SCIENCE:

Some climatologists worry that Texas' mega-drought could endure for years

Texas State Climatologist John Nielsen-Gammon made headlines last week when he predicted his state's devastating drought could last until 2020.

That's yet another heaping helping of bad news for Texas, where unusually dry conditions this year have caused $5.2 billion in damages to the state's agriculture sector.

But the prediction is also notable because scientists don't forecast drought years in advance. The federal government's latest drought outlook only extends through December.

So is it even possible to predict whether Texas will be locked into drought in 2015, let alone 2020?

Nielsen-Gammon, a professor of atmospheric sciences at Texas A&M University, admits it's more of an art than a science. But he sees a lot of similarities between conditions now and the worst recorded drought in Texas history, which lasted from 1950 to 1957.

Scientists have put much of the blame for the current drought on La Niña, a weather phenomenon signaled by unusually cool surface waters in the tropical Pacific Ocean.

"Drought in the southern Great Plains tend to be very much linked to La Niña conditions," said Siegfried Schubert, a senior research scientist in the Global Modeling and Simulation Office at NASA's Goddard Space Flight Center. "But there are issues of times when the drought will persist longer than La Niña conditions, and there are questions about what other oceans perhaps are playing a role."

Atlantic Ocean may play a role

A strong La Niña emerged last fall and fizzled in early summer. Now a new La Niña is emerging, setting Texas up for another dry winter, said David Miskus, a drought specialist at the National Oceanic and Atmospheric Administration's Climate Prediction Center.

But Nielsen-Gammon says there's another factor at play -- unusually warm surface waters in the tropical Atlantic Ocean, which also factored into the historic 1950s drought.

He believes those warm waters are a product of a long-term climate pattern, the Atlantic Multidecadal Oscillation (AMO), now in a "warm" phase that could last for another 15 years.

"Unfortunately, if you go back to that record [of the 1950s], it's pretty similar to what's going on right now," he said. "That's the only time in the past 100 years when [the ocean conditions] had a similar configuration to how they are today."

The current drought is just about a year old. As September drew to a close, it was on the verge of breaking Texas' record, set in 1956, for the driest 12-month period. Roughly 95 percent of the state is now experiencing "severe" or "exceptional" drought, according to the National Drought Monitor.

"We know from the drought of the 1950s and older droughts we see in tree-ring data that this area does experience drought that lasts a decade or two decades," Nielsen-Gammon said. "It's not likely this will last another five to 10 years without a break, but it's a possibility."

A higher frequency of droughts

Experts agreed that the combination of cold tropical Pacific waters and warm tropical Atlantic waters is a potent recipe for drying in the southern Great Plains and northern Mexico.

"They really reinforce each other to produce the most intense droughts," said Schubert, the NASA climate modeler.

But whether that "perfect arrangement" of ocean conditions will remain in place through 2012, let alone to 2020, isn't clear, said Richard Seager, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory.

"There's a good chance this drought will persist through this winter, at which point it will be a year and a half old," he said. "But beyond that, next summer might be wet."

La Niña and its counterpart, El Niño, are notoriously hard to forecast more than six to 12 months in advance. There's no telling how long the current La Niña will last.

And Seager's not convinced that the current high temperatures in the tropical Atlantic are a product of the AMO's warm phase -- he believes the Atlantic will cool off some time this winter.

If the tropical Atlantic cools and La Niña ebbs, that could bring sweet relief to parched Texas, Seager said, but it's not a lock.

"The funny thing about that area and the whole southern U.S. is that since we started monitoring drought in that region in the late 1990s, one or the other part of the southern United States has been in drought, with the exception of summer 2010, regardless of how Pacific and Atlantic sea-surface temperatures have been varying," he said. "There's been a drought popping up or persisting for over a decade now."

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