California burns every year. But amid a record-breaking heatwave, 2020 is the fieriest year yet.
As The Economist went to press, more than 7,600 fires had burned over 2.5m acres (1m
hectares) of land. The season still has months to run.
That fits a long-term trend, for California's wildfires are getting steadily worse. Blazes in the
2010s burned 6.8m acres on average, up from 3.3m acres in the 1990s.
The fire season lasts nearly three months longer now than it did in the 1970s. Over the past
decade, the state has spent an average of $3.7bn a year fighting fires.
Add the cost of rebuilding, treating casualties and restoration, says Headwaters Economics, a
think-tank, and that is perhaps a tenth of the total cost. Although smaller than this year's, the
2018 fire season was particularly destructive. It killed 100 people and burned tens of thousands
of buildings.
The reason is a double whammy of climate change and development. More homes are being
built next to forests, in what experts call the "wildland-urban interface" (WUI).
A 2018 study estimated that roughly a third of American homes were in the WUI. The problem
is acute in California. Pricey housing has pushed people onto cheaper land close to the
wilderness.
At the same time, climate change is extending the dry season, which stores up fuel for fires. In
California, a chronic "megadrought"-in which dry years become more common and wet ones
scarcer-is making matters even worse.
One paper, citing tree-ring data, concluded that the drought, which started around 2000, is the
second-worst in the past 1,200 years. It, too, has been linked to climate change. Since neither
trend shows much sign of reversing,
people on America's west coast will have to learn to co-exist with more, and more frequent,
fires. "It's not that different to building on an earthquake-prone landscape," says Max Moritz, a
wildfire expert at the University of California at Santa Barbara.
Buildings and communities can be built in such a way that fires sweep through them-or better
still, around them-leaving them more-or-less intact. Infrastructure can be made more resilient.
And forests themselves can be managed to reduce the risk of catastrophic blazes.
Start with the buildings. Most buildings burn not when the flaming front of a fire reaches them,
but when embers (also called "firebrands") thrown off by distant fires land on them.
A 2010 paper tracked how a 1991 fire in Oakland Hills burned steadily in a cluster of houses
before embers were lifted by strong winds, landing on other houses hundreds of metres away
and igniting more than a dozen new "spot fires".
Estimates of the share of buildings lost to firebrands vary, but all are large-between 60% and
90%. Clever design can help make buildings resistant to fires that spread in this way.
Materials such as concrete, adobe or stucco are a better bet than cladding walls in flammable
wood. Some composite panels promise to hold back the flames for two hours or more. Gaps
under roofs can be blocked up, to stop embers drifting in.
Vents can be covered with mesh, or eliminated entirely. Heat-resistant windows, which are less
likely to break, help keep firebrands out. Experts recommend a five-foot "non-combustible
zone" around the base of homes.
Neighbourhoods can be toughened up, too. In a report published in April, Dr Moritz and his
colleague Van Bustic at the University of California in Berkeley describe how entire communities
can be planned to resist fires.
Building near water is one tactic. But moats are not the only defence. Open agricultural
lands-including the vineyards common in the Napa Valley- can offer a useful buffer, too.
Even golf courses can serve as firebreaks. Rather than lining the greens with homes, Dr Moritz
suggests doing the opposite, and putting houses in the middle. Burying electricity lines can help
avoid blackouts, as well as subsequent costly rebuilding.
It can also prevent power lines themselves sparking fires. That is a persistent problem in
California, and one which has cost Pacific Gas & Electric, a utility, billions in settlements.
Australia, which also suffers from wildfires, has experimented with bunkers specially designed
to withstand flames for an hour or more- long enough for a flaming front to move through.
These offer a last-resort option for trapped residents.