Abstract
As directed by Congress in Section 9505 of the SECURE Water Act of 2009 (Public Law 111-11), the U.S. Department of Energy (DOE), in consultation with the federal Power Marketing Administrations (PMAs) and other federal agencies including federal dam owners, has prepared a comprehensive assessment examining the effects of climate change on water available for hydropower at federal facilities and on the marketing of power from these federal facilities. This ORNL/TM, referred to as the “9505 Assessment.” describes the technical basis for the Report to Congress that was called for in the SECURE Water Act. The 9505 Assessment included: 1) a historical analysis of the sensitivity of federal hydropower operations to climate variables, 2) a climate modeling analysis that projected climate conditions and impacts to hydropower into the future, and 3) a literature review of other related climate studies for comparison to the 9505 modeling results. The assessment used consistent methods across all PMA regions, to enable nationwide policy analysis.
Federal hydropower is an important part of the national renewable energy portfolio, because it accounts for approximately half of the U.S.’s installed conventional hydropower capacity. The 132 federal hydropower projects that were studied have produced an annual average of 120.6 billion kWh over the period from 1971 to 2008. For the first time, the 9505 Assessment quantified how this federal power responds to water availability, as measured by runoff aggregated over upstream watersheds. A series of climate simulation models were then used to make projections of regional climate conditions for 30 years into the future in 18 assessment areas and four regions across the country, one region for each of the PMAs. Assessment variables included annual and seasonal estimates of air temperature, precipitation, runoff, frequency of occurrence of water year types, and an index of drought severity. Results show how global climate changes will affect runoff and power generation, but the patterns of these changes are both spatially and temporally complex. Aggregated to a national level, the median change in federal hydropower is between 1 and 2 billion kWh/yr, with a model uncertainty range of +/- 9 billion kWh/yr. While those estimates are similar to the recently observed variability of generation from federal hydropower and may appear to be manageable, the extremes water years, both wet and dry, will pose significantly greater challenges to water managers.
The 9505 Assessment gives federal hydropower administrators the opportunity to plan their operational or contracting responses to these changes in order to minimize any negative impacts on future hydropower generation, water quality, and water availability for other uses. This effort will promote better understanding of the sensitivity of federal power plants to water availability, and will provide a basis for planning future actions that will enable adaptation to climate variability and change. Future assessments of climate impacts are anticipated under the Section 9505 – these can be improved by incorporating improved climate models and data that will become available soon, by closer examination of extreme events and longer-term change, and by addressing the interactions among hydropower and other water uses at a more project-specific level.