Gauging impacts of climate change on the Pacific Northwest using observed climate variations

As a basis for estimating the potential impacts of future climate change on natural resources in the Pacific Northwest, we have performed quantitative analyses of the impacts of past variations. In particular, the low-frequency variations of the Pacific Decadal Oscillation (PDO) provide a useful surrogate for gauging the impacts of possible future climate change. Subtle changes in temperature and precipitation associated with the PDO have had a dramatic impact in the past on the region's water resources, on salmon abundance, and on forest fires. In the PNW, the primary impacts pathway is via the region's water resources.

Scenarios for future climate suggest that changes in temperature and precipitation will raise snow lines and cause snow to melt earlier in the year. Thus, the annual cycle of the water supply and the annual flow amount are expected to change. Similar, albeit probably smaller, changes have been noted on decade-to-decade time scales as a result of PDO climate variations. Such changes in snowpack and summer water supply would cause drought stress in forests, possibly leading to extensive and permanent reductions in forested area, and spawning and rearing difficulties for salmon (in addition to the difficulties posed by rising water temperatures). Winter landslides and flooding could also become more frequent.

For humans, the consequences of climate change extend beyond the abovementioned direct effects on natural resources. Reductions in summer water supply would increase stress on managed watersheds due to unavoidable conflicts among water supply for irrigation and urban uses, instream flow, recreation, hydropower, and other uses that rely on storage of winter snowpack. The effects of increasing regional population are expected to exacerbate conflicts over declining water supplies.