The drought that gripped the Southeast from 2005 to 2007 was not unprecedented and resulted from random weather events, not global warming, Columbia University researchers have concluded. They say its severe water shortages resulted from population growth more than rainfall patterns.  The researchers, who report their findings in an article in Thursday’s issue of The Journal of Climate, cite census figures showing that in Georgia alone the population rose to 9.54 million in 2007 from 6.48 million in 1990.  “At the root of the water supply problem in the Southeast is a growing population,” they wrote.  Richard Seager, a climate expert at the Lamont-Doherty Earth Observatory who led the study, said in an interview that when the drought struck, “people were wondering” whether climate change linked to a global increase in heat-trapping gases could be a cause.  But after studying data from weather instruments, computer models and measurements of tree rings, which reflect yearly rainfall, “our conclusion was this drought was pretty normal and pretty typical by standards of what has happened in the region over the century,” Mr. Seager said.  Similar droughts unfolded over the last thousand years, the researchers wrote. Regardless of climate change, they added, similar weather patterns can be expected regularly in the future, with similar results.  In an interview, Douglas LeComte, a drought specialist at the Climate Prediction Center of the National Weather Service, said the new report “makes sense.” Although Weather Service records suggest the 2005-7 drought was the worst in the region since the 1950s, Mr. LeComte said, “we have had worse droughts before.”  Some climate models developed by scientists predict that the Southeast will be wetter in a warming world. But the Columbia researchers said it would be unwise to view climate change as a potential solution to future water shortages.  As the region’s temperature rises, there may be more rain, they wrote, but evaporation will increase, possibly leaving the area drier than ever.  Mr. LeComte said that creating greater water storage capacity  say, in reservoirs  could mitigate drought effects in areas where population was rising.  “I am not going to criticize any governments for what they did or did not do,” he said. “But if you have more people and the same amount of water storage, you are going to increase the impact of droughts.”  The researchers said rainfall patterns in the Southeast were linked only weakly to weather patterns like La Niña and El Niño, the oscillating warm and cold conditions in the eastern Pacific linked to precipitation rates in the Southwestern United States.  Instead, they wrote, any variation in rainfall in the Southeast commonly “arises from internal atmospheric processes and is essentially unpredictable.”
Researchers also concluded that rapid population growth was more responsible for the severe water shortages than rainfall patterns were.