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<br />FEATURE ARTICLE FROM INTERMOUNTAIN WEST CLIMATE SUMMARY, JUNE 2006
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<br />1500 1550 1600 1650 1700 1750 1800 1850 1900 195.0 2000
<br />Ending Year Qf 5-yr Runnin~ Mean
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<br />50
<br />15Q0
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<br />1550
<br />
<br />1000
<br />
<br />1650 1700 1'750 1 aoo 1 aso
<br />Encllng Year (It 5-yr RunnrnQ Mean
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<br />1900
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<br />195(1
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<br />
<br />50
<br />1500 1550 1600 1650 1700 1'750 1800 1850 1900 1950 2000
<br />Ending Year (If 5-yr Running Mean
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<br />Figure 1 d. Current drought in long-term context from Lees- A recon-
<br />struction five-year running means of natural flow at Lees Ferry, AZ.
<br />Observed flow and reconstructed flow with 0.10 non-exceedance prob-
<br />ability. Flow plotted as percentage of 1906-95 mean of observed mean
<br />annual flow, 15.232 MAF.
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<br />droughts in the Upper Colorado River basin have a tendency
<br />to be widespread, affecting the Green, San Juan, and Colorado
<br />mainstem basins. The most severe multi-year and multidecadal
<br />droughts at Lees Ferry are al\:vays reflected in the sub-ba-
<br />sins, although there are some differences in the magnitude of
<br />droughts among the sub-basins. Most periods of low flow in
<br />one sub-basin coincide with low flo\:vs in the other sub-basins.
<br />Very occasionally, periods of low flo\:v (IO-year averages) in
<br />the Green River have coincided with higher flows in the San
<br />Juan basin that resulted in low flo\:vs at Lees Ferry flows (e.g.
<br />the 1930s). This suggests that drought in the Green River can
<br />have a dominant influence on Lees Ferry flows, even when high
<br />flows prevail on the San Juan.
<br />The widespread nature of many single and multi-year
<br />droughts across the reconstructions suggests a common source
<br />of regionallo\:v-frequency hydroclimatic variability. Statistical
<br />associations have been demonstrated between North American
<br />drought and North Atlantic, North Pacific, and Indian Ocean
<br />variability (see WGM, 2006 for references), but more research
<br />is needed to understand ho\:v sea surface temperature variability
<br />is related to Upper Colorado River flows. The relationships
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<br />between atmospheric and oceanic circulation and hydroclimatic
<br />variability in the Upper Colorado River basin likely involve
<br />complex processes.
<br />
<br />2000
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<br />Implications for Management
<br />Reconstructions of streamflo\:v for the Upper Colorado River
<br />basin confirm that severe, sustained droughts have been a major
<br />feature of the Upper Colorado River basin over the past five cen-
<br />turies. These reconstructions also indicate that streamflow varies
<br />over decadal and longer timescales, suggesting that short-term
<br />records are inadequate for long-term planning. These results
<br />suggest eventual conflicts between water demand and supply
<br />in the upper Colorado River basin as demands on the Colorado
<br />River now exceed average water availability. Predicted climatic
<br />changes, in particular, a shift in the ratio of sno\:vfall to rainfall
<br />and earlier snowmelt and runoff (Cayan et al. 2001, Stewart et
<br />al. 2004), \:villlikely increase the stress on Colorado River water
<br />resources. Reconstructions of past streamflo\:v can aid in plan-
<br />ning by providing insights into the range of long-term natural
<br />variability and extreme hydrologic events that are not observed
<br />in gage records. In concert \:vith information on projected climate
<br />changes, reconstructions of long-term variability should guide
<br />planning for drought management and economic development in
<br />the basin in the future.
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<br />References Cited:
<br />
<br />Cayan, D. R., S. A. Kammerdiener, M. D. Dettinger, J. M. Caprio,
<br />and D. H Peterson (2001), Changes in the onset of spring in the
<br />western United States, Bull. Am. Meteorol. Soc., 82, 399-415.
<br />
<br />Hidalgo, H. G., T. C. Piechota, and J. A. Dracup (2000), Alternative
<br />principal components regression procedures for dendrohydrologic
<br />reconstructions, Water Resour. Res., 36, 3241-3249.
<br />
<br />Stewart, I. T., D. R. Cayan, and M. D. Dettinger (2004), Changes in
<br />snowmelt runoff timing in western North America under a "business
<br />as usual" climate change scenario, Clim. Change, 62, 217-232.
<br />
<br />Stockton, C. W., and G. C. Jacoby (1976), Long-term surface-water
<br />supply and streamflow trends in the Upper Colorado River Basin,
<br />Lake Powell Res. Proj. Bull. 18, Natl. Sci. Found., Arlington, Va.
<br />
<br />Woodhouse, C. A., S. T. Gray, and D. M. Meko (2006), Updated
<br />streamflow reconstructions for the Upper Colorado River Basin,
<br />Water Resour. Res., 42, W05415, doi: 10,l029/2005WR004455.
<br />
<br />On the Web
<br />- For Lees Ferry reconstructions extending to 1490 visit: www.ncdc.noaa.gov/paleo/pubs/woodhouse2006/woodhouse2006.html.
<br />- Tree-ring reconstructions of streamflow for Colorado: http://lwf.ncdc.noaa.gov/paleo/streamflow/
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<br />FEATURE ARTICLE I 4
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