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Overview Underlying Assumptions
Collaborators  Tree-Ring Based Framework
Background Summary
Exploratory Scenarios Collaboration Plans

OBJECTIVEThe main objective of this resource is to provide a framework for the use of tree-ring data in creating drought scenarios for water managers.

COLLABORATORS - This resource was developed as part of a collaboration between the University of Arizona's Laboratory of Tree-Ring Research (LTRR), Arizona State University's Decision Theater, and the East Valley Water Forum.  Support was provided by the Arizona Water Institute.

The tree-ring research which supplied streamflow reconstruction data for this resource was funded by the Salt River Project (SRP).  Dave Meko and Katie Hirschboeck were the LTRR researchers collaborating with SRP on this project. 
π LTRR-SRP-I Project Wepage

In addition to the above, this website includes input and links from many other contributors, especially the SAHRA Scenario Development Group and the Western Water Assessment (WWA) site on "Tree-Ring Reconstructions of Streamflow for Water Management in the West" authored by Jeff Lukas and Connie Woodhouse.


Tree rings have become increasingly recognized as important sources of information about the longterm variability of both climate and streamflow.  As ongoing drought in western U.S. continues to impact water supplies from Colorado to Arizona to California, new collaborations between water managers  and tree-ring researchers have been forged to explore ways in which multi-century, high-resolution tree-ring reconstructions can be used to inform water resource planning and management decisions.  One such project was the LTRR-SRP collaboration noted above titled:  "A Tree-Ring Based Assessment  of Synchronous Extreme Streamflow Episodes in the Upper Colorado & Salt-Verde-Tonto  River Basins" (hereafter referred to as LTRR-SRP-I). The results can be found on the LTRR-SRP-I Project website and have since been incorporated into aspects of SRP's water resources operations. 

The AWI-funded project "Improved Tools for Drought Planning and Management" proposed a collaboration between Arizona State University, the University of Arizona, and the East Valley Water Forum (EVWF) with the goal of using both ASU's Decision Theater visualizations and the LTRR-SRP-I tree-ring results to aid in the generation of drought scenarios for the EVWF Management Plan. Originally, a standard set of guidelines for determining drought scenarios based on tree-ring records was planned. However, as the project developed it became apparent that a single set of guidelines would be too constraining.  The project was re-focused on developing a “framework” that could display one or more different approaches and tools to use in scenario development, based on varying managerial needs. The resulting website titled "A Framework for Generating Exploratory Scenarios of Drought Conditions Using Tree-Ring Information" is meant to be viewed as an evolving resource that will eventually combine with similar efforts in other regions (e.g., under NOAA "Coping with Drought" initiatives).


To begin envisioning how tree ring information can be used as tools to generate drought scenarios, some scenario background is necessary.

π  See the links: About Scenario Development and What Are Scenarios? for background information on types of scenarios and how they are constructed.

Tree-ring reconstructions are most useful for generating Exploratory Scenarios:

EXPLORATORY SCENARIOS describe the future according to known processes of change and extrapolations from the past by incrementally progressing through time. They rely on logical induction, by using clues from the past and present and working out the pathways that the future may take.

                                            SOURCE: SAHRA Scenario Development Group

A schematic diagram of the Exploratory Scenario process is shown below.  While comprehensive drought scenario development must also include a much wider range of scenario inputs (i.e. Anticipatory and Strategic Scenarios, Management Scenarios, Policy Scenarios, etc.), the diagram illustrates two ways in which tree rings can be used in exploratory scenario development: (1) by providing information on the full range of past patterns of climate and streamflow behavior (projective scenarios), and (2) by using  past climate and streamflow behavior as a baseline from which to construct alternative processes or patterns that significantly vary from the past, e.g., under future climate change (prospective scenarios).  The framework presented here addresses possible ways in which tree-ring reconstructions of streamflow might be used in both projective and prospective scenario approaches.

Projective Scenarios are based on extrapolating trends, cycles, and other patterns that have been experienced over some past period
Prospective Scenarios incorporate changes in processes or patterns
that significantly vary from the past


The framework for using tree-ring information in generating exploratory scenarios of drought conditions in Arizona is based on the following assumptions:

 • Tree-ring reconstructions of streamflow are reliable indicators of past streamflow, and they can adequately capture the range of natural streamflow variability.

π  See the Tree Ring Data and Reconstruction Methods links for background and discussion of this basic assumption.

 • The principle of uniformitarianism holds, such that reconstructed streamflow patterns and behaviors of the past can be interpreted in the same way as present streamflow behavior. 

π  Find a link to other principles related to tree-ring analysis on the Tree Ring Data webpage

 • The magnitude and variability of surface water supplies are key inputs needed in developing drought management scenarios and groundwater management plans, such as the EVWF's.   

• Multi-year sequences of flow extracted from longterm tree-ring reconstructions of streamflow can be useful inputs into surface/groundwater models to illustrate different modes or patterns of streamflow that have been experienced in the past (projected scenarios), or may be experienced in the future (prospective scenarios, via altered magnitudes, frequency, persistence, or amplitude).  


Here is a brief overview of the components of the framework:
Tree ring
background information
with links
is provided
Framework for Scenario Development
Streamflow Sequence spreadsheet is provided so users can select, plot, and/or analyze additional sequences as needed
Streamflow reconstruction data sets are available from the website
Statistics are
provided for the streamflow reconstructions
Visualizations are provided to aid interpretation and analysis
Sequences are extracted and
plotted to illustrate different modes or patterns of past streamflow
Suggestions are provided for use of the sequences in projective and prospective scenarios


This website presents a framework for using tree-ring information in generating exploratory scenarios of drought conditions.  In addition to links and relevant background material on tree rings and reconstruction methods, the website provides access to data spreadsheets, descriptive statistics and visualizations for streamflow reconstructions of the Upper Colorado and Salt-Verde-Tonto River Basins.

Seventeen multiyear sequences of past streamflow covering different time frames (30-year, 20-year, 11-year, and 7-year) were selected from the reconstructions for possible use by water mangers in exploratory scenario development and planning for future drought conditions.  An effort was made to select sequences that represent a wide range of past (and possible future) streamflow behaviors, including severe and sustained low flow sequences, high flow episodes, and periods with high amplitude variability.

Suggestions are provided for use of the 17 sequences in projective and prospective exploratory scenarios. The Streamflow Sequence Data Spreadsheet is available for downloading and contains the reconstructed flow data, quantile visualizations, and graphs for each sequence.  Users can use the spreadsheet to select, plot, and/or analyze additional sequences if desired.

Ongoing and future collaborations with water managers will provide the opportunity to evaluate the usability and applicability of this framework for drought scenario development.


This webpage can be expanded to meet the needs of the EVWF in their examination of various management scenarios under drought conditions.  Toward this end, Katie Hirschboeck will continue to collaborate with the EVWF as needed as a principle investigator with the Climate Assessment of the Southwest (CLIMAS) program.

Designed as a platform which can be augmented and expanded, this webpage is also intended to serve as a regional resource for the Southwest and eventually become one of several components of a proposed “TreeFlow” webpage and paleo toolkit project that will cover the entire Western United States (in collaboration with Connie Woodhouse, Univ. of Arizona, WWA and CLIMAS).

 • Home •   Overview •  About Scenario Development • Tree-Ring Data •  Methods •
Streamflow Reconstructions •   Statistics & Visualizations  • Streamflow Sequences