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Santa Fe NM (SPX) Mar 24, 2011 New York City and Atlanta have both experienced droughts in the past few decades that required them to implement water restrictions and conservation measures. However, a new study of tree-ring data spanning the past 400 years indicates that droughts in those cities and their surrounding regions were typically longer and more frequent centuries ago than they were for most of the 20th century. In addition, recent decades have brought longer drought cycles similar to those prevalent before the mid-1800s. A return to drought patterns of past centuries, the study's authors say, could seriously strain the water resources of both of those densely populated regions. "We can handle two to three-year droughts, but if three and four and five-year droughts are possible, we're not prepared," says Neil Pederson, a research professor with the Tree Ring Laboratory at Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, which created the new tree-ring drought records. He adds that the familiar scene in the western U.S. of fights and lawsuits over water "is starting to play out here in the East." By the fall of 2007, during the second year of a three-year drought, Atlanta had roughly three month's supply of water remaining while Athens, Georgia, was down to approximately 50 days. Another drought dramatically lowered New York City reservoirs to 33 percent of capacity in 1981. A return to historic climate patterns would bring more frequent and prolonged droughts, Pederson says. He and his graduate students collected tree cores from several species of trees in the Atlanta and New York regions that have lived as long 500 years. The team included additional species that are not usually sampled for drought records, including tulip poplar and hickory, to help better account for annual variability and give a more accurate picture of the wet and dry periods in these regions. It usually takes at least 18 different tree cores to get a statistically accurate drought record in each forest, Pederson says, and being able to draw on additional tree species helps them find more very old trees that can provide additional data. The cores show that there were three severe droughts in the 1700s in the southern Appalachian region that were soon followed by regional die-offs of trees with about 8 to 10 percent of the trees being lost. Today, "these relatively minor droughts are setting off water conservation measures and draining reservoirs. That's the scary thing," given that longer droughts that may lie ahead, he says.
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