WEB Notes: They determined this by tree ring data. I do not doubt this, it is extremely dry in this region. It is predicted the West will have an El Nino event this year which would bring much needed rain. Hopefully it will add to the snow pack as well. Of course intense flooding is never good, but it beats the alternative of no water.
A new study, published in Nature Climate Change on September 14, 2015, shows the spring amount of snow on the Sierra mountains has sunk to its lowest levels in the last 500 years. The current circumstances of exceptional drought across the state of California thus represent a potential warning, as the mountain range is especially important for California’s annual water supplies.
An official survey conducted in the Sierra on April 1, 2015 showed the snow levels throughout the mountain range were as low as 5% of the annual average since the 1950s. The snowpack of the mountain range can provide up to 30% of California’s yearly water supplies. On the same day of the striking results the Governor of California issued an executive order mandating a 25% in potable urban water use statewide.
Source: Sierra Nevada seasonal snowpack lowest in the last 500 years