Tree rings hold clues to our drought risk

Dr. James Stagge is a USU Professor, a hydrolgist and engineer with an interest in drought risk.

By analyzing centuries-old growth rings from trees in the West, he and his team of research colleagues have been looking centuries into the past to better understand our uncertain water future.

By examining these growth rings they have extracted data about monthly streamflow trends from periods long before the early 1900s. That includes monthly streamflows dating back to 1605 for the Logan River and as far back as 1400 for the Bear and Weber rivers.

“The issue here in the intermountain west,” said Stagge, “is that our earliest river gauges are about 70 to maybe 100 years old. That gives us a relatively small catalog of drought events to compare against.

“The idea is that because we didn’t have an instrument in the river recording water flow hundreds of years ago, we use the next best thing, which are tree rings in this area. We are very fortunate to have some of the oldest trees in the world right here.

“We can now reconstruct an additional 600 years or so of streamflow. That gives us seven times more drought events, so now we can test our system and see how we would fare in a major drought from the past.”

Dr. Stagge said the researchers have learned they can dig down and get into a monthly scale which is a lot like what water managers in this area today need to make decisions more on a monthly scale than an annual scale.

“This gives us a whole better set of drought events that we can test against to see how vulnerable this area’s water resources might be moving forward, with current populations.”

He said America’s Dust Bowl droughts of the 1930s were significant.

“We have always considered that to be the ‘Drought of Record’. But by digging back into hundreds of years of records, we could see there were drought events that were longer and potentially more severe, in the previous centuries.

“So we do need to be preparing for significant drought events. We have been relatively fortunate over the past 50 years or so.”

Joining Dr. Stagge as co-authors of the study were Dr. David Rosenberg, R. Justin DeRose of the U.S. Forest Service and Dr. Tammy Rittenour of the USU Department of Geology.

The findings were published in the Jan. 6 Journal of Hydrology.

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