Rapidly Spreading Wildfires Impact Northern California Wine Country

Kevin Van Leer, senior product manager – Model Product Management, RMS

17:00 UTC Tuesday, October 10

Figure 1: Neighborhood near Coffey Park in Santa Rosa, California. Image credit: Golden Gate California Highway Patrol

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.

Table 1: Most destructive California fires (Napa Valley Fire reported count as of 4 p.m. PT Monday, October 9, 2017) Source: CALFIRE Redbooks

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.

Figure 2: VIIRS satellite data and RMS digitized burn footprints compared with urban areas (Source: NASA Earth Data and RMS as of 6 p.m. Pacific Time, Monday, October 9, 2017)

 

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.

Figure 3: Smoke plume from satellite imagery. Source: Colorado State – GOES-16 Satellite

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.

Senior Product Manager, Model Product Management
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.

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