Mar 15, 2012
Tree rings reveal past water woes for south-eastern US
When it comes to US drought it's the semi-arid west that springs to mind but the humid tropical south-east has water worries too. The drought in the region from 2006–2009 left a number of cities, including Atlanta, with just two to four months' water supply.
Now a study of tree-rings in the Apalachicola-Chattahoochee-Flint river basin indicates that the current south-eastern drought is not as bad as many in the past 346 years. Droughts of extended duration occurred more often from 1696–1820, the trees revealed. What's more, today's water plans are based on data for the unusually wet period in the mid-20th century.
"The significance of our results is not simply that there were more severe droughts in the past," Neil Pederson of Lamont-Doherty Earth Observatory told environmentalresearchweb. "This is a common theme in most palaeo research. What we found was that the period of instrumental record is generally wetter than prior centuries. And the period that was initially declared as the levels that Lake Lanier should be maintained – the mid-1970s – follows one of the wettest periods in the last 340 years. This does not seem to be a good long-term water use strategy."
Lake Lanier – a reservoir in northern Georgia – has been the source of an intense legal battle over water resources between the US Army Corps of Engineers and the states of Georgia, Alabama and Florida.
"The other finding is that these humid regions experience significant drought," said Pederson. "The palaeo community knows this in general. It is not clear that the public or governments are aware of the possibility of prolonged and severe drought in the moist eastern US."
According to co-author Andrew Bell of Lamont-Doherty Earth Observatory, what really made things difficult in the recent drought is that there are so many people and activities drawing water. "The idea we are trying to draw attention to is 'what if we have this many people and this much withdrawal AND we experience a climatically severe drought like those we see in previous centuries?'" he said.
Pederson, Bell and colleagues from Eastern Kentucky University, College of Saint Benedict and Saint John's University, West Virginia University, USDA Forest Service, Appalachian Arborists and SUNY-College of Environmental Science and Forestry collected the first tree-ring records throughout the Apalachicola-Chattahoochee-Flint river basin.
"The main trigger for this study was a call I got from Will Blozan, the citizen scientist co-author of the paper, who asked if I wanted to core some old-growth oaks just north of Atlanta," said Pederson. "This reminded me of the 2006–2009 drought that threatened Atlanta and regional cities. I looked in the International Tree Ring Databank and realized there were no publicly available tree-ring records from north Georgia. So I saw this as an opportunity to understand how this drought measured to droughts in previous centuries."
According to Bell, tree rings are a different form of knowledge to climate models or forecasts. "They are a history of events that have happened and as such have a different 'face validity'," he said. "That is, people trust and perceive them differently than other forms of information. Our lab has spent time over the last few years developing a variety of decision-aids in agricultural and water risk management using tree rings, and we are very interested in learning more about how they get perceived and (hopefully) used."
The researchers reported their work in Environmental Research Letters (ERL).
About the author
Liz Kalaugher is editor of environmentalresearchweb.