Questions, theories of why this is happening

The fires sweeping Southern California raise provocative questions about global warming, growth and even evacuation patterns, underscoring how little we know at a time when more people are settling on the fringes of wilderness.

In the past four years, two closely spaced, horrific fire seasons have struck the south state.

In a region known for sporadically devastating blazes, the latest fires could be nothing more than natural variation, or they could be an early sign of the climate extremes that may accompany global warming.

Either way, the impacts of such major fires are wide-ranging – and growing. While at least 80,000 residents fled Southern California fires in 2003, this time hundreds of thousands are on the move.

"We're really dramatically increasing our population in the western United States in these very arid regions," said Anthony Westerling, an environmental engineering professor at the University of California, Merced, who has studied the role of climate in the 2003 fires.

He warns that along with global warming lurks another, serious risk: sharp climate variations that have sparked major droughts on this continent over the past 2,000 years.

"We're pushing ourselves closer and closer to the limits of our vulnerability, and we've only got 100 years or so of experience to draw on," Westerling said.

He wasn't ready to lay the blame for these fires definitively on human-induced climate change, caused by burning fossil fuels that release greenhouse gases.

There are just too many other factors driving droughts, although Westerling and several other scientists say that, as trends are tracked for the next 20 years or so, this dry spell could add a piece to the climate change puzzle.

"Some speculate these extremes will become more normal, if you will," said Mark Svoboda, a climatologist at the National Drought Mitigation Center at the University of Nebraska.

"I think the jury is still out on that," he said. "It's early to say."

Southern California is in the grip of a deep drought. Los Angeles received just one-fifth of its normal rainfall last winter, its driest water year on record. San Diego had its third-driest year.

The drought that baked forests and grasslands, providing fuel for wind-whipped flames, is an underappreciated hazard for much of the southern United States, said Svoboda.

"Droughts are a very normal part of the climate cycle. ... They can last months or they can last years," he said.

While we don't have enough data to say whether droughts are increasing, Svoboda said, we do know that burgeoning populations are making bigger demands on a finite amount of water.

"That makes it tougher for us to adapt," he said.

The challenges come not just in water supply, but in how people live in a landscape that can turn dangerously dry.

In Southern California, the wooded outskirts of cities, where houses intermingle with the natural vegetation, can be especially precarious.

Known by ecologists as the "wildland-urban interface," these coastal hills and arroyos are predominantly chaparral, the perfect fuel for wildfires.

The evergreen thickets of manzanita, sage and rosemary contain highly flammable oils. The whitethorn ceanothus is tough on crews cutting fire breaks. And the deadwood of the scrub oaks and mountain mahogany make excellent kindling.

Yet growing numbers of Southern Californians are immersing themselves in chaparral. Of the 90,000 San Diego County homes built in the 1990s, 72,000 of them – three out of four – were in wildlands, said Volker Radeloff, a University of Wisconsin ecology professor who studies development in fire-prone regions.

"These are attractive places to live, but they are the worst from a fire-safety point of view," Radeloff said.

Sometimes, it takes disaster to hammer home the risks.

After 22 people died in the 2003 south state fires, some while trying to flee swift-moving flames, "we learned our lessons," said San Diego County spokesman Luis Monteagudo. "We're doing a better job communicating, coordinating with all the agencies," he said, and have improved a phone system that can call hundreds of thousands of households to alert them to emergencies.

In addition, "We've been stressing to people that when we tell you to evacuate, don't wait around. Don't hesitate. Evacuate," Monteagudo said. Residents in areas that might be at risk are being alerted to pack up and get ready in case an evacuation order is issued.

The biggest factor driving the massive 2007 evacuations in San Diego County is that this year's fires are more widely scattered than those of four years ago, Monteagudo said.

Coming a close second, though, is that previous fire deaths and Hurricane Katrina have combined to raise people's awareness of how deadly natural disasters can be.

"People have a better understanding now that when they're told to leave, they should leave," he said.

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