"Whenever we have events at the rancher or farmer level, we try to include a paleoclimatology [the study of ancient climates] talk, and without fail it generates the most interest and questions," said climatologist Mark Svoboda from the center's University of Nebraska-Lincoln headquarters.
"When people learn of droughts in the 1600s that [were] shown to have had a major impact on the places where they live, it makes them realize the natural variability of climate," he said.
"The frequency of these occurrences is shown to have been there if you look at tree rings, lake sediments, ice cores, whatever," he added. "We can't dismiss that, and it opens some eyes."
Though future droughts are inevitable, the business of predicting themeven if they do come in cyclesis tricky.
Peter Leavitt, a biology professor at the University of Regina in Saskatchewan is at work in the Canadian prairies. He's reconstructing ancient climates in an attempt to forecast coming droughts.
"We're trying to identify any pattern in the past that will help us forecast the future," he said. "For example, people talk about '100-year floods' or '150-year floods.' We don't tend to do that with droughts, but there is no real reason why we shouldn't."
Despite the striking patterns that have emerged, the Kettle Lake drought cycles were irregular or even absent at timesthe droughts don't always show up when the model says they should. As a result, the data don't exactly encourage short-term forecasting. "The long period of these fluctuations makes this kind of variability a bit difficult to deal with," Clark, the Duke ecologist, said. "In some ways it's predictable. It does have an actual period, but it's hard to adapt to variability on such a long time scale."
Rapid regional changes add further challenges. In recent centuries humans have irreparably altered the Plains ecosystem with agriculture and fire suppression.
The impacts on drought cycles are not yet known. Clark, though, suspects that drought cycles will continue.
"Drought cycles of the past show that rising aridity appears to have been enough to really increase erosion," he said. "These fluctuations in aridity due to natural forces are probably alive and well."
Many atmospheric models of global warming forecast dryer days ahead for continental centers. Though no one knows for sure, the change may worsen drought conditions.
"When you try to superimpose the human-caused aridity that we can expect with this sort of natural variabilityextreme droughts every century or so[it provides] all the more reason to be concerned.
The University of Regina's Leavitt suggests that people must prepare for recurring droughts regardless of the impacts of global warming.
"We've seen historic droughts in some cases five to seven decades long, with severity along the lines of [the Dust Bowl of] the 1930s," he said, noting that he expects such droughts to return. "They have occurred for the last several thousand years, so there's no reason to expect anything different."
Free E-Mail News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES