Impact of climate change on Pacific
The Pacific Northwest (PNW) hydropower resource, central to the region's electricity supply, is vulnerable to the impacts of climate change. The Northwest Power andConservation Council (NWPCC), an interstate compact agency, has conducted long termplanning for the PNW electricity supply for its 2005 Power Plan. In formulating its power portfolio recommendation, the NWPCC explored uncertainty in variables that affect theavailability and cost of electricity over the next 20 years. The NWPCC conducted an initialassessment of potential impacts of climate change on the hydropower system, but these results are not incorporated in the riskmodel upon which the 2005 Plan recommendations are based. To assist in bringing climate information into the planning process, we present an assessment of uncertainty in future PNW hydropower generation potential based on a comprehensive set ofclimate models and greenhouse gas emissions pathways. We find that the prognosis for PNW hydropower supply under climate change is worse than anticipated by the NWPCC's assessment. Differences between the predictions of individual climate models are found to contribute more to overall uncertainty than do divergent emissions pathways. Uncertainty in predictions of precipitation change appears to bemore important with respect to impact on PNW hydropower than uncertainty in predictions of temperature change. We also find that a simple regression model captures nearly all of the response of a sequence of complex numerical models to large scale changes in climate. This result offers the possibility of streamlining both top-down impact assessment and bottom-up adaptation planning for PNW water and energy resources.