Colorado Water Dec 2003

• Year: 2003
• Title: Colorado Water
• CWCB Section: Administration
• Author: Water Center of Colorado State University
• Description: December 2003 Issue
• Publications - Doc Type: Newsletter

THE TREEFLOW PROJECT:
APPLICATION OF TREE -RING DATA
TO SUSTAINABLE WATER MANAGEMENT IN COLORADO
by Jeff Lukas', Connie Woodhouse' ,2, and Robert S. Webb'
'INSTAAR, University of Colorado, 2NOAAINCDC Paleoclimatology Branch,
3NOAA-CIRES Climate Diagnostic Center, Boulder, CO
Introduction
Sustainable water management requires knowledge of the natural variability in streamflow over time. What is the low-
est annual streamflow one might expect over a given period of time? What is the highest? What is the long -term average?
How many below- average years in a row might be expected? What is the probable return period of a low -flow event of a
given length and intensity?
The main, if not sole, basis for this knowledge has been gaged records of streamflow, which are usually 20 to 50 years
long and at best 100 years long —too short to capture the full range of the variability in water supply. Reconstructions of
streamflow derived from the ring- widths of moisture - sensitive trees, however, can span 300 years or more and thus more
fully describe the natural variability in streamflow, including the extreme low -flow events of most concern to water manag-
ers. With the TreeFlow project, we are working in partnership with water managers to develop new tree -ring reconstruc-
tions of streamflow in Colorado and enhance their utility to water management. Part of the project is to make these data as
accessible as possible through a project website (see sidebar below). In this article, we provide background on the project,
outline the process of developing the reconstructions, and describe how several water providers are using the data in their
planning and operations.
Background
The first studies to examine the relationship
between tree growth and streamflow in the
western U.S. were carried out in the 1930s and
1940s (e.g., Schulman 1945), including work
by Denver Water Board engineer H.L. Potts,
who correlated the growth of trees in South
Park with South Platte annual flow. Over the
next 50 years, streamflow was reconstructed
for a numbere of watersheds across the U.S.
The most notable of these was the reconstruc-
tion of annual streamflow for the Colorado
River at Lees Ferry (Stockton and Jacoby
1976). In Colorado, however, extended
records of streamflow from tree rings had not
been applied to water resource management,
largely because a sparse network of suitable
tree -ring collections hampered the reconstruc-
tion of key gages.
Figure 1. Locations of'new moisture- sensitive tree -ring chronotogies
(triangles) and new streamflow reconstructions (circles) in Colorado.
To address this problem, since summer 2000, we have systematically collected tree -ring samples in western Colorado and
the Front Range, from which we have developed about 50 site chronologies (Figure 1). These chronologies complement
another 20 collected in eastern Colorado and adjacent states in 1998 for a National Science Foundation - funded project
reconstructing the climate of the western Great Plains.
In spring 2002, we received funding from the NOAA Office of Global Programs to use our new chronologies to develop
reconstructions of streamflow and work with water resource managers to make these reconstructions more applicable to
their needs. The extreme drought event in 2002 spurred interest in our work, and by spring 2003 a number of entities had