Want climate news in your inbox?Â
A pregnant woman went into labor while being evacuated. Videos showed dozens of harrowing drives through fiery landscapes. Pleas appeared on social media seeking the whereabouts of loved ones. Survivors of a mass shootingÂ were forced to fleeÂ approaching flames.
This has been CaliforniaÂ since the Camp Fire broke out early Thursday morning, burning 80 acres per minute and devastating the northern town of Paradise. Later in the day, the Woolsey Fire broke out to the south in Ventura and Los Angeles Counties, prompting the evacuation of all of Malibu.
What is it about California that makes wildfires so catastrophic? There are four key ingredients.
The (changing) climate
The first is Californiaâs climate.
âFire, in some ways, is a very simple thing,â said Park Williams, a bioclimatologist at Columbia Universityâs Lamont-Doherty Earth Observatory. âAs long as stuff is dry enough and thereâs a spark, then that stuff will burn.â
California, like much of the West, gets most of its moisture in the fall and winter. Its vegetation then spends much of the summer slowly drying out because of a lack of rainfall and warmer temperatures.Â That vegetation then serves as kindling for fires.
But while Californiaâs climate has always been fire prone, the link between climate change and bigger fires is inextricable. âBehind the scenes of all of this, youâve got temperatures that are about two to three degrees Fahrenheit warmer now than they wouldâve been without global warming,â Dr. Williams said. That dries out vegetation even more, making it more likely to burn.
Californiaâs fire record dates back to 1932; of the 10 largest fires since then, nine have occurred since 2000, five since 2010 and two this year alone, including the Mendocino Complex Fire,Â the largest in state history.
âIn pretty much every single way, a perfect recipe for fire is just kind of written in California,â Dr. Williams said. âNature creates the perfect conditions for fire, as long as people are there to start the fires. But then climate change, in a few different ways, seems to also load the dice toward more fire in the future.â
Even if the conditions are right for a wildfire, you still need something or someone to ignite it. Sometimes the trigger is nature, like a lightning strike, but more often than not humans are responsible.
âMany of these large fires that youâre seeing in Southern California and impacting the areas where people are living are human-caused,â said Nina S. Oakley, an assistant research professor of atmospheric science at the Desert Research Institute.
Deadly fires in and around Sonoma County last year were started by downed power lines. This yearâs Carr Fire, the stateâs sixth-largest on record, started when a truck blew out its tire and its rim scraped the pavement, sending out sparks.
âCalifornia has a lot of people and a really long dry season,â Dr. Williams said. âPeople are always creating possible sparks, and as the dry season wears on and stuff is drying out more and more, the chance that a spark comes off a person at the wrong time just goes up. And thatâs putting aside arson.â
Thereâs another way people have contributed to wildfires: in their choices of where to live. People are increasingly moving into areas near forests, known as the urban-wildland interface, that are inclined to burn.
âIn Nevada, we have many, many large fires, but typically theyâre burning open spaces,â Dr. Oakley said. âTheyâre not burning through neighborhoods.â
Itâs counterintuitive, but the United Statesâ history of suppressing wildfires has actually made present-day wildfires worse.
âFor the last century we fought fire, and we did pretty well at it across all of the Western United States,â Dr. Williams said. âAnd every time we fought a fire successfully, that means that a bunch of stuff that would have burned didnât burn. And so over the last hundred years weâve had an accumulation of plants in a lot of areas.
âAnd so in a lot of California now when fires start, those fires are burning through places that have a lot more plants to burn than they would have if we had been allowing fires to burn for the last hundred years.â
In recent years, the United States Forest Service has been trying to rectify the previous practice through the use of prescribed or âcontrolledâ burns.
The Santa Ana winds
Each fall, strong gusts known as the Santa Ana winds bring dry air from the Great Basin area of the West into Southern California, said Fengpeng Sun, an assistant professor in the department of geosciences at the University of Missouri-Kansas City.
Dr. Sun is a co-author of aÂ 2015 studyÂ that suggests that California has two distinct fire seasons. One, which runs from June through September and is driven by a combination of warmer and drier weather, is the Western fire season that most people think of. Those wildfires tend to be more inland, in higher-elevation forests.
But Dr. Sun and his co-authors also identified a second fire season that runs from October through April and is driven by the Santa Ana winds. Those fires tend to spread three times faster and burn closer to urban areas, and they were responsible for 80 percent of the economic losses over two decades beginning in 1990.