Oct 31, 2016

Perspectives on the causes of exceptionally low 2015 snowpack in the western United States

Mote, Philip W., Rupp, David E., Li, Sihan, Sharp, Darrin J., Otto, Friederike, Uhe, Peter F., Xiao, Mu, Lettenmaier, Dennis P., Cullen, Heidi, Allen, Myles R.
Geophysical Research Letters

The story in 2015 was really the exceptional warmth. Historically, droughts in the West have mostly been associated with dry winters, and only secondarily with warmth. But 2015 was different, especially in California, but in Oregon and Washington as well — the primary driver of the record low snowpacks was the warm winter.

Dennis Lettenmaier, UCLA geography professor, one of the authors of the study

  • Augments previous papers about the exceptional 2011–2015 California drought
  • Offers new perspectives on the “snow drought” that extended into Oregon in 2014 and Washington in 2015
  • Finds over 80% of measurement sites west of 115°W experienced record low snowpack in 2015
  • Estimates a return period of 400–1000 years for California's snowpack under the questionable assumption of stationarity
  • Hydrologic modeling supports the conclusion that 2015 was the most severe on record by a wide margin. Using a crowd-sourced superensemble of regional climate model simulations, we
  • Shows that both human influence and sea surface temperature (SST) anomalies contributed strongly to the risk of snow drought in Oregon and Washington: the contribution of SST anomalies was about twice that of human influence
  • Finds, by contrast, that SSTs and humans appear to have played a smaller role in creating California's snow drought
  • Finds that in all three states, the anthropogenic effect on temperature exacerbated the snow drought