Why are Wildfires Bigger and More Frequent Today?

Fires can occur for many reasons, but more often than not they are caused by people. According to a 10-year study published in the Proceedings of the National Academy of Sciences in 2007, 84% of fires firefighters were called to fight were caused by humans. More recently and especially during the summer, when land is so dry and hot something as simple as a lit cigarette flicked out of the window of someone’s car, a downed powerline or a tire rim that scrapes the surface of pavement causing a spark can be the beginnings of a fire. These things may seem small but are actual reported causes of wildfires.

Fires need three things to proliferate: heat, oxygen, and fuel. High temperatures allow for the fire to spread. It evaporates moisture from the air and plants, making them dry, brittle and quick to catch.

Oxygen flow in the form of wind allows for oxidation reactions to occur creating more heat and gas. Fuel, which in this case are the plants, provide burnable material. The United States has a deep history of fire suppression, dating back to Peshtigo Fire in 1871 and the Great Fire of 1910. For most of the 20th century, wildfires were put out as quickly as possible for fear of them becoming uncontrollable or especially destructive. These practices have created rather unstable ecosystems as fires are just as much a part of the natural cycle necessary for growth as any other ecological process.

For example, imagine a forested region with a diverse range of plant species. In one scenario this land is allowed to burn, let’s say it burns naturally every 10 years. It only burns hypothetically about 20 acres at a time and afterword essentially “resets” to regenerate new foliage. Early successional plants such as annual “weeds” and some annual grasses occur in the first year, followed by perennial grasses and broadleaf plants. Then by the time we reach year 10, many shrubs and tree saplings will appear while the annual plants decline. Once fire occurs again, this system “resets” once more. Too much or too little fire could lead to an ecosystem shift such as the land becoming a grassland or a desert. This cycle of disturbance enables this region to persist as a forest decade after decade.

Bugaboo fire in Florida 2007 (FEMA Image)

Now let’s look to scenario number two, houses are built within this forested area which is called an “wildland-urban interface” where over 43 million homes (as of 2010) are built within. In this scenario, fire is suppressed for 100 years in order to “protect” the homes and because people don’t like the occasional smoke in their backyard. The foliage that would have burned grows taller and spreads, while new species, such as those grasses and shrubs, also grow and thrive as well. One year, they have a really dry season, where more than 200 days have gone without rain and it’s also the warmest summer on record. All of the plants have become dry and brittle, so all it would take is a simple spark…

This second scenario is the reality of Paradise, California. The Camp fire that engulfed the town of Paradise in the north, burning 80 acres per minute, occurred because of the years of fire suppression and the spark of a powerline. It was deadliest and most destructive fire in California history, occurring simultaneously while two other fires were raging in Southern California: The Woolsey Fire and Hill Fire.

Camp Fire near Paradise California (NASA)

This isn’t just happening in California. Around the world, the air is warmer and more susceptible to fire because of climate change. The increased amount of greenhouse gases in our atmosphere, trap heat and subsequently warm the planet leading to an increase in the fuel and heat required for fire to occur. These extreme events will most-likely increase as the climate continues to warm and people who live within the “wildland-urban interface” may become more and more at risk.