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5.3 Model inputs and outputs for scenarios on the web-based server. <br />Task 6: Alternate Historical Hvdrolo~y <br />objective: <br />The objective of Task 6 is to extend historical hydrologic data using currently available tree-ring <br />data and stochastic methods to develop alternate hydrologic traces in formats usable in the <br />CDSS. The task includes agency coordination, literature review, diagnostic analysis, data <br />preparation, and model testing of the alternate historical hydrology traces. <br />Background: <br />Reconstructions of streamflow in the Colorado River Basin and elsewhere indicate that draughts <br />that were longer and more intense than those observed in the instrumental record may have <br />occurred in prehistoric periods. Until recently, methods were not readily available to incorporate <br />reconstructed streamflows into detailed water resources planning studies. The technical obstacle <br />was that streamflow reconstructions were done at one point, or at most a few points, in a basin, <br />while water resources models might require inflows at tens to hundreds of points. In addition to <br />technical obstacles, the nature of streamflow reconstruction as a "research" activity probably <br />hindered the adoption of these methods into practice. The recent drought increased interest in <br />the use of reconstructed paleo streamflows, and this, coupled with more robust results from <br />maturing methodologies, has increased confidence in reconstructions. <br />Ln 2007, the U.S. Bureau of Reclamation used reconstructed streamflows to conduct sensitivity <br />analyses in support of the development of interim guidelines for Lower Basin shortages and <br />coordinated operation of Lake Powell and Lake Mead. The reconstructions used by Reclamation <br />were done with new methods that are anchored in the observed record and can be thought of, at <br />least in some variants, as simply re-sequencing observed streamflows to represent the year-to- <br />year variability and the distribution of wet and dry spells captured in the tree-ring records. <br />For this Study, the CWCB requested development of an alternate historical hydrology data set. <br />This data set will be an extension of historical streamflows that represents the annual variability <br />of streamflows and the distribution of wet and dry spells captured in the tree ring record. This <br />alternate hydrology will serve as input to STATEMOD to assess water availability and to <br />develop a "base" case of flow and water availability conditions against which comparisons can <br />be made with currently available historical hydrology and with climate change and forest change <br />scenarios to be developed in Task 7 below. <br />Colorado River Water Availability Study Scope t4 8/28/2008 <br />CRWAS Phasel Contract Scope EX A Final <br />