NOAA/WDS Paleoclimatology - Sierra Nevada, California 500 Year Snowpack Reconstruction

California is currently experiencing a record-setting drought that started in 2012 and recently culminated in the first ever mandatory state-wide water restriction. The snowpack conditions in the Sierra Nevada mountains present an ominous sign of the severity of this drought: the 1 April 2015 snow water equivalent (SWE) was at only 5% of its historical average. In the Mediterranean climate of California, with 80% of the precipitation occurring during winter months, Sierra Nevada snowpack plays a critical role in replenishing the state's water reservoirs and provides 30% of its water supply. As a result, a multi-year and severe snowpack decline can acutely impact human and natural systems, including urban and agricultural water supplies, hydroelectric power and wildfire risk.
The exceptional character of the 2012-2015 drought has been revealed in millennium-length palaeoclimate records, but no long-term historical context is available for the recent snowpack decline. Here, we present an annually resolved reconstruction of 1 April SWE conditions over the whole Sierra Nevada range for the past 500 years. We combined an extensive compilation of blue oak tree-ring series that reflects large-scale California winter precipitation anomalies with a tree-ring-based California February-March temperature record in a reconstruction that explains 63% of the Sierra Nevada SWE variance over the instrumental period.