Although October is usually known for Atlantic hurricane activity and sometimes a second peak of severe weather that can occur as summer wanes, this month is also the height of the California wildfire season, which typically runs from spring to late fall. Unfortunately, it should be no surprise that this western wildfire season has been one of the worst on record – in May, I briefly mentioned that it could likely get ugly. So far, the U.S. budget for fighting wildfires has topped out at $2.35B, which does not include the recent fire-fighting efforts. Year to date, the wildfires have burned 8.5 million acres across 51,000 fires.
California has had nearly five years of extreme drought followed by record rains last winter, producing a bumper crop of grasses and fine fuels on top of drought-dried, diseased and stressed heavier fuels. Fuel analysis ahead of the Columbus Day firestorm were at all-time record dry levels. Like many previous firestorms, when this situation is combined with the Santa Ana/Diablo wind events that occur every year and the right weather conditions, any fire ignitions that occur will cause fire explosions that race along the landscape.
Columbus Day firestorm cause
The Oakland Hills, CA fire of 1991 had been the seminal fire event that changed the insurance industry’s perspective on wildfire loss, much like Andrew did with hurricane loss. However, the Columbus Day firestorm will no doubt be viewed as a considerable event in a growing list of large wildfires that have impacted the insurance industry in recent decades. There are very few natural catastrophic events that result in such destruction as a wildfire, although the effects of an EF 5 tornado are similar. However, the damage from wildfires is often worse since everything is reduced to ash, with virtually nothing being recoverable. With EF 5 tornado damage, some personal belongings can usually be salvaged. This is often not the case in fires, which make them a different beast entirely.
— SFChronicle (@sfchronicle) October 11, 2017
The exact cause of most of the Columbus day fires are still under investigation, it is most likely they were either human triggered or a result of sparking from down power-lines due to the high winds that occurred. No thunderstorms were in the area so that can be ruled out at this time.
The weather conditions that created the firestorm are often referred to Diablo winds, which follow the same type of pattern as Santa Ana winds – the northern and southern California areas simply use different names for the same weather phenomenon. The increased fire conditions start when a big ridge of high pressure sets up over the Great Basin in the inter-mountains west from Utah to Nevada. This causes air to flow from east to west across California, from high elevation to sea level. It is at this point that the first law of thermodynamics takes over. As the air is compressed when moving from a higher elevation to a lower elevation, it heats up. During this movement of air, the moisture in the air does not change much, but with a rising temperature, a large disparity between the temperature and the moisture in the air is created and pushes the relative humidity to very low levels. As the air gets compressed, it moves faster, forced over mountains and pushed through canyons.
Leading up to Monday’s firestorm, the pressure at Reno, NV at 9:00 p.m. on Sunday, October 8 was at 1020 mb, and the pressure at Napa, CA was even lower at 1008 mb. This difference in pressure was the catalyst for the Diablo winds, which in some places gusted to 79 mph.
As of Thursday morning, 22 wildfires were burning across northern California, which is an increase from the 14 that were originally reported on Monday. Looking ahead, until there is a major North American weather pattern change, the Diablo/Santa Ana wind events could occur every few days. With a La Nina building in the Pacific Ocean, the long-term prospects for rain are slim across the state, particularly in the south. A large subtropical ridge is forecasted to be in the area until at least next week, as moisture-laden storms rumble ashore over the Pacific Northwest and keep California dry. Currently, the National Weather Service has a Red Flag Warning in effect until Thursday the 12th until 5 pm PDT, which means that critical fire weather conditions are either occurring now or will be shortly. The combination of strong winds, low relative humidity, and warm temperatures can contribute to extreme fire behavior.
Although the wind is not expected to be as strong as observed earlier in the week, this warning is due to the increasing north to northeast wind and low humidity that will generate critical fire weather conditions again. New and existing fires could rapidly spread during this time period.
Measuring insured loss of Columbus Day Firestorm
The latest figures from the Associated Press suggest that the Columbus Day firestorm destroyed at least 3,500 homes and businesses. PCS has issued two separate catastrophe bulletins which cover the Atlas Fire near Napa, CA and the Tubbs Fire near Santa Rosa, CA. However, these are just two of the most destructive fires across the region. For example, the Canyon Fire 2 near Anaheim Hills is now 60% contained, but burned 26 structures, damaged another 36, and continues to threaten 3,500 structures. Therefore, the wildfire losses will be more far-reaching than PCS has reported, since it only designates losses of $25m or more. For the latest information on these fires and their containment levels, please see Cal Fire Incident Information, which gets updated as often as needed.
If the AP estimate of at least 3,500 homes burned is correct, then as a combined event, this will be one of the largest wildfire insured loss events in U.S. history, if not the largest. Below is a chart illustrating some of the most damaging North American wildfires and the estimated insured losses if they were to occur today.
With the understanding that the Tubbs and Atlas Fires had a large impact on the expensive Napa/Santa Rosa areas, it is assumed that the losses will be much higher than past fires such a the Oakland hills fire of 1991 because of the effects on commercial property. At least 14 commercial wineries, a Hilton hotel, a Kmart, a McDonalds and even the historic Fountaingrove Round Barn have been destroyed by the fires. Many other commercial properties have been destroyed and if not destroyed will have business interruption. Smoke related clean up that could also work its way into the insured losses from this event even if the structure did not have damage.
Catastrophe Model can’t come fast enough
Many areas of California have a long and active wildfire history. Typically, about 10,000 wildfires are ignited in California every year. Of those, only about 20 cause property losses and fewer still cause losses large enough to be designated a catastrophe. But when conditions are right, the losses can be truly catastrophic, as we saw with the Columbus Day firestorm. Many areas of the state are characterized by narrow valleys surrounded by steep, hilly terrain. The interface between wildland areas and development, exposed residents and businesses is increasing the wildfire risk. In the last several decades, the combination of firefighting technology, fire suppression policies, environmental regulation, and development trends has led to increased fuel loads, greater occupancy of remote areas and greater potential for catastrophic wildfires. This is a trend occurring all across the country.
The risk for wildfire is increasing across all 50 states, with the costly wildfire outbreaks in Texas, Tennessee, and Colorado being recent examples, yet the insurance industry still lacks the access to a full probabilistic wildfire loss model for the entire U.S. For years, the insurance industry has had access to assess the wildfire hazard from various sources and, of course, there are several tools built into the catastrophic loss models that help with accumulation management. Some catastrophic modeling companies have developed loss models for California only as a result of the high losses that occurred after the devastating fires that hit southern California in October and early November 2007. However, limited updates have been made since the initial release.
The good news is that modeling companies are currently working on U.S.-wide probabilistic wildfire loss models. However, as we have shown, wildfires can be very complex, with embers traveling several miles and igniting new fires. The models that are in development will need to incorporate the newest landfire fuel databases that seem to change constantly with growing vegetation across the U.S. These models need to have fire-spread algorithms and account for human fire suppression decision-making through stochastic simulations of man-made fire breaks. They should also model the possibility that a wildland-urban interface fire will transform into an urban conflagration, such as we saw in the Santa Rosa area.
To understand wildfire behavior, the models will need to include historical data on average hourly wind speed and direction based on weather stations, but those might not address the varied microclimates that can occur in a complex terrain. Of course the models will need to account for a wide-range of residential and commercial constructions, including the presence of mitigating factors, such as fire-resistant roofing and siding materials, which are becoming more and more popular.
Also, as we have seen in past wildfires, defensible space and vegetation control have a huge impact on site-specific loss. In fact, fire-wise communities, resilience efforts and research by the IBHS are helping to minimize wildfire loss.