Tree Ring Study Warns of Long Droughts

A new study of tree rings adds to evidence that Texas has experienced at least one 10-year drought every 100 years, as well as several "mega-droughts" lasting 15 to 30 years over the centuries.

The peer-reviewed study, published Wednesday in the Texas Water Journal, argues that Texas' reliance on a 1950s drought as the "drought of record" — the worst-case standard for water planners today — is off-base.

"This and previous studies indicate that severe decadal-scale droughts have occurred in Texas at least once a century since the 1500s," wrote the study's authors, who are based at the University of Arkansas at Fayetteville, the Guadalupe-Blanco River Authority, and the University of Texas at Austin.

Past studies have also looked at tree rings, but this one extends further into history, says Jay Banner, a University of Texas geology professor who is one of the authors. The new results show that droughts don't usually hit all regions of the state equally.

The study included three new chronologies from bald cyprus trees found in South Central Texas, and used data from West Texas Douglas firs and Central Texas oaks.

The mega-droughts of centuries past had the worst impact in far West Texas, the study said.

"It can be expected that droughts as bad as or worse than the 1950s will occur in the future," the study said. "A future that may very well see accelerating climate change and continuing rapid population growth does not bode well for Texas water resources."

As for future studies, Banner said, scientists need to look even further back in history and also examine seasonal changes and climate modeling.

Of course, for tree-ring studies to work, the trees must survive the drought. The Texas Forest Service estimated this week that the current drought, which is the most intense since records began in 1895, killed up to 10 percent of the state's trees.