Recent dry spells not so bad compared to past centuries
FRISCO — A tree-ring reconstruction of Utah’s climate going back to 1429 shows that the state has experienced several mega-droughts in past centuries that would be life-changing if they happen again, according to Brigham Young University professor Matthew Bekker.
The worst drought of the modern era, the 1930s Dust Bowl, barely ranks on the top 10 list of droughts in that 500-year span,” Bekker said. The findings reinforce similar studies for the Colorado River Basin.
“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 Bekker, a geography professor at BYU. “We would really have to change the way we do things here.”
Bekker analyzed rings from drought-sensitive tree species. He found several types of scenarios that could make life uncomfortable in what is now the nation’s third-fastest-growing state:
- Long droughts: The year 1703 kicked off 16 years in a row with below average stream flow.
- Intense droughts: The Weber River flowed at just 13 percent of normal in 1580 and dropped below 20 percent in three other periods.
- Consecutive worst-case scenarios: The most severe drought in the record began in 1492, and four of the five worst droughts all happened during Christopher Columbus’ lifetime.
For this study, Bekker took sample cores from Douglas fir and pinyon pine trees. The thickness of annual growth rings for these species is especially sensitive to water supply. Douglas firs more than 700 years old have been used to reconstruct historic climate in the Colorado River Basin.
Using samples from both living and dead trees in the Weber River basin, the researchers built a tree-ring chronology that extends back 585 years into Utah’s natural history. Modern stream flow measurements helped them calibrate the correlation between ring thickness and drought severity.
As Bekker and his co-authors report in the Journal of the American Water Resources Association, the west’s climate usually fluctuates far more than it did in the 1900s. The five previous centuries each saw more years of extremely dry and extremely wet climate conditions.
“We’re trying to work with water managers to show the different flavors of droughts this region has had,” said Bekker. “These are scenarios you need to build into your models to know how to plan for the future.”
Bekker collaborated with researchers from the U.S. Forest Service, Columbia University and Utah State University. The team is currently working on a climate reconstruction based on tree rings that date back more than 1,000 years.