Study sheds light on Utah’s water history

LOGAN – Utah’s precipitation history is clear – at least dating back to when the area was settled and records were being kept. According to Justin DeRose of the USDA Forest Service, the state’s records show a high-variability of water flow, but much less is known about the area’s water history before the recorded observations.

DeRose is part of the WAsatch Dendroclimatology Research (WADR) group that conducted a study to see if the same variability is reflected in the years before written records. DeRose said the study could give Utah water users a better understanding of what to expect and how to prepare.

“The further back into the past we can look, the better idea we have of the range of possibilities that are out there in terms of climate,” said Daniel Barandiaran, a Utah State University Ph.D. student who has worked with both DeRose and USU professor Simon Wang – another scientist behind the study.

The study was implemented using dendrochronology, a scientific method of dating carried out by analyzing tree rings. The samples taken were from south-facing Utah juniper stands near the Bear River. By examining the rings, DeRose said the group was able to create a very precise record that dates back more that 1,200 years.

“It’s really hard to find a 1,200 year old tree in Utah,” he said. “But it’s not really hard to find wood that’s been sitting on the ground for more than 1,000 years. So by linking those two together we’ve been able to end up with a really strong record of the variability in ring width, and then what we do is we just correlate that to our instrumental record of stream flow. In the case of the Bear River, the correlation was incredibly high.”

The results of the study showed a continuation of the high variability of water flow over the last 1,200 years. DeRose said both the instrumental record and the study show a repeating pattern of 10-15 wet years followed by 10-15 dry years in Northern Utah.

“This just corroborates that information and gives us a few hundred years to show that that sort of relationship has been ongoing for the last millennium,” he said.

DeRose said this is the first time the Utah juniper has been used for this kind of study and the first record of its kind that analyzes the Wasatch Front for such an extended length of time.

“There’s going to be a lot of things we can do with the record people haven’t been able to do yet in terms of understanding the variability of past climate,” he said. “We think that kind of information will be useful to water managers to know whether or not we’re in a generally wet or generally dry period.”

Barandiaran said the state is currently passing through a dry period and most likely will be transitioning into a wet period soon, but there is a chance that won’t be the case.

“There is a little bit of a caveat to that,” he said. “Weather and climate systems are very complex and they don’t necessarily follow their rules.”

The study revealed some exceptions. It showed both extended dry periods and extended wet periods that lasted several decades.

“One thing that’s kind of important to recognize about these extended periods of drought, its not necessarily 70 consecutive years of below-average rain or snow or whatever the case may be,” Barandiaran said. “Embedded in there there’s going to be better years and worse years, but when you kind of smooth them out and do a running average of the time period you see extended below average rain.”

DeRose said the Bear River was chosen for the study because it may be one of the few rivers in Utah with excess water to work with.

“What eventually ends up in Utah still has development potential,” he said “If we’re going to store more water we want to know in the future if there is going to be larger ability in the delivery of that water back to our state.”

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