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Wildfires

How Do Wildfires Start & Can We Predict Them?

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By Paul Walsh on August, 3 2021
Wildfires

As climate change makes annual wildfire seasons longer and more devastating, predicting when and where these disastrous blazes will spread has become crucial. But is it actually possible to do this?

How Weather Conditions Feed the Combustion Triangle 

In order to start, a wildfire needs fuel, oxygen, and something to ignite it. In many cases, certain weather and climate conditions combine to make wildfire events more likely - affecting how they spread and how much land they burn through within short timeframes. 

Lightning Creates Fires and Vice Versa

Lightning is globally recognized as the dominant natural cause of wildfire ignition, producing the largest wildfires in many regions. 

Scientists are also beginning to understand how lightning and wildfires can function as two parts of the same self-perpetuating cycle.

  • Heat from extreme fire events evaporates moisture into the air. 

  • This makes water vapor rise into the atmosphere, which often generates ‘dry’ thunderstorms, whose rainfall can evaporate before reaching the ground due to extreme heat.

  • The wildfire smoke leads to enhanced charge separation in the thunderstorm cloud which in turn creates lightning

  • Lightning strikes further dry vegetation and spark a wildfire.

  • The ignited fires produce excessive heat and more smoke pollution.

  • The cycle repeats once again.

When dry thunderstorms can unleash over 700,000 lighting strikes in a single day, wildfires become almost inevitable. Scientists predict areas burned by lightning-ignited wildfires in the Southern Eastern US will see a 30% increase by 2060.

Extreme Temperatures

As global temperatures increase, longer and more extreme heat waves contribute to an increased likelihood of wildfire events by evaporating moisture from the surface to the atmosphere as hot air can contain more moisture than cold air and thus acts kind of like a sponge. This creates a high abundance of dry vegetation, which is fuel for a wildfire. A lack of rainfall will enhance this effect and drastically increase a fire season’s severity.

2021 has seen a catastrophic heat wave in parts of southern Europe and Siberia, as well as record-breaking extreme heat events that ignited massive wildfires across Western North America (more info here).

This climate-change-induced extreme heat trend can become a regular occurrence in the coming years. Projections say that at the current rate of emissions, we could reach 2°C global warming by 2040. At which point, such extreme heat wave events, estimated to occur once in 1000 years, could repeat every half or full decade.

Scientists estimate reaching a 3°C global average warming scenario by the end of the century could impact 300 million Europeans, resulting in 96,000 annual extreme-heat-related fatalities.

Heat & Dry Weather Dehydrate Vegetation  

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Low humidity combined with rising temperatures helps to turn shrubbery, grass, and trees into kindling for wildfires - without sufficient moisture, dry vegetation becomes readily available wildfire fuel.

Atmospheric Instability

Unstable vertical movement of air, which occurs as hot air rises and cold air descends (much like in boiling water) can have a direct impact on a fire’s behavior:  A fire can become more intense due to unrestricted updraft air currents just as if you open the damper of your stove. The additional heat of the fire enhances this effect. And it also helps smoke pollution climb higher. 

How Strong the Wind Blows

As atmospheric instability increases, stronger gusts of wind in changing directions can occur more frequently. Strong winds can then accelerate the dehydration of vegetation and carry small burning debris, helping to spark new fires and give existing ones more fuel.

Wind also supplies fire with oxygen and serves to fan wildfires, dictating fire intensity and directional spread. 

The Right Stuff to Burn

The geographical features of a region also greatly impact the burning potential and likelihood of a wildfire event: In particular, forested areas can become arid and highly flammable during droughts and extreme heatwaves. Even a tiny spark can turn into a raging blaze.

Until recently, mountainous regions were considered safer due to colder air and increased moisture at higher altitudes. However, a new climate change study suggests forest fires have started reaching higher, wetter elevations, and now threaten an additional 11% of western US forests.

How Humans Contribute to Wildfire Events

Experts estimate human-caused wildfires may be more destructive during wildfire season, as they often occur near populated areas, and drought and heat facilitate fast-burning conditions:

  • Campfires - failure to put them out properly or leaving campfires unattended means nearby vegetation can catch fire. 

  • Burning Debris - byproducts of human activity such as burning yard waste can ignite dry vegetation nearby.

  • Fireworks - In 2021, scientists urged North Americans to avoid using fireworks on the 4th of July due to record-breaking temperatures.

  • Cigarettes - A decline in adult smoking helped reduce the number of annual cigarette-caused wildfires in the USA by 9%. However, extreme heat and low humidity still make vegetation highly susceptible to the smallest cigarette ember.

  • Vehicles & Equipment - Car crashes, engine sparks, and equipment failure can easily start wildfires when weather conditions facilitate fast burning. 

  • Arson - Caused often by malicious intent or deceitful attempts to receive insurance compensation, hot weather conditions, and dry vegetation make arson-caused wildfires a major threat.

  • Utility Lines - Whether knocked over by strong winds or improper maintenance failing to prevent sparks, power lines can present a real danger. In fact, between 2019 to 2013, over 1500 California wildfires, including the deadliest in the state’s history, were caused by utility lines.

Information is Power

It’s not always possible to predict the precise trigger or spark for a wildfire event, but wildfire risk can be estimated to some extent by understanding how climate, topography, weather, and land cover impact fire behavior and the likelihood of a fire spreading. (We discuss this in more detail in this webinar).

As climate change contributes to worsening wildfires, it’s never been more important to consider how different environmental factors come together to dynamically impact our health and safety during fire season.

Dive Deeper with this On-demand Webinar:

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