Rapidly Spreading Wildfires Impact Northern California Wine Country
Kevin Van LeerOctober 10, 2017
Kevin Van Leer, senior product manager – Model Product Management, RMS
17:00 UTC Tuesday, October 10
Driven by Diablo wind gusts of up to 70 miles per hour (112 kilometers per hour) and with very low relative humidity, 14 fires burning across swaths of eight Northern California counties have resulted in significant property damage and loss of life.
These strong winds caused the fires to spread quickly. The Tubbs Fire, located just north of Santa Rosa, grew from 200 acres on Sunday night (October 8) to over 20,000 acres by Monday morning (October 9) and is now over 27,000 acres. As of 4 p.m. Pacific Time (PT) on Monday, October 9, the Tubbs Fire together with the Atlas Peak Fire, located just north of Napa, combined have destroyed over 50,000 acres of land, and impacted several wineries along with high value residential and commercial structures. So far, 1,500 structures are reportedly destroyed, making this at least the fifth most destructive fire in California history as shown in the table below.
RMS staff are monitoring the development of this event using real-time remote sensing data. Unlike imagery of wind damage or storm surge damage, there are many satellite sensors designed to detect thermal signals. In terms of estimating the number of damaged structures and loss, typically the first pieces of information available are fire perimeter shapefiles.
Estimates of burn perimeters can be created using satellite imagery, such as from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) — see Figure 2, operated by the U.S. Department of Agriculture. This near real-time imagery detects burning fires using spectral temperature comparisons against the surroundings. The data from these satellites enables a quick estimate of the burn perimeter in the absence of ground truth data, as expected during the early days of an ongoing event.
This analysis shows that there are approximately 15,000 structures in the overlap of the burn area and exposure, though not all structures within the footprint will be damaged. In addition to the burned structure damage, smoke may also be a major source of loss from this event.
Historical analysis performed by RMS shows that smoke loss can contribute between 5 percent and up to 50 percent of the overall event loss. The smoke plume (Figure 3) produced by these fires was blown primarily to the south and southwest throughout Monday, resulting in air quality alerts throughout the Bay Area. In terms of damage, it is critical to understand the concentrations of smoke impacting the exposure. The perimeter of damaging smoke can be much larger than the burn perimeter, though smaller than the smoke plume extent, and would be typically tied to health considerations and the need for smoke residue clean-up.
Evacuation orders have been issued for over 20,000 people on Monday across the impacted areas as the fires continue to spread. The situation on the ground is still evolving and conditions conducive to the rapid spread of wildfires remain in the area. The National Weather Service has issued a Red Flag Warning until Tuesday morning PT for a large portion of Northern California that highlights the continued high wind gusts and low relative humidity.
RMS continues to monitor the situation and will release further information through the RMS Owl Event Response page on Tuesday morning PT.
You May Also Like
January 22, 2018
Southern California: Thomas Fire Loss Estimate and Mudslide Commentary
California Wildfires: Exposure Impacted by the Thomas Fire
As the Thomas Fire continues to climb the list of the top twenty largest California wildfires for both acres burned and structures destroyed, many in the insurance industry are asking how this fire, in addition to the other burned areas across Southern California, will impact their portfolio. A critical element in understanding the industry impact, but also the significance for an individual book, is the insured value of the burned structures. The Thomas Fire, which at 60 percent containment at the time of publication is already the second largest fire in California history with a reported burn area of 272,000 acres (110,074 hectares), has affected several different communities with wide ranges of average insured value.
Figure 1: Top 20 Largest California Wildfires. Source: CAL FIREWhile damage assessments are still ongoing and counts of damaged or destroyed structures are actively being reported, we can use RMS high resolution exposure data and the latest burn footprint available from Geospatial Multi-Agency Coordination (GeoMAC) to gain a perspective on the total amount and average value of exposure across different areas within the perimeter.
Figure 2: Map of the Thomas Fire Perimeter. Source: GeoMAC as of 0100 UTC on December 18, 2017.As of December 18, portions of ten different ZIP codes are located within the Thomas Fire perimeter, spanning across Santa Barbara and Ventura counties. While the fire started north of Santa Paula around sunset on December 4, it has now spread approximately 50 miles (80 kilometers), primarily to the west, to the hills north of Montecito and Santa Barbara. So far, during two weeks of spread the fire has impacted the communities of Santa Paula, Ojai, Ventura, Oak View, Wheeler Springs, Carpinteria, Montecito, and several others. Each of these communities vary in average residential exposure value, making “average” estimates across the entire perimeter more difficult.
Table 1 below compares the residential exposure for the high value 93108 ZIP postal code that spans the Montecito area against the exposure outside of that ZIP code. All values correspond only to exposure located within the Thomas Fire perimeter, according to the RMS high resolution exposure database. The average residential structure exposure value for 93108 is on average three and a half times higher than structures located outside of that ZIP code. Structures in 93108 accounts for only three and a half percent of the number of structures within the fire perimeter, but 12 percent of the total exposure value.
Table 1: Residential Exposure Values in the Thomas Fire Perimeter.As noted in prior blogs about the Wine Country wildfires, it is important to note that only a fraction of the structures within the perimeter will be damaged or destroyed in this event. The reported numbers so far from CAL FIRE are 1,024 structures destroyed and 250 damaged. Comparing this against the total number of structures within the perimeters, the ratio is approximately 37 percent, which is far lower than the 75 to 80 percent seen in the Wine Country wildfires in October this year, but higher than the other historical Southern California events that have been analyzed (Cedar in 2003 and Witch in 2007).
Figure 3: Percentage of damaged or destroyed structures within historical fire footprints.Also, a comparison of the percentage of destroyed structures versus the total number in the perimeter between the Thomas Fire (1,024 destroyed versus 1,274 total or 80 percent) and the Wine Country Tubbs Fire (6,957 destroyed versus 7,443 total or 93 percent), raises important questions for understanding the key differences between the events. This may indicate a stronger presence of fire suppression, lower impacts of embers, more distributed exposure, differences in surface fuel characteristics (e.g. chaparral versus forest) or a combination of these and other factors in the Thomas Fire. A further review of these event-specific factors, including the weather conditions, will provide more clarity around key drivers of these differences.
By extracting information about the differences between these two events, RMS will continue to build insight into the development of the RMS® U.S. Wildfire HD model, part of the RMS North America Wildfire HD Models suite, due for release in 2018. RMS is still monitoring the ongoing events affecting Southern California and will continue to provide updates through RMS Owl.…
As a senior product manager in the Model Product Management group at RMS, Kevin is responsible for RMS climate-peril products for the Americas, including wildfire and custom vulnerability analytics. Kevin has been actively involved in model releases for both severe convective storm and hurricane models over the last four years at RMS. Kevin holds a master’s degree in atmospheric science from the University of Illinois at Urbana-Champaign, where he authored a thesis on tornado-genesis and severe convective storms, and a bachelor’s degree in atmospheric science from Purdue University. He also holds the Certified Catastrophe Risk Analyst (CCRA) designation from RMS. Kevin is a member of the American Meteorological Society (AMS), a mentor for the AMS Board of Private Sector Meteorologists, and a voting member of the ASCE Standards Committee on Wind Speed Estimation in Tornadoes.