Idaho State University researcher Finney helps reinterpret past U.S. West weather patterns

Idaho State University research scientist Bruce Finney's ultimate goal is to help create accurate weather maps of the past for the American West that can be used to better predict future weather patterns.

It is a complicated endeavor, as the results of his recent research suggests, and a work in progress that is becoming more sophisticated as Finney examines the ancient sediment layers in lakes in the Pacific Northwest.

Finney, an ISU Biological and Geosciences professor, participated in a study "1,500 year quantitative reconstruction of winter precipitation in the Pacific Northwest" that was recently published in the Proceedings of the National Academy of Sciences. That study has received wide publicity and attention because of its surprising results found by Finney and his colleagues at the University of Pittsburgh, Penn State and Ohio State. The researchers compared the data from the analysis of tree rings to that from lake sediments to see how they related. It turns out some periods of weather in the past were misidentified as being in drought.

"Water is a big deal in the West so we've been trying to get a longer-term perspective on how often and long droughts come and why they occur by analyzing lake sediments," Finney said. "This paper focuses on last 1,500 years. The lakes tell us more about what happened in the winter time, the trees tell us more about the summer."

Generally, in the short term the tree rings and sediment samples matched up, but in the long term they showed differences, showing that dry summers sometimes paired up with wet winters, or vice versa. This has caused scientists to reinterpret past weather patterns: some periods that were identified as drought based on tree ring data are now classified differently because lake sediment data showed wetter than average winters during the same period.

"It's not that one data set is correct and the other is wrong," Finney said. "The data is complementary because of the different seasons it corresponds with and that gives us a more detailed view of what happened in the past."

Drought is a common feature in the West's weather history, with several in the last 1,500 years lasting decades, according to Finney. One of those periods of generally droughty conditions in this region began about 500 years ago during the "Little Ice Age" ending about 1850.

"The climate has been all over the place in recent years," Finney said, "with wet years followed by dry years, but we’re dryer than normal over the last dozen or so years."

The important part of this research is what it contributes to the big picture of the West's climate.

"We will now be able to compare these results to what we are determining happened in Idaho, Alaska and other places effected by weather patterns originating from the North Pacific Ocean over the same period," Finney said. "We're basically trying to put together maps to see what controlled wet and dry periods in the past to help know where the climate system is going in the future."

For his part in the study, Finney examined lake sediment core samples collected from Castor Lake, which is in northwestern Washington with funding from the National Science Foundation, and is currently involved in similar studies in Idaho, Alaska and other regions surrounding the North Pacific Ocean.

###