Bay Nature reporter Daniella Garcia-Loos Almeida spoke with climate scientist Daniel Swain about potential local impacts of El Niño and a marine heat wave that’s been sitting off the coast of Southern California all year. The conversation has been condensed for space and clarity. Read more from Swain and other experts: A ‘Super’ El Niño Is Here. What Does It Mean for the Bay Area?
BN: How will El Niño and the marine heat wave interact and impact nature and the people of the Bay Area?
Swain: There’s now very high confidence in a very strong El Niño event this year. This will profoundly affect California for the next six to 12 months and in different ways in different seasons.
El Niño is an episodic warming of the Eastern Tropical Pacific Ocean, by definition. It’s not a heat wave. It’s not heavy rain. It’s not something that comes to California. This is literally something happening thousands of miles away at the surface of the Pacific Ocean off the coast of Peru.
There’s also this big marine heat wave across the subtropical Pacific, extending all the way from Hawaii to South America to California, and that’s been in place since this winter. The first wave of that [marine heat wave] preceded any kind of El Niño event. But it probably helped, in part, to facilitate the development of a strong El Niño.
The first obvious effect of El Niño is that later this summer and fall the nearshore ocean will start to heat up even more, and that’s because coastal upwelling will start to decrease.
But the main impact, from about December through March, will likely be a more amplified Pacific storm track. So the jet stream, that river of high-velocity air that kind of defines the storm track, is more likely to be both stronger farther south than usual and extended more eastward than usual, right into California. That increases the likelihood of persistent wet stormy periods during winter, and the nearshore ocean height, so literally the water levels will probably increase.
You might have brief periods during either major winter storms or king tide events where the water level is several feet higher than we’re used to. That might well be enough to put a lot of coastal Bay Area highways and even some coastal neighborhoods and developments underwater for extended periods. This year’s king tides could be the highest king tides we’ve ever seen. I’m really eyeing that as a major impact in the Bay Area, specifically, as we get toward the winter, and that could be very disruptive.
And I really wanted to get to this, because there’s a lot of misleading stuff out there: If you just look at general relationships between El Niño and general California precipitation, the relationship is pretty weak, but that’s not what we’re talking about this year. We’re talking about possibly the single strongest El Niño event ever observed. During the strongest El Niño events, that wet winter signal does actually extend all the way up through and past the Bay Area into Northern California.
BN: Do you think managers learned from the El Niño in 2015–16? Are there any lessons from that?
Swain: I think a lot of people learned exactly the wrong lesson from that one. I almost universally hear that that El Niño proved El Niño doesn’t matter for California precipitation, which is absolutely not what happened. There was no climate scientist or meteorologist who said “this winter is going to be wet.” The forecast was a greatly increased likelihood that winter would be wetter than average, and it wasn’t. The problem is you can’t evaluate the accuracy of that kind of prediction with an “n equals one.” But just because an n of one—a strong El Niño event did not yield a wet winter—absolutely does not mean that this one will not be wet.
BN: On the marine heat wave, will that continue to be a second consideration?
Swain: Yes, it’s likely to considerably intensify and become a lot more broad. I think that’s going to be a really, maybe even, dramatic feature of the conditions in fall and winter, and that will certainly affect ecosystems as it has during previous major El Niño events. This is likely to be something that’s with us for some time to come.
This is a very different type of marine heat wave than the 2013–2014–era Blob. That was hundreds of miles off the coast. This marine heat wave will be right along the immediate coast. People in the Bay Area will notice a significant increase in the ambient humidity and the local air temperatures later in the fall.
For ecosystems, they’ve kind of had it rough over the last couple of decades with a number of major marine heat waves, and this will likely be another one.
