Drought and Flood Magnitude and Frequency with Uncertainty
Long-term (5 to 10-year) annual streamflow (reservoir inflow volumes) probability estimation and forecasting of droughts are needed for water-supply and operations management. Recent research on water-supply and drought prediction indicates that tree-ring records are useful proxies for streamflow reconstructions and record extension.
* Can Reclamation effectively develop and/or utilize tree-ring based streamflow reconstructions for water-supply and drought prediction, including uncertainty, and transfer ideas from the Colorado River draft EIS to other sites? This is the question that will be investigated for this research.
This scoping study is an initial effort to gather tree-ring data, streamflow and tree-ring based modeling techniques, and identify other potential application sites. The work will examine data availability, modeling, simulation, uncertainty of predictions, transferability of reconstructions, and ways for decisionmakers to use the information.
Need and Benefit
This research is an initial investigation to develop a tool that can be used by Reclamation for long-term (5 to 10-year) annual streamflow and water supply simulation and drought probability estimation based on data from streamflow gauges and tree-ring (proxy) records. The end product of this work might potentially be a generalized methodology for the use of tree-ring based streamflow reconstructions. These streamflow reconstructions would then be used in a stochastic streamflow model for prediction and forecasting. The streamflow model results could then be used by decisionmakers in long-term operations and planning.
Recent research on long-term water-supply and drought forecasting and prediction has indicated that tree-ring records are useful proxies for streamflow reconstructions and record extension. While this information is not yet routinely used within Reclamation for long-term water-supply planning and analysis, there are ongoing studies using dendrochronology in the Upper and Lower Colorado River basins (e.g., Woodhouse et al. 2006, NRC 2007, Prairie et al. 2007). In particular, the National Research Council (NRC) (2007, p. 110) clearly highlights the value of this data: "Recent studies based on tree-ring data, covering hundreds of years, have transformed the paradigm governing understanding of the river's long-term behavior and mean flows. These studies affirm year-to-year variations in the gaged records. They also demonstrate that the river's mean annual flow--over multidecadal and centennial time scales, as shown in multiple and independent reconstructions of Colorado River flows--is itself subject to fluctuations. Given both natural and human-induced climate changes, fluctuations in Colorado River mean flows over long-range time scales are likely to continue into the future. The paleoclimate record reveals several past periods in which Colorado River flows were considerably lower than flows reflected in the Lees Ferry gaged record, and that were considerably lower than flows assumed in the 1922 Colorado River Compact allocations."
This scoping-level study is an initial effort to gather together tree-ring data, streamflow and tree-ring based modeling techniques, and to identify potential application locations for Reclamation facilities. The work will touch on several points that may be lacking from several recent studies:
* What are the methods to use the streamflow reconstructions in simulation models for prediction?
* Are techniques mature and have they been standardized for routine water-supply applications?
* Are there advantages to using nonparametric as opposed to parametric models?
* Is uncertainty in the reconstructions properly incorporated into the results?
* Is this uncertainty carried through into simulation models for estimating prediction uncertainty?
* Can recent improvements in nonlinear multiple regression improve on the reconstruction models?
* Are results from localized studies such as on Boulder Creek (Woodhouse 2001) transferable to other locations?
* Is there a framework in place for decisionmakers to use the information?
Existing capabilities in drought and tree-ring based streamflow reconstructions are predominately from external sources such as the Laboratory of Tree-Ring Research at the University of Arizona and the Lamont-Doherty Earth Observatory at Columbia University. Some in-house Reclamation expertise exists within the Technical Service Center (TSC), Boulder Canyon Operating Office (BCOO) and the Upper Colorado (UC) Regional Office.
This research does have potential for broad application across Reclamation. The main limitations are potentially data and availability of reconstructions. These will be explored via spatial analysis of the existing tree-ring databank and merging with Reclamation facilities and project areas. The tools might potentially be applicable, for example, on the Middle Rio Grande Project, the Colorado Big Thomp
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