What does a potential El Niño mean for cities around the world? #ColoradoRiver

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Here’s a look at the potential effects of an El Niño on cities around the world from Eric Holthaus writing for Slate. Here’s an excerpt:

To be declared an official El Niño, surface water temperatures in the equatorial Pacific Ocean must warm by half a degree Celsius averaged over three months and maintain that level for five consecutive three-month periods. That’s an arbitrary definition, sure, but it gives us the ability to crunch the numbers on weather patterns that tend to associate with El Niños on a global scale.

Statistically, this time of year has the least predictability at any time all year. But peering below the ocean’s surface, water temperatures are already off-the-charts-hot. If that warm water makes it to the surface, the planet could be in line for one of the most intense El Niños ever recorded. That would be enough to shift weather patterns worldwide and make the next couple of years among the hottest we’ve ever known. Earlier this month I wrote that taking into account current forecasts, El Niño could be the biggest global weather story of 2014. The new data shows that forecast is still on track. And that means El Niño could officially begin in a matter of weeks…

…there are some parts of the world that have a relatively predictable weather signal when El Niño rolls around.

There have been only a handful of El Niño events in the last few decades, and in many cases it’s difficult to generalize based on such a small sample size. Only once in the last 30 years—1998 (see above animation)—were subsurface water temperatures as warm as they are now. Which makes forecasting even more difficult.

But by averaging all the recent El Niño events together, we can take a guess at the general trends for what the next few months might bring. (Since all the websites offering El Niño impacts seem to be based on a Microsoft Encarta CD-ROM from the late 1990s, I figured we needed an update.) Let this be your warning: Not all of these predictions will come to pass. Some surely won’t. Frankly, I’m overgeneralizing a lot of nuance here. The below should be read as a tilt of the odds, not a black-and-white forecast. But it’s grounded in the past, and given the current state of the ocean and atmosphere, it offers a good idea of how planet Earth might deal in 2014–15…

Denver: Colorado Front Range snowstorms are significantly heavier during El Niño autumns and springs, though precipitation as a whole is roughly the same. A National Center for Atmospheric Research analysis shows a 20-inch snowstorm is roughly seven times more likely in an El Niño year than in a La Niña year. Neutral years—neither El Niño nor La Niña—are somewhere in between.

The Colorado River basin: Some good news! El Niño could help fill dwindling reservoirs and boost water supplies by bringing unseasonably heavy rains across the Southwest…

The Corn Belt: In sharp contrast to other major agricultural regions (India, Southeast Asia, Australia, Central America, Brazil), the U.S. Corn Belt could be in for a relatively mild summer. Near-average temperatures and slightly above-average rainfall could provide ideal growing conditions this summer, with farmers taking advantage of price spikes caused by shortages in other parts of the world. Midwest farmers could pay for it during summer 2015, though, if global temperature spikes as predicted. Poor corn harvests have been documented in Iowa in the year following El Niño…

The Antarctic: El Niño brings warmer winds to the frozen south during the summer months of December through February, and has been linked to greater loss of ice from the Antarctic Peninsula and the West Antarctic Ice Sheet. These are two of the regions on Earth that contribute most to sea level rise.

The Arctic: El Niño winters tend to be cooler than average across the Arctic Ocean, but only by a degree Celsius or so. That’s not enough to offset the rapid warming the region has seen over the last few decades—twice the rate of the planet as a whole. The impact of this year’s El Niño on the long-term trend toward ice-free summers in the Arctic should be minimal.

Greenland: There isn’t a whole lot of evidence pointing to impacts in Greenland one way or the other during El Niño years. Southern Greenland may be slightly warmer than normal, but El Niño’s impacts peak in midwinter, which this isn’t melt season here, so the effects on ice should be minimal.

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