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How tree rings can help reconstruct streamflow
Published May 23, 2007
Records from the annual growth rings of many trees in the U.S. West can be used to extend, or reconstruct, streamflow records based on gaged measurements. These streamflow reconstructions can provide water managers and stakeholders with a much longer window— 300 years and more—into the past hydrologic variability of a river system, and have the potential to inform sustainable management of water resources.
Successfully applying these paleohydrologic data to water management depends on sustained interaction between the scientists who develop the data and the managers who have interest in using them, with each group coming to better understand the operational environment and methodologies of the other. To this end, the Western Water Association (WWA) began presenting a series of workshops for water managers and stakeholders in 2006, with some contributions from the Climate Assessment for the Southwest (CLIMAS). The initial planning workshop was held in Tucson in May 2005.
The goal of these technical workshops is to comprehensively cover the methods of generating reconstructed streamflow from tree rings, so that water managers interested in applying these data have a better basis of understanding from which to work. The core of the all-day workshop is a multi-section instructional presentation, interspersed with hands-on activities, lab tours, and group discussions. Participants respond to a pre-workshop survey so that each workshop’s content can be tailored to meet the needs and interests of the specific group. Some points from the workshops are described on page 4.
The first workshop was held in Alamosa, Colorado, in late April 2006, following interest expressed by the Rio Grande Water Conservation District the previous year. The participants—San Luis Valley water managers and natural resource managers—grasped the tree-ring data as an important means to convey to water users and stakeholders in the San Luis Valley the need to constrain demand, particularly groundwater pumping, to accommodate the inevitable sustained dry periods.
A half-day field trip to the foothills west of Boulder to demonstrate field techniques for extracting tree-ring cores from living trees was part of the second workshop in Colorado, held in May 2006. The 14 participants represented a broad spectrum of water agencies and interests in Colorado and the Colorado River basin. The workshop included discussion of applications of the treering data, with each of the participants briefly describing their current and intended use of the data. Some examples are given in Figures 1 and 2.
An October 2006 workshop and field trip in Tucson attracted water managers from across the Southwest and even one from Canada to The University of Arizona’s Institute for Study of Planet Earth. Researchers from CLIMAS and the UA Laboratory of Tree-Ring Research also helped out. The workshop featured presentations by Chris Cutler of the U.S. Bureau of Reclamation, Charlie Ester of the Salt River Project, and Bill Girling of Manitoba Hydro on their respective uses of the streamflow reconstructions for management purposes.
Participants’ feedback indicates the workshops have fulfilled their objective of conveying relevant information about the tree-ring data. They have also been a venue for water managers to share information with each other about applications of the data, and for researchers to learn more about water management in the region.
Researchers have filled the role of providing data and technical assistance, while the managers and their consultants are developing particular application methodologies (e.g., disaggregating annual tree-ring data into daily time steps for model input). The workshops clearly have enhanced the communication needed to bridge research data and management applications.
Future workshops will continue to mix instruction with discussion of applications as dictated by the participants’ needs and backgrounds. A half-day workshop in Durango, Colorado, will be held on May 31, and other 2007 workshops could include Albuquerque, Las Vegas, and southern California.
As a companion to the workshops, web pages hosted by WWA feature the instructional presentations as well as the applications presentations given by water managers. The pages also describe several applications of the streamflowreconstructions to water resource planning, list the water agencies currently using tree-ring reconstructions for management purposes, and provide links to archived reconstruction data for the western United States. The web pages are available at: http://wwa.colorado.edu/ resources/paleo/.