by Blown wildfires, fire whirlwinds, loud thunderstorms: When fires get big and hot enough, they can create their own weather.
In these extreme fire situations, normal firefighter methods of controlling the fire directly do not work, and wildfires get out of control.
But how can fire create weather?
I am an atmospheric scientist who uses data collected by satellites in weather forecasting models to better predict extreme fire weather phenomena. Satellite data shows that fire-produced thunderstorms are much more common than anyone realized just a few years ago. This is what is happening.
The wild and weather ties
Imagine a wild landscape with dry grass, brush and trees. A spark lands, perhaps from lightning or a tree branch hitting a power line. If the weather is hot, dry and windy, that spark could quickly ignite a wildfire.
When vegetation is burned, large amounts of heat are released. This heats the air near the ground, and that air rises like a hot air balloon because warm air is less dense than cool air. Cooler air then rushes in to fill the vacuum left by the rising air.
This is how wildfires create their own wind patterns.
What happens next depends on the stability of the atmosphere. If the temperature cools rapidly with elevation above the ground, the rising air will always be warmer than its surroundings and will continue to rise. If it rises high enough, the moisture will condense, forming a cloud called pyrocumulus or flammagenitus.
If the air keeps rising, at some point the condensed moisture will freeze.
Once a cloud contains liquid particles and frozen water, collisions between these particles can lead to a separation of electrical charges. If the charge build-up is large enough, an electrical discharge – better known as lightning – will occur to neutralize the charges.
Whether a fire cloud becomes a thunderstorm depends on three main ingredients: source of elevation, instability and moisture.
Dry lightning
Wildfire environments tend to have limited moisture. When conditions in the lower atmosphere are dry, so-called dry lightning can occur.
No one who lives in a wildfire-prone environment wants to see dry lightning. It occurs when a thunderstorm produces lightning, but the precipitation evaporates before it reaches the ground. That means there is no rain to help light any fires with lightning.
Fire strikes
As air rises in the atmosphere, it can encounter different wind speeds and directions, a condition known as wind shear. This can cause the air to spin. The rising air can tilt the spin vertically, like a tornado.
These fire vortices can have powerful winds that can spread flaming ash, fueling new areas of fire. However, they are usually not true tornadoes because they are not associated with rotating thunderstorms.
Rotting storms
Eventually, the thunderstorm that fueled the wildfire will begin to fade, and what went up will come back down. The downdraft from a rotten thunderstorm can produce gusty winds on the ground, further spreading the fire in directions that can be difficult to predict.
When fires create their own weather, their behavior can become more unpredictable and erratic, increasing their threat to residents and firefighters battling the blaze. Anticipating changes in fire behavior is important for everyone’s safety.
Satellites show that fire weather has not been created so rarely
Meteorologists recognized the potential of thunderstorms to cause fires in the late 1990s. But it wasn’t until the launch of the GOES-R Series satellites in 2017 that scientists had the high-resolution images needed to see that fire-triggered weather really is common.
Today, these satellites can alert firefighters of a new fire even before phone calls to 911. That’s important, because there is an increasing trend in the number, size and frequency of wildfires around the world. of the United States.
Climate change and rising fire risks
Heat waves and the risk of drought are increasing in North America, with rising global temperatures more often leaving dry landscapes and burning forests. And climate model experiments show that human-caused climate change will continue to increase that risk.
As more people move into fire risk areas in this warming climate, the risk of fires also starts to rise. With fires comes cascading hazards that last long after the fire is over, such as burn-scarred landscapes that are much more susceptible to landslides and debris flows that affect water quality and ecosystems.
Communities can reduce their vulnerability to fire damage by building defensible spaces and fire breaks and making homes and properties less vulnerable. Firefighters can also reduce surrounding fuel loads with prescribed fire.
It is important to remember that fire is a natural part of the Earth system. As fire scientist Stephen J. Pyne wrote, we as humans will have to redirect our relationship with fire so that we can live with fire.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Written by: Kyle Hilburn, Colorado State University
Read more:
Kyle Hilburn receives funding from the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration.
