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California: More Drought, Weather Extremes on Tap

It is clear now that California’s drought is continuing in most of the state and we may also be in for a future of more extreme weather patterns – including more drought. Here’s a look at new research on the Ridiculously Resilient Ridge, why El Niño disappointed and what all this means for water management.

Written by Tara Lohan Published on Read time Approx. 5 minutes
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Fingers were crossed at the beginning of winter that a strong El Niño could be the antidote to California’s drought. But while the state is definitely in better shape than it was this time last year, most of California is a long way from being drought-free.

Northern California fared the best, with reservoirs filled to the brim, but statewide snowpack is 87 percent of normal and Southern and Central California missed out on much of the winter’s precipitation.

The bad news is that California is still in drought – even worse may be research indicating that weather extremes are occurring more frequently in the state.

“We’re seeing increasing temperatures and relatively little change in average precipitation, but an increase in the variability and the occurrence of both wet and dry extremes,” said Daniel Swain, an atmospheric scientist at Stanford’s School of Earth, Energy & Environmental Sciences and the lead author of a new paper published in Science Advances. “Those are both trends the best evidence suggests will probably continue in the 21st century.”

Swain and a team of three other researchers from Stanford, Northwestern and Columbia universities looked at data between 1949 and 2015 to see if there were any trends in the kinds of atmospheric patterns that historically resulted in meteorological extremes in California in terms of both temperature and precipitation.

Were the atmospheric pressure patterns that caused extreme dry and extreme wet periods happening more frequently? The answer, they found, is mostly yes and the reasons why have big implications for water managers (and the rest of California).

Extremes Expected

What the researchers found quite definitively was that warm and dry patterns, like those that have characterized the past several years of California’s drought, are actually happening more often. But when it comes to wet weather things get a little more complicated.

“The increase in the extreme dry patterns in the atmosphere isn’t necessarily occurring at the expense of patterns conducive to really wet conditions,” said Swain.

Instead, there appears to be more variability – or an increase in extremes.

“When we do the analysis for the patterns that have led to historical wet extremes we actually get slightly different answers, depending on which method we use,” he said. “One method suggests little change over time in the occurrence of these patterns and the other one suggests an increase.”

The researchers concluded that there is high confidence not only that there has been an increase in these warm and dry patterns, but also that there has been no corresponding decrease in the wet patterns, and there may actually have been an increase, explains Swain.

So, we’re definitely having more very dry periods but that’s not causing fewer very wet periods, and in fact there may be more very wet periods, too.

The researchers used recent historical data and not climate modeling, so the study does not make any future predictions, but Swain says the findings appear to be consistent with other climate research that reveals there is little change in average precipitation, but an increase in the amount of very wet or very dry periods.

If you’re a water manager or policymaker, you should take note of this.

“It’s really important from a management perspective because we don’t need to worry about the years that are slightly dry or slightly wet or slightly warm – it’s those years that are really wet or really dry or really warm that cause problems in terms of drought impacts or flood impacts,” Swain said.

If we base our policy and management decisions on simply looking at data on average temperatures, we’re going to be in trouble. We’ll need to see the bigger picture of weather extremes, precisely the kind of events that can lead to catastrophic droughts and disastrous floods.

Don’t Blame El Niño

Swain’s research hinged, in part, around an atmospheric pattern dubbed the Ridiculously Resilient Ridge (RRR). This high-pressure system was parked off the West Coast from Southern California up to Alaska as California’s drought intensified beginning in 2013. It deflected storms away from all of California (and much of the entire West Coast) during the past several winters.

It is precisely this type of system that Swain’s research found has been occurring more frequently in California. And it may also have something to do with the disappointing results of this winter’s El Niño.

El Niño was predicted to be very strong this year. And it was in fact one of the strongest El Niños on record, says Swain – it just didn’t give California, especially Southern California, the precipitation it needed.

This year, the high-pressure ridge was positioned a little differently and didn’t end up blocking storms from hitting the entire coast. “Instead the storm track ended up aimed over far northern California and even more often over the Pacific Northwest,” said Swain. “Which is why the northern part of the state did OK but not great and the southern part of the state really missed out this winter, which was the biggest surprise of the year.”

“Partly what this shows is there is a diversity of atmospheric patterns that can lead to dry conditions in California,” he said. “But also that something this year seemed to be disrupting the influence of El Niño.”

Blame Climate Change?

There are a number of factors at play in the severity of California’s drought. One is likely related to climate change. Research has shown that drought risk is increasing because the state is experiencing higher temperatures. These higher temperatures are also increasing the severity of the drought.

This has led many to wonder whether or not the Ridiculously Resilient Ridge is also related to climate change. Earlier research from Swain and others took on this issue. “We were looking at whether or not global warming has made the occurrence of extremely high pressure in the region on an annual basis more likely,” he said. “In that paper we found the answer was yes.”

That research discovered that these stubborn high-pressure systems are more likely to occur now than in pre-Industrial Revolution days, before our onslaught of greenhouse gas emissions. But now we also have more information that augments that research and it has to do with where and how the warming is occurring, which is not uniformly.

“One could imagine the situation where it warmed exactly the same amount everywhere and it wouldn’t actually have this effect,” said Swain. “But because that warming pattern is non-uniform and the non-uniformity happens to align with the West Coast, that’s a big reason why we’re seeing what we’re seeing.”

And this, Swain says, is critically important because it defines the direction of the storm track, which in turn determines California’s wintertime precipitation. How much rain or snow falls during the winter months defines whether or not the state will be lifted from drought or mired in another year of overdrafted aquifers, fallowed fields and browned lawns.

Top image: Women run as the sun sets in San Diego, on Feb. 23, 2016. Winter, especially in the southern half of the state, was drier than hoped for during this El Niño period. (Gregory Bull, Associated Press)

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