Pacific northwest regional assessment: The impacts of climate variability and climate change on the water resources of the Columbia River Basin

The Pacific Northwest (PNW) regional assessment is an integrated examinatio n of the consequences of natural climate variability and projected future c limate change for the natural and human systems of the region. The assessme nt currently focuses on four sectors: hydrology/water resources, forests an d forestry, aquatic ecosystems, and coastal activities. The assessment begi ns by identifying and elucidating the natural patterns of climate variabili ty in the PNW on interannual to decadal timescales. The pathways through wh ich these climate variations are manifested and the resultant impacts on th e natural and human systems of the region are investigated. Knowledge of th ese pathways allows an analysis of the potential impacts of future climate change, as defined by IPCC climate change scenarios. In this paper, we exam ine the sensitivity, adaptability and vulnerability of hydrology and water resources to climate variability and change. We focus on the Columbia River Basin, which covers approximately 75 percent of the PNW and is the basis f or the dominant water resources system of the PNW. The water resources syst em of the Columbia River is sensitive to climate variability, especially wi th respect to drought. Management inertia and the lack of a centralized aut hority coordinating all uses of the resource impede adaptability to drought and optimization of water distribution. Climate change projections suggest exacerbated conditions of conflict between users as a result of low summer time streamflow conditions. An understanding of the patterns and consequenc es of regional climate variability is crucial to developing an adequate res ponse to future changes in climate.