The Impacts of Climate Variability and Climate Change on the Water Resources of the Columbia River Basin

The University of Washington's Climate Impacts Group (CIG) has developed methods for assessing the consequences of climate variability and change on the natural and human systems that control the cycling of water at and near the land surface within the Columbia River Basin. Our efforts are oriented both towards the natural storage of water within the system (primarily as snow and soil moisture) and in the extensive man-made reservoir system that controls movement of water in the river system. We have developed a predictive capability that links nested atmospheric models with a macroscale hydrologic model of the Columbia River system, and in turn with a water management model. This model chain allows us to assess the implications to future streamflows of a) land management alternatives; b) natural variability in the climate system at seasonal to interannual lead times, and c) long-term anthropogenic climate change. At the seasonal to interannual time scale, the most important climate drivers affecting Columbia River runoff are ENSO, and the Pacific Decadal Oscillation. We describe an experimental ensemble forecast system that utilizes ENSO and PDO information to improve operation of the reservoir system, primarily through adaptive allocation of flood storage in the fall and winter based on long-range climate forecast information. At the time scale of anthropogenic climate change, regional climate change projections based on Intergovernmental Panel on Climate Change (IPCC) scenarios routed through CIG macroscale hydrology and water management models suggest the nature of water management conflicts that might occur as a result of reduced reliability of hydropower production, reduced summer water supply for irrigation and urban needs, inability to meet instream flow targets in the spring and summer, and lengthening of the seasonal (summertime) low streamflow period.