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KNP Complex Fire
The 2021 KNP Complex Fire was a large wildfire in Sequoia National Park and the Sequoia National Forest in Central California's Tulare County. After lightning ignited the Paradise and Colony fires in the southern Sierra Nevada on September 9, the twin blazes merged and burned a total of 88,307 acres (35,737 hectares). The fire was not declared contained until mid-December, after several atmospheric rivers delivered rain and snow to the mountains. The number of firefighting personnel reached more than 2,000 and firefighting costs surpassed $170 million.
The KNP Complex forced the communities of Three Rivers, Wilsonia, and Cedar Grove to evacuate, and caused the temporary closure of Sequoia and Kings Canyon National Parks while damaging roads, trails, and cabins within. The fire also heavily impacted the endangered giant sequoia, which grows in less than a hundred natural groves in the western Sierra Nevada. National Park Service scientists calculated that the KNP Complex Fire killed roughly 1,300–2,400 large giant sequoias (hundreds more died in the Windy Fire in the Sequoia National Forest, which burned contemporaneously). The fires are estimated to have killed three to five percent of the total population of large giant sequoias.
The KNP Complex Fire took place during a severe fire season for the western United States, and particularly for California. During the state's 2021 wildfire season nearly 2.6 million acres (1,100,000 ha) burned: the second largest area on record after 2020. The national preparedness level hit the maximum level of 5 on July 14 and remained there until September 20, the longest period on record. Officials took drastic measures to try and limit new ignitions: between August 31 and September 15, the U.S. Forest Service’s Pacific Southwest Region closed all of California's national forests to public use because of fire conditions.
In the decades preceding the fire, average temperatures in the Sierra increased measurably even as precipitation did not. This trend was driven partly by climate change. Climate change and consequent warming in California has helped produce hotter and more severe droughts, such as the one California endured between 2012 and 2016. Acute stress from that drought killed many trees in the Sierra Nevada, particularly at middling elevations.
The lack of water also crippled trees' abilities to resist the predations of bark beetles, which resulted in "greatly elevated mortality" for many major tree species in Sequoia National Park, including the ponderosa pine, the sugar pine, the incense-cedar, and the white fir. Annual tree mortality rates nearly doubled in the park just between 1983 and 2004. A park representative estimated in 2021 that Sequoia and Kings Canyon National Parks held over one million beetle-killed trees that were helping drive the KNP Complex Fire.
California saw its second-driest water year ever in 2020–2021, exceeded only by that of 1923–1924. It was the driest ever water year on record for the southern Sierra Nevada, with 9.9 inches (25 cm) of rainfall compared to the region's average of 28.8 inches (73 cm). The summer of 2021 was also California's hottest ever recorded. The hot and dry conditions kept vegetation moisture levels "critically low".
The drought and dead trees added to the high levels of vegetation that had already accumulated in Sierra Nevada forests. Prior to European-American settlement, frequent fires of lower severity occurred, leaving most sequoia trees unharmed and aiding regeneration in the forest by consuming dry fuels. This ceased in the 20th century when the U.S. federal government began extinguishing every wildfire as a matter of policy. This led to elevated fuel loads in forests, including giant sequoia groves.
Not until the 1960s was fire reintroduced to some groves. While approximately 30,000 acres (12,000 ha) used to burn naturally and annually in the Sequoia and Kings Canyon parks, as of 2022 the parks burned only around 10,000 acres (4,000 ha) annually in prescribed burns. Much of the KNP Complex Fire footprint had no recent wildfire burn history. A 2023 study identified "old, large-diameter fuels like fallen logs" as the likely culprit for the fire's high intensity after analyzing radiocarbon signatures in samples of the smoke, consistent with prior research demonstrating that fire suppression and the resulting accumulation of fuels have contributed to elevated fire intensities in the Sierra Nevada.
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KNP Complex Fire
The 2021 KNP Complex Fire was a large wildfire in Sequoia National Park and the Sequoia National Forest in Central California's Tulare County. After lightning ignited the Paradise and Colony fires in the southern Sierra Nevada on September 9, the twin blazes merged and burned a total of 88,307 acres (35,737 hectares). The fire was not declared contained until mid-December, after several atmospheric rivers delivered rain and snow to the mountains. The number of firefighting personnel reached more than 2,000 and firefighting costs surpassed $170 million.
The KNP Complex forced the communities of Three Rivers, Wilsonia, and Cedar Grove to evacuate, and caused the temporary closure of Sequoia and Kings Canyon National Parks while damaging roads, trails, and cabins within. The fire also heavily impacted the endangered giant sequoia, which grows in less than a hundred natural groves in the western Sierra Nevada. National Park Service scientists calculated that the KNP Complex Fire killed roughly 1,300–2,400 large giant sequoias (hundreds more died in the Windy Fire in the Sequoia National Forest, which burned contemporaneously). The fires are estimated to have killed three to five percent of the total population of large giant sequoias.
The KNP Complex Fire took place during a severe fire season for the western United States, and particularly for California. During the state's 2021 wildfire season nearly 2.6 million acres (1,100,000 ha) burned: the second largest area on record after 2020. The national preparedness level hit the maximum level of 5 on July 14 and remained there until September 20, the longest period on record. Officials took drastic measures to try and limit new ignitions: between August 31 and September 15, the U.S. Forest Service’s Pacific Southwest Region closed all of California's national forests to public use because of fire conditions.
In the decades preceding the fire, average temperatures in the Sierra increased measurably even as precipitation did not. This trend was driven partly by climate change. Climate change and consequent warming in California has helped produce hotter and more severe droughts, such as the one California endured between 2012 and 2016. Acute stress from that drought killed many trees in the Sierra Nevada, particularly at middling elevations.
The lack of water also crippled trees' abilities to resist the predations of bark beetles, which resulted in "greatly elevated mortality" for many major tree species in Sequoia National Park, including the ponderosa pine, the sugar pine, the incense-cedar, and the white fir. Annual tree mortality rates nearly doubled in the park just between 1983 and 2004. A park representative estimated in 2021 that Sequoia and Kings Canyon National Parks held over one million beetle-killed trees that were helping drive the KNP Complex Fire.
California saw its second-driest water year ever in 2020–2021, exceeded only by that of 1923–1924. It was the driest ever water year on record for the southern Sierra Nevada, with 9.9 inches (25 cm) of rainfall compared to the region's average of 28.8 inches (73 cm). The summer of 2021 was also California's hottest ever recorded. The hot and dry conditions kept vegetation moisture levels "critically low".
The drought and dead trees added to the high levels of vegetation that had already accumulated in Sierra Nevada forests. Prior to European-American settlement, frequent fires of lower severity occurred, leaving most sequoia trees unharmed and aiding regeneration in the forest by consuming dry fuels. This ceased in the 20th century when the U.S. federal government began extinguishing every wildfire as a matter of policy. This led to elevated fuel loads in forests, including giant sequoia groves.
Not until the 1960s was fire reintroduced to some groves. While approximately 30,000 acres (12,000 ha) used to burn naturally and annually in the Sequoia and Kings Canyon parks, as of 2022 the parks burned only around 10,000 acres (4,000 ha) annually in prescribed burns. Much of the KNP Complex Fire footprint had no recent wildfire burn history. A 2023 study identified "old, large-diameter fuels like fallen logs" as the likely culprit for the fire's high intensity after analyzing radiocarbon signatures in samples of the smoke, consistent with prior research demonstrating that fire suppression and the resulting accumulation of fuels have contributed to elevated fire intensities in the Sierra Nevada.