The most intense firestorms in the world

Marc Castellnou, a Spanish wildfire investigator, was called to Portugal after the first incident to help the government investigation unearth what had happened. A trained firefighter and fire engineer, Castellnou had roved between large wildfires in Europe, the Americas, Africa and Australia since the mid-1990s, trying to understand their behaviour better. He knew that wildfires were a common and normal event in Portugal – but not like this. It did, however, look worryingly familiar.

Five months earlier, Castellnou had headed up an EU team to investigate huge wildfires in Chile's Maule municipality, about 270km (168 miles) south of Santiago. Like in Portugal, the fires in Maule went through a sudden huge acceleration, says Castellnou. "By 25 January, the fire had been burning for 10 days, but that night it suddenly grew four times larger, fanning out 110,000 hectares [425 sq miles] in one night," he says.

Afterwards, Castellnou walked the path of the fire and flew a helicopter over to look for clues.

He found a distinct pattern – "streets" of trees that had all fallen in one direction, and also trees that showed no sign of flames having reached their tops, as they normally would in an intense fire. This meant the fire had stayed largely on the ground but had also created its own air circulation system – a wind strong enough to batter down trees.

"We realised that this was not classical wildfire behaviour and the energy had to come from somewhere else," says Castellnou. "It meant the fire was getting cold air, and the only way to get that was vertically. Somehow the fire was sucking in air from the higher part of the atmosphere and that must have been battering down flames to the ground. Those flames could then burn a lot more fully, creating more energy that helped lift the smoke plume higher to touch cold air.

"Every time the plume doubled its height, the wind multiplied by six on the surface. That meant that the wind could [rapidly] go from 5-10km/h (3-6mph) to 150km/h (93mph)," he says.

In addition to these ferocious winds, Maule had experienced the same "collapsing" pyroCb cloud that Portuguese villages had described. But in the Maule fire, the unusual weather wasn't confined to Chile. Smoke from the fires travelled 1,000km (620 miles) north to just off the coast to the Juan Fernández Islands, where it caused humidity to fall from 90% to 20% and temperatures to lower by 3-4C, says Castellnou.

"Fires [like this] are not behaving according to the weather that we can predict in our models – they do not depend on topography, meteorology or fuels anymore," says Castellnou. "Instead, the fire behaves according to the weather it is creating, which means we can also no longer predict the weather when such a fire is occurring. It's what we call wildfire dynamic behaviour."

In the three years after these fires in Chile and Portugal, Castellnou was called to investigate pyroCbs and other extreme wildfire behaviours in South Africa, Bolivia, Australia – and three times in California. Currently, he has 83 open investigations into this type of wildfire behaviour involving meteorological phenomena. In the 1990s, he had two or three.

Understanding pyroCbs better is now his main preoccupation. "Analysis is crucial. If we can predict then we can protect… but otherwise we can lose everything."

from Hacker News https://ift.tt/3w3I5vJ