Value of Climate/Streamflow Forecasts for Non-Firm Energy Production in the Columbia River Basin

Recent advances in long-lead climate forecasts (e.g. ENSO forecasts) have made experimental streamflow forecasts for the Columbia River developed by the JISAO Climate Impacts Group and the Department of Civil Engineering at the University of Washington available roughly six months earlier than current operational forecasts that rely on snow pack measurements or simulations. The Columbia reservoir operating policies currently do not use streamflow forecast information in the period from August-December. Long-lead streamflow forecasts provide opportunities to make the reservoir operating system more directly responsive to interannual climate variability in this period.

To provide an input pathway for the streamflow forecasts, we propose an alternative rule curve called the "refill to least flood curve" for the major storage dams on the Columbia. This rule curve frees reservoir storage for energy production in fall and early winter in years that are likely to be wet, while increasing restrictions on the use of storage in dry years. Using retrospective streamflow forecasts from water year 1931 to 1987, and variable non-firm energy targets based on retrospective climate forecasts, this alternative operating system is simulated by the ColSim reservoir model to increase August-December spot market revenue by about $140 million per year on average without reducing the effectiveness of the reservoir operating system in meeting other operational objectives.