Dixie is California’s second largest wildfire in history – why can’t it be tamed?

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California’s Dixie fire has now burned through nearly a million acres of land, making it the second biggest wildfire in the state’s history.

Spanning five counties and more than 1,500 square miles in California’s heavily forested north-eastern wilderness, the blaze has razed whole neighbourhoods, cost taxpayers about $540 million so far to contain, and remains only 75 per cent surrounded by fire defences or natural barriers.

It is second only to last year’s August Complex, a rare “gigafire” that covered more than 1 million acres, destroyed 935 structures, and killed one person, according to the state firefighting agency Cal Fire.

Both are part of a wave of record-breaking infernos that has seen all but two of California’s top 20 biggest wildfires break out within the last 20 years, and nine of them in either 2020 or 2021.

What made Dixie such a monster? One spotlight has fallen on the Pacific Gas and Electric Company (PG&E), a publicly traded utility company with a monopoly over Northern California, which last year pleaded guilty to 84 counts of manslaughter stemming from the horrifically destructive 2018 Camp Fire.

Dixie was sparked on 13 July by a fir tree that had fallen against a PG&E power line near Dixie Mountain in Butte County, but PG&E did not cut off the power until nearly 10 hours after the first signs of trouble.

By the next morning, Dixie had exploded from one acre to 1,200 acres, making it impossible to quickly contain. A US federal judge is now investigating PG&E’s role, as well as an unauthorised drone that impeded early firefighting efforts. PG&E has denied any involvement with the latter.

“Your company is a convicted felon that poses a safety hazard to the state of California,” Judge William Alsup told company lawyers on Monday. A former criminology professor named Gary Maynard is also accused of mounting an arson spree behind the lines of first responders, potentially risking their lives. Maynard denies setting any fires.

But the stage was set for these incidents by years of drought and rising heat in California, driven by the climate crisis, that have made its ancient forests a tinderbox and extended wildfire season by two months.

Average temperatures in the state have risen by about 1C over the past century, with the last seven years the warmest ever. This year was particularly bad, with the hottest summer in state history and a world record 24-hour temperature reading in Death Valley on 11 July.

Meanwhile, California has suffered so many droughts that some experts combine them into one 20-year “megadrought”. A study of tree ring records suggests that 2000 to 2018 was the driest period since the 16th century, attributing about 40 per cent of the deficit to climate change.

The rising heat has led to early snow melts in the Sierra Nevada mountains, which have historically acted as a gigantic reservoir that stores up water during the winter and slowly releases it throughout spring and summer.

Now much of that snow is melting all at once, and some of it is falling as rain, drying out the forests ahead of schedule. At high altitudes, some woods that were previously cloaked in white until June or July are now going naked by April.

According to Jay Lund, co-director of the Center for Watershed Sciences at the University of California, Davis, about 1 per cent of the Sierra Nevada water runoff has migrated from spring to winter every year for the past 50 years.

And although the less frequent rainy seasons are now more intense when they do arrive, plant life often needs multiple wet years in a row to recover from sustained dehydration. It is these two factors – heat and drought – that have together made California’s forests dry and brittle for longer each summer, creating the perfect conditions for wildfires.

These trends are exacerbated by the way the USA historically managed its forests. Whereas many native American tribes set controlled fires to rejuvenate the ecosystem, the US has tended to suppress as many as possible, allowing fuel-rich undergrowth to accumulate.

Meanwhile, California’s housing shortage and exorbitant prices have led to more people settling on the edge of wilderness, putting a larger number of homes in the path of ruin.

So far, Dixie has been less destructive to property than other major fires, wrecking about 1,329 structures. The worst ever was the Cedar Fire near San Diego in 2003, accidentally started by a lost hunter who was trying to signal for a rescue.