Alan F. Hamlet (hamleaf@u.washington.edu)

Dennis P. Lettenmaier

JISAO Climate Impacts Group

Department of Civil and Environmental Engineering

University of Washington

Abstract

Recent advances in long-lead climate forecasts have made experimental streamflow forecasts developed by the JISAO Climate Impacts Group (CIG) 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. These forecasts provide apparent opportunities to make the Columbia Basin reservoir operating system more directly responsive to interannual climate variability in the early fall and winter months. In the current operating system, the so called "critical" and "assured refill" rule curves that restrict releases for hydropower in the period from August to December are based on the critical and third lowest flow sequence respectively. These rule curves provide appropriate protection of energy capacity and reservoir refill in low flow conditions, but are unnecessarily restrictive in normal and high flow years. A new rule curve called the "refill to least flood" curve has been proposed by the authors for the major storage dams to make effective use of extended streamflow forecasts and provide more management flexibility in the fall and early winter while protecting against low flow conditions when appropriate.

Use of Long-Lead Streamflow Forecasts to Improve Columbia Basin Reservoir Management (MS Word Document)