Last week, firefighters held the line along Highway 101 in Sonoma County as the Kincaid Fire raged. They ultimately succeeded in preventing the fire from jumping across the highway, where it would have found a dense, tinder-dry forest that had not burned since the 1940s. This plentiful fuel, along with powerful winds, would likely have driven the fire all the way to the Pacific Ocean and the town of Bodega Bay, after having first engulfed communities along the Russian River.
While California has suffered a string of historic fires in recent years, the problem has been getting steadily more costly for decades. Since 2014, California has used nearly 90 percent of the FEMA funding allocated to states for wildfires, up from a mere 15 percent between 1988 and 2013.
But it’s not just rising cost. The fires themselves are also getting worse. A 2019 study showed that the annual area burned by wildfires in California has increased by 500 percent since the 1970s.
Why is California’s wildfire problem intensifying? Climate change and faulty power lines are a frequently cited culprit, but such explanations miss a basic dynamic in fire risk and arguably a more proximate cause. More development in fire-prone areas certainly puts more people and property in harm’s way and brings more electrical infrastructure to spark fires, but it also raises the incentive to suppress them. And successful fire suppression, paradoxically, increases fire risk by enabling the growth of dense vegetation that serves as abundant fuel in dry conditions. But the controlled burns and vegetation clearing that is needed to lower fire risk may not be the most popular solution among local communities.
Without a doubt, climate change is at play. A 2016 study showed that climate change is responsible for over half the increase in fuel aridity (drier fuel load), and has doubled the cumulative forest area burned. Rising average global temperatures have led to higher spring and summer temperatures, which in turn have led to earlier spring snowmelt. Further, there is evidence that climate change is causing winter rains to come later in autumn, and stop earlier in spring. This is extending the area and time periods in which forests become combustible, and in parts of California, fire season is now 50 days longer than in 1979.
In addition to climate change, California faces natural variability in precipitation that leads to drought conditions. Drought has weakened trees and led to massive bark beetle outbreaks in the Sierra Nevadas, killing up to 70 percent of the trees in high impact areas and increasing the fuel load for fires.
California also suffers from variable extreme wind events, which have triggered some of the most destructive fires in the state with wind speeds topping 100mph. With climate change pushing the rainy season back, these wind events will converge more often with a dry and highly flammable landscape.
But as impactful as they are, anthropogenic climate change and natural variability are best understood as amplifying a more immediate cause.
As of 2010, more than 30 percent of the housing stock in California was in the wildland urban interface (WUI), defined as development in close proximity to large patches of wildland or within wildland itself. This number has most likely grown sharply in the past decade.
The drivers of housing growth in the WUI are complex. People move to be closer to nature, to have a lower cost of living, and because their livelihoods depend on proximity to natural resources — for example, those in the timber and ranching industries.
While the drivers are debatable, their effect on fire risk is not. When homes, roads, and distribution lines are in close proximity to the WUI, it increases the risk of ignition and the pressure to suppress fires. And the resulting build up of fuel means that when fires do start, they burn much more intensely and are much more challenging to control.
The long-term risks of fire suppression can be mitigated with practices like prescribed fires and vegetation removal, but more development in the WUI introduces a barrier to the execution of these measures: opposition from local landowners.
Human activity has long disrupted natural fire cycles. In California and much of the western US, ecosystems are adapted to cyclical wildfire patterns. These natural fire regimes have been disrupted as a result of America’s long history of fire suppression, which started in the late 1800s in an effort to protect timber supplies and watersheds. This suppression built up a backlog of forest restoration needs — the US Forest Service now estimates that between 65 and 82 million acres are in need of restoration across National Forest lands.
The incentive to suppress fires has only intensified as land managers struggle to protect homes in California’s expanding WUI, and this dynamic is likely a key factor in why California fires have become less frequent but larger over time. Today, the biggest concentrations of forested WUI are in the foothills of the central Sierra, around the margins of the San Francisco Bay Area, and in the mountains of Southern California. These areas are also where we have seen some of California’s most destructive fires.
When homes, roads, and distribution lines are in close proximity to the WUI, it increases the risk of ignition and the pressure to suppress fires.
Compounding the problem, more costly fires have also made it more difficult to fund the forest management needed to control them. From 1995 to 2017, the percentage of the US Forest Service’s annual budget spent fighting fires rose from 16 percent to more than half. In response, the Forest Service has been forced to pull funds from other programs to cover the cost, a practice called “fire borrowing.” Often, this means less available money for proactive forest management, such as prescribed burns and the removal of dead trees and brush. In California, federal agencies have a critical role to play in managing wildland — fifty-seven percent of the state’s 33 million acres of forest are controlled by the federal government.
More money allocated to forest management is an obvious fix, and more money is indeed on the way. In 2018, Congress passed a measure giving the Forest Service an additional $2 billion a year to tackle firefighting needs starting in 2020, which will free up additional funds to help manage forests. But restoring natural fire regimes to the landscape will take decades of collaborative work between federal, state, and local stakeholders.
Development at the WUI isn’t going anywhere. People aren’t going to stop wanting to live closer to nature or find more affordable housing. While insurance markets may respond by making such development more costly, we should be realistic about the persistence of existing WUI development, and that burying or hardening power lines alone will not negate the threat.
A critical solution may be as necessary as it is unpopular: stricter rules for future wildland development in a state already suffering from a housing crisis, and stricter vegetation controls in communities that cherish access to natural landscapes.
As much as climate mitigation can prevent wildfires from getting worse over the long term, it will do nothing to prevent the wildfires we face today.