Fires are natural in California: Many of its ecosystems, from the chaparral of southern California to the pine forests of the north, evolved to burn frequently. But since the 1980s, the size and ferocity of the fires sweeping across the state have tended to increase. Fifteen of the 20 largest fires in California history have occurred since 2000.
Most of the hottest and driest years in the state have also occurred during the past two decades.
Over the past century, California has warmed by about three degrees Fahrenheit. That extra-hot air sucks the water out of plants and soils, leaving trees, shrubs, and rolling grasslands dry and ready to burn.
The drying effect of vegetation increases with each degree of warming, explains Daniel Swain, a climate scientist at the University of California, Los Angeles, which means plants lose their water more efficiently today than before climate change raise California temperatures.
Climate 101: Wildfires
Because of this effect of climate change, wildfires are increasing in size, both in California and throughout the western United States, says Park Williams, a fire expert at Columbia University. Since the 1980s, he and a colleague reported in 2016, climate change contributed to the additional burning of 10 million acres in western forests, an area the size of Massachusetts and Connecticut combined.
Changes in precipitation are another factor. The summer dry season in California has also been prolonged. Each additional day allows the plants to dry out further, increasing their susceptibility to burns.
"Usually, or I don't want to say anything more because things are changing so fast, we get some showers around Halloween that fog us up," says Faith Kearns, a scientist at the University of California Oakland Water Resources Institute. But in recent years, those rains haven't come until much later in the fall, November, or even December. [Mks_pullquote align = ”right” width = ”300 ″ size =” 20 ″ bg_color = ”# d0bee2 ″ txt_color =” # 000000 ″] The state is hotter and drier than it used to be, and that's driving a trend toward bigger fires. [/ Mks_pullquote]
That may seem like a minor problem, but it has big effects. In the fall, California is often buffeted by gusty winds. Therefore, if a fire does break out, it can spread fast and strongly. That's what happened this year, as well as last year's Thomas fire.
"We have lengthened the fire season by shortening the rainy season, and we are warming up," says Swain. "That is essentially what has allowed these recent fires to be so destructive, at times of the year when I really wouldn't expect them."
The total number of wildfires in California has not increased; in fact, the numbers were much higher in the 1980s and 1990s than in the past decade. The total area burned varies considerably from year to year, depending on many factors, including luck: rain buffers things early or fires start in places where they are easier to contain.
But climate change is driving a clear trend: When wildfires occur in California, they have a greater opportunity to grow large and destructively.
"These same fires today are occurring in a world about three degrees Fahrenheit warmer than it would have been without warming," says Williams. "Which means that today's fires are probably more difficult to fight than they would have been in a colder world."
By alejandra borunda
Illustrations by Kennedy Elliott
Original article (in English)