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reconstructions. The trees capture both year -to -year variations and multi -year anomalies. All of the re- constructions show a broader range of variability in streamflow than that seen in the much shorter gaged flow records, including one -year droughts similar to or worse than 2002 and multi -year events worse than those of the 1930s or 1950s (Figure 4). Application of the reconstructions The reconstructed streamflows are 400000 d v 300000 c 200000 LL N 100000 a 1450 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 Figure 4. Blue River at Dillon Reservoir tree -ring reconstructed annual streamflow, 1450 -2002 (thin line) with a S year filter (thick line) showing multi -year events. Several years (e.g., 1685, 1845) have reconstructed flows lower than the reconstructed and gaged flow for 2002 (- 105,000 acre feet). used by our partners as inputs for their water supply models to test the ability of their systems to meet demand under the broader range of flow conditions represented by the reconstructions. Even with the inherent uncertainties in any paleoclimate reconstruction, and the under- standing that past conditions are not direct analogs of future conditions, the tree -ring derived streamflow reconstructions are considered valuable information and have been incorporated into the decision - making process for water management in the region. Future work Over the next year, we plan to expand the spatial coverage of our reconstructions to include other major river basins in Colorado. We will also expand the range of data products available. We have had promising results in using latewood —the part of the annual ring more responsive to summer conditions —in reconstructing summer drought and thus overall water demand. We are also applying an approach from short-term climate forecasting —the ensemble method —to better under- stand the uncertainty in our tree -ring reconstructions. With the ensemble method, many model solutions, each based on a different calibration period and using a different set of predictors, are generated. The spread of the solutions for each annual value varies and thus provides insight into the temporal variability of uncertainty in the tree -ring data. TreeFlow web pages - introduce and describe the project, - explain the reconstruction process in detail, and - provide access to the reconstructed and gaged flow data. e intend the site to be a general resource for the water sources community, and the data are freely available. The ;bsite provides our contact information if you have ques- ins about the project. cd+Pate�dirYi�tQtogy-,Ffogram eocaamaa =,,. TreeFlow Treerting-reamnstwe[ioms - aadie >nsi resources F1:aF rzltery References Schulman, E. 1945. Tree -ring hydrology of the Colorado Basin. University of Arizona Bulletin 16(4). Laboratory of Tree -Ring Research Bul letin No. 2. 51 pp. Stockton, C., and G. Jacoby. 1976. Long -term surface water supply and streamflow levels in the Upper Colorado River Basin. Lake Powell Research Project Bulletin No. 18, University of California, 70 pp. Acknowledgments Funding was provided by National Science Foundation grants ATM - 9729571 and ATM - 0080889; NOAA Office of Global Pro- grams grant GCO2 -046; Regional Integrated Sciences and Assessments Program - Western Water Assessment; and Denver Water. Undepleted gaged streamflow data for the Blue River provided by Denver Water.