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Fire in California is just part of the natural order. Forests there have always burned. But scientists say the way people manage forests, on top of a changing climate, has created an environment in which big fires thrive. NPR's Christopher Joyce reports on what's driving these megafires.
CHRISTOPHER JOYCE, BYLINE: As the fires in California spread last week, President Donald Trump blamed poor management of forests by the state. Yesterday, California Governor Jerry Brown hit back. He said, yes, managing forests is one part of the solution. However...
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JERRY BROWN: Managing all the forests in every way we can does not stop climate change. And those who deny that are definitely contributing to the tragedies that we're now witnessing and will continue to witness.
JOYCE: Fire experts agree. In California, the average temperature has risen at least one degree Fahrenheit since the middle of the last century, in some places even more than that. In a dry climate, it's a simple equation. More heat equals more drying. Hot, dry air literally sucks the moisture out of the ground and out of vegetation.
JENNIFER BALCH: With just a little bit of drying, you get a substantial increase in the amount of burning.
JOYCE: Jennifer Balch is a fire ecologist at the University of Colorado. She studied fire in the Amazon as well as the American West. In the West, recent years of severe drought have brought more big fires. But it started decades ago.
BALCH: What the trend has been is that we've seen the number of large fires increase fivefold since the 1970s.
JOYCE: The warming climate is also responsible for smaller snow pack in the California mountains. That's the source of much of the state's water. Less snow pack means drier conditions in many parts of the state. And scientists recently found that a warming climate seems to be reducing the amount of fog that rolls in off the Pacific Ocean, another cause for dry vegetation.
People's carelessness also can make things worse. Balch notes that 84 percent of the wildfires in the last 20 years were started by people. And people are putting themselves more at risk.
BALCH: We also have more and more people literally building homes in the line of fire. Today there are about 1.8 million homes at high fire risk across the western U.S.
JOYCE: So California and the West are caught between a changing climate as well as a growing population moving into those risky neighborhoods. Malcolm North is an ecologist with the U.S. Forest Service. He says the dry weather and strong winds mean small fires are bigger now. And big fires become monsters, the kind that both damage trees and climb up into the tree canopy and kill whole forests. And it's relentless.
MALCOLM NORTH: In much of California, we're getting to a - pretty much of a year-round fire season, as in the past it used to be limited to more, like, five or six months out of the year.
JOYCE: North notes that forest managers spent the last century putting out every fire they could. Without small natural fires, forests get choked with too many trees now ready to burn. Federal and state managers can and do thin out forests, either by cutting some of the trees or burning some of the overgrown areas. But steep slopes, protected wildlife or complaints from homeowners about smoke limits where they can do that. So North says the forests are still tinderboxes.
NORTH: Literally probably 80 to 90 percent of these dry, mid-elevation forests are chock full of fuels that really drives high-intensity fire.
JOYCE: The kinds of fire that nature rarely ever produced before. Christopher Joyce, NPR News.
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