If Hal Anderson is right - and he's the first to admit he could be wrong - southern Idaho may be at the bottom of a drought cycle that repeats about every 111 years.
Anderson, chief of the technical services bureau at the Idaho Department of Water Resources, said time-series analysis of 400-year-old tree-ring data suggests three interweaving drought cycles - including two shorter ones repeating at roughly 11- and 23-year intervals and lasting only a year or two.The century cycle, however, is distinguished by droughts enduring for five to 30 years.
"I'm not saying that we're right or wrong," said Anderson, "but when we looked at it, that's what we saw."
Anderson noted that, in geological time, 400 years of data is not very much and that analyzing tree rings is admittedly "trying to crystal-ball it a little bit." But he said the policy implications are crystal clear.
"We may not be out of this next year or even five years from now," he said. "We need to be cautious about how we manage the resource."
But he said deep snows this winter wouldn't surprise him a bit. That's because the year-to-year variation in precipitation revealed by the tree rings is quite large.
Western tree-ring analysis - or dendrochronology - is centered at the University of Arizona. David Meko, an adjunct assistant professor at that university's tree ring laboratory, said that ideally two cores each are dug from about 20 standing trees in a 1-mile-diameter area.
Meko isn't ready to define what he sees in tree-ring data as cycles, only as "very gradual trends that may or may not be repeated." At best, he said, tree-ring data allows scientists to estimate the probability that "you will pull out of the current drought within a certain number of years."
"It's extending the information beyond what you could say if you only had climate data."
University of Idaho state climatologist Myron Molnau said National Weather Service data from most Idaho stations dates only to about 1892.
At the U.S. Geological Survey in Carson City, Nev., research hydrologist Dave Nichols has analyzed tree rings in northeastern Nevada to correlate the 30-year long-term cycles used by the National Weather Service with the much longer memory of pinyon pines.
Comparing staggered 30-year intervals beginning every decade since 1601, Nichols said average precipitation for the periods varies by plus or minus 12 percent.
"But we didn't really see cycles," he said. "Everybody is interested in cycles, and we tried to look a little bit at cycles, but we didn't see strong cycles in the data."
John Jannuzzi, meteorologist in charge at the Idaho office of the National Weather Service, said sea-surface temperatures in the equatorial eastern Pacific are cooling rapidly, indicating that the El Nino impacts of the past year are dissipating. But while Jannuzzi said that's likely to bring with it a colder winter, it may not end the drought.
"El Nino was not by any means the sole reason for our drought," he said. "The fact that it is ending means that this next winter season wouldn't have the combined effects."