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.