At the height of the drought that gripped the southeastern United States between 2005 and 2007, the water level of the massive reservoir that provides Atlanta's drinking water dropped 14 feet below normal.

The dry spell intensified an ongoing legal battle among Georgia, Florida and Alabama over fresh water supplied by the Apalachicola-Chattahoochee-Flint River Basin, which runs through the three states.

But a new study suggests things could have been far worse.

Climate records gleaned from tree rings show the recent drought pales in comparison to droughts that hit the region in the 17th and 18th centuries. In fact, the research suggests that the 20th century stands out as an unusually wet blip in the 350-year history reconstructed using those tree rings.

"This is a reminder of what could happen," said the study's lead author, Neil Pederson, a forest ecologist at Columbia University's Lamont-Doherty Earth Observatory.

The study, published yesterday in the journal Environmental Research Letters, doesn't project whether climate change will make drought more or less likely in the future, he noted.

"The importance of this kind of work is showing that in these areas where there are a lot of people, severe droughts are not unusual," Pederson said. "We have to be prepared for that."

The new study draws on previously collected tree rings, including bald cypress samples analyzed by University of Arkansas scientists, and new samples taken throughout the Apalachicola-Chattahoochee-Flint River Basin.

Research began 'out of the blue'
"The study came about partly because one of the co-authors on this paper, Will Blozan" -- an arborist based in North Carolina -- "emailed me out of the blue one day and said, 'Hey, would you like to core some old-growth oaks just north of Atlanta?'" Pederson recalled. "I went, 'Yeah, wow, of course I would.'"

Later, the team tapped a stand of tulip poplars growing in north Georgia that were scouted by study co-author Jess Riddle, a graduate student at the State University of New York's College of Environmental Science and Forestry. Those trees ranged between 350 and 470 years old, Pederson said.

The tree-ring record the researchers cobbled together confirms earlier research that suggests the mid-18th and early 20th centuries were the driest periods in the southern Appalachian Mountains since at least 1700, while extending the record further back in time to document a "substantial" drought from 1669 to 1709.

And while the drought that hit the region in 1986 stands as one of the worst of the past 350 years, the 20th century -- when the agreements that govern the basin's water use were first established -- was the wettest period in the region since the late 1600s.

"We're developing our habits of how we use water during one of the wettest periods of the last 300 years," Pederson said. "That might not make us well-prepared for future droughts."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500