A TREE-RING RECONSTRUCTION OF ANIMAS RIVER STREAMFLOW AND ITS USE IN WATER MANAGEMENT Workshop Discussion Summary June 13, 2008 Durango, CO Workshop Powerpoint available at: http://wwa.colorado.edu/resources/paleo/Lukas_Durango_2008.pdf After Jeff Lukas (CU Boulder & Western Water Assessment )presented the methods and results of the reconstructions of the Animas River and the associated reconstruction of Los Pinos River, we asked participants to describe how they are likely to use this information: * All of the participants expressed interest in using the reconstructions to educate water managers, users, and other constituents such as elected officials. The group discussed preparing an outreach brochure in a similar format to one developed previously by the Western Water Assessment. WWA could develop the brochure and MSI would seek funds for printing. We'd want some water managers to review a draft. * We discussed the best way to present the data. The three-year average was thought to be an important time frame. Three year low flow events are rare but within our experience. * Some of the participants thought that they’d use the information qualitatively, as a contextual tool to integrate with their other information sources. The comparison of the recent 2002-04 drought and mid-1900s wet period with past events was very useful. In general the results helped participants to understand the duration and frequency of low periods beyond the 80 year gaged period. Also it helps when thinking about water storage needs in planning – what is a “long” drought in the reconstruction? * The US Forest Service could use the reconstructions as context for how to respond to increasing demand for water rights on public lands while leaving enough for ecosystems. First, they have been asked how earlier snowmelt timing in relation to timing of irrigation season would change land use permitting because many water rights are connected to flow timing. Western Water Assessment has a project on this subject: http://wwa.colorado.edu/resources/western_water_law/water_rights_and_climate_change_project.html. Second, looking at past variability in combination with likely reductions due to climate change is important context for evaluating new proposals for additional water storage on public lands. Also, these results are an impetus for doing a better job of incorporating paleo-reconstructions into Forest planning. * A few participants are interested incorporating the reconstruction results into modeling simulations. For example, the Bureau of Reclamation would be interested in running the reconstruction info through the Animas-La Plata Project (ALP) model. Would ALP be able to meet full supply during historic drought periods? How often would ALP run into supply problems? The data would need to be disaggregated into monthly data using information on monthly variability. Denver Water has done this and used the reconstruction in combination with climate change projections. Some participants would like to learn more about what Denver Water has done and if it could be repeated here on the Animas or other rivers. * There was a suggestion that if the simulation modeling was too complex or expensive that as a combination quantitative-qualitative tool, a certain percentage of flow could be knocked off the reconstructed flows to simulate climate warming. Other discussion topics of note: * The Colorado Statewide Water Initiative incorporated increased population into projections but did not include stream flow paleo-reconstructions or climate change. The new Colorado River Water Availability study will use paleo-reconstructions and climate change GCM output in their models however. * Tree-rings have been used to reconstruct April 1 snow water equivalent (SWE) with R2 around 0.6 (explaining 60% of the variability). There is some loss of information because trees respond to April-June precipitation which is not part of SWE. * Similarly, the use of trees for stream flow reconstructions has limitations due to tree ecology. There could be years with low October to June precipitation and high July to September precipitation but the tree rings respond mainly to the winter precipitation and not the summer. So tree-rings don't do a great job of recording late summer/fall precipitation.