Drought prediction a thorny matter

A new federal study indicates that the northern Great Plains, including Nebraska, is a far tougher place to forecast drought than the southern Plains.

The two major droughts of the past century struck those areas.

The study found a principal climatic cause of the 1950s southern Plains drought — lower-than-normal Pacific Ocean temperatures, according to Martin Hoerling, the report's lead author.

But there was no clear culprit for the 1930s drought, known as the Dust Bowl, that struck with greatest intensity in the northern Great Plains, Hoerling and his colleagues found.

The bottom line for the Nebraska region: Much less warning of an unfolding, prolonged drought disaster.

Hoerling is a meteorologist at the Earth Systems Research Laboratory, which is a part of the National Oceanic and Atmospheric Administration. The laboratory is in Boulder, Colo.

The idea that ocean temperatures contribute to drought is not new, but one of the principal findings of this study is an apparent lack of connection between droughts in the northern U.S. and ocean conditions.

Mark Svoboda, a climatologist at National Drought Mitigation Center, housed at the University of Nebraska-Lincoln, said Hoerling's study confirms his suspicions that drought in the northern Great Plains — an area locked in the interior of the continent — is “inherently more complex” than drought farther south and closer to the Pacific.

Svoboda said he isn't prepared to concede that ocean temperatures don't play any role, given other research involving the North Atlantic Ocean.

“I don't think it's a unanimous slam dunk,” he said.

Svoboda's colleague, UNL professor and climatologist Steven Hu, is among those who draw a connection between drought in the central and northern Plains with water temperatures in the North Atlantic Ocean.

“The atmosphere doesn't have that sort of long memory, to produce persistent, year-after-year drought, nor does the land surface process,” Hu said. “It must have some sort of support from ocean anomalies.”

Oceans, climatologists universally agree, play a tremendous role in weather because of their ability to move heat, energy and moisture around the globe.

The Dust Bowl and Nebraska's most recent drought of the early 2000s both occurred at a time when the North Atlantic was warmer than normal, Hu said.

All three researchers agree that more study is needed — particularly of regional feedbacks that can amplify or lessen drought conditions.

One of those regional factors, they said, is soil moisture.

Wet soil absorbs heat and stalls an increase in atmospheric temperature. Dry soil, on the other hand, feeds temperature increases and can intensify drought conditions.

“The Holy Grail would be to be able to forecast drought,” Svoboda said. “We're not there yet.”

Contact the writer:

444-1102, nancy.gaarder@owh.com