2022 wildfire in Northern California
The Mosquito Fire was California's largest wildfire in 2022. The fire began on September 6, burned in Placer and El Dorado counties in September and October, and was pronounced fully contained on October 22. It affected the Tahoe and Eldorado National Forests and destroyed 78 structures in the rural communities of Michigan Bluff, Foresthill, and Volcanoville. The fire suppression effort cost more than $180 million, and at its peak involved more than 3,700 firefighters. The precise cause of the fire is not known, but the possible role of Pacific Gas &amp; Electric Company (PG&amp;E) equipment is the subject of multiple civil lawsuits and a Forest Service investigation. The Mosquito Fire was one of 7,477 wildfires in California in 2022, which burned a combined .
Background.
In early September California experienced a record-breaking heat wave, which peaked on September 6. Climate scientist Daniel Swain described the heat wave as "the worst September heat wave on record" for Northern California. Vegetation moisture levels in the northern Sierra Nevada had already been nearing record lows, and the heatwave exacerbated the trend. On September 2, the National Interagency Fire Center had issued a "Fuels and Fire Behavior Advisory" for most of Northern California, warning of elevated fire weather concerns with "conditions conducive to long range spotting, rapid fire growth, and high resistance to control." A California Department of Forestry and Fire Protection (Cal Fire) fire behavior analyst later compared the spread of the Mosquito Fire to that of the 2014 King Fire, which burned in the same region. Both fires were driven primarily by the extreme dryness of the vegetation in their respective years.
Progression.
September 6.
The Mosquito Fire was first reported on September 6 at approximately 6:27 p.m. PDT, above Oxbow Reservoir and near Mosquito Ridge Road (for which the fire was named). Firefighting aircraft arrived by 6:47 p.m., and they reported that the fire had burned of brush and timber. Steep terrain and access issues hindered the fight: an old landslide on a road obstructed fire engines, and the fire was burning on the shadowed side of a canyon, making it difficult for larger air tankers to drop water or fire retardant. Aircraft were forced to leave once night began to fall at roughly 7:41 p.m., less than an hour after arriving on scene.
At around 9:00 p.m., the fire was fanned by outflow winds from nearby thunderstorms, and crews reported being challenged by the gusty winds and an increased rate of spread. As the fire began to spot ahead, evacuations were ordered for Michigan Bluff and surrounding roads. The fire jumped the North Fork of the Middle Fork American River and continued to spread, reaching before midnight and producing a smoke plume visible from as far away as Auburn, to the southwest. The fire continued to burn actively through the night, moving northwest up the side of the Middle Fork American River canyon.
September 7–8.
On September 7, the Mosquito Fire grew considerably, developing a massive pyrocumulus cloud and exhibiting extreme behavior that made it difficult to directly combat the fire. Other concurrent wildfires caused fire personnel to compete for limited firefighting resources, such as Very Large Airtankers (VLATs). As the fire burned in all directions, it burned structures in the community of Michigan Bluff.
The next day, September 8, saw the single largest day of growth on the Mosquito Fire. The fire was mapped by FIRIS (the Fire Integrated Real-time Intelligence System, using aircraft with infrared sensors) at . Shortly afterwards, at approximately 1:00 p.m. PDT, the Mosquito Fire spotted across the American River and crossed southward into El Dorado County, burning towards Volcanoville and destroying structures along Volcanoville Road. The fire burned an additional in just four hours. An elderly couple was trapped behind the fire line when their vehicle became disabled and a wild pig attacked their dogs, necessitating a sortie through the flames by an El Dorado County Sheriff's deputy.
As fire activity intensified and became plume-dominated, the Mosquito Fire produced an enormous pyrocumulonimbus cloud that reached more than into the atmosphere, visible from as far away as Chico and Sonoma, more than 120 miles away. A NOAA aircraft flew around the plume in order to conduct research with San Jose State University's Fire Weather Research Laboratory and the University of Nevada, which had researchers on the ground nearby, on fire and atmospheric processes. Radar showed that the pyrocumulonimbus cloud contained updrafts with speeds in excess of 30 meters per second. The Mosquito Fire continued to generate a pyrocumulonimbus cloud after sunset, in what scientists said was an indication of the vast amount of heat the fire was putting out.
During this time, scientists recorded a "very strong fire-generated vortex", both visually and on radar, on the southeast flank of the Mosquito Fire. This cyclonic vortex within the rotating column of smoke was connected to the ground, had a circulation extending up to approximately , and generated winds equivalent in strength to an EF-1 tornado. Similar vortices have occurred in multiple California wildfires, including the 2020 Creek Fire, the 2020 Loyalton Fire, and the 2018 Carr Fire.
September 9 onwards.
Officials warned of "great potential" for continued fire spread.
On September 9, firefighting conditions improved with slightly cooler temperatures and low winds, causing the fire to remain under an inversion of its own smoke. On September 10, those temperatures and higher relative humidities continued to moderate fire behavior, but increasing winds pushed the fire further north and northeast and prompted more evacuations, primarily between the fire and the Sierra crest.
By the morning of September 11, fire crews had achieved 10% containment, primarily on the southwest flanks of the fire in the vicinity of Volcanoville and Quintette. The fire remained active on the 11th, particularly once the inversion lifted again, but did not spread rapidly. Firefighters began to remove trees and brush from old fire lines from the 2013 American Fire and the 2014 King Fire, in anticipation of reusing them as containment lines. By the evening of September 12, containment rose to 16% as firefighters continued to strengthen containment lines near Foresthill and Volcanoville, on the northern and southern flanks respectively.
On September 13, remaining tropical moisture from the remnants of Hurricane Kay left the area and was replaced by persistent southwest winds. Though firefighters achieved 18% containment by the morning, the winds allowed smoke to clear and the inversion to break, leading to an uptick in fire activity. The entire eastern flank of the fire was highly active, and new evacuation orders were issued for the Stumpy Meadows area. Between 2:00 and 2:30 p.m, the fire spotted from the south side of the Middle Fork American River to the north side, below Todd Valley and Foresthill, on the west flank of the fire. The spot fire grew aggressively and became established, creating a large plume as it burned up towards Foresthill, which had been under a mandatory evacuation for several days by that point. Some personnel working on dozer lines in the canyon were forced to abandon their equipment and flee from the rapidly growing fire. Fire crews hastily set backfires between Foresthill Road and the fire to the south in order to consume the fuel between the two and prevent the fire from overrunning the community. A massive airshow attempted to halt the fire, as 16 different aircraft, including all four of the Very Large Air Tankers operated in the United States, aided ground crews. Those tankers also dropped massive amounts of retardant to reinforce the firefighting efforts—just shy of 200,000 gallons on September 13 alone. By that evening, the fire was mapped at approximately 58,000 acres, representing nearly of growth in a day, with 25% containment.
On Wednesday, September 14, the fire burned an additional , reaching and surpassing the McKinney Fire to become California's largest wildfire of the year.
The fire continued to burn to the east, in steep and inaccessible terrain in canyons upriver from the confluence of the Middle Fork American River, where the North Fork of Middle Fork American River, the Middle Fork American River, and the Rubicon River come together. It burned through much of the footprint of the 2006 Ralston Fire, as well as parts of the burn scars from the American and King fires.
The fire was moderated by an unseasonably early Pacific storm that brought wetting rains to the area in mid-September, after which the fire grew little and containment steadily increased. Beginning on September 18, it brought rain to much of Northern California, including the Sierra and the Mosquito Fire. The fire increased in acreage on the 17th, fueled by gusty winds ahead of the storm, but the ensuing precipitation tamped down fire activity. This allowed fire crews to finish gaining containment around the fire perimeter on the southern, western, and northern sides, leaving the wide eastern flank as the only remaining open fire front. This effort, along with the storm, allowed several thousand people to return to their homes as evacuation orders were lifted or reduced. Concerns that heavy rain could cause flash flooding and ash/debris flows in the burn scar led to a flash flood watch being issued for the entire Mosquito Fire burn area on September 18 and 19. In the meantime, steep and muddy terrain posed new challenges for firefighting. On September 19, for the first time since igniting, the Mosquito Fire did not increase in acreage, though smoking hot spots were still visible during gaps in the rain.By September 21, all evacuation orders in both Placer and El Dorado counties were lifted. Firefighters struggled to complete the last 5% of containment line, hampered by the extremely difficult terrain of the river canyons, but ultimately declared the fire 100% contained on October 22, 46 days after it began. The fire was officially declared controlled on November 10. The total cost of fighting the Mosquito Fire was estimated by the National Interagency Fire Center at $181.1 million.7
Effects.
No deaths were reported as a result of the Mosquito Fire. At least two firefighters were injured; one hurt their wrist in a fall and another stepped into a still-burning stump hole, sustaining second-degree burns on their leg.
At least 78 structures were destroyed and 13 were damaged; on September 7, the fire burned in the area of Michigan Bluff, on September 8 the Mosquito Fire impacted structures near Volcanoville and Quintette, and on September 13 the fire impacted structures in Foresthill. Local and regional infrastructure was affected: the Georgetown Divide Public Utility District declared a local emergency after the fire affected its water service infrastructure, including damaged canals and flumes. The Placer County Water Agency, which operates the Middle Fork Project (a water supply and hydroelectric power generation system, and California's eight-largest public power project), sued PG&amp;E after alleging that the fire had caused, in addition to physical damage to its facilities, the loss of tens of millions of dollars in power production sales.
Also threatened was the Placer County Big Trees Grove, a group of six old-growth giant sequoias and the northernmost giant sequoia grove in California. The U.S. Forest Service conducted defensive burning operations and cleared fuel around the grove while treating the trees with water, and the fire was eventually stopped four miles from the grove.
The Mosquito Fire led to evacuations in several communities in Placer County and El Dorado County. By September 11, at least 11,260 people were under evacuation orders. That number included residents of Michigan Bluff, Foresthill, and Todd Valley in Placer County, and Volcanoville and Georgetown in El Dorado County. At least eight people were arrested in evacuation areas for crimes "against evacuated properties" (one person in Placer County and seven in El Dorado County). One person apprehended for burglary posed as a PG&amp;E contractor to get past law enforcement checkpoints. 
A large portion of the Tahoe National Forest was closed, and recreation areas such as the French Meadows Reservoir and the Western States Endurance Run trail were expected to be closed at least through the end of 2022. An area encompassing of the Western States Endurance Run route burned. The Rubicon Trail (a popular 4x4 road/trail) was also closed.
Environmental impacts.
Smoke from the Mosquito Fire routinely led to hazardous air qualities in many nearby regions in Northern California and Nevada, including the Lake Tahoe Basin and the cities of Folsom and Auburn. Air quality indices of more than 1,000 were recorded in the Sierra foothills south of Interstate 80,