HR: 12:05h
AN: H12E-07    [Abstracts]
TI: Reduction of Uncertainty in Water Mass Balances
AU: * Trask, J C
EM: jctrask@ucdavis.edu
AF: Hydrologic Sciences Program, Veihmeyer Hall, University of California at Davis, Davis, CA 95616, United States
AU: Fogg, G E
EM: gefogg@ucdavis.edu
AF: Hydrologic Sciences Program, Veihmeyer Hall, University of California at Davis, Davis, CA 95616, United States
AB: Two novel approaches that reduce uncertainty in lake, watershed, and basin water balances are presented and applied in the Lake Tahoe basin. A novel residual redistribution technique reduces random error in water balance component estimates. This technique is well-grounded in standard statistical methods, and is simple, robust, and of broad general applicability. Reduction of random error in areal precipitation and streamflow estimates is validated using independent data. Remaining random error variance in areal precipitation estimates is markedly small. Reduction of random error in annual areal precipitation estimates resolves watershed ‘memory' of precipitation from prior water-years (WY). The signal of precipitation from prior WY is often obscured in random error noise associated with established methods for estimating inter-annual variations in total annual areal precipitation. It is shown that the relationship of eastern Tahoe sub-basin annual streamflow to precipitation from prior WY can be inferred in the absence of gage data, using noise-filtered precipitation data and whole basin water yield data. Limited stream gage records from eastern Tahoe sub-basins confirm the inferred dependence on precipitation from prior WY, and thus that watershed moisture storage changes are significant to the water mass balance over time scales of several years. Such long time scales for storage change effects on streamflow are typically not accurately accounted for in watershed hydrology models. Inter-annual changes in watershed moisture storage are readily distinguishable from inter-annual variations in watershed ET. Application of a novel precipitation-decorrelation technique yields an estimate of Lake Tahoe mean annual evaporation with associated rigorously quantified uncertainty. This novel estimate agrees closely with several independent standard measurement-based evaporation estimates; and has uncertainty comparable to that of a high-quality energy balance approach. The two novel techniques used together yield robust lower bounds on the magnitudes of mean annual areal precipitation and atmospheric loss (ET, sublimation) in the Tahoe Basin. These lower bounds indicate that several previously published investigations have likely underestimated actual areal precipitation and atmospheric loss.
DE: 1854 Precipitation (3354)
DE: 1873 Uncertainty assessment (3275)
DE: 1876 Water budgets
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting