Variability in California snowpack, and the contribution of extreme storm events

Authors: Gregory S. Bohr*, California Polytechnic State University, San Luis Obispo
Topics: Climatology and Meteorology
Keywords: Climate variability, precipitation, Western United States
Session Type: Paper
Day: 4/12/2018
Start / End Time: 3:20 PM / 5:00 PM
Room: Poydras, Sheraton, 3rd Floor
Presentation File: No File Uploaded

Winter precipitation accumulating as snowpack in the high elevations of the Sierra Nevada mountain range is a critical source of spring and summer water supply in California. Ongoing climate change in the western United States is likely to affect the amount (water equivalent) of this snowpack, as well as the timing of peak snowpack and the onset of the spring melt. Extreme precipitation events tend to contribute disproportionately to precipitation totals; changes in the magnitude and/or frequency of these events is therefore likely to have an outsized impact on snowpack levels in the future. In this project, daily snow water equivalent (SWE) observations from 119 automated snow pillows distributed throughout high elevation regions in and around California are used to quantify the contribution of extreme events to annual snowfall and examine trends in this contribution. Extreme (90th percentile) accumulation events average approximately 4” of SWE, typically last three days or fewer, and contribute an overall average of about 40% of total snowpack. This contribution is significantly higher in wet (top tercile) years, in which it reaches 50%, and falls to around 30% in dry (bottom tercile) years. Trends in the frequency of extreme accumulation events are generally negative, with significant trends in the southern portion of the Sierra. The total contribution of extreme events to seasonal snowpack likewise appears to be diminishing, albeit with less overall significance.

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