California and the Western United States are no strangers to fire, but this week's awful wildfires in the Los Angeles area have taken the destruction inside one of America's greatest cities.
Key themes from this episode include the complex interplay of natural and human factors in wildfire ignition and spread, the unintended consequences of past fire suppression policies, the escalating impact of climate change, the unique challenges presented by Southern California's weather patterns, and the devastating impacts of wildfires on both the natural environment and human communities.
Key Themes and Findings --
Historical Context and Policy Missteps:
The 1910 firestorm in the Western US led to a policy of aggressive fire suppression by the US Forest Service. While initially effective, this has had unintended long-term consequences.
The suppression of low-intensity fires has allowed for the accumulation of fuel (dead leaves, branches, etc.), making forests more vulnerable to severe, high-intensity fires. As one source notes, "Low burning fires clear the forest floor and lower branches from trees. Then, if a more intense fire moves through the same area, it’s slowed by a lack of fuel."
The lack of regular, low-intensity burns disrupts the natural fire cycle that is beneficial for many ecosystems.
Factors Influencing Fire Spread:
Fuel Load: The amount and type of vegetation is a major determinant of fire spread and intensity. This includes not just surface fuels, but also "ladder fuels" that allow fire to reach the forest canopy.
Weather Conditions: Hot, dry, and windy conditions are conducive to wildfire development. In California, Santa Ana winds play a significant role in spreading fires and embers (which can spark new spot fires far away.) As one source notes, "The air of the Santa Ana winds is unusually dry because it originates in the desert environment of the Great Basin."
Topography: Land shape impacts the availability of sunlight, water, and the speed of fire spread, with steep slopes often accelerating fire movement.
Moisture Content is crucial; dry vegetation burns much more easily, and some sources noted extreme dryness in Southern California this year.
Embers: Embers blown by high winds can ignite spot fires well ahead of the main fire front. As one source notes, "embers from the fire flames were being blown more than a mile...spark[ing] new spotfires."
Climate Change Amplification:
Climate change is intensifying the risk of wildfires globally, with hotter, drier conditions and more extreme weather patterns. A quote from one of the sources notes that "Climatic cycles with wet periods that create substantial fuels, followed by drought and heat, often precede severe wildfires. These cycles have been intensified by climate change."
Multiple sources noted that 16 of the 20 most destructive fires on record in California have occurred in the past decade.
There is a climate pattern, caused by a ridge of high pressure, that is deflecting storms away from Southern California which leads to drier conditions in the south and wetter ones in the north.
Wildfires in California:
California experiences severe wildfires due to its dry climate, hot summers, and frequent winds. Historically, before 1800, up to 11.9 million acres burned annually. Currently, since 2000, the annual area burned has ranged from about 90,000 to 1,590,000 acres, with the 2020 wildfire season burning nearly 4.5 million acres.
The August Complex fire in 2020 consumed over 1 million acres, the largest in California history. Many of the largest fires on record have occurred in the past decade.
Some areas of California experience repeated ignitions and fires.
Southern California is experiencing extremely dry conditions this year, with downtown Los Angeles having received just 0.16 inches of rain since October 1, while the normal amount should be 4.56 inches.
Ecological Impacts and Benefits:
Wildfires can expose nutrient-rich soil, which supports
Show more...
