Global warming may bring more infernos in San Diego: Scientists say 2003, 2007 fires may usher in an age of megafires

North County Times (San Diego, California): After dodging two waves of catastrophic wildfires in four years, surely we don't have to worry about another one invading our neighborhoods for a while, right? Not so fast. Some climate experts say last month's enormous, wind-driven infernos, which torched 368,000 acres and destroyed 1,751 homes and businesses in San Diego County alone, could become a regular feature of life in Southern California. "There is more to come, unfortunately," said Thomas Swetnam, director of the University of Arizona's Laboratory of Tree-Ring Research, in a telephone interview last week. We may be able to thank global warming for that.

... "There is a potential for the Southwest to more or less enter a permanent dust bowl situation," Swetnam said. "The extended drought that we are in now may become the norm." Southern California is in store for "a big, heavy drying spell," said Norm Miller, a climate scientist at UC Berkeley's Lawrence Berkeley National Laboratory. Miller is a member of the Intergovernmental Panel on Climate Change, which published several global warming reports and shared the Nobel Peace Prize with Al Gore this year. Miller said 19 of 23 climate models scientists developed for California suggest many future storms will veer north, showering Seattle with more rain than it receives now and causing less to fall between Sacramento and the border. And, he said, "we're seeing more heat waves in Southern California. They're just going off the charts."

Making matters worse, Miller said, the hotter and drier conditions are likely to be accompanied by more episodes of hurricane-force Santa Ana winds that peak around Thanksgiving, rather than at the end of October. Miller and Nicole Schlegel, a scientist at UC Berkeley's Department of Earth and Planetary Science, highlighted the increased Santa Ana threat in a study published in August 2006 in the Geophysical Research Letters, a monthly publication of the American Geophysical Union. The University of Arizona's Swetnam termed it the first significant peer-reviewed study linking climate change with the future of wildfire in Southern California, although one that has yet to be verified by other studies. Miller said more wind not only could mean more fires overall, but more mammoth ones like those that ravaged five Southern California counties last month.

But some scientists say it is not a foregone conclusion that megafires will flare up more often. Tony Westerling, a UC Merced professor of environmental engineering and principal investigator for the California Climate Change Center at UC San Diego's Scripps Institution of Oceanography, said that is because the fires of the future will depend on many factors, not just warming. "Climate matters, but (its effect on Southern California fires) is sort of marginal compared to other places," Westerling said. "This is a place that (already) gets hot and dry every summer." And the region's signature chaparral and coastal sage scrub plants already burn on a regular basis, he said. Given that, extra Santa Anas may or may not significantly increase the fire threat, Westerling said. Because those winds are expected to arrive late in the year, they could follow rain at times when it is cooler and not trigger more fires, he said. "The reason Santa Anas matter so much in October is because you're coming off of the long, hot summer," he said.

However, Miller said those predicted extra winds are likely to follow on the heels of an even longer dry season that will persist through December. Westerling countered that while it is fairly certain the region will get hotter, it is unclear whether the heavily populated portion of Southern California on the coastal side of the mountains will get drier. He said some models suggest the region will receive less rain than now, while others suggest San Diego County and western Riverside County will become wetter. "It's not a simple story," Westerling said.

Nor is there a simple answer for the question of whether this year's fires are a direct consequence of global warming, scientists say. That's because conditions that contributed to the firestorms, such as the recent drought, Santa Ana winds and dry plants, cannot be linked conclusively to global warming, Swetnam said. It is in fact difficult to link any one event, including the Hurricane Katrina disaster of 2005, to global warming, Swetnam said. One can say only that, as climate changes become entrenched, the odds are Southern California firestorms will return more often, he said.

Hugo Hidalgo, a project scientist with the Scripps Institution of Oceanography, said the evidence is abundant, however, that the drought conditions that influenced the fires are being fueled in part by a weather phenomenon called La Nina. The climatic opposite of its better-known cousin, El Nino, which occurs when central Pacific waters warm more than normal and send heavier-than-normal rainfall California's way, La Nina occurs when the ocean is cooler than usual. La Ninas tend to deliver dry years. And the rainfall season that ended July 1 was one of the driest on record in San Diego and Riverside counties. "We hope that the conditions in the tropical Pacific will change and bring more moisture to the Southwest," Hidalgo said. "But it is certainly going to be a dry winter."