We know that climate change is driving hotter and drier summers, and making fire seasons worse, and this is already impacting on mountain environments. Last summer there were significant fires across eastern Victoria and the Victorian Mountains, as well as in Tasmania. While the largest one burned in the Bunyip state park about 65km east of Melbourne, there were also fires which closed the Southern Alps and Foothills areas of the Alpine National Park, especially around Dargo and Licola.
One of the features of these fires was the formation of pyrocumulus clouds (as shown in the image above, taken from the north of the fire burning out of the Dargo River and onto the Dargo High Plains, with Mt Blowhard in the foreground). The Licola fire burnt with such ferocity it was visible on the Bureau of Meteorology’s radar. A huge thundercloud formed from the fire, which then produced more than 1,200 lightning strikes, some of which sparked new fires. It created unpredictable weather conditions that hampered fire fighting efforts.
Energy rising from the fire creates an intense convection column which becomes more powerful than the wind closer to ground level. Hilly terrain, lots of dry fuel, heat and instability in the air contribute to the creation of these updrafts (also called plume-dominated fire). If the pyro cumulus cloud becomes large enough, it then starts to generate its own localised weather, including lightning (called pyrocumulonimbus – a thunderstorm created by a bushfire).
While pyrocumulus clouds are not necessarily of concern to firefighters, if they interact with the upper atmosphere they can radically alter fire behaviour through increasing fire intensity by creating their own weather which may change the fire’s speed and direction.
The CFA estimates that the plume from the Licola fire reached 12 kilometres into the atmosphere. These fires are generally uncontrollable by both ground and aerial fire fighting resources, meaning that fire authorities can only hope to contain it and wait for conditions to change.
The CFA notes that during last summer’s fires there was an ‘unprecedented’ number of these plume dominated fires. CFA Fire Behaviour Analyst Musa Kilinc says ‘with climate change, the potential for more frequent plume-dominant fire behaviour is very real.’
These fires appear to represent another dimension of the ‘new normal’.
An update from 2022 highlights that this is becoming a global concern.
‘Catastrophic wildfires, exacerbated by catastrophic climate change, had produced a rash of pyrocumulonimbus plumes over the western United States and Canada’ during the terrible summer they are enduring.
According to a report in Wired:
“You can think of them as like giant chimneys, funneling smoke that’s being released by the fire up into a thunderstorm,” said David Peterson, a meteorologist at the research laboratory, during the Zoom press conference. “You can imagine this extremely dirty thunderstorm, with all these smoke particles for water to condense on.”
Unlike a typical thunderstorm, though, the resulting water droplets don’t tend to get large enough to fall as rain. “But it is a cloud that can produce a lot of lightning,” Peterson added. These clouds can then advance across the landscape, sparking new wildfires as they go. So not only can the blaze propagate itself by flinging embers ahead of the main fire line (California’s wildfires are so deadly in part because of strong seasonal winds that push them at incredible speeds), it can also produce so much hot, rising smoke that it in essence recruits the atmosphere to light more fires for it. It’s a runaway self-proliferating machine.
The formation of these kinds of clouds may not be a bug but rather a feature of a climate gone bizarro. “We’ve been in a wave of pyroCb activity in North America—near daily activity in recent days,” Peterson said. “This pyroCb outbreak is actually the latest in a series of pyroCb outbreaks that we’ve seen worldwide in recent years.”
The original post (2019) was based on a story written by Shaunnagh O’Loughlin of the CFA. Source Brigade magazine, spring 2019. State of Victoria (Country Fire Authority) 2019.
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