The disastrous wildfire chewing through Yosemite National Park won't be the last blaze of a hot, dry summer in the West. Why there are more fires to come

Justin Sullivan/Getty Images The Rim Fire has charred parts of Yosemite National Park and threatened San Francisco

Here’s the good news, of sorts, as a massive wildfire eats through the heart of Yosemite National Park and threatens the water and power supplies of San Francisco: it could be a lot worse. For all the attention around the Yosemite fires — and earlier fires in Arizona that led to the deaths of 19 elite firefighters — compared with the past several years’, this fire season has been mild. More than 31,900 fires have burned some 3 million acres (1.2 million hectares), compared with the 67,700 fires that burned more than 9 million acres (3.6 million hectares) last year in the second worst fire season on record.

Still, the Rim Fire near Yosemite is devastating, already the 14th largest wildfire in California history — and it’s far from done. The state has long been accustomed to wildfires — dry weather, ample forests and lots of people are a dangerous combination — but the conditions on the ground this year couldn’t be worse. California is suffering through the driest year to date on record, receiving a record low of 4.58 in. (11.63 cm) of precipitation during the first six months of the year. That’s nearly 10 in. (25.4 cm) below the average, even as a brutal heat wave earlier this summer sucked the remaining water from the ground. The result is forest as tinderbox, making infernos like the Rim Fire just a matter of time.

(MORE: Ocean Acidification Will Make Climate Change Worse)

As Andrew Freedman pointed out in a good post over at Climate Central, the drying and drought conditions in California are being seen throughout much of the West, making fires all the more common:

Parts of the West have been warming faster than the rest of the lower 48 states since the 1970s, a trend tied to climate change as well as natural climate variability. Anthony Westerling, a climate scientist at the University of California at Merced who studies how climate change affects wildfires, said that increasing temperatures promotes evaporation, which leads to more frequent instances of ‘extreme fire conditions.’

Nor does it help that snowpack levels in the Sierra Nevadas this year were well below normal, which is another factor priming the forests to burn. Expect that to become more common in the future as well as winters warm, ensuring that what winter precipitation that does fall comes increasingly as rain, rather than snow. A study published in June projected that snowfall levels in the mountains surrounding Los Angeles could fall 30% to 40% below 2000 levels by midcentury.

Forest fires in the West do seem to becoming more common. A University of Arizona report in 2006 found that large forest fires have been happening more often in the western U.S. since the mid-1980s, a period when temperatures have been on the increase. A 2012 study found that climate change is likely to significantly change the fire pattern around the planet by the end of the century, with increases projected in the high-altitude boreal forests in the northern hemisphere — which happens to include places like Yosemite. Climate change is expected to increase periods of intense heat and intense dryness, even as precipitation increases globally overall. That’s a formula for more fires.

(MORE: As Northeast Asia Bakes, Climate Scientists Predict More Extreme Heat Waves on the Horizon)

But forest fires aren’t just a function of the climate and the weather. Firefighting policy may play a role as well. For decades the U.S. Forest Service’s policy has been to suppress all fires, including the natural blazes that have long been a part of the ecology of the Southwest, even well before human beings came on the scene. As a result, forests become denser, as brush that would otherwise burn in smaller natural fires builds up. So when a fire does break out, there’s a lot more fuel to burn, as Craig Allen, a research ecologist at the U.S. Geological Survey in Los Alamos, told Brad Plumer at the Washington Post:

The basic story has been a convergence of climate and changing fuels in the forests due to land use. And this wasn’t even a partisan issue — it’s been the standard practice of forest management for the past century.

Of course, one of the reasons that the Forest Service has sought to suppress wildfires whenever possible is that more and more people have moved into once remote and underpopulated forests in the Southwest. The investigative-journalism group I-News estimates that over the past two decades, a quarter-million people have moved into Colorado’s red zones, the parts of the state most vulnerable to forest fires. People can help start forest fires — accidentally and on purpose — and their property adds to the damage wrought by any blaze.

So forest fires are bad, and they’re likely to keep getting worse. That might be the case this year — the fire season is far from over, and California could be in further trouble if the fall’s Santa Ana winds, typically the harbinger of forest fires, are especially hot and dry. (Joan Didion called it “malevolent persistent wind,” and Raymond Chandler wrote that on nights the wind blew, “anything could happen.”) Even worse news: for the second straight year the federal government has already run through its budget for fighting wildfires, with months left in the fire season. There’s more to burn.

MORE: As Temperatures Rise, Empires Fall: Heat and Human Behavior

