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Suburbia Is Fueling More Dangerous Wildfires

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The way we plan our cities makes fires far more destructive

Flames from the Sand Fire encroach upon the suburbs of Santa Clarita, California

A fast-moving wildfire continues to rage out of control just north of Los Angeles, issuing evacuations for 10,000 homes and sending ash falling like post-apocalyptic flurries in backyards 50 miles away. The blistering temperatures of yet another abnormally dry summer are to blame for sparking dozens of similar wildfires in the West. But another factor is making these types of fires much more destructive: sprawl.

Fires in the Western US have been happening more frequently in recent decades. Due to climate change, fires are starting earlier in the season and burning longer and hotter, requiring more time and resources to put them out. It’s estimated that the fire season has lengthened by 20 percent since 1979. Just as an example, LA’s Sand Fire is the the region’s fourth major fire of the season, which is unprecedented by mid-July. And the hottest days of summer are still to come.

While it’s true that years of below-average precipitation—and the nonexistent snowpack, low soil moisture, and millions of dead trees—are responsible for the conditions which make wildfires more common, the way cities are growing is actually putting more humans into these dangerous situations.

As people move into the fringes of cities, neighborhoods are pushed right up against heavily forested hillsides or vast grasslands. These places where human habitats overlap with wilderness areas are known as the wildland-urban interface (WUI), and these are the areas of greatest concern to fire safety officials. Last year, 4,636 structures were burned by wildfires nationwide, a record. California’s exurban communities, where culs-de-sac curve deep into chaparral canyons, are picture-perfect examples of these highly volatile regions.

As the risk of wildfires has increased, so has the number of people who will be potentially affected by those fires: In the past 40 years, the number of Americans living in WUI lands has doubled, and 60 percent of new homes have been built on WUI lands since 1990.

The fire hazard severity zone for Southern California shows very high risk for exurban communities

Communities that abut fire-prone lands often tout the steps they’re taking to prevent fires, like smoking bans and aggressive brush clearance policies. But a study of WUI lands published in Nature says that’s not enough. The problem is that people still think of wildfire as something that can somehow be prevented. In fact, fire is inevitable, argues the study. And if suburbanization doesn’t allow the landscape to regenerate naturally, years of accumulating dead timber turns a manageable fire into a megafire.

“The ‘command and control’ approach typically used in fire management neglects the fundamental role that fire regimes have in sustaining biodiversity and key ecosystem services,” writes the lead author Max A. Moritz. “Unless people view and plan for fire as an inevitable and natural process, it will continue to have serious consequences for both social and ecological systems.”

After looking at several particularly devastating WUI fires, the study authors recommend that the best way to protect humans from increasing risk of fire is actually an urban planning shift towards risk management and recovery—in other words, thinking about wildfire just like any other natural disaster. This would mean treating the way we build in fire-prone areas much the way construction is handled in other high-risk areas like on floodplains or near fault lines.

An Oakland Hills house designed after a catastrophic 1991 fire that killed 25 people and destroyed 3,500 homes uses fire-resistant steel and concrete
Courtesy Leger-Wanaselja Architecture

There have been some recent attempts to change the way WUI communities are designed. Earlier this year, President Obama signed an executive order that moves towards new building codes which encourage the use of fire-resistant materials, and larger efforts to clear dead trees, in a practice called fuel reduction.

The most effective way to mitigate WUI fires will likely be controversial in the neighborhoods that are most at-risk. Prescriptive burns, which help with fuel reduction in the way that nature intended, are by far the best ecological choice. But they’re not very popular with people who would prefer not to have their lucrative real estate investments against the backdrop of a charred, ashen landscape.

Then again, when the alternative is losing a home entirely, what’s a blackened hillside for a few years?