Why are California's fires so historic? For starters, a diablo is at work

A Christmas tree stands as a lone sentinel in the front yard of an evacuated home in Carpinteria, California. Photo / AP

Why is California burning? One answer is simple: California always burns.

But this latest inferno - three bushfires eating at the hills in and around Los Angeles, America's second-largest city - is frightening even for people who are accustomed to big burns. What's more, it follows the state's deadliest fire on record by only a few weeks.

It gets even worse.

The recent Sonoma County fires north of San Francisco that left more than 40 people dead, and the current Thomas Fire that has destroyed 800 structures and damaged or threatens more than 18,000 others in the Santa Barbara area, are so bad that they've rendered last year's horrid Blue Cut Fire that wiped out more than 300 homes near San Bernardino a distant memory.

California Governor Jerry Brown, (D), appeared stricken in an address to his state, calling the gargantuan blazes "the new normal" in one sentence and "the new reality" in another, before finally saying: "With climate change, some scientists are saying California is literally burning up".

There is a lot of blame to go around.

Blame the devil.

Or more precisely, said Jon Keeley, a research geologist for the US Geological Survey, the dreaded diablo - "devil" in Spanish - winds.

Usually, winds in the area "flow from the west, carrying cool, humid air from the [Pacific Ocean] onshore," Keeley wrote in a blog post.

But the hot, dry diablos reversed course, blowing at 65km/h from the northeast towards the ocean with gusts of up to 120km/h. Winds don't put out fire. They give it a ride and deposit flames all over.

"These hot, dry winds develop from an unusual pattern of high and low pressure cells, and are most prominent in autumn. They follow the normal summer and fall drought that occurs in this Mediterranean-type climate, leading to severe fire weather conditions," Keeley wrote.

They've played a role in California's most catastrophic fires, he said, including the 1991 Tunnel Fire in Oakland that left 25 people dead. "The speed of these fires is a major factor leading to the loss of human lives."

Blame county planners and housing developers.

Two million homes bump against wildlands in the West, the majority in two states with the highest risk, Washington and California, according to Headwaters Economics, an independent nonprofit group that studies bushfire prevention.

People get to live and work in remote locations with beautiful views, but the value of properties at a moderate to high risk of being engulfed is about US$500 billion, according to CoreLogic, a company that studies real estate economics, not to mention the risk to people's lives.

"It's a witch's brew," Tom Harbour, the former national fire and aviation director for the Forest Service, said to me for a 2015 story about the challenges his firefighters faced when he sent them to fight fires that are better left alone to burn. "The risk keeps increasing. I'm putting firefighters in harm's way."

Keeley adds a key point here. The explosion of development close to woods increases fire drama. "Nearly all fires in Sonoma County are caused directly or indirectly by people, such as intentional ignitions or power lines igniting fires. Population growth raises the probability of fire igniting under severe weather conditions," he wrote.

Blame the climate.

"It never rains in California" is just a saying and a song. It often pours in winter - rain in the southern portion of the state and snow in the northern and central mountains. As a result, foliage blooms in a range of colors in every corner of the Golden State.

Then it dries in the hot summer. Not normal dry, but baked dry, devoid of any moisture. "Plants are happy and growing well in the winter time, and when summer proceeds to the fall they get drier and drier," said Marti Witter, a fire ecologist for the National Park Service's Santa Monica National Recreation Area.

"The amount of water in the plants get lower and lower and lower; it means that they are very dry. When it gets to critical threshold level and a fire comes through, they're very flammable. It happens every year," Witter said.

In August last year, Columbia University's Earth Institute released a study that offered evidence that global warming has contributed to California's drought.

The year before, a Stanford University study led by associate professor Noah Diffenbaugh used historical data from the US National Climatic Data Centre to conclude that the state will experience more drought as its climate continues to warm.

County fire hand crew member Nikolas Abele keeps an eye on a hillside for any stray embers during a firing operation in Santa Monica. Photo / AP

Dry doesn't begin to describe what California is right now.

The state emerged from an unprecedented five-year drought only last year. Consider these recent headlines about what it wrought: "Scientists say California hasn't been this dry in 500 years." "As water runs dry, Californians brace for a new way of life." "California's terrifying climate forecast: It could face droughts nearly every year." "Wild animals in drought-stricken western states are dying for a drink." "Millions of pine trees on hillsides are dead and bone dry."

Like every state, California has a great diversity of plants, including an abundance of dry shrubland called chaparral. Since the addition of housing near wooded landscapes forces firefighters to douse blazes that would normally burn away vegetation in a natural low-intensity fire cycle, new plants grow when it rains and join the old dried-out growth in summers. Together they sit and wait for a potential fire catastrophe.

Also, because humans track and traffic nonnative species from across the world, more fire-resistant grass that's native to California has given way to faster growing and faster burning grasses that don't belong on the landscape. They basically become a fuse that leads flames to dry vegetation, which combusts when the fire reaches them.

"When they catch on fire, they burn beautifully," Witter said. "There's a lot of biomass and . . . that contributes to the spectacular fire you're seeing." He referred to the Thomas Fire that is spreading north from Ventura County into Carpinteria and Montecito, where the rich talk-show celebrities Oprah Winfrey and Ellen DeGeneres own mega-homes.

Blame the Santa Ana winds.

"The intensity of the Santa Ana winds is about as extreme as they get," Witter said of the winds that have driven the Thomas Fire into legend as the fifth-largest in California history. Witter kept repeating the word extreme.

"It's definitely extreme. I wouldn't say they're completely unprecedented. We're basically having a firestorm that happened in 1993, 2003, 2007, the Soberanes Fire, Rim Fir and Station Fire. It's certainly an extreme event" on path to break even more records, since the Thomas Fire is only 10 per cent contained.

What drought-prone California needs is something it doesn't get consistently enough. "We haven't had rain yet," Witter said. "If we had had a normal October or November rain of a couple inches, that would have put an end to our fire season."