television channel ABC News the former American vice-president Al Gore, who had received a Nobel Peace Prize in 2007 for his commitment to the climate.” Today they say that if we don’t stop using our atmosphere as a garbage can and if we don’t stop these emissions (of greenhouse gases) which trap heat, things will get worse”, he hammered, before concluding: “The survival of our civilization is at stake”.

95% of fires are of human origin. This is a figure that climatologists and experts have been repeating over and over since the beginning of the year, as 2022 seems to be the year of repeated conflagrations. The Cal Fire agency explains it these days on American TV sets, taking the example of the “Agua Fire” fireplace which was ignited on July 18 by the spark of a car engine in the county of Mariposa burning a total of 420 hectares. With this in mind, the agency encourages residents to mow their lawns before 10 a.m., and to equip their chainsaws and other gasoline-powered machines with devices that prevent the spread of sparks. However, if we take the example of the megafires of August 2020, a particularly destructive period for American flora, the origin of the fire lies in the dry lightning that had hit the United States.

This park has become one of the most famous in the world thanks to its giant sequoias, thousand-year-old trees that the region strives to protect from bad weather. At the end of July, it is dangerously threatened by the flames which threaten to lick the branches of its immense trees. As a precaution, one of the roads leading to Yosemite National Park was cut off, but the park itself was not closed.

Unfortunately, this is not the first fire alarm for the park and its region. The “Oak Fire” is already the third fire to affect the Yosemite area since the beginning of July 2022. Firefighters remember with bitterness last July 7, when the “Washburn Fire” burned 2,000 hectares, but without seriously threaten the thousand-year-old redwoods that had been protected by controlled fires carried out for decades in its groves to reduce the fuel present on the ground. This time again, the soldiers of the fire fight tirelessly “using bulldozers, manual crews and aircraft,” as reported by Cal Fire, the department responsible for managing wildfires in the state of California.

The firefighters continue to fight this July 27 in the afternoon. Unfortunately, they could only be at the start of a long, fiery wrestling season. “Given the burning conditions and the wildfires that we’re talking about, we expect to have another four, five or six very tough months,” California fire chief Brian Fennessy warned in June.