Tree Rings Reveal A History Of Drought In Utah
May 2, 2014

Utah’s Severe Droughts Recorded By Trees

Brett Smith for - Your Universe Online

New research on tree rings in Utah has revealed that some droughts of the past 576 years were much more severe than anything seen since the start of the 20th century.

The study team said tree rings provide a much longer historical record than climate and stream flow logs, which only go back about 100 years. According to the team’s report in the Journal of the American Water Resources Association, the most severe drought of this century barely cracks the top ten dating back to 1429.

“We’re conservatively estimating the severity of these droughts that hit before the modern record, and we still see some that are kind of scary if they were to happen again,” said study author Matthew Bekker, a geography professor at Brigham Young University. “We would really have to change the way we do things here.”

In their attempt to reconstruct stream flow for the Weber River, BYU researchers analyzed tree rings from species particularly sensitive to drought. The amount of rainfall in a year can be determined by measuring the thickness of the rings – with very narrow rings representing drought years.

“As we are trying to identify patterns in wide and narrow rings, you can kind of think of that as a bar code in the food that you might buy in the store,” Bekker said in an accompanying video. “Trees in an area are going to have not exactly the same pattern, but a similar pattern of wide and narrow rings just like that bar code. We get to the point where we can just look across a sample and just say, ‘Ok there’s 1580, there’s 1735.’ We know where those difficult years are.”

[ Watch the Video: Dendrochronology: Tree Rings Record Extreme Weather Cycles ]

Of the study team’s numerous historical finds based on their analysis, they noted a 16-year drought in the study area that began in 1703. In 1580, the Weber River flowed at just 13 percent of its normal and it fell below 20 percent at three other points. Interestingly, the most severe drought in their analysis took place in 1492, the year Christopher Columbus reached the Americas.

To reach their conclusion, the researcher first took pencil-sized sample cores from Douglas fir and pinyon pine trees. Their analysis of these tree rings was then compared to stream flow measurements, which allowed them to calibrate ring thickness to drought severity.

Bekker noted that past centuries in Utah have seen both extremely wet and extremely dry years.

“We’re trying to work with water managers to show the different flavors of droughts this region has had,” Bekker added. “These are scenarios you need to build into your models to know how to plan for the future.”

In February, NASA released images showing record drought that ravaged California earlier this year. The images showed considerable dryness with respect to vegetation and mountainous regions.

“In a normal year, much of the green areas near the mountains would be snow-covered,” said Ramakrishna Nemani, a vegetation sensing expert at NASA’s Ames Research Center. “Since there is not much snow this year, the evergreen vegetation appears anomalously green. In fact, that is bad news for this time of the year.”

“If you showed me this image without the date, I would say: ‘This is California in early fall after a long, hot summer, before the fall and winter rains and snows arrived,’” said Bill Patzert, a climate scientist at NASA’s Jet Propulsion Laboratory. “This is no California winter postcard.”