A scientist explains the ‘why’ of California’s wildfire crisis

Unexpected bad news hit California more than 11,000 times last week. That’s the estimated number of lightning strikes that unleashed two of the biggest fires in state history. The fires are burning at the same time across more than 1.4 million acres, sending a cloud of smoke stretching across the Western U.S.

Daniel Swain, a climate scientist at the University of California, Los Angeles and the National Center for Atmospheric Research, has emerged as one of the foremost voices explaining how California became a climate tinderbox. Forests dried out over years of rising temperatures, then the ecosystem suffered through the most intense heat wave in decades (and millions of people suffered through the first rolling blackouts in 20 years).

The heat and dryness left everything primed for a catalyst to set off a drastic impact.

Lightning sparked the first of what are now more than 7,000 fires. Last year at this time, according to the governor’s office, there were 4,300 fires that burned 56,000 acres.

The fiery consequences of extreme heat are not a surprise. In fact, Swain co-authored a paper that came out just last week with a remarkably prescient and straightforward title: “Climate change is increasing the likelihood of extreme autumn wildfire conditions across California.” The timing is a shock, however, since autumn is still a month away.

Swain’s research and blogging – his post on the underlying environmental dynamics has drawn more than 1,500 comments so far – have made him a public face of climate science while his home state burns. He spoke to Bloomberg Green about the heatwave, what to expect once coastal winds start the real fire season, and where he sees good news in all this. The interview has been condensed and edited for clarity.

Q. Last week you said the recent heat wave in California would raise the risk of wildfires. That was a worry for the fall, something weeks or even months away – and then fires exploded within 48 hours. What happened?

A. A really big lightning event. Usually this time of year there’s a limited number of fire-starts in Northern California. But unfortunately the state got 11,000 opportunities for fires to take hold, and several hundred of them did. Usually the peak of fire season is autumn – unless you get 11,000 lightning strikes without any rain.

Q. How rare is that?

A. No one saw it coming seven days out, but it was in the forecast the day before. In terms of climate change, forecasters don’t really know if these (lightning) events will become more or less common as the climate warms. You can’t really generalize about thunderstorms. The thunderstorms you get in California are actually quite different from the thunderstorms you get in most of the rest of the world.

Q. Do these fires mean California is off the hook for the fall?

A. Offshore wind can start some time in September. A lot of the fires currently burning won’t be out for weeks, after the traditional offshore-wind fire season begins. The vegetation that hasn’t burned yet is still extremely dry. There wasn’t really any meaningful rainfall anywhere. This has catapulted us forward to a bad fire season already, regardless of what happens moving forward.

Q. But shouldn’t there be a very tiny silver lining here? Things can’t burn twice.

A. One of the interesting things we saw, especially in the LNU complex fire in Napa, Solano and Lake counties, is a lot of the areas that burned have already burned in the past couple of years – in some cases twice. There are some places where this is the third time they’ve burned in six years. Usually you would expect burn scars to last for a few years and reduce, if not prevent, fires. Most folks would think we’d have at least five or seven years of reduced risk in some of these areas. But there was just enough time for the vegetation to grow back and support a fire.

The warming and drying effect has been so profound that stuff that had regrown was actually dry enough to burn pretty intensely.

Q. How freaked out should we be about the very old trees in Big Basin Redwood State Park?

A. They’re a fireresilient species, generally speaking, but it was also a particularly intense fire. If you look at their tree-ring core history, a lot of them have witnessed four or five fires over a 1,000-year life. They can clearly thrive in low to medium intensity fires. This is a pretty high intensity fire. There’s going to be a ton of studies on what happened in Big Basin a few years down the line. It’s going to tell us a lot about the resilience of redwood to our new fire regime – not the one that they evolved in and thrived under for thousands of years.

Q. Have forests come back after fires over the last few years?

A. Sometimes an intense fire would have been survivable had it not been followed up by extremely dry and hot conditions after the fire. The fire doesn’t always kill the tree. Sometimes the drought following the fire kills the tree.