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Tree-ring studies show drought is recurring event in California

Just as California was emerging from the 2007-09 drought work began on a tree-ring study and streamflow reconstruction project that allows planners to look outside of the state’s 100-year observed history for climate trends.  Researchers were able to look as far back as the year 900 in the Sacramento and San Joaquin Basins and the 1500’s in the Klamath Basin.

With numerious periods when streamflows were low for four or more years, the report shows drought is a recurring theme in California—and drought conditions are often prevalent statewide with all three basins sharing major periods of low flow conditions.

Tree-rings provide researchers with a source of information that is otherwise unavailable.

“Streamflow reconstruction from tree rings takes advantage of the great longevity and climate sensitivity of several tree species in California and Oregon,” said lead author David Meko, a University of Arizona Research Professor of Dendrochronology. “The tree-ring patterns record unusual climate events and modes of variability that occurred before the short period of gaged streamflow.”

The data and reconstructions—along with climate change studies—can be used to inform planners and allow them to expand their planning horizons.

Report co-author Connie Woodhouse, professor and interim head of the University of Arizona School of Geography and Development, said, “These tree-ring records document the range of drought characteristics, including duration, that have occurred in the past, under natural climate variability. These droughts could occur in the future, but under warmer temperatures that will further exacerbate their impacts.”

Jeanine Jones of DWR said, “Drought prediction skillful enough to use for water management decision-making remains a research challenge for the science community. Having improved climate forecasting capabilities at time scales of months to a year in advance would provide great benefit for drought preparedness.”

Researchers at the University of Arizona completed the study for DWR, with funding for part of the work in the Klamath Basin provided by the U.S. Bureau of Reclamation WaterSMART program.

Read the report

Written by Marta Weismann