Managing Water Resources in the West Under Conditions of Climate Uncertainty A Proceedings (1991) / Chapter Skim
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9. The Implications of Climate Change for Streamflow and Water Supply . . .
9. The Implications of Climate Change for Streamflow and Water Supply . . .
Pages 158-176
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From page 158... ...
Despite recent advances in modeling the atmosphere, large uncertainties remain about the details of regional hydrologic changes. Until current climate models improve both their spatial resolutions and their hydrologic parameterizations, information on the hydrologic effects of global climatic changes can best be obtained using regional hydrologic models.
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From page 159... ...
In addition, an aggregated model has been developed that divides the entire upper Colorado basin into two elevation zones and uses a limited number of meteorological stations to predict inflow into Lake Powell. In addition to this twoelevation model, we selected three subbasins that were known to make a substantial contribution to basin flow: the White River at Meeker, the East River at Almont, and the Animas River at Durango.
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From page 160... ...
The output from the model is actual streamflow, reservoir levels, hydropower production, reservoir spills, salinity, and water deliveries. The model incorporates a large set of supply constraints and decision rules that determine reservoir operation, including the allocation of shortages and surpluses among various water users.
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From page 161... ...
RESULTS Hydrologic (NWSRFS) Model Large changes in the magnitude of annual flow in the Colorado basin may result from plausible climatic changes (Tables 9.2 through 9.5~.
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From page 163... ...
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From page 164... ...
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From page 165... ...
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From page 166... ...
Overall, runoff in the White River is slightly less affected by temperature increases than is runoff in the Animas and East rivers. Annual average flows are normally distributed on the East River and approximately lognormally distributed on the White and Animas rivers.
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From page 167... ...
Accordingly, a 10 percent decrease in natural flow produces a 30 percent decrease in upper basin storage and only a 12 percent decrease in flow at the compact point. A similar effect can be seen for actual flow below Imperial Dam, where a 10 percent increase in natural flow produces an 11 percent increase in actual flow, whereas a 10 percent increase in natural flow results in only a 7 percent decrease.
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From page 168... ...
.......................... -10% -5% 0 5% 10% Change in Natural Flow ° Green River, WY ~+- Compact Point Imperial Dam FIGURE 9.3 Effect of changes in natural flow on changes in actual flow at three stations.
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From page 169... ...
A 5 percent decrease in natural flow corresponds to a 4 to 8 percent decrease in actual flow but results in a 15 percent decrease in hydropower production. A 10 percent increase in natural flow creates a 10 to 15 percent increase in actual flow and a 20 percent increase in annual average hydropower production.
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From page 170... ...
......... / ' ' 'Lit it ¢+ ~n Or NINE -20% -10% -596 0 5% 10% 20% Change in Natural Flow -- E}- Upper Basin +- Lower Basin - H< Mexico FIGURE 9.5 Effect of changes in natural flow on average annual consumptive water use.
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From page 171... ...
_ Our results suggest that at least a 20 percent increase in natural flow would be needed to bring the salinity levels in the lower basin into compliance with existing standards (Figure 9.6~. Although the scenarios presented here result in only moderate changes in salinity, the problem is already so severe in the base case that even moderate declines in water quality are of particular con cern.
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From page 172... ...
range of scenarios presented here, mean annual runoff changes nearly linearly with precipitation, although this relationship begins to break down as precipitation increases by 20 percent, at which point runoff begins to increase more quickly. Our analysis suggests that variations in mean annual runoff of 30 percent are possible as a result of climatic change, with even greater changes likely in the most arid subbasins, but that precipitation changes of more than 10 percent would be necessary before changes in annual runoff would be significantly different from the historic flow series (Nash and Gleick, 1991~.
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From page 173... ...
This, in turn, would cause reductions in storage of 60 to 70 percent, reductions in power generation of 60 percent, and an increase in salinity of 15 to 20 percent. A temperature increase of 2°C accompanied by an increase in precipitation of 20 percent corresponds roughly to a 20 percent increase in runoff, a 30 to 60 percent increase in storage, a 40 percent increase in power production, and a 13 to 15 percent decrease in salinity.
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From page 174... ...
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From page 175... ...
1973. National Weather Service River Forecast System: Snow Accumulation and Ablation Model.
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From page 176... ...
1983. Effects of a carbon dioxide-induced climatic change on water supplies in the western United States.
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