Snowpack, Hydrology & Drought

Mountain snow, or snowpack, acts as a natural water reservoir. By slowly melting over the summer months, snowpack provides water during what is typically the Pacific Northwest’s warmest and driest time of year. As with much of the American West, rising temperatures in the Pacific Northwest are making it far more likely that precipitation will fall more as rain and less as snow. This trend is expected to continue as temperatures continue to rise under human-caused climate change. Climate change-induced alterations of the Pacific Northwest’s hydrology have already led to water scarcities in our region. Probably the best example of this happened in 2015 when abnormally warm winter temperatures and near- normal precipitation resulted in record low snowpack across Oregon and Washington. A good deal of CIRC research has revolved around tracking how the loss of snowpack has affected our region’s hydrology in the near term as well as how the loss of snowpack is likely to affect our region in the future.

Key Findings 

  • Watersheds in the Pacific Northwest that receive a mix of rain and snow and derive a substantial portion of streamflow from spring snowmelt are most sensitive to future warming expected during the winter months (Vano et al. 2015).

  • The Cascade Mountains in Oregon and Washington are expected
    to be particularly hard hit by declines in snowpack with a projected decrease of 65%—or 37.5 km3—in April 1 snow water equivalent (SWE) storage—by the 2080s under the high emissions scenario (RCP 8.5) (Gergel et al. 2017).

  • By the mid-21st century (2040–2069) under the high emissions scenario (RCP 8.5), every SNOTEL site in the West is likely to see less snowfall and that snowfall is more likely to come in extreme snowfall events (Lute et al. 2015). (SNOTEL sites are automated snow- observing stations.)

  • Sites that currently experience average winter temperatures that hover just above freezing are projected to see the largest decreases in the amount of snow that falls during extreme snowfall events, declining 20–50% from historical records. These include most of the SNOTEL sites in Oregon and Washington (Lute et al. 2015).

  • In the Cascade Mountains are some of the hardest hit SNOTEL sites, which are projected to experience a 35–70% reduction in snowfall from historical levels (Lute et al 2015).

  • Low snowfall years will become common in the Cascades by the mid- 21st century, whereas high snowfall years will become exceedingly rare (Lute et al. 2015).

  • The water year 2014–2015 was dubbed a “snow drought” because precipitation was near-normal while abnormally warm temperatures led to record low snowpack. Record low spring snowpack measurements were set at 80% of mountain recording sites (or SNOTEL sites) in the Western United States (Mote et al. 2016).

  • Spring snowpack in 2015 was the lowest on record for Oregon—89% below normal—and tied for lowest on record for Washington (Mote et al. 2016).

  • Anthropogenic forcing added about 1° C (1.8° F) of extra warming to the water year 2014–2015 exacerbating the “snow drought” (Mote et al. 2016).

Publications: 

  • Gergel, Diana R., Bart Nijssen, John T. Abatzoglou, Dennis P. Lettenmaier, and Matt R. Stumbaugh. “Effects of Climate Change on Snowpack and Fire Potential in the Western USA.”
    Climatic Change 141, no. 2 (2017): 287-299.
    https://doi.org/10.1007/s10584-017- 1899-y.

  • Lute, A. C., John T. Abatzoglou, and Katherine C. Hegewisch. “Projected changes in snowfall extremes and interannual variability of snowfall in the western United States.”
    Water Resources Research 51, no. 2 (2015): 960-972.
    https://doi. org/10.1002/2014WR016267.

  • Mote, Philip W., David E. Rupp, Sihan Li, Darrin J. Sharp, Friederike Otto, Peter F. Uhe, Mu Xiao, Dennis P. Lettenmaier, Heidi Cullen, and Myles R. Allen. “Perspectives on the Causes of Exceptionally Low 2015 Snowpack in the Western United States.”
    Geophysical Research Letters 43, no. 20 (2016).
    https://doi.org/10.1002/2016GL069965.

  • Vano, Julie A., Bart Nijssen, and Dennis P. Lettenmaier. “Seasonal Hydrologic Responses to Climate Change in the Pacific Northwest.”
    Water Resources Research 51, no. 4 (2015): 1959-1976.
    https://doi. org/10.1002/2014WR015909.