HR: 16:15h
AN: GC52B-02    [PDF]
TI: Does the 2002 Tree Ring Reflect Low Flow Values in the Upper Colorado River Basin?
AU: * Woodhouse, C A
EM: connie.woodhouse@noaa.gov
AF: NOAA/NCDC Paleoclimatology Branch, 325 Broadway, Boulder, CO 80305 United States
AU: Lukas, J J
EM: lukas@colorado.edu
AF: INSTAAR, University of Colorado, 450 UCB, Boulder, CO 80309 United States
AB: Streamflow in water year 2002 was the lowest on record at many gages in Colorado. This `unprecedented' event motivated water managers to consider using tree-ring-based reconstructions of streamflow to place the 2002 event into a longer context than that afforded by the gaged record. In assessing 2002 flow values relative to tree-ring reconstructed streamflow, water managers were particularly interested in how well the 2002 tree ring captured the extreme low flow values in the upper Colorado River basin. To address this, 12 previously sampled tree-ring sites in western Colorado were recollected in June 2003, and the 2002 ring was analyzed with respect to instrumental records for the 20th century. Analyses suggest that the 2002 tree ring, although consistently narrow, and completely missing in a number of samples, did not fully reflect the extreme low streamflows of 2002 since several other annual rings, in particular 1977, were generally narrower. The discrepancy between the tree rings and streamflow in 2002 was explored by examining seasonal snowpack. Snowpack measurements in the Upper Colorado River basin show April 1 snow water equivalent (SWE) values to be low in 2002, but lowest in 1977 (from 1942-2002), corresponding to the results from the 2002 tree-ring analysis. This result coincides with water managers' assessment of the spring runoff, which was much lower than expected given the April 1 snowpack in the upper Colorado River basin. During a very warm and dry April, much of the snowpack was apparently either absorbed by soils desiccated by two years of drought or sublimated into the atmosphere. While that portion of the snowpack which replenished soil moisture did not reach the stream channels, it may have benefitted tree-growth in 2002, contributing to a less extreme value for the 2002 ring width. We examine the snowpack and gage records for similar occurrences in previous years to determine how rare an event this was, evaluate the corresponding tree-growth response in these years, and discuss the implications for tree-ring reconstructions of drought.
DE: 1812 Drought
DE: 1833 Hydroclimatology
DE: 1860 Runoff and streamflow
DE: 3344 Paleoclimatology
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting