Is the Sierra Nevada going to lose its snow? Investigate how 21 st Century scenarios of climate change impact spring snowpack in California Dan Cayan(1,2), Tapash Das(3,1), David Pierce,(1) Mike Dettinger(2,1), Mary Tyree(1) 1. Scripps Institution of Oceanography, UC San Diego 2. US Geological Survey 3. CH2MHill Sponsors: California Energy Commission NOAA RISA program USGS DOE California Department of Water Resources AGU December 2011

Now consider 32 simulations 16 AR4 GCM’s 16 A2 and 16B1 BCSD downscaled to 12 km Map depicts elevation >800m Sierra Nevada+ high terrain Hydrology translated using VIC (Variable Infiltration Capacity) driven by downscaled precipitation and temperature

VIC snow accumulation agrees closely with observed snow course observations variability of Apr 1 Snow Water Equivalent (SWE), VIC modeled vs. observations avg of 35 snow courses GUIDO, JOHN—note that the aggregated observed Apr 1 SWE from this selection of 35 snow course locations does not have much trend (either from the direct snow course aggregate or from the VIC model version of the same aggregate. This may be close to what John Christy is showing. But the story doesn’t end here—See the pdf from Phil Mote, which explains the bigger picture, including California and how these can be taken apart According to precipitation-driven and temperature driven trends..

Source: Mote et al. (2004) Downward Trends in April 1 Snow Water Equivalent

Projected warming Sierra Nevada+ is substantial, though range is broad ( +1.5 to +4.5°C ) 16 GCMs, 16 A2 and 16 B1 emissions scenarios annual temp change A2(red) and B1 (brown)

precipitation change projected for Sierra Nevada+ --incremental and lacks consensus 16 GCMs, A2 and B1 emissions scenarios

Apr 1 snow water vs precipitation and Temperature dot size ~1/SWE

but change in snow water projected for Sierra Nevada+ is substantial 16 GCMs, A2 and B1 emissions scenarios declining Apr 1 SWE: 2050 median SWE ~ 2/3 historical median 2100 median SWE ~ 1/3 historical median

Summary California’s snow pack varies considerably between years. Over 21 st Century for whole Sierra, spring snow water ranges by factor of 10 (highest to lowest). In today’s climate snow variation caused by precipitation is more important than that from temperature, In the future, the temperature influence in diminishing spring snowpack becomes as large or larger than that from variations of precipitation. Warming-driven snow loss begins in early winter and prevails throughout the winter and spring. Under an ensemble of A2 and B1 AR4 scenarios, there is marked reduction in spring snow pack that continues through the 21 st Century: by 2050 median of projected Apr 1 SWE has diminished to 2/3 historical median. by 2100 median of projected Apr 1 SWE has diminished to 1/3 historical median. by 2100 chance of achieving historical median SWE falls to about 10%. by 2100 chance of SWE at or below 10 percentile historical rises to about 40%.