Why Do Wildfires Happen?

Why Do Wildfires Happen?

27 September 2010

published by news.discovery.com

USA —  During the wildfire season from April to October, sometimes all it takes is a gunshot to ignite a blaze.

Large-scale wildfires have sizzled around Utah for months, consuming acres of land and driving hundreds of residents out of their homes.

But drought conditions and hot temperatures weren’t to blame for one that recently broke out in Herriman, Utah. Instead, machine gun fire from a National Guard artillery exercise sparked the blaze, and fast winds fanned the flames far and wide.

The basic wildfire trifecta consists of bone-dry grasses and timber, summer heat and oxygen-rich winds. When the parched kindling reaches its flash point, it releases volatile gases that combust in the presence of oxygen, and a blaze breaks out.

And as the Herriman “Machine Gun” fire demonstrates, people playing with fire – or even bullets that spark when they ricochet off of rocks – are often the catalysts that stoke the wildfire process.

According to the U.S. Fire Administration, nearly 80,000 wildland fires scorched more than 5 million acres of land in 2009. Although that’s a significant drop from the roughly 97,000 fires in 2006, and this season has been quiet so far, the rate of wildfire outbreaks appear to be rising.

“In the region I work in, the western U.S., forest fires have increased in recent decades, especially in mid-elevation mountain areas where snow melt dates have been significantly affected by warming,” said Anthony Westerling, a wildfire expert with the Sierra Nevada Research Institute at the University of California at Merced.

Human error is the most common wild card in the wildfire recipe, but climate change and its accompanying rising temperatures are likely responsible for the upward trend that has affected the western United States as well as other vulnerable areas around the world.

“Anecdotally, fires seem to be increasing in other areas around the world, but it is difficult to establish conclusively, one, that they are increasing and, two, why,” Westerling told Discovery News. “Long-term data are not available in most places, and other effects such as land use changes also play a big role in changing fire regimes.”

Multiple environmental variables, such as urban development, elevation and seasonal climate, influence the likelihood of wildfires, which makes it difficult to formulate global assessments.

“(The rate of wildfires) is location-specific, in that different types of ecosystems respond differently to climate variations,” Westerling explained. “In some regions, yes, it seems pretty conclusive that climate change is leading to an increase in large forest fires in the western U.S., especially in the Northern Rockies.”

In 2006, Westerling collected large-scale wildfire data from the western U.S. dating back to 1970. His analysis verified a climate-related uptick in outbreaks. Understanding those types of ecological correlations will help researchers better predict and manage future wildfires.

“(Wildfire forecasting) is an area that has improved substantially in recent years,” Westerling said. “This is both because we have the data and computing resources now to do rigorous, quantitative forecast modeling, and because we understand climate variability on these time scales better now.”

Yet even as experts fine-tune forecasts and account for climate change’s impact on wildfire outbreaks, they still can’t entirely account for careless human activity that can ignite an inferno from something as simple as a smoldering cigarette butt.

Just ask the National Guard officials in Herriman, Utah, who’ve made the media rounds apologizing for their ill-timed artillery practice.

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