SoCal Scorched: Santa Anas Fuel Costliest Ever Wildfire Event
On Sunday, October 21rst, Santa Ana winds from the California desert fanned the first in a series of fires that may rank as the costliest wildfire event in the history of the insurance industry. The sweltering siege prompted Governor Arnold Schwarzenegger to declare a state of emergency in a seven county span stretching from Santa Barbra to the Mexican Border. Throughout the state, California experienced its largest ever evacuation as residents of San Diego, Los Angeles and surrounding areas fled spreading flames.
Fueled by a particularly extreme set of conditions—very low humidity, temperatures over 90 degrees, and the aforementioned Santa Ana winds—23 fires devastated more than 500,000 acres of Southern California’s most expensive property, including homes in Rancho Santa Fe, the highest-income community in the United States. The first blaze was sparked in the wealthy coastal community of Malibu. Dubbed the Canyon Fire, it was ignited by a downed power line late Sunday afternoon and spread more than 2,000 acres by nightfall.
Twenty-two more wildfires followed suit, ravaging some 2,000 homes and 800 outbuildings, cutting off power to thousands of residents and businesses, and forcing the evacuation of 1 million people in Southern California. These fires were primarily sparked by downed power lines or out of control campfires. Arson was also to blame.
As the blazes marched on, scorching acre upon acre of California land, firefighters working to contain them were thwarted by Santa Ana winds. The Santa Anas wreaked havoc by carrying burning embers up to 2 miles from old fire sites, feeding new blazes, and instead of lasting just a day or two, which is typical, these winds persisted for several days after their weekend start.
On Wednesday, fire crews finally gained the upper hand. Santa Ana wind speeds, previously gusting to 70 and 80 mph, dropped to single-digits. Consequently, crews were able to stabilize the perimeters of 22 of the 23 fires charring Southern California. This process is known as containment. Only the Slide Fire in the mountainous regions of San Bernardino County still burned out of control. It devastated 5,000 acres of land between Thursday and Friday, as well as some 200 homes. After burning nearly 8,000 additional acres and 70 homes over the weekend, the Slide Fire was 90 percent contained on Monday, October 29th. It was also one of only seven fires not yet fully contained by fire crews at this time.
Even among fires fully contained, however, risk was not doused; hot spots susceptible to flare-ups, which often still burned within fire perimeters, could easily be revitalized by a return sweep of the pesky Santa Ana winds. In preparation, vigilant firefighters repositioned themselves throughout the course of the fires, ready and waiting should the Santa Anas resurge.
The Santa Ana Winds
Santa Ana winds, nicknamed “Devil’s Breath” play a particularly significant role in the sometimes uncontrollable spread of wildfires. In fact, they were reported during each of California’s seven highest loss-causing fires. These winds typically blow between October and February, peaking in December, and they pack at least 20 mph winds, typically lasting for 24 to 48 hours.
The Santa Ana winds that fueled October’s wildfires were an exception. They persisted nearly five days and were unusually strong. Top gusts reached 108 mph northeast of Los Angeles. Below mountain passes and canyons, gusts of 85 mph were common.
These uncharacteristically fierce winds were spawned early in the day on Saturday, October 20. That morning, a cool high pressure system moved into the Northeastern portion of the Great Basin. As the high pressure system progressed eastward, it continued to strengthen, creating a huge pressure gradient between it and the surrounding low pressure system in coastal Southern California. This large gradient powered the winds that funneled through canyons and swept along the coast, altering the course of existing weather systems.
Outside of Los Angeles in Riverside, California, winds previously blowing from the west-northwest tracked a new northeast course and increased in speed from relative calm to 20 mph. Meanwhile, dew points dropped nearly 50 °F, resulting in 10% humidity. Rather anomalously, temperatures in Southern California warmed as well, rising to 90 or 95 °F. This high heat occurred across locations that had had little to no rain for several months, and the combination of dry fuel, high temperatures, low humidity, and sustained winds created the ideal wildfire setting.
The hot, windy conditions did not lessen until Wednesday, October 24th, when the high pressure system weakened and moved eastward in response to a low pressure system entering the Pacific Northwest. This low pressure system brought relief: increased humidity, cooler temperatures and lighter winds.
The Wildland Urban Interface: Wildfire Damage and Suppression
Since 2000, more than 55,000 people have moved into some 16,000 new homes in the neighborhoods impacted by October’s fires. More than 2,000 of these homes, or nearly 15%, were destroyed by the time the winds subsided and the fires died. By the end of October, some 8,000 people had contacted the Federal Emergency Management Agency (FEMA) for assistance rebuilding their houses.
The damage in Southern California highlights a recent trend: in the past few decades, there has been a clear tendency for increased property loss due to wildfires. This is a direct consequence of the rapid construction growth in the wildland-urban interface (WUI)—a region where primitive, undeveloped forest meets urban expansion. California has the highest number of homes in these areas; crowded coasts have pushed people wanting larger plots to the mountains for space and views.
In the face of a growing WUI population, there is an ongoing state-wide campaign to encourage home-owners to create and maintain generous setbacks—distances from the house to surrounding vegetation. In addition to techniques to reduce fuels close to the home, California residents are demonstrating increased efforts to fireproof the structures in which they live.
In Rancho Santa Fe, near San Diego, residents are learning to practice a strategy known as “shelter-in-place.” It is designed to insulate homes from flames if people cannot evacuate. As part of the “shelter-in-place” plan, the local fire department scrutinizes every tree and bush in a neighborhood. Trees must be a certain distance from the house and cannot exceed a certain height. Roofs must be nonflammable and shrubs near the house must always be watered. Construction companies use masonry, stucco, or precast concrete to build columns. Wood fences cannot touch the home.
Last week’s wildfires were the first major test of these stringent construction and landscaping standards, adopted in Rancho Santa Fe in 1997, and it seems they were a success; while the San Diego suburb lost 53 houses, none of them were in the five subdivisions that had embraced restrictions limiting such landscape design. Home owners who had wanted to dot the yards of their hacienda-style homes with jacarandas and avocado trees were grateful they had not.
Despite the devastation in Southern California and widespread acknowledgement that fires will strike again, there is little doubt that homeowners will be allowed to rebuild on the same lots that went up in October’s flames. Meanwhile, the unpredictable nature of the wildfire peril complicates risks for insurers underwriting properties in fire-prone zones.
Conclusion
The wildfires of October 2007 serve as a reminder that disasters can happen just about anywhere in the United States, and that homeowners need to be prepared. As the growth in the number and value of properties in the WUI continues unabated, insurers underwriting properties exposed to the wildfire hazard must reevaluate; they cannot rely on historical data to estimate wildfire-driven losses. Instead, they must evolve their risk assessment strategies accordingly through the use of catastrophe models that better quantify the threat by accounting for a wide range of factors influencing wildfire development.
.MGW.
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