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The Big Differences Between SoCal's Summer and Fall Fires

Southern California's wildfire season has already been raging for months now, but a new, scarier kind of fire is about to arrive as we head into fall. There are actually two unique types of wildfires in the region and, using fire records and meteorological information, climate scientists have now been able to detail how each type of fire has its own season, its own turf, and its own particular style and degree of devastation; the new research from University of California scientists has just been published in the journal Environmental Research Letters.

Santa Ana fires are fanned by those famous offshore winds and they appear in the fall—October through April. Their counterpart is, predictably, the non-Santa-Ana fire, which pops up in June through September due to the summer's high temperatures and dry conditions. Santa Ana fires burn in "high-wind corridors and coastal areas," whereas non-Santa-Ana fires occur mostly in harder-to-reach inland areas. Santa Ana fires are usually larger than their summertime counterparts, and they burn in the "urban-wildland interface," nearer to where larger communities and urbanized areas meet the wilderness; non-Santa-Anas mainly burn in local forests and the rural areas near them.

In addition to the different locations where they tend to burn, these fires also have different burning styles. Santa Ana fires burn more intensely, says a release on the findings from the UCLA Newsroom. They're also usually larger than the summer fires. Perhaps because of that, they do most of their damage more quickly than the non-Santa-Ana summer fires do. "[I]n a typical Santa Ana fire, half of the territory burned is consumed in the first day of the blaze," but non-Santa-Ana fires are slow and steady, igniting only about 20 percent of their final burn area in their first two days and ultimately lasting longer than Santa Anas usually do.

One reason Santa Ana fires are more economically devastating than non-Santa-Ana ones is their location: they burn closer to urban areas, where there are more structures and property that can be damaged. Santa Ana fires also spread three times faster and have happened to occur in or near areas with higher property values. These three factors together made Santa Ana fires responsible for more than 80 percent of the total economic losses from fires in SoCal between 1990 and 2009, according to the paper in the ERL. (In terms of area burned, they both damaged about the same amount of land.)

One thing these two distinctive types of fires have in common is that they're both predicted to get bigger. Using "future-climate projections" and fire ecology models, researchers found that, by the middle of this century, Santa Ana fires will burn 64 percent more area (due mostly to what they expect will be drier air when the winds pick up) and that the area burned by non-Santa-Anas will jump by 77 percent, mostly because they expect temperatures to be higher.
· Southern California wildfires have split personalities, and both will burn more acreage by midcentury [UCLA Newsroom]
· Identification of two distinct fire regimes in Southern California: implications for economic impact and future change [ERL]
· Forecast For 21st Century LA: Average Rain, Way Less Snow [Curbed LA]
· The Many Terrifying Ways Global Warming Will Soon Be Ravaging California [Curbed LA]