A fast-moving, massive wildfire in northern California has prompted the evacuation of 53,000 people and the entire city of South Lake Tahoe on Monday, August 30, 2021.^1,2

The resort city, best known for its access to ski resorts and lakeside beaches in the Tahoe Basin, received the mandatory evacuation order on Monday after the first flames crossed over a ridge overlooking the city.

The Caldor Fire, ignited on August 14 due to unknown causes, has already burned over 191,000 acres and 669 structures.³ The fire was only 16 percent contained on August 31.

Pictured: On August 31, air quality in South Lake Tahoe and in neighboring communities was measured as “hazardous”. Source: IQAir

Hazardous air quality threatens evacuees

The Caldor Fire, one of four large-scale fires burning across NorthernCalifornia, has also fueled “hazardous” air quality across the Lake Tahoe region, with the worst measurements registering in the 600s. Hazardous measurements of air pollutant concentrations on theair quality index are within the range of 301 and up.

The California and Nevada border region from South Lake Tahoe to Carson City and Virginia City in the northeast experienced heavily polluted, smoky haze.⁴

Pictured: Air quality in northern California and northwestern Nevada has been severely degraded by several major fires; the historic Dixie Fire, the Monument Fire, the Caldor Fire, and the remnants of the Tamarack Fire as well as several smaller wildfires. Much of the region has ranged from “unhealthy” to “hazardous” on the air quality index. Source: IQAir

Until recently, the Tamarack fire had been the greatest threat to lives, structures, wildlife, and air quality in the area south of Lake Tahoe.⁵ That fire, caused by a lightning strike on July 4, grew to 68,637 acres. By the end of August, it had been 82 percent contained.

Wildfire smoke affects cities miles from source

Smoke from two other exceptionally large wildfires, theDixie Fire and the Monument Fire, has fed into exceptionally poor air quality in Northern California and as far east as Wyoming.^6,7 Spread across five counties, the Dixie Fire had burned through more than 807,000 acres by August 31, at 48 percent containment. The Monument Fire in Trinity County has created “unhealthy” to “hazardous” air quality conditions in and aroundRedding, California.

Smoke from wildfires can drift thousands of miles from its source, carrying numerous dangerous air pollutants in the wind. The most dangerous among those found in smoke arePM2.5(airborne particulate matter that measures only 2.5 microns in diameter) andultrafine particles(even smaller PM measuring less than .1 micron in diameter).

Pictured: Smoke from Northern California’s fires has traveled east, negatively impacting air quality in Idaho, Nevada, Utah, Montana, and Wyoming. Source: IQAir

Further east from the fires, poor air quality measurements were recorded in major western cities. Cities with air quality measuring “unhealthy for sensitive groups” or worse on August 31 included:

Carson City, Nevada
Logan, Utah
Idaho Falls, Idaho
Cheyenne, Wyoming
Billings, Montana
Bozeman, Montana

Some fires, like the exceptionally large Dixie Fire, have been moving into higher elevations than previously recorded.⁸ Already record-breaking as the largest non-complex fire in California history, the Dixie Fire set Lassen Volcanic National Park ablaze at as high as 8,500 feet above sea level. Higher elevation burns could make those areas more likely to be prone to wildfires in future years – and become more difficult for firefighters to access and control.

Major California fires force policy change

As California’s extreme fire season posed exceptional challenges to the state, public officials enacted preventative policy changes for public safety.

On August 30, the U.S. Forest Service ordered the closure of all California National Forests from September 1 until September 17.⁹ The decision is intended to reduce the potential for new fires and to reduce the threat of hikers and visitors getting caught in a potential wildfire’s path.

The takeaway

Wildfires and wildfire smoke carry exceptional health risks for anyone in their path. During wildfire season, be prepared to take action to protect your home and family.

• Don’t wait around- evacuate when ordered. Delays can cost lives.
• Monitor airborne pollutants in your neighborhood with anair quality monitor and plan to curtail outdoor activities as well as close doors and windows on days with poor air quality.
• Use an air purifier for wildfire smoke to help clean the air and filter particles when they enter the home.
• Wear an air pollution mask if outdoor activity is absolutely essential.