TreeFlow is a comprehensive web resource on tree-ring reconstructions of streamflow and climate for the US, providing access to data for over 70 streamflow reconstructions as well as information on data development and applications. While the primary users of streamflow reconstructions are water resource professionals, people in many other sectors and disciplines may find the data useful.

TreeFlow is intended to be a dynamic resource. Since 2002, when TreeFlow was first launched, we have expanded pages as reconstructions have become available for other basins, and as new applications have been developed. We welcome the contributions of other researchers and water providers. We also provide links to other hydrologic reconstruction resources, including a network of Rocky Mountain snowpack reconstructions and North American monsoon reconstructions

TreeFlow is a collaborative effort of researchers affiliated with two NOAA-funded Regional Integrated Sciences and Assessment (RISA) programs:Climate Assessment for the Southwest (CLIMAS) at the University of Arizona, and Western Water Assessment (WWA) at the University of Colorado. The TreeFlow website is housed on a server at the University of Arizona.

The following topics are included below:

    A Quick Tour of TreeFlow
    The TreeFlow Team and Support
    A Brief History of TreeFlow
    Assessment of Scientific Outreach Study

A Quick Tour of TreeFlow

The top-level pages of TreeFlow (listed in the side navigation bar) are as follows:

Basin Data Access
Links to the basin homepages, which provide easy map-based access to reconstruction data for each of the major hydrologic basins in the US for which we currently have reconstructions, as well as other informational resources specific to each basin.

Background Information
What are tree-ring reconstructions? How are they developed? How can they be used? Informational resources which provide increasing levels of detail in answering these questions.

Describes how water managers can use, and are using, tree-ring reconstructions, with summaries of specific applications from several basins.

Reports and presentations from the workshops on tree-ring reconstructions convened by Connie Woodhouse, Jeff Lukas, and colleagues around the western US since 2006.

Colorado River Streamflow: A Paleo Perspective
Multi-page feature describing the development of tree-ring reconstructions of streamflow for the Colorado River and the broader perspective they provide.

Other Resources
Provides references and web links to information resources on tree-ring reconstructions, and related topics (climate variability and change, hydrology) for the western US.

The TreeFlow Team and Support

The TreeFlow Team:

    Connie Woodhouse, University of Arizona & Climate Assessment for the Southwest 
    Jeff Lukas, Western Water Assessment, University of Colorado
    Becky Brice, University of Arizona & Climate Assessment for the Southwest 

Others at the University of Arizona involved with TreeFlow's development:

    Katie Hirschboeck
    Holly Hartmann
    Marla Kostuk
    Ellen Lay
    Dominic Martinez
    Ben McMahan
    Anju Shah

Collaborators & Data Contributors:

    Steve Gray, USGS Alaska Climate Science Center
    Dan Griffin, University of Arizona (now at the University of Minnesota)
    Jeremy Littell, USGS Alaska Climate Science Center
    Ellis Margolis, University of Arizona
    Stockton Maxwell, Radford University
    David Meko, University of Arizona
    David Stahle, University of Arkansas
    Ramzi Touchan, University of Arizona
    Erika Wise, University of North Carolina-Chapel Hill 


The TreeFlow team is grateful for funding or other support from the following entities:

NOAA Climate Program Office - Regional Integrated Sciences and Assessments Program (RISA) and Sectoral Applications Research Program (SARP)
Western Water Assessment (WWA)
Climate Assessment for the Southwest (CLIMAS)
University of Arizona Institute of the Environment

And the many water resource managers, consultants, and others who have provided valuable feedback, and information on applications, and without whom this effort would not have been possible

A Brief History of TreeFlow

The great potential of tree rings to provide information about past climate and hydrology in the western US was first recognized in the early 1900s, but not until the advent of computers and new statistical techniques in the 1960s and 1970s, were the first “modern” reconstructions of annual streamflow developed. From 1975 to 2000, a number of streamflow reconstructions were developed for the Colorado River basin and major rivers in California, but reconstructions were not widely used in water planning and management.

The persistent drought conditions that emerged across the West in 1999, especially the extreme drought year of 2002, indicated that the observed records of streamflow in the region did not capture the full range of natural hydrologic variability. This drought, along with increasing demands on water supplies led to a need to assess the range of drought conditions that were likely to occur. Tree-ring reconstructions of streamflow, extending several hundred years or longer, provide a more complete representation of past variability. Accordingly, streamflow reconstructions attracted more interest within the water management community as a potentially useful tool for planning.

Starting in 2002, a new research and outreach project met this growing interest in tree-ring data. With a multi-year NOAA grant, Connie Woodhouse (then at NOAA), Robert S. Webb (NOAA), and Jeff Lukas (U. of Colorado) partnered with water managers in Colorado to develop over 20 streamflow reconstructions, which were made accessible through the original TreeFlow website hosted at the NOAA National Climatic Data Center's Paleoclimatology Branch. A subsequent research effort by Connie with Stephen Gray (then the Wyoming State Climatologist, now with the USGS) and David Meko (U. of Arizona) generated 10 new reconstructions for theUpper Colorado River Basin, published in 2006. In addition, a California TreeFlow website was developed with the encouragement of the California Department of Water Resources. 

In 2006, with funding from Western Water Assessment, Connie and Jeff began presenting one-day technical workshops to water managers and other river stakeholders across the West, describing the new reconstructions and their use in planning. The next year, a revised TreeFlow web resource made its debut at Western Water Assessment. At the same time, David Meko and Katie Hirschboeck (U. of Arizona and Climate Assessment for the Southwest) were working with the Salt River Project to develop reconstructions for the Lower Colorado River Basin. Steve Gray and his colleagues at the University of Wyoming were generating more reconstructions for river basins in Wyoming. Water managers in other basins, such as the Pacific Northwest, expressed interest in having this type of resource for their area as well, which led to new work in the Pacific Northwest by Jeremy Littell then at the University of Washington's Climate Impacts Group.

It became clear that an expansion of the TreeFlow web resource to allow it to grow and cover the western US was needed, providing basin-centered access to the reconstructions and information about their use. A NOAA Climate Program Office grant in 2008 to Connie and the TreeFlow Team funded the development of the new, comprehensive, TreeFlow website, combining the efforts from researchers associated with Western Water Assessment, Climate Assessment for the Southwest, and the Climate Impacts Group. This version of the TreeFlow web resource was designed to be a dynamic resource that could accommodate reconstructions and applications from researchers and water professionals across the US. The latest version of TreeFlow has transitioned the site to a platform that is more easily updated and expanded, to encourage even further growth.

Drought, Tree Rings, and Water Resource Management:
Assessment of the Application of Tree-Ring Data to Water Management Study

In 2008, Jennifer Rice of the University of Arizona (now at University of Georgia), assisted by Connie Woodhouse, Jeff Lukas, and Brad Udall, conducted a study evaluating the outcomes of scientific outreach efforts of the Western Water Assessment's TreeFlow project. This study had two related parts: (1) an evaluation, based on interviews, of the outcomes of collaborative research with several water managers, consultants, and utility directors in Colorado, and (2) an evaluation, based on a web survey, of outcomes of the technical workshops for water managers and stakeholders. The study focused on how water practitioners are actually using tree-ring data in their day-to-day operations, hydrologic models of water supply, resource planning and decision-making, and the challenges they have encountered in using the data, as well as the effectiveness of the workshops in conveying information that is used by the participants.

Final report to the Western Water Assesssment and Appendices:

    Final Report (PDF)

    Appendix A - Information Sheet (PDF)

    Appendix B - Interview Questions (PDF)

    Appendix C – Web Survey Questions (PDF)

Presentation on project at 2009 meeting of American Association of Geographers (AAG):

    J. L. Rice and C. A. Woodhouse, "Climate Science and Decision-Making:
    The Case of Water Managers and Tree-Ring Data in the Western United States." (PDF)

Paper on project published in the Journal of the American Water Resources Association (JAWRA):

    Rice, J., Woodhouse, C., and Lukas, J. (2009). Science and decision-making: Water management and tree-ring data in the western United States. Journal of the American Water Resources Association 45(5): 1248-1259. (PDF)