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.
Michaelsen et al. (1990)
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).
Hidalgo et al. (2000)
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.
For more information about the Severe Sustained Drought study, see this monograph published by the Powell Consortium and made available through the Water Resources Research Center at the University of Arizona. It includes all 13 papers comprising the study that were originally published in a special issue of Water Resources Bulletin.