Drought, 38" H x 55" W
Embroidery on silk explains how snow water equivalent data and tree ring science were used to determine
California’s “500 year drought.”

In 2015, California was in the fourth year of a severe drought. At the annual April 1st mountain snow measurement, state officials found no snow in the Sierra Nevada for the first time in 75 years. Valerie Trouet and colleagues at the University of Arizona’s Tree-Ring Research Laboratory analyzed blue oak tree rings In California’s Central Valley and demonstrated that the amount of mountain snow was the lowest since the 1500’s. Snow water equivalent data is gathered annually on April 1st in the Sierras.

Snow Water Equivalent, or SWE, is a commonly used measurement used by hydrologists and water managers to gage the amount of liquid water contained within the snowpack. In other words, it is the amount of water that will be released from the snowpack when it melts. SWE is used to summarize snowpack conditions for spring and summer water supply forecasting. There are over 830 SNOTEL stations across the western United States to measure snowpack, precipitation and a number of other parameters for seasonal water supply forecasting. These sites transmit data hourly for use by hydrologists, water managers, recreationists, and the public. Link to Natural Resources Conservation Service (NRCS) website about measuring SWE.