Fall begins on Tuesday, Sept. 22, 2020, in the United States and throughout the Northern Hemisphere. The autumn equinox — also known as the autumnal equinox, the fall equinox, or the September equinox — occurs when the sun moves directly over the Earth’s equator, bringing virtually the same amount of daylight and darkness on that particular day.
So now that we got that out of the way, what does fall mean for California? The turning of the leaves, cooler days, chilly nights? No, save that for flowery poetry and fairy tales. In the 21st century, in an era of a rapidly heating planet, it means that fire season has only just begun.
Fire months— In the past, the fire season was from about May to October. However, with climate change as a contributing factor, most recent disasters show that the season is beginning earlier and ending later each year, with some experts suggesting that the fire season in California is now year round.
Many people mistakenly believe that peak fire season takes place during the hot summer. Contrary to popular belief, however, September and October are the most vulnerable months for wildfires, with peak fire season running from July to October.
In July and August, we here in Kaweah Country are at greater fire risk from lightning strikes due to the monsoon buildup over the Sierra that occurs that time of year. The region just endured the hottest August on record with an extended heatwave that lasted nearly the entire month.
In September and October, when the offshore winds, which are dry and fierce, begin in Northern California (Diablo winds) and Southern California (Santa Ana winds), wind-frenzied fires have leveled towns (Paradise Fire, 2018) and killed masses of people.
But no matter where in California, hot, dry summer temperatures followed by little to no rain in the fall contributes to parched vegetation causes the most destructive fires to occur in September and October. It is safe to conclude that all areas of California are most susceptible to wildfires during these months.
The first significant rainfall of autumn or winter typically brings the end of the fire season in California. However, in recent years, there is a trend for delayed autumn precipitation. Rising temperatures contribute to dryer vegetation, making fuel sources for wildfire more readily available. When paired with decreased autumn rain, California’s new fire season stretches well into winter.
For any fire to occur, there are three elements needed — heat, fuel, and oxygen:
Heat. There are many potential heat sources that can create embers and ignite wildfires. Many of these are human caused, but the current SQF Complex was ignited by lightning. The Creek Fire, however, was most likely of human origin.
Fuel. California’s arid climate and abundant, bone-dry vegetation as well as beetle-killed forests of standing dead trees provide unlimited amounts of fuel for wildfires.
Oxygen. California’s infamous Santa Ana winds produce gusts averaging 45-50 mph with record gusts clocked at over 160 mph. These winds fan the flames and spread embers, leading to truly devastating wildfires because there is no defense against the fire-wind combination. These offshore wind events take place mainly in the fall. The Kaweah canyon, on the other hand, rarely has wind events, good news on the fire front and bad news for the year-round air quality readings.
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