The six-decade-long drought was remarkable for the absence of very wet years. At the core of the drought was a period of 25 years in which Colorado River flow averaged 15 percent below normal.
762, said the tree-ring scientists from The University of Arizona in Tucson who led the research team.
The work extends the continuous tree-ring record of upper Colorado streamflows back seven centuries earlier than previous reconstructions."The biggest drought we find in the entire record was in the mid-1100s,"
Colorado River flow was below normal for 13 consecutive years in one interval of the megadrought, which spanned 1118 to 1179.
Meko contrasted that with the last 100 years, during which tree-ring reconstructed flows for the upper basin show a maximum of five consecutive years of below-normal flows.
The Colorado supplies water for cities and agriculture in seven western states in the U.S. and two states in northwestern Mexico. Los Angeles, Las Vegas, Denver, Phoenix, Tucson and Albuquerque are among the many cities dependent on Colorado River water.
The Intergovernmental Panel on Climate Change predicted in a recent report that the southwestern U.S. will become hotter and drier as the climate warms.
Co-author Connie A. Woodhouse said, "We have natural variability that includes this time in the 1100s. If we have warming it will exacerbate these kinds of droughts."
The newly documented droughts "could be an analogue for what we could expect in a warmer world," said Woodhouse, a UA associate professor of geography and regional development and dendrochronology.
Meko, who was asked by the California Department of Water Resources to pursue the research, said understanding more about natural variability in the Colorado is important to the region's water managers.
"Water managers rely on wet years to refill reservoirs," he said.
The team's research article, "Medieval drought in the upper Colorado River Basin," is scheduled to be published online in the American Geophysical Union's journal Geophysical Research Letters on May 24.Meko and Woodhouse's co-authors are Christopher A. Baisan, a UA senior research specialist; Troy Knight, a UA graduate student; Jeffrey J. Lukas, of the University of Colorado at Boulder; Malcolm K. Hughes, a UA Regents'
Professor of dendrochronology; and Matthew W. Salzer, a UA research associate. The California Department of Water Resources, the U.S. Geological Survey and the U.S. Bureau of Reclamation funded the work.
Just about a year ago, Woodhouse and Meko and colleagues published a continuous tree-ring record for the upper Colorado River Basin that went back to 1490, the longest record for the area until now.
Other paleoclimatic research had suggested that epic droughts occurred in much of the western U.S. during the Medieval Climate Anomaly of about 900 to 1300, a time when some parts of the world were warmer than now. In addition, tree-ring data from a large network of sites showed that the areal extent of drought in western North America peaked prior to 1400.
Meko, Woodhouse and their colleagues wanted to take a closer look at what happened in the upper Colorado River basin during that time.
For the record back to 1490, the scientists took cores from old, living trees and looked at the rings' tell-tale pattern of thick and thin that indicates wet years and dry years.
Extending the record further required an underutilized technique, the analysis of logs, stumps and standing dead trees, known as remnant wood.
Baisan said, "Everyone was surprised that we could do this."
Woodhouse said, "It's so arid that wood can remain on the landscape for hundreds of years. The outside of some of our remnants date to 1200, meaning the tree died 800 years ago."
The scientists took pencil-thin cores from the living trees and cross-sections of the remnant wood from 11 different sites. The researchers then pieced together the long-term record by matching up the patterns from the cores to those from the cross-sections.
Baisan said, "This is part of ongoing work to try to understand the climate system that creates these patterns. You need the basic data about what happened before you can ask questions such as 'Why were there 60 years of low-flow on the Colorado?'"
The team's next step is collecting additional samples from the study sites and adding additional study sites in the upper Colorado River basin.Contact information:
UA's Department of Geography and Regional Development http://geog.arizona.edu/
Colorado River Streamflow: A Paleo Perspective http://wwa.colorado.edu/resources/paleo/lees/
Mari N. Jensen | University of Arizona
Clear as mud: Desiccation cracks help reveal the shape of water on Mars
20.04.2018 | Geological Society of America
Hurricane Harvey: Dutch-Texan research shows most fatalities occurred outside flood zones
19.04.2018 | European Geosciences Union
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy