Rancho Palos Verdes Fire Destroys Homes, While Others Threaten L.A.

Smoke from fires in Angeles National Forest near Los Angeles, California.

Photo: Kevork Djansezian / Getty Images

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With one wildfire already having destroyed buildings in Rancho Palos Verdes, three other wildfires are raging across Southern California in the suburbs of Los Angeles. Hundreds of residents have been told to evacuate La Canada Flintridge.

The fire season suddenly sprang to life as dry conditions and high heat made conditions ripe for fire. (Global warming is expected to make heat waves more frequent and intense in Southern California and elsewhere, according to a recent report.)

Overall, 2009 to date has witnessed more fire than average, but fewer acres burned. Through Thursday, 64,172 had burned more than 5.2 million acres (approaching the size of New Jersey), according to the latest wildfire statistics from the National Interagency Fire Center. That's about five more fires than the 10-year average, but 7% fewer acres.

Forecasters expect this and subsequent seasons to be wicked. A forecast recently released by the Forest Service says hot, dry weather should produce an above-average fire season, according to press reports. An historic drought in Texas and other Gulf Coast areas could see some relief thanks to the onset of El Nino conditions (though it hasn't yet), and the persistent drought in California and Nevada isn't expected to abate (the U.S. Drought Monitor called the annual monsoon season "dismal".

And the coming years will only see the fire season get worse. That's nothing new: Scientists have said that global warming has already caused the fire season to lengthen and intensify across the West, and that it would continue to do so in the coming decades. Gov. Arnold Schwarzenegger famously declared the end to a single fire "season," now that a persistent drought and an altered climate have made the California landscape fire-prone year-round. (Forest management and the suburbanization of forested and fire-prone areas also are key contributors to risk of fires and fire damage, but scientists have separated out the various risk factors and determined that climate change is alone a driving force, independent of the other factors.)

A recent study published in the Journal of Geophysical Research quantifies the risk in what authors characterize as a "conservative" estimate: The area burned by wildfires will increase 50% by 2050, with the Rocky Mountains (175% increase) and the Pacific Northwest (78% increase) shouldering the brunt of the new burn.

The bigger fires will also contribute to a 40% increase in soot in the air, a serious pollution problem that affects human health and visibility at national landmarks like the Grand Canyon. Another study recently published in Forest Ecology and Management points out how global warming seems to be affecting some of our most cherished national landmarks, too: From the 1930s and 19902, large trees in Yosemite National Park declined 24% and the remaining trees are more likely to be intolerant to fire. Both conditions make it more likely that these trees will succumb to fire, and researchers say climate change is one likely cause of the change in forest composition.

How Global Warming Increases Wildfire Risk

How does global warming increase wildfire risk? By creating conditions on the ground that increase the chances of a new fire forming: Global warming results in more hot, dry days ripe for a fire, dries out vegetation to make it combustible and can even provide the spark. Here's how The Daily Green explains it:

1. More heat equals earlier snow melt.
A buffer to the Western fire season is high mountain snow and ice that accumulates through the winter and melts through the spring, running off and irrigating the valleys below. Global warming is creating conditions that lead to less snow and, more consistently, more evaporation and a faster, earlier runoff. That leaves the valleys below more prone to drought earlier in the year, and more prone to extreme drought throughout the year. Drought dries out trees, shrubs and grasses, making them combustible.

The figure at right shows projected future changes in the timing of runoff in snow-dominated areas of the western United States. The timing of runoff shifts earlier in almost all areas as greenhouse gas concentrations increase. These snow-dominated areas currently act as natural reservoirs, with melting in the spring and summer providing critical fresh water throughout the western United States.
Credit: Purdue University/Diffenbaugh Laboratory

2. More heat equals more evaporation.
Similarly, whatever moisture does flow into the valleys is more likely to evaporate before it sinks in and nourishes plants, leading to drier vegetation.

3. More heat equals new tree pests.
As the West has warmed, pine bark beetles have spread throughout millions of square miles of forest from New Mexico up into Canada. As the bugs do their work, trees are weakened or killed, creating yet more wild firewood.

4. More heat equals stronger storms.
Scientists have predicted -- and observed -- the formation of more frequent, intense storms as a result of a warmer climate. That means two things: One, more frequent thunderstorms and lightning strikes that can naturally ignite wildfires; and two, flashier rainstorms that result in bursts of rain running off in streams, rather than soaking into the ground and substantially irrigating the landscape.

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