What are fire clouds or pyrocumulonimbus? How they originated over the French fires — Explained

As firefighters battle one of France’s worst forest fire seasons in recent years, an unusual atmospheric phenomenon has caught the attention of scientists: pyrocumulonimbus (pyroCb), also known as fire cloud or cumulonimbus flammagenitus.

The French National Federation of Fire Fighters (FNSPF) said the giant fire in the south-west of the country had produced a pyrocumulonimbus – a phenomenon they described as never seen before in France. The appearance of these towering clouds underscores not only the intensity of the fires, but also the dangerous feedback they can create and worsen wildfire conditions.

What is a pyrocumulonimbus or fire cloud?

A pyrocumulonimbus is essentially a thunderstorm created by a forest fire rather than the sun heating the earth’s surface.

Quick answers to key questions

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Pyrocumulonimbus, or fire clouds, form from intense fires that release heat, smoke and moisture into the atmosphere. As this superheated air rises, it cools and condenses and can develop into a massive thunderstorm.

These clouds create their own weather, producing strong winds and lightning that can unpredictably spread fires and ignite new wildfires, complicating firefighting efforts.

They can exacerbate wildfire behavior by generating high winds and severe weather, including hail and intense downdrafts, which pose additional risks to emergency responders and surrounding communities.

Although climate change does not directly create pyrocumulonimbus clouds, it increases the likelihood of conditions such as intense heat waves and droughts that facilitate their formation.

Yes, although rare, pyrocumulonimbus clouds have been documented during significant fires, including recent forest fires in France, underscoring the phenomenon’s increasing importance as conditions worsen.

According to NASA, these clouds form when an intense wildfire releases huge amounts of heat, smoke and moisture into the atmosphere. The superheated air quickly rises like a giant chimney, sending ash and water vapor high into the sky.

As the rising air cools, moisture condenses into clouds. If the updraft is strong enough, the cloud will grow into a towering thunderstorm known as a pyrocumulonimbus.

Scientists also refer to it as cumulonimbus flammagenitus, reflecting its origin caused by fire.

How are fire clouds formed?

The process takes place in several stages:

– A massive fire heats the surrounding air to extreme temperatures.

– Hot air mixed with smoke and moisture rises quickly.

-As it rises higher, the air cools and the water vapor condenses to form a pyrocumulus cloud.

-If the plume continues to rise into the cooler layers of the atmosphere, ice crystals develop within the cloud.

-These ice particles generate electrical charges and transform the cloud into a full blown pyrocumulonimbus thunderstorm.

Unlike normal storms powered by solar heating, the energy driving these clouds comes almost entirely from the forest fire itself.

Why are pyrocumulonimbus clouds dangerous?

Fire clouds are not just a visual spectacle – they can significantly worsen fire behavior.

1. They create their own weather

Pyrocumulonimbus clouds generate strong and unpredictable winds that can quickly change the direction and intensity of a fire.

These winds can spread flames to previously untouched areas, making firefighting efforts much more difficult.

2. They produce lightning

Like conventional thunderstorms, pyroCb clouds can produce lightning.

Lightning strikes can ignite entirely new wildfires several kilometers from the original fire, multiplying the state of emergency.

3. They can cause bad weather

Scientists say these clouds can also produce:

-In rare cases of tornado-like vortex

These conditions create additional hazards for emergency responders and nearby communities.

Why do scientists pay so much attention to it?

NASA describes pyrocumulonimbus clouds as giant atmospheric chimneys because they can blow huge amounts of smoke into the lower stratosphere.

Unlike smoke trapped in the lower atmosphere – which is usually washed away within days – stratospheric smoke can remain dormant for months or even years.

Scientists say the largest pyroCb events can send smoke into the atmosphere in quantities comparable to that released by a mild volcanic eruption.

Because smoke reaches such high altitudes, it can spread across continents and even around the world, potentially affecting climate and air quality far from the fire itself.

Read also | Forest fires in France force 300,000 evacuations as Macron calls crisis cabinet

Have they been observed before?

Although rare, pyrocumulonimbus clouds have been documented during some of the world’s most destructive wildfire seasons.

One notable example occurred during NASA and NOAA’s FIREX-AQ mission in August 2019, when a NASA DC-8 flying laboratory flew directly over a pyrocumulonimbus cloud that formed over a wildfire in eastern Washington state.

Scientists used the mission to study the chemistry of wildfire smoke and better understand its effects on air quality, weather and climate.

NASA notes that while fire-generated clouds themselves are relatively common during intense wildfires, only a small number of fully developed pyrocumulonimbus clouds have been extensively documented because they require exceptionally intense fires and favorable atmospheric conditions.

Why did one arise over France?

A forest fire in southwestern France has burned tens of thousands of hectares amid prolonged heat, dry vegetation and strong winds.

These extreme conditions supplied the enormous heat needed to drive the smoke and moisture high into the atmosphere, allowing the pyrocumulonimbus to form.

Forecasters also warned that temperatures in Spain and parts of France could approach 40C, with low humidity and dry winds creating ideal conditions for further fire growth and potentially further fire cloud formation.

Does climate change play a role?

Scientists caution that climate change does not directly create pyrocumulonimbus clouds, but increases the likelihood of the conditions that create them.

More frequent and more intense heat waves, longer droughts, and larger, hotter wildfires mean the atmosphere is increasingly capable of generating these extreme fire-triggered storms.

Read also | Fires in Spain and France have killed at least one, more than 265,000 have been evacuated: What are we