HR: 16:20h
AN: H44A-01 INVITED     [Abstracts]
TI: Colorado River Droughts Inferred from Tree Rings
AU: * Meko, D M
EM: dmeko@LTRR.arizona.edu
AF: Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, United States
AU: Woodhouse, C A
EM: conniew1@email.arizona.edu
AF: Department of Geography and Regional Development, University of Arizona, Tucson, AZ 85721, United States
AB: Tree-ring reconstructions for the Colorado River at Lee Ferry, Arizona, have consistently indicated that the modern gaged flow record is unrepresentative of the past few centuries both in the long-term mean annual flow and the severity of extended hydrologic droughts. Information on past droughts can be considered most reliable for the past 500 years, when tree-ring site coverage is relatively dense. Alternative reconstructions using different modeling methods and basic tree-ring data differ in details but are consistent in the timing of periods of relative drought and wetness, and in identifying the late 1500s as the most severe multi-year drought of the last 500 years. Reconstructions for major tributaries emphasize the spatial coherence of droughts and wet periods over the UCRB. The Lee Ferry record of annual flows can be extended back beyond 500 years, with diminished confidence, by analysis of tree rings from dead standing trees and logs. A new reconstruction covering the period A.D. 762-2005 was generated by a series of reconstruction models with time-varying subsets of 11 recently developed tree-ring chronologies from the Upper Colorado River Basin (UCRB) as predictors. The percentage of variance of annual flow at Lee Ferry accounted for by these models decreases from 77 percent after A. D. 1365 to 60 percent before A. D. 1182, as the number of available tree-ring chronologies drops from eleven to three. Correlation analysis and cross-spectral analysis support the hydrologic interpretation of annual as well as decadal fluctuations in the extended reconstruction. The singular multi-decadal event is a drought in the mid-1100s, when the lowest 25- year mean is estimated to be just 84 percent of the modern observed long-term mean. Absence of high flows rather than presence of record-low flows is characteristic of this drought. Results suggest the mid-1100s drought was more severe in the western part of the UCRB than the well-documented North American mega-drought of the late 1500s. Greater site coverage and sample depth (number of trees) are essential to reducing the uncertainty of assessments of hydrologic drought severity in the early part of the tree-ring record.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1812 Drought
SC: Hydrology [H]
MN: 2007 Joint Assembly