Story at a glance

  • Australia is experiencing an unprecedented fire season.
  • The raging bushfires are giving rise to “fire clouds” that often produce lightning strikes and can start more fires.
  • Here’s how they work and why scientists say they’re becoming more common.

The bushfires in Australia have killed at least nine people and scorched more than 12 million acres since they ignited in September. Now, the blazes are creating giant thunderstorms that could spark more fires, according to the Bureau of Meteorology in Victoria.

A pyro-cumulonimbus is what it sounds like: a cloud borne of flames. With bushfires raging across the country and temperatures topping 104 degrees in each state, the amount of heat and moisture in the smoke is so great, they condense into these dangerous storm clouds. But instead of rain, embers fall from the sky. 

Specifically, the clouds form when an updraft generated by a fire’s intense heat sucks smoke, ash and water vapor up into the sky. The higher this moisture-laden plume goes the cooler it gets, and eventually it forms a “fire cloud” that looks and behaves like the ones that cause regular thunderstorms. These pyrocumulonimbus clouds frequently produce lightning, and as they sweep across the landscape their bolts of electricity can ignite new conflagrations, Yale E360 reports

The clouds are accompanied by powerful winds that can fling glowing embers up to three miles and even create a truly hellish phenomenon sometimes called a “fire tornado.”

As climate change makes wildfires bigger, more frequent and more intense, these fire clouds seem to be getting more common, Mike Flannigan of the Canadian Partnership for Wildland Fire Science at the University of Alberta told Yale E360. Warmer air temperatures and more intense fires are sending even more smoke, ash and moisture up into the air, making the formation of pyrocumulonimbus clouds more likely, Flannigan explained.

The bushfires have reached “catastrophic” levels and reduced air quality to unsafe levels. Since the fires started in September, 10 people have died and thousands have been forced to leave their homes. The most recent victim was a volunteer firefighter who died Dec. 30 in New South Wales while battling the Green Valley Fire. Two other firefighters were injured. Forecasters say that southeastern Australia is experiencing record heat, creating “severe to catastrophic” fire danger. 

In New South Wales, the Rural Fire Service tweeted that a fire-generated thunderstorm formed over two other fires in the region. 

Australia’s already struggling koala population is also at risk, and almost one-third of koalas in the New South Wales region may have been killed, according to Australia’s Federal Environment Minister Sussan Ley.

Published on Dec 30, 2019