We've entered the month of October, a month when Santa Ana winds over the past 10 years have stoked fires that destroyed thousands of homes. Vegetation is the fuel that feeds a wildfire.
But some people who have studied the behavior and destruction of San Diego's massive fires of 2003 and 2007 say that managing the vegetation surrounding your home may not be critical. A bigger issue is topographical location.
C.J. Fotheringham, with the U.S. Geological Survey, said it matters, for instance, whether your house is on a ridge line.
"If you're on the windward side of a ridge line you're in trouble," she said.
Fotheringham has examined maps and photographs of the October fires to see why some homes burned and others didn't. Another one who's done that work is Alexandra Syphard, a research scientist, based in San Diego, with the Conservation Biology Institute.
"There are strong Santa Ana wind corridors within the region, so if you place your home in a wind corridor it may be more at risk," said Syphard.
Both women say urban planning makes a huge difference when it comes to being at risk for fire. Fotheringham said being on a ridge line not only puts you in the fire's cross hairs, it makes it harder for fire trucks to reach your home.
While location is key, both Syphard and Fotheringham said the type and volume of vegetation near a house is an issue. But not in the way you might think. Conventional wisdom, and official policy, tells us to make sure we clear flammable brush within a hundred feet of our homes to prevent fire. Syphard said, for one thing, doing that can mean grassy weeds will grow in their place, and that actually increases fire risk.
"Because when you convert native shrub-lands into grasslands, you're actually ending up with a fuel type that is much more flammable," she said.
Fotheringham added that when it comes to Santa Ana-wind fires, clearing the vegetation leading up to your house misses the point.
"And the reason," she said, "is because we don't have fires that move across the landscape in a nice orderly fashion. We have ember storms."
Santa Ana winds can cast those embers for miles causing fires to leapfrog from one hillside to the next, or to the next housing tract. Those embers land on roofs. That's one reason wooden shake shingles are so dangerous. But even if you've got a tile roof, Fotheringham said embers will burn down your house if they land in the right place.
"When you have a tree canopy overlapping your house leaves fall down, onto the house or in the gutters, which most people are aware of, but also underneath the tiles," she said. "And you have a perfect place for an ember to land and start a fire."
Both experts say the plants immediately surrounding your house are the ones you need to be most concerned about. You don't necessarily have to chop down that big pittosporum tree that's been shading your house. But do take some time this month to clean off the roof, and make sure you don't have piles of plant litter around the foundation.
Getting back to location, Syphard said she's working on a new and improved map of San Diego that will identify the areas that are the most fire-prone in the county.
