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May
17, 2007 An epic drought
during the
mid-1100s dwarfs any drought previously documented for a region that
includes
areas of 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 The new
tree-ring-based
reconstruction documents the year-by-year natural variability of
streamflows in
the upper The work extends the
continuous
tree-ring record of upper "The biggest drought
we find
in the entire record was in the mid-1100s," said team leader David M.
Meko, an associate research professor at UA's Laboratory of Tree-Ring
Research.
"I was surprised that the drought was as deep and as long as it was. 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 The
Intergovernmental Panel on
Climate Change predicted in a recent report that the southwestern 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 "Water managers rely
on wet
years to refill reservoirs," he said. The team's research
article,
"Medieval drought in the upper 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 Other paleoclimatic
research had
suggested that epic droughts occurred in much of the western Meko, Woodhouse and
their
colleagues wanted to take a closer look at what happened in the upper 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 The team's next step
is
collecting additional samples from the study sites and adding
additional study
sites in the upper
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