A climate scientist discusses how to think about and weigh the variables that led to the current disaster.
The fires in and around Los Angeles have already claimed dozens of lives, destroyed thousands of homes, and led to evacuation orders for hundreds of thousands of people. The economic damage is projected to be as much as a hundred and fifty billion dollars. Daniel Swain is a climate scientist at U.C.L.A. and the University of California Agriculture and Natural Resources who studies extreme weather events and their connection to climate change. He and I recently spoke by phone. Our conversation, edited for length and clarity, is below. In it, we discuss what really caused these fires to rage out of control, how he tries to communicate the role that climate change plays in natural disasters, and how the Los Angeles area became so vulnerable to catastrophe.
What makes these fires unique other than the extent of the damage they have caused?
I do think the sheer scope of the damage in terms of the number of structures lost and the economic losses is what jumps out the most. That said, there are other aspects of the over-all situation that are very different from anything we’ve seen before, too.
Let’s start with what’s not unusual, since I think that’s helpful for setting the stage. It is not unusual for strong dry winds to occur in the mountains and valleys near Los Angeles in January. This particular event was notably strong and did extend across more of the high-population and lower-valley regions than usual. But if you were to pick a time of year when you would expect to see strong dry winds, it would be now.
These are the Santa Ana winds you’re speaking of?
Yeah, these are Santa Ana-like. These were a little bit different from a traditional Santa Ana event because they were driven by a slightly different low-pressure system in a slightly different spot. That is partly why the winds are coming more from the north than from the east, and also why they were stronger than usual and reached deeper into the valleys than usual. But if you can think of it as being Santa Ana or Santa Ana-adjacent, it’s the same general idea. We only see winds that strong every five or ten years or so. So it’s notable for sure, but it’s far from unprecedented in its own right.
The preconditions, though, were drastically more unusual, bordering on unprecedented—specifically how dry conditions have been. And that is essentially quantified by looking at how much rain has or has not fallen in the Los Angeles area or San Diego area. And what we find is that this is now either the driest or second-driest start to the season on record throughout Southern California, going back a hundred years. In modern history, it has not been this dry this late in the ostensible rainy season.
That is something that really sets the stage for these fires, because had these same winds occurred following, say, an inch or two of rain so far in the season, even if that’s below average, it’s still a good soaking. If that had occurred, we wouldn’t be seeing the fires that we’re currently seeing. We wouldn’t have that explosively dry vegetation. It essentially has not rained in Los Angeles since last spring—in many areas, about a tenth of an inch or less, which is insignificant from a wildfire perspective.
On top of that, the inland parts of Southern California—the mountains, the elevated plateaus, and the desert regions—experienced their hottest summer on record. The city of Los Angeles did not, to be clear. But then, in early September, even the city of Los Angeles and really the entire Los Angeles basin did experience a record-breaking heat wave. And that was actually associated with the major wildfire outbreak at the time, if you recall, in early September. Many structures were destroyed. It remained unusually warm and hasn’t rained at all since then. That is the real anomaly here, with the winds being sort of a second-order anomaly.
From newyorkor.com
