Measuring drought impact via tree-ring & streamflow records

context to ongoing Upper Colorado River Basin megadrought

Researchers from United States Bureau of Reclamation (USBR), University of Arizona, United States Geological Survey (USGS), and Northern Arizona University have developed a new tree-ring based ensemble streamflow reconstruction spanning the past 2,000 years for the for the Colorado River.

In particular, analysis of streamgage records at Lees Ferry, Arizona (USGS monitoring location 09380000) combined with statistical reconstructions of drought history dating to the year 1 CE, derived from tree ring analyses, revealed grave concerns:

The ongoing 22-year drought is “unmatched in severity by any past period of low Colorado River streamflow” in the Upper Colorado River Basin.

"A hot dry summer (2022) leads to soil moisture deficits which we now know have a significant impact on how much of next year's winter snowpack runs off into the river and how much goes towards replenishing dry soils," said co-author Connie A. Woodhouse, University of Arizona.

The purpose of the study is to extend the Colorado River beyond the 116-year gage record period of 1906 through 2021. “Evidence from both tree-ring data and paleoclimate data from lakes, bogs, and caves supports the existence and severity of this (present) drought in the context of the last two millennia,” explain the authors in the research letter.

Access the study published by AGU’s Geophysical Research Letters on 9 June 2022.

Upper Colorado River Basin mega drought impact, image source USBR

The Upper Colorado River Basin (UCRB) is outlined in gray; selected major tributaries are shown as blue lines that converge at the Lees Ferry USGS streamflow gage. Living Blended Drought Atlas grid points are shown; 122 with Palmer Drought Severity Index data, 1–2017 CE (red filled circles), and three with missing data for 1–209 CE (black filled circles).