| Subsequent
Efforts (1980s and 1990s)
In the 1980s and 1990s, three studies, described below, built
on the work of Stockton and Jacoby. The first two studies entailed
new tree-ring reconstructions of streamflow at Lees Ferry. In
the third, the Stockton and Jacoby reconstruction for Lees Ferry
was used to construct drought scenarios for a major multidisciplinary
assessment of drought impacts in the Southwest.
In the late 1980s, researchers at the University of California
headed by Joel Michaelsen developed a set of tree-ring based
reconstructions of streamflow for the California Department
of Water Resources. Among the reconstructions was one for the
Colorado River at Lees Ferry. This study shared some of the
same tree-ring data as used by Stockton and Jacoby, but also
included tree-ring chronologies from a broader geographic region.
As in Stockton and Jacoby’s study, the common end date
of the tree-ring data was in the early 1960s. The reconstruction,
extending from 1568-1962, had a long-term mean of 13.8 MAF and
shared many of the features of the Stockton and Jacoby reconstruction,
including the early 20th century period of high flows and the
sustained drought in the late 16th century. Two subsequent papers
also describe and discuss the Michelsen et al. reconstruction:
Loaiciga et al. (1992)
and Tarboton (1994).
Hugo Hidalgo, Thomas Piechota, and John Dracup of University
of Nevada-Las Vegas developed a tree-ring reconstruction of
annual flow at Lees Ferry in which they used virtually the same
tree-ring dataset as Stockton and Jacoby, but a different principal
components analysis (PCA) modeling technique to calibrate those
data with the natural flow record. The resulting reconstruction
had a lower long-term mean (1493-1962, 13.1 MAF) than Stockton
and Jacoby, and the low-flow periods were even lower than the
difference in means would suggest. For example, the lowest 20-year
running mean during the late 1500s drought was only 9 MAF in
the Hidalgo et al. reconstruction, compared to 11 MAF in Stockton
and Jacoby. The Hidalgo et al. reconstruction demonstrated the
sensitivity of reconstructions to choices made in the modeling
process, a subject treated in more detail later.
The
Severe Sustained Drought Study (late 1980s and early 1990's)
In the late 1980s, a major interdisciplinary study began on the
impacts of a severe, sustained drought in the Southwest. Two drought
scenarios derived from Stockton and Jacoby's Lees Ferry reconstruction
were used as the basis for assessing social, political, legal,
and economic impacts of severe, sustained drought. One drought
scenario was Stockton and Jacoby's reconstructed flows for 1579-1600,
and the other was a re-ordering of those 22 years so that flows
progressively declined over the period of the drought.
The Severe Sustained Drought Study was novel in that a drought
reconstructed from tree-rings was used to represent a future
drought scenario. It attempted to answer the question, what
would happen if the late 15th century drought seen in the tree-ring
record (or a variation of it) were to recur today? Unfortunately,
the study was largely ignored by the water resource management
community, perhaps in part because water supplies in the Southwest
had rebounded after a drought from 1988-1992, and the year the
study was published (1995) saw well above average flows on the
Colorado.
On to...The latest reconstructions
(2006-2007)
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