Two of the largest wildfires in California’s history swept through the Bay Area region this month, scorching hundreds of thousands of acres as they left a path of destruction in their wake. Thousands of homes and infrastructure fell victim to the blaze as countless others remain threatened.

“We’ve never seen fire of this scale in this part of the state,” California Gov. Gavin Newsom said on Wednesday. “It demonstrates the reality – not just the point of view – of climate change and its impact in this state.”

While climate change is largely to blame for the drier, hotter conditions fueling the flames, the conversation has also turned to the growing wildland-urban interface (WUI). This term refers to the dense areas of housing development that commingle with natural terrain that’s historically prone to wildfires. In other words, as more people move into the WUI, they’re more likely to be affected by wildfires.

At the same time, those natural fires that help to regenerate forests and renew soil are suppressed, causing them to burn more severely later and consequently cause more damage.

The Chronicle talked to J. Keith Gilless, the dean emeritus of the University of California’s College of Natural Resources and chair of the California Board of Forestry and Fire Protection about what you need to know.

>> Why has the WUI recently become such a widely discussed topic?

“The losses of homes and other structures in the fires California has experienced over the last decade have drastically changed people’s perceptions of wildfire,” said Gilless.

“People are now thinking in terms of how fires affect communities to a much greater extent, whereas in the past, it was more of an environmental impact,” he continued. “We did have catastrophic fires, but the frequency of fires that have burned hundreds of homes has not been lost on the public. It makes us think: Are we living in a way that is consistent with the natural fires that characterize California?”

Though Gilless believes that the devastation caused by the wildfires is comparable to the catastrophic structure losses following the Loma Prieta earthquake in 1989, he said people are reacting with more urgency due to the sheer frequency of wildfires they’ve faced in recent years. That frequency, he added, is highly unusual.

“Normally, people are exposed in a significant way to some natural hazard that’s characteristic of where they live very few times over the course of a lifetime,” said Gilless. “Due to the recent wildfires in both Northern and Southern California, wildfire as a natural hazard has been brought to the consciousness of the public on a much more frequent basis than some other natural hazards, which are just as serious and should require just as organized of a social response.”

>> What’s the difference between “good” and “bad” fires — and why do I keep hearing about them?

Establishing a clear distinction between the two helps provide a more nuanced message to the public, said Gilless.

“The whole Smokey the Bear message seems to tell us that all fire is bad, which is not the case,” he added. “Fire is a part of our lives and will be a part of our lives, no matter what actions we take. We have to find a way to live with fire.”

Historically, the state's attempts to suppress wildfires have led to higher rates of “fuel loading,” or the rate of fuel volume per acre where a fire is taking place. The higher it is, the more heat a fire will produce. Good fire, then, is fire that acts to reduce fuel loading and eliminate latter fuels. These fires also cause what Gilless calls “good mortality” because they create an environment that’s conducive to the needs of certain species of wildlife.

“It’s also patchier on the landscape in the sense that we don’t create homogenous forests,” he added. “Having the burn there that’s light enough and on a scale consistent with the inherent regenerative mechanisms of the forests makes a good fire.”

Conversely, bad fires not only create a vast area of high mortality, but damage wildlife habitats for several species.

“They create a landscape where the scale of the efforts that are necessary to restore it are not ones that our political process is used to dealing with,” he said. “The bigger the scale of the fire, the harder it is to say, ‘How will we deal with this in a timely fashion? What resources will be mobilized? Where will the financing for reforestation come from?’ You’ve got the spikes and the need for a social response that affects institutions and budget mechanisms.”

Referring to recent lightning complex fires, he added, “Part of the problem there is if you’re set up to attack fires in one county and are faced with hundreds of lightning strikes in that area, you might find you have to respond to more incidents than you have the resources to deal with in your usual fashion.”

>> How many Californians are living in the WUI? 

According to a 2018 study from the National Academy of Sciences, approximately one in three houses are now in the WUI across the United States. Though the states with the largest WUI areas are Georgia, North Carolina, Pennsylvania and Texas, California touts the largest number of houses inside the WUI (4.5 million, according to U.S. Census data), as well as the greatest number of people – 11.2 million – living in it.

Additionally, nearly half of the homes built in the state of California between 1990 and 2010 are based in WUI zones, putting these households at “high or extreme risk for wildfire,” according to the Center for Insurance Policy and Research.

>> So, why live in places that are prone to burn?

As the high costs of housing in California continue to climb, so does the pressure to develop in less-populated regions of the state. Much of the housing development in the WUI is simply more affordable, also luring people in with the promise of clean air, gorgeous views and a natural setting.

"We have a large population. We’ve had a large growing population; people need housing," said Gilless. "I’m more concerned that we build housing cognizant of the risks inherent to any area we might build than that we declare some portions of the California landscape off limits to housing.”

>> Should we limit the amount of development in the WUI?

“This is a complex topic, and some of the rhetoric strikes me as perilously close to blaming the victim,” explained Gilless, who added that fire is “a fundamental ecological driver” in Northern California's Mediterranean climate.

“It’s true that this is a natural hazard unlike any other. It’s a part of the environment you live in, and you need to be cognizant of the measures you should take against the risk. But it’s interesting to me that we never talk about how crazy it was to build cities on top of earthquake faults in the same way. We don’t tell people to move to areas that are less seismically active.”

Yet, the WUI is one of the most rapidly growing classifications of land use in the United States, with the majority of it – 97 percent – going toward new housing.

>> With that in mind, how can these communities adapt to living in places that burn?

Gilless believes that there are several mitigation strategies that could protect people living in the WUI – and that the government has a big role to play at a federal and local level in ensuring they are implemented.

“We need to ask, ‘What does our experience and science tell us about what kind of road networks are necessary to support public safety actions at the same time they’re supporting evacuations in the other direction?” said Gilless.

This includes specifying building codes that are consistent with the natural hazards in the WUI – similar to how construction in cities like San Francisco and Los Angeles need to be cognizant of the threat of seismic activity, he said.

“You should not be building a house with a brick foundation in these cities any more than you should be building a house with attic vents that aren’t designed to prevent ember intrusion into your attic space,” he said.

Amending requirements for new development as well as retrofitting the infrastructure of the WUI — considering types of windows, siding, roofing material, plus the amount of vegetation people should be expected to maintain — are all helpful ways to mitigate the risks of wildfire. Home insurance could also be a key component in discouraging residential overgrowth in WUI zones and reducing firefighting costs. Making changes in the transportation sector to improve air quality is yet another solution. Then again, who is responsible?

“That’s no longer a science discussion, but a tough one of public policy,” said Gilless. “Sure, we could do more studies to ensure the risk or benefit can be quantified in a way that insurance markets can function efficiently. But in the meantime, when communities recognize these risks and organize themselves effectively with local Fire Safe Councils, engaging in good evacuation planning at a grassroots level … that’s crucial. When you have a rapidly evolving situation, neighbors save neighbors.”

“I’m very sad about why communities are becoming more organized in response to this hazard,” he continued. “But it’s great to see people doing it – it’s a way to live in harmony with the environment in which you’ve chosen to be.”