Impacts of Potential Climate Change on Colorado-Big Thompson System Operations

by C. Moen, US Bureau of Reclamation, Denver, United States,
M. Brewer, US Bureau of Reclamation, Denver, United States,
V. Leverson, US Bureau of Reclamation, Denver, United States,

Document Type: Proceeding Paper

Part of: Management of Irrigation and Drainage Systems: Integrated Perspectives


The objective of this study is to examine the response of the Colorado-Big Thompson (CBT) system to specific local changes in climate, using the model CBTAOP to project the operating plan with hydrologic sequences associated with the 30 year historical record. The CBTAOP model is used as a forecasting tool whereby various alternative operating plans can be examined to ensure that priorities can be maintained. Stochastically generated four year low flows were used as the natural inflows, based on nine hypothetical cases, each at five different levels of nonexceedance probability. Each of the probability levels relates to an entire 30-40 year synthetic hydrologic record and the four year low flow period is selected from each of those levels, therefore the actual probability of the inflows used in the model is in the range of 3-5%. The nine cases are defined by combinations of 0°, 2° and 4° C temperature increases and 0 and ±10% precipitation change. These changes allow the program to interpret variations in the operation of the system which could be specifically attributed to the defined climate change cases. Interpretation of the results places emphasis on risk analysis and worst case scenarios for drought in terms of impacts on Lake Granby synthetic inflows and end of month storage volumes, Adams Tunnel transfers and power generation. The results indicate that it might be possible to define firm energy as approximately 40% of average. The model meets 100% of the stated average or most probable supply condition deliveries except for specific cases with -10% precipitation which exhibit failure to meet average deliveries at all probability levels. The results reveal a possible need to cut back to 50 or 60% irrigation demand in August/September of year four, also of year three if Lake Granby is down to minimum storage through February and March of the previous year. The global climate change (GCC) effects on system operations appear to intensify the duration and magnitude of the drought sequence as temperature increases and precipitation decreases.

Subject Headings: Inflow | Climate change | Low flow | Risk management | Hydrologic models | Climates | Temperature effects | Droughts | Colorado River

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