The Los Angeles fire crisis isn’t over yet. Unusually dry conditions and hurricane-force seasonal winds are fueling multiple fast-moving and destructive wildfires in Los Angeles County. In recent weeks, flames have devastated various portions of the metropolis, causing the death of at least 28 people and destroying over 16,000 buildings. But if the two main fires – the Pasilades and the Eaton fire – are now mostly under control, in the last few hours two other fires have broken out: one in the area of the Castaic artificial lake north of the city (which triggered new evacuation orders) and another in the Bel-Air neighborhood.
Why are these wildfires happening in the winter?
While fire season in Southern California is generally thought to stretch from May to October, recent research has shown that rising temperatures and decreased precipitation trends are expanding the fire season’s duration, and that widening of the season is projected to continue in the future. In some parts of the state, fire season is already considered to be an all-year affair.
What is driving these fires to such extreme intensities?
One of the big reasons the Los Angeles–area fires are growing so out of control is that Santa Ana winds are blowing across the region. These winds typically occur in the fall and winter, and they involve dry wind blowing from inland, high desert areas toward the California coast. Along the way, the wind blows over mountain ranges. As the wind descends the mountains, it becomes compressed due to the increased atmospheric pressure and warms. That in turn lowers the relative humidity of the already dry desert air, making it better at desiccating vegetation that can fuel fires.
The other big driver of the extreme fires is the abundance of dried-out grass and vegetation, a consequence of recent weather patterns.
In a very dry year, there is a lot less grass that grows in Southern California versus a wet one, but last year was very wet in Southern California. This leads to an excessive fuel loading, a lot of extra fuel for potential fires. Now, since September, Southern California has seen the driest start to the winter on record, period, as well as among the hottest starts to winter on record.
It was the combination of these two elements — the Santa Ana winds and high fuel loads — that set the stage for the devasting burning occurring now.
How much is human-caused climate change to blame here?
While it will take a little bit more time for researchers to determine exactly how much the burning of fossil fuels has influenced these specific wildfires, it’s undeniable that human-caused climate change has exacerbated weather conditions favorable for more intense wildfires in California.
It’s not just that drier conditions are perpetually more likely in the warming climate. Moreover wettest years will continue to become even wetter, but at the same time, we’re also getting much hotter summers and drier falls, as well as an increasing likelihood of dry winters.
Wetter years grow more vegetation, and the drier years that follow then prime those fuels for burning.
Landscapes dominated by grass and brush — like much of the area now burning in Southern California — are especially sensitive to this weather whiplash.
Many non-native species can spread fires more quickly.
Southern California is dominated by shrublands known as chaparral. The landscape was historically characterized by short, shrubby plants, with evergreen native grasses that maintained moisture and greenness for most of the year. Fires were rare because lightning was infrequent. And even when they flared up, they remained confined because the open spaces between the plants acted as natural firebreaks.
Non-native species, which evolved together with pastures and livestock, have outcompeted the native species and filled the empty spaces in the shrubby areas, creating a carpet of flammable material especially near the roads, where fires often start. Unlike native evergreen grasses, this type of non-native vegetation dies each year and then regrows. Their short life cycle leaves behind a thick layer of dry, dead vegetation by late spring. These grasses fill every available space, a phenomenon known as fuel continuity.
Eucalyptus trees, introduced to California in the mid-19th century from Australia, add another layer of risk. Known for their aromatic scent, these trees have incredibly flammable and oily leaves. Their bark, which has a paper-like consistency, peels off and remains in the wind, carrying the embers up to almost a kilometer away.
Possible solutions
Vegetation management plays a critical role in wildfire mitigation. There are areas that are experimenting with sheep grazing as a low impact method of managing grass growth. Some areas of Southern California are even testing a “BurnBot,” a machine that moves across the ground setting off controlled fires to eliminate both existing vegetation and seeds.
Furthermore, creating a self-sustaining community of native perennial grasses, so as not to have to do constant maintenance, could restore the area’s natural defenses.
References:
www.sciencenews.org/article/california-wildfire-burning-winter
www.wired.it/article/incendi-los-angeles-piante-invasive/
