By Justin Worland
December 7, 2017

The Southern California wildfires spreading through Ventura and Los Angeles counties are among the devastating wildfires residential communities have seen in the decades since developers have expanded further and further onto land prone to natural disaster.

But in several ways California’s fires are unusual. They come late in the year when weather conditions typically stifle potential fires and some have sprouted up in the middle of dense urban areas typically far from fire zones. California’s unusual wildfire activity comes largely thanks to dry conditions in the region and the state’s Santa Ana winds.

The Santa Ana winds are a common occurrence in Southern California between October and March as warm air blows in from the desert leading to blustery days in the region. At their most powerful, the winds can wreck destruction throughout the region, knocking down trees and power lines. The wind’s heat also helps dry vegetation, making it easier to burn. And when there’s a fire, the winds can also transport flames quickly spreading fire from place to place.

That’s what scientists say happened in Southern California in recent days as at least four serious fires spread in scattered locations across Ventura and Los Angeles counties, prompting thousands to evacuate and freeways like the 405 to partially close. The Santa Ana wildfire threat index, which measures the potential for the winds to spread fire, ranked the threat level at high or extreme on Thursday from just south of Santa Barbara to the Mexican border.

The hot and dry weather in the region has also contributed to the rapid spread of California’s fires. This year was the second hottest on record when measured half way through the year. And downtown Los Angeles has received just 0.11 inches of rainfall since the beginning of October, typically the region’s west season, according to data from the National Weather Service. That leaves lots of material that’s ready to burn.


Lingering over recent California fires is the question of long-term climate change. Warmer temperatures dry out vegetation, making them easier to burn, and scientists say vulnerable regions like California should expect a spike in wildfires in the coming decades as temperatures continue to rise. The effect of climate change on the Santa Ana winds remains uncertain, though a 2006 study in the journal Geophysical Research Letters suggested that warming could shift the winds’ season leading to larger areas burned by fires.

Still, even as humans continue to stem climate change-causing greenhouse gas emissions at a pace scientists say is too slow to adequately address climate change, a slew of policy changes can reduce the impact of wildfires like those affecting Southern California from changes in land use patterns to making better use of controlled burns.

But Southern California’s fires should be a wake up call.

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