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Unprecedented behavior: Wildfires have jumped the Sierra Nevada

The Caldor Fire, burning in eastern California and western Nevada, became the second incident to take wildfire behavior in a direction never recorded before 2021: Across the Sierra Nevada Mountains. This followed a similar jump by the earlier Dixie Fire, the New York Times reported.1

Fireline Risk Reports

The threat to South Lake Tahoe resorts highlighted business interruption risk.

Approaching seven weeks after it ignited, the Caldor Fire was approximately 222,000 acres as of September 30. Nearly 1,100 structures were damaged or destroyed and five people were reported injured across California’s El Dorado, Amador, and Alpine counties and Douglas County in Nevada, according to reports from the California Department of Forestry and Fire Protection (CAL FIRE) and InciWeb.

More than 53,000 people were ordered to evacuate throughout the affected counties, 22,000 of them in South Lake Tahoe as the California resort community was threatened, CNN reported, highlighting another concern for the insurance industry when considering wildfire risk: The potential for business interruption claims from the area’s thriving tourism industry.2

The fire was 83 percent contained as of September 30 and the cause remained under investigation, according to InciWeb.

Verisk analysis of the Caldor Fire

FireLine®, Verisk’s wildfire risk management tool, is guiding the analysis of risk factors, including direct exposure to fire damage as well as exposure to smoke and ash damage, seen within and around the perimeter of the Caldor Fire. Approximately 95 percent of the area is in high or extreme risk FireLine categories.

The AIR Wildfire Model for the United States, Verisk’s wildfire catastrophe risk modeling solution, simulates wildfire ignitions, spread, property damage, and associated insured loss, involving tens of millions of potential wildfires in the 13 western states. According to that model, wildfire events causing insured losses are expected to occur in Alpine and Douglas Counties about every 14 and 8 years, respectively.

Sophisticated and innovative new technology from Verisk’s AER, able to continuously monitor active wildfires in the United States, captured the Caldor Fire’s very rapid growth as it more than doubled in size within the first 24 hours. FireLine continually incorporates technological advancements from AER, which benefit from connections to NASA and the U.S. Department of Defense.

The FireLine state risk report for California identified Alpine county as having the state’s highest concentration of housing units at high or extreme wildfire risk, at nearly 90 percent. Douglas County meanwhile was ranked second in Nevada by number and percentage of housing units at high or extreme risk.

Download our latest FireLine Risk Reports to gain greater insight into wildfire risk.


Dr. Arindam Samanta

Dr. Arindam Samanta is director of product management at Verisk. He can be reached at Arindam.Samanta@verisk.com.


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  1. Scott Reinhard and Jugal K. Patel, “Caldor Fire’s March to the Edge of Lake Tahoe,” The New York Times, September 5, 2021, < https://www.nytimes.com/interactive/2021/09/05/us/caldor-fire-lake-tahoe.html >, accessed on September 7, 2021.
  2. Aya Elamroussi, Joe Sutton and Theresa Waldrop, “Coming hours are make or break for Lake Tahoe resort city, fire officials say,” CNN, September 1, 2021, < https://www.cnn.com/2021/09/01/weather/us-western-wildfires-wednesday/index.html >, accessed on September 7, 2021.