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Past Droughts Geographically Widespread In The West, According To Tree-ring Data

Date:
August 20, 2005
Source:
University of Arizona
Summary:
When it's dry, it's dry all over, according to a new analysis of more than 400 years of annual streamflow in the Upper Colorado and Salt/Verde river basins. By using data from tree rings, University of Arizona researchers conclude that severe droughts and low-flow conditions in one basin are unlikely to be offset by abundant streamflow in the other basin. The study covers waterways from the states of Arizona, Colorado, New Mexico, Utah and Wyoming.

When it's dry, it's dry all over, according to a new analysis of morethan 400 years of annual streamflow in the Upper Colorado and Salt andVerde river basins.

By using data from tree rings, University of Arizona researchersconclude that water supply for those western rivers fluctuated insynchrony during periods of severe drought. The study goes back almost800 years in the Salt-Verde basin and covers waterways from the statesof Arizona, Colorado, New Mexico, Utah and Wyoming.

The project's overall conclusion is that severe droughts andlow-flow conditions in one basin are unlikely to be offset by abundantstreamflow in the other basin.

"Prior to the findings from this study, the conventional wisdomwas that runoff from the Colorado River would be available to make upfor deficits on the Salt and Verde rivers during times of extremedrought," said Charlie Ester, Salt River Project's manager of WaterResource Operations. "The bottom line is that the Upper Colorado Basinand the Salt and Verde basins work together as one entire region."

Tree-ring-based reconstructions of streamflow can peer backinto time much further than the records available from stream-flowgauges. Ester said such reconstructions could provide importantinsights into the hydrologic variability of a river basin over time.

The findings represent just the first phase of a studypartnered by SRP and The University of Arizona's Laboratory ofTree-Ring Research. UA scientists Katherine K. Hirschboeck, anassociate professor of climatology, and David M. Meko, an associateresearch professor, conducted the tree-ring analysis.

The study's second phase, which will begin this month, willtake a closer look at more recent history when scientists from thetree-ring lab will re-core trees in the Salt and Verde watersheds togather new data from the last 40 years, a period when the watershedshave experienced both record wet and record dry episodes. The findingsof the second phase will likely be available in the summer of 2007.

Key project conclusions from the tree-ring study:

  • Extreme events, either low flows or high flows,tended to occur simultaneously in the Upper Colorado and Salt/Verderiver basins;

  • Such synchronous low-flow and high-flow events tended to cluster in time;

  • The longest continuous period when both basins had extreme low-flow years was three years;

  • Within any four-year period, having either highflow or low flow for two consecutive years occurred more than 20percent of the time;

  • For the Salt/Verde river basin, the recent drought is similar to that experienced in the 1950s;

  • The tree-ring record reveals that between 1200 and1903, the Salt/Verde river basin had at least eight droughts as severeas the 1950s drought.

    Ester said the findings will help devise an assessment tool forimplementing the project's results into operational water supplydecision-making.

    Hirschboeck said the study's findings offered some revelationsfor the Laboratory of Tree-Ring Research's scientists. "Dave and I weresurprised that the two distant basins, the Upper Colorado and theSalt/Verde, were so much in synch during periods of extremely high orextremely low flow." She added, "The recent joint drought, whilesevere, is not unprecedented when compared to those in the previousfive centuries."

    The findings of the first phase are being shared withrepresentatives of various federal, state and local agencies such asthe National Weather Service, U.S. Bureau of Reclamation, ArizonaDepartment of Water Resources, Central Arizona Project and cities inthe Phoenix metropolitan area.

    The tree-ring study in partnership with The University ofArizona is the one of many initiatives taken by SRP in response to anongoing drought that is in its 10th year. Even counting this pastwinter when 2,017,580 acre-feet of runoff -- the first above-normalrunoff season since 1998 -- filled the reservoirs on the Salt and Verderivers, stream flows into the Salt and Verde have been below normal foreight of the last 10 January-through-May runoff seasons.

    Phoenix-based SRP is the largest provider of water to the greater Phoenix metropolitan area.

    The University of Arizona's Laboratory of Tree-Ring Research wasestablished in 1937 by A. E. Douglass, the founder of modern tree-ringscience.

    ###

    More details on the tree-ring report are available at http://www.ltrr.arizona.edu/srp.



  • Story Source:

    The above story is based on materials provided by University of Arizona. Note: Materials may be edited for content and length.


    Cite This Page:

    University of Arizona. "Past Droughts Geographically Widespread In The West, According To Tree-ring Data." ScienceDaily. ScienceDaily, 20 August 2005. <www.sciencedaily.com/releases/2005/08/050819094701.htm>.
    University of Arizona. (2005, August 20). Past Droughts Geographically Widespread In The West, According To Tree-ring Data. ScienceDaily. Retrieved September 2, 2014 from www.sciencedaily.com/releases/2005/08/050819094701.htm
    University of Arizona. "Past Droughts Geographically Widespread In The West, According To Tree-ring Data." ScienceDaily. www.sciencedaily.com/releases/2005/08/050819094701.htm (accessed September 2, 2014).

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