• At the height of the fire season in the American West, the "Dixie Fire" has already burned more than 110,000 hectares in three weeks.

  • The town of Greenville was reduced to ashes overnight Wednesday through Thursday.

  • Things won't get better right away: the fire is so powerful that it creates its own climate around it

The fire season is getting longer and more intense each year in California.

2021 is no exception with, in particular, the “Dixie Fire”, which burned tens of thousands of hectares and is already the third most important fire in the history of the State.

And it's probably not over.

It is so powerful that it creates its own climate.

20 Minutes

goes around the fire.

What is the Dixie Fire?

"Dixie Fire" is the name given to a giant fire that ravages part of northern California around Lake Almanor. The fire started around July 14 and burned 110,000 hectares of vegetation in three weeks. To give you an idea, this represents almost twice the territory of Paris and the three departments of the inner suburbs (Val-de-Marne, Hauts-de-Seine, Seine-Saint-Denis). In recent hours it has become the third worst fire in the history of the state. On Friday evening, four people were missing but no injuries were to be deplored, according to local authorities.

The flames seem out of control and favored by continuous winds and of course the heat.

The small town of Greenville, 800 residents, was wiped off the map overnight from Wednesday to Thursday.

Orders to evacuate residents to the east have been issued.

Without, always, being followed by the facts: "We have firefighters who find themselves facing weapons aimed at them, because of people who do not want to evacuate", explained to AFP Jake Cagle, head of section within of the crisis management team.

How did the Dixie Fire start?

There are several ways to start a fire but there are always sine qua non conditions, explains

Florence Vaysse, the national referent for vegetation fire issues

, to

20 Minutes

. First you need fuel, "that is to say dry vegetation, so a long period without rain". Then you need "favorable" weather conditions. Three factors must be combined: high temperatures, wind and very low air hydrometry. "We often forget this last condition and it is very important: if in a sector you have dry vegetation, high temperatures, wind but 80% humidity in the air, there will be no fire" , explains the specialist.

California, which experiences repeated droughts year after year, is in this case but it is not enough.

In France, 90% of fires have a starting spark of human origin, says Florence Vaysse.

This is probably the case with the Dixie Fire too.

The investigation remains to be done but all eyes are on the power lines crossing the forest.

The mayor of the neighboring town of Paradise, ravaged by the flames of Camp Fire, in 2018, told NPR that the fire started in the same place.

Probably because of the same bad lines.

Why do we say that it "creates its own climate"?

Small or large, a fire is all weather. When there is a fire, a mass of warm air is created above it. "As in a fireplace, this air rises and leaves room, which creates a call for air", describes Florence Vaysse. This is what causes wind around a fire and fuels the flames. In the case of the Dixie Fire, the hot air encountered a mass of moist air. “From there, it's a classic process: hot air meeting humid air, it forms a cumulus cloud. In this case, a pyrocumulus.

As the Dixie Fire is a very intense fire, it did not create a pyrocumulus but a pyrocumulonimbus: a thunderstorm cloud.

The Dixie Fire has, in a way, created itself something to nurture and grow, with lightning being pretty much the only non-human cause of fire, along with volcanic eruptions.

This is the worst-case scenario: "Lightning can create new fires, there are huge drafts which cause a lot of wind and can carry incandescent sparks very far which, in turn, can generate new ones. fires, ”describes the Météo-France specialist.

How can firefighters stop it?

It is a veritable army of firefighters, 7,500, who fight against the flames of the Dixie Fire. In this disproportionate fight, one can only try to avoid the worst, without always succeeding, as with the fire of Greenville. The emergency services seem disarmed: "These are not the same fires we were used to ten years ago,"

Chris Aragon, the California fire chief

, told the

New York Times

. They are so hot and spread so fast. "

One thing is certain, at this level of fire, the firefighters will not be able to control the flames on their own.

They will need a helping hand from the sky: we are talking about the weather.

In the next few hours the wind should ease, paradoxically the immense cloud of smoke will therefore lower the temperature on the ground a little, explains the

New York Times

.

The respite might be short-lived and the fire burns for weeks to come.

World

Three years after Paradise, a neighboring town destroyed by the flames of the "Dixie fire"

World

Firefighters confronted with "Dixie Fire" which generates its own climate

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