Southern California wildfires exhibit split personalities
Wildfires have ravaged both populated and unpopulated regions of Southern California at an increasing rate over the past few decades, and scientists from three University of California campuses and partner institutions are predicting that by midcentury, as a consequence of climate change causing hotter and drier summers, a lot more will go up in flames.
In a paper published in the journal Environmental Research Letters, the scientists discuss the split-personality nature of Southern California wildfires. They describe two distinct wildfire types – those driven by offshore Santa Ana winds that kick up in the fall and those that result primarily from hot, dry conditions in the summer. In terms of the amount of acreage consumed, the two fire types are roughly equal, but the Santa Ana fires, which tend to hit more developed areas, have been 10 times more costly over the period studied, 1990 to 2009. The researchers relied on NASA satellite data and decades’ worth of fire records from the California Department of Forestry and Fire Protection and the U.S. Forest Service.
Non-Santa Ana fires, by contrast, burn more slowly and tend to occur in more remote mountain areas. Non-Santa Ana fires, such as the Station Fire that scorched large portions of the Angeles National Forest in 2009, rely on hot temperatures and are more sensitive to the accumulation of woody debris and other dried out vegetation that serve as a fuel source. Both types of fires are costly and damaging, but the researchers see change on the horizon.
The researchers said that firefighting agencies at the local, state, and national levels should begin now to prepare for a future with more wildfires in Southern California and the rest of the western United States. In fact, one issue the researchers point to is the potential for more regional competition in summer for firefighting resources – air tankers, vehicles, and personnel. The disproportionate impact of Santa Ana fires also has implications for optimizing resources. “The large economic and human impacts of Santa Ana fires raises the question of whether more resources during fall could be marshalled for suppressing these fires,” said James Randerson, Chancellor’s Professor of Earth system science at UCI and senior author on the paper.
NASA satellite images show the difference between Santa Ana and non-Santa Ana (summer) fires in Southern California. Santa Ana fires are driven by offshore winds originating in the desert that blow through mountain passes and canyons. Summer fires are characterized by onshore winds and long-burning blazes fed by high heat and dry conditions. NASA Earth Observatory