What Causes Wildfires?
The wildfire season started early this month in the northwestern U.S. and the huge blaze still burns in Fort McMurray Canada after three weeks of fighting the flames. What causes wildfires on this scale, and how can we prevent them?
Sabrina Stierwalt, PhD
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What Causes Wildfires?
Although three weeks have passed since the fire started, there remain over 1,000 firefighters and 50 helicopters in Fort McMurray, Canada to fight the wildfire raging there. One thousand more firefighters are expected in the next week and the fire remains “out of control.” The fire covers more than 522,000 hectares, but is no longer considered a threat to nearby communities. Also fortunately, gas and electricity have been restored to the surrounding areas, and residents will be allowed to start returning to their homes in the areas deemed safe starting in June.
Wildfires, also known as forest fires, grass fires, or even bushfires in Australia, are uncontrolled fires that usually happen in so-called “wild” areas uninhabited by people. However, they spread quickly, especially in times of drought, and can extend into areas where there are houses and other agricultural resources. They can burn twice as hot as the surface of Venus and reach higher than 50 meters (over 160 feet).
What Causes Wildfires?
Wildfires are most commonly caused by people, but can also be ignited by lightning or even volcanic eruptions. To grow, wildfires need fuel in the form of trees or other vegetation, so the climate must be moist enough to support plant growth but also involve long, dry heat waves. They are most common in wooded areas in the United States and Canada, as well as Australia and the Western Cape in South Africa. The USDA Forest Service provides an up-to-date map of any active fires in the United States.
In southern California in particular, wildfires are often accelerated by the Santa Ana winds, hot, dry air that blows in from the desert. These powerful, fast-moving winds can help wildfires cover 40 miles in a single day.
What Are the Repercussions of Wildfires?
If the conditions are right, wildfires can also produce what is called a fire tornado or a fire devil or sometimes even a firenado. This weather phenomenon appears to be just what it sounds like: a tornado made of fire, although its formation is more similar to that of a dust devil than an actual tornado.
When hot, dry air rises quickly from the ground it forms a column within which the density of the air decreases with height. The less dense air at the top will cool and dissipate, leaving the column, while more, hotter air gets pulled in from the bottom. Thanks to angular momentum, this creates a vertical vortex where the spinning hot air picks up fire debris like embers, ashes, and hot gases. Although at heights of hundreds of feet they can be terrifying looking, firenados usually only last a few minutes. However, they are fast moving, and so can cause wildfires to spread while causing their own significant damage in their short lifetimes.
One positive outcome from wildfires can be making the conditions just right for the growth of fungi. Although we know that mushrooms grow from formations known as sclerotia, when these growths will actually produce the tasty mushrooms we can eat is sometimes a mystery. Some sclerotia exist for years before they bear fruit. Moderate wildfires, however, are known to inspire the growth of so-called “post-fire morels,” which typically pop up a few weeks after a fire and can continue to grow for up to two years afterward.
Last year, wildfires in Idaho, Oregon, and Washington consumed almost a million acres of forest and have created conditions ripe for mushroom picking. If you’re out on a hunt for these tasty treats yourself, mushroom experts recommend looking for the western white trillium flower which acts as a beacon for finding the fungi.
How Can We Fight Wildfires?
The best hope for fighting a wildfire is often a huge dousing of rain, but of course we are not always so lucky. In the absence of precipitation, firefighters will attempt to create their own by dropping water or phosphate fertilizer, a fire retardant, over the fire. Not everyone is behind the use of fertilizer, however, since some claim the research is unclear on whether or not it actually helps slow down the fire. The fact that the chemicals used are not just fire retardants but also fertilizers could actually lead to the growth of some weeds. Perhaps more importantly, the chemicals are also clearly bad for the environments where they are dropped, especially when they make their way into nearby lakes and rivers.
Also part of an aerial assault are smoke jumpers, brave men and women who parachute into fires in remote areas. Without the need to make the trek to the fire by land, these firefighters are able to arrive much sooner to start fighting the fire and better rested.
To attack a wildfire from the ground, firefighters known as hot shots will cut off the fire’s fuel by creating a fireline, a strip of land around the perimeter of the fire from which they have cleared all plant debris. They use a special tool called a Pulaski, a combination ax and hoe, to get the job done. Forest fires usually require firelines on the order of 60 feet wide.
How Can We Prevent Wildfires?
The season when we are most vulnerable to wildfires is expected to get longer as global average temperatures continue to rise. The season is already nearly three months longer than it was forty years ago. The wildfire season in the northwestern US began early this year with two large blazes already consuming over 300 acres in Washington state earlier this month.
In the US alone, the Forest Service spent $320 million fighting just the ten largest fires. That figure is expected to reach nearly $2 billion in the next ten years. (Note that different sources give much higher estimates, ranging up to $5 billion.) So what can we do to prevent them?
Occasionally targeted, controlled fires will be started on purpose in order to decrease the amount of material available for potential future fires. And as many of us already know from Smokey the Bear, most wildfires are caused by humans. This includes as many as 90% in the US, many due to carelessness. Don’t leave campfires unattended or toss lit cigarettes while hiking in the woods.
If you are concerned about wildfires, first, learn if you live in a vulnerable area. If you do, you can take some simple measures like planting fire resistant shrubs around your home and obtaining a garden hose with a long reach. Sign up for emergency notifications to alert you if there is a fire in your area. Also be sure to have an evacuation plan if necessary, as well as a standard emergency preparedness kit.
Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email.
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