Horses as evacuated as the Prado Dam fire rages in California, 19 April 2015. Photo: NBC News

By Linda Carroll
25 April 2015

(NBC News) – There was a time when fire season in California started around May and went through September. Now, thanks to a drought that's stretching into its fourth year, the state seems to have become a year-round tinderbox.

The long running drought has "created explosive fire conditions," said Mike Mohler, a fire captain with the California Department of Forestry and Fire Protection (CAL FIRE). "Five years ago without a drought in California you would still get wildland fires. But the vegetation wouldn't burn as quickly. Now there's zero moisture and you get explosive fire growth."

The drought has fed into a trend that's been developing for over the past decade, said Daniel Berlant, chief of public information for CAL FIRE.

"Since 2000 we've been seeing larger and more damaging fires," he said. "What we're seeing now is that the rain is starting later and stopping much earlier. The fires are burning at explosive speed because the vegetation is so dry and that allows them to get much larger."

It's not just the low precipitation that's the problem, Berlant says. It's also the higher temperatures.

Those high temperatures are baking the moisture out of the soil and air, leaving vegetation especially dry and vulnerable to catching fire, said Park Williams, an assistant research professor at the Lamont Doherty Earth Observatory of Columbia University.

Rising temperatures alone can boost the risk of wildfires, Williams said. "When you see wildfires in the Sierra Nevada and Northern Coast Ranges occurring early in the season it's a testament to how warm conditions have become in spring," he adds.

In a recent study published in the International Journal of Wildland Fire, Williams found that, in the Southwest, rising temperatures raised fire risk even in wetter years. That finding is likely to hold true for California, too, he said.

"Forests are excellent gauges of climate because they are not irrigated and they live for a very long time, allowing for tree-ring records and other aspects of forests to tell us how recent conditions fit into a long-term context," Williams said. "As temperatures rise, the amount of water necessary to reduce a forest's flammability goes up. In the absence of substantial increases in precipitation, warming causes increased flammability, and that very reliably translates to increased areas of forest burned."

The hot and dry conditions seem to have boosted the likelihood of fires in California even in the early part of this year. In past years on average between January 1 and April 18, there would be 492 fires burning 1,300 acres. During the same time period in 2014, it was 862 fires burning 2,417 acres, and in 2015, 838 fires scorching 3,534 acres.

In just the past week, there were more than 170 new wildfires that popped up in California.

Although the ongoing drought has intensified the problem, there's been a growing trend toward greater flammability in California.

"Over half of the top 20 largest wildfires have occurred since 2000," CAL FIRE's Berlant says. "It's important to note that the drought hasn't created the problem, it only magnifies it. Because the vegetation is so dry it burns at an explosive rate. And then the fire gets large before we can even get on the scene. In the King Fire last year we saw about 60,000 acres burned in a six-hour period." [more]

California Drought Drives an 'Explosive,' Longer Wildfire Season



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