Quantifying Snowpack Metric Trends in the Sierra Nevada, California

Abstract:

The California Sierra Nevada snowpack stores a vast amount of water each winter - far more than any set of built reservoirs. However, trends in this mountain range scale critical water supply are not well quantified. This study uses a 90-m gridded daily Sierra Nevada snow water equivalent reanalysis (SNSR) over a 32-year period (1985-2016) to quantify and characterize snowpack trends. We used an innovative combination of the pixel-level remote sensing metrics, snow cover frequency (SCF), and snow disappearance date (SDD), with spatially aggregated volumetric SWE estimates from the SNSR to investigate snow cover trends related to elevation zones at both basin-wide and mountain range scales. This combination of metrics provides a more robust view of the variability of snowpack properties. Preliminary results show there is no significant trend for magnitude of maximum SWE at the mountain range scale. Similarly, there is no significant trend for the date of maximum SWE at the mountain range scale. Continued work will focus on basin-scale snowpack elevation gradient analysis. We hypothesize that there will a relationship between decreasing elevation and negative trends in the magnitude and timing volumetric SWE, average SCF, and average SDD. Further investigation will also work towards understanding the hydroclimatic factors driving these changes. Identifying any significant trends in the temporal and spatial distribution of SWE at will provide useful hydrologic information to water managers across the Sierra Nevada.