Key Facts

Global warming is bringing winter rains, early spring runoff, and drier summers to the Columbia River of the Pacific Northwest. Scientists expect those changes to worsen with growing global-warming emissions, further endangering already depleted salmon populations.

• Climate change imposes stresses on salmon throughout their lifecycle. Winter rains and earlier spring snowmelt are particularly treacherous to salmon reproduction.²
• Stream flow at The Dalles—a key junction on the Columbia River—is projected to peak as much as a month earlier by mid-century, under a business-as-usual emissions path.¹³
• Unless we act now to curb heat-trapping emissions, scientists expect rising temperatures to likely render about one-third of the Northwest's current habitat for salmon and other coldwater fish unsuitable by the end of the century.²

Details

As the climate of the Pacific Northwest warms, more winter precipitation is falling as rain, compared with historical averages.² With declining snowpack in Oregon's Cascade Mountains, peak stream flows are occurring earlier, and summer flows are declining.² These changes are expected to continue as heat-trapping emissions grow, putting more stress on already endangered salmon that return to the Columbia and other rivers in the region to spawn.²

Snowpack on April 1 has declined throughout the Northwest. In the Cascades, where cool-season temperatures have risen 2.5° F (about 1.4° C) over the past 40 to 70 years, snowpack has declined by an average of 25 percent—and up to 60 percent in some areas.^3,4,5

Warmer winters in the Cascades are causing the earlier spring runoff. Increases in winter and early-spring stream flow—followed by decreases in late spring, summer, and early fall—have already been observed over the past 50 years.⁶ Peak spring runoff is occurring anywhere from a few days to 25-30 days earlier throughout the region.⁷

Human activities such as dam building, logging, pollution, and overfishing have already depressed salmon populations in the Northwest to historically low levels.² Many salmon species are classified as threatened or endangered. Salmon populations in the Columbia River system are down more than 90 percent,² and most wild Pacific salmon are either extinct or imperiled in more than half the range they once occupied in the Northwest and California.⁸

Climate change imposes stresses on salmon throughout their lifecycle.² Winter rains and earlier spring snowmelt are particularly treacherous to salmon reproduction. Elevated stream flows in winter make spawning more difficult, damaging nests and washing away incubating eggs. Earlier peak runoff sweeps young salmon out of rivers into estuaries when they are smaller, and more vulnerable to predators.^2,9,10

What the Future Holds

As temperatures in the Northwest continue to rise this century, scientists expect snowpack to keep declining.² In the Cascades, scientists project a reduction of as much as 40 percent in the amount of snow on April 1 by the 2040s, under a business-as-usual emissions path.^11,12

Peak spring runoff is also projected to continue to occur earlier—20 to 40 days earlier by the end of the century.^7,12 Scientists project stream flow at The Dalles on the Columbia River to peak as much as a month earlier by mid-century.¹³ On the western slopes of the Cascades, runoff between April and September is projected to drop by 30 percent or more by mid-century.^2,14

The more water that flows out of the mountains earlier, the more likely that reservoir capacity may not meet competing demands for hydropower and stream flow to support salmon.¹¹ Lower water levels and warmer water temperatures in summer degrade stream habitat for salmon in the Northwest. Storing more water in reservoirs and refilling them earlier can help salmon at the expense of a small decline in hydropower capacity.¹¹

If global-warming emissions continue to grow at today's rates, scientists expect rising temperatures to render about one-third of the Northwest's habitat for salmon and other coldwater fish unsuitable by the end of the century.^2,12 Climate change poses another obstacle to the already monumental challenge of restoring depleted salmon stocks.²

Credits

Endnotes

1. Photograph: Native Americans dip-netting salmon on the Columbia River. U.S. Army Corps of Engineers/Wayne Buchanan. ↑
2. U.S. Global Change Research Program. 2009. Global climate change impacts in the United States. Edited by T.R. Karl, J.M. Melillo, and T.C. Peterson. Cambridge University Press. ↑
3. Mote, P.W. 2006. Climate-driven variability and trends in mountain snowpack in western North America. Journal of Climate 19(23):6209-6220. ↑
4. Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. 2005. Declining mountain snowpack in western North America. Bulletin of the American Meteorological Society 86(1):39-49. ↑
5. Christensen, J.H., B. Hewitson, A. Busuioc, A. Chen, X. Gao, I. Held, R. Jones, R.K. Kolli, W.-T. Kwon, R. Laprise, V. Magaña Rueda, L. Mearns, C.G. Menéndez, J. Räisänen, A. Rinke, A. Sarr, and P. Whetton. 2007. Regional climate projections. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller. Cambridge University Press, pp. 847-940. ↑
6. Peterson, T.C., D.M. Anderson, S.J. Cohen, M. Cortez-Vázquez, R.J. Murnane, C. Parmesan, D. Phillips, R.S. Pulwarty, and J.M.R. Stone. 2008. Why weather and climate extremes matter. In: Weather and climate extremes in a changing climate: Regions of focus—North America, Hawaii, Caribbean, and U.S. Pacific Islands. Edited by T.R. Karl, G.A. Meehl, C.D. Miller, S.J. Hassol, A.M. Waple, and W.L. Murray. Synthesis and Assessment Product 3.3. Washington, DC: U.S. Climate Change Science Program, pp. 11-34. ↑
7. Stewart, I.T., D.R. Cayan, and M.D. Dettinger. 2004. Changes in snowmelt runoff timing in western North America under a "business as usual" climate change scenario. Climatic Change 62(1-3):17-232. ↑
8. Francis, R.C., and N.J. Mantua. 2003. Climatic influences on salmon populations in the northeast Pacific. In: Assessing extinction risk for West Coast salmon. Edited by A.D. MacCall, A.D., and T.C. Wainwright. NOAA technical memo NMFS-NWFSC-56. Washington, DC: National Marine Fisheries Service, pp. 37-67. Online at http://www.nwfsc.noaa.gov/ assets/ 25/ 3946_06162004_130044_tm56.pdf. Accessed April 13, 2010. ↑
9. Janetos, A., L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. 2008. Biodiversity. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. Edited by P. Backlund, A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M.G. Ryan, S.R. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. Synthesis and assessment product 4.3. Washington, DC: U.S. Department of Agriculture, pp. 151-181. ↑
10. Crozier, L.G., A.P. Hendry, P.W. Lawson, T.P. Quinn, N.J. Mantua, J. Battin, R.G. Shaw, and R.B. Huey. 2008. Potential responses to climate change in organisms with complex life histories: Evolution and plasticity in Pacific salmon. Evolutionary Applications 1(2):252-270. ↑
11. Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier. 2004. Mitigating the effects of climate change on the water resources of the Columbia River basin. Climatic Change 62(1-3):233-256. ↑
12. The business-as-usual scenarios referred to in this hotspot reflect the runs of the National Center for Atmospheric Research Parallel Climate Model (DOE/NCAR PCM) known as B06.44, B06.46, and B06.47. The high-emissions scenario is the Intergovernmental Panel on Climate Change scenario known as A2. ↑
13. Climate Impacts Group. Climate impacts on Pacific Northwest water resources. Seattle, WA: University of Washington. Online at http://cses.washington.edu/ cig/ pnwc/ pnwwater.shtml#figure3. Accessed April 13, 2010. ↑
14. Hamlet, A.F., and D.P. Lettenmaier. 2007. Effects of 20th century warming and climate variability on flood risk in the western U.S. Water Resources Research 43, W06427, doi:10.1029/2006WR005099. ↑