California's been in the grips of a record-setting drought since 2012. But don't just blame a lack of precipitation. "It's nothing exceptional in the context of the last 1,000 years. However—higher temperatures, this is the feature of this drought." 

Soumaya Belmecheri, a paleoclimatologist at the University of Arizona. She and her colleagues used two different sets of historic tree ring records to reconstruct 500 years of climate history: blue oak tree rings as a proxy for winter precipitation, and another set of rings from a variety of trees, as a proxy for winter temperatures. The tree ring data made it possible to model Sierra Nevada snowpack going back to the year 1500. And the researchers found that today's snowpack is just five percent of its average level over the last five centuries. The finding is in the journal Nature Climate Change. [Soumaya Belmecheri et al, Multicentury evaluation of Sierra Nevada snowpack]

Belmecheri says that the decline in snowpack is a big deal in a place like California, with its Mediterranean-like climate. "You can think about it like a water bank that can be used later in the spring and the summer when it melts." But since temperatures don't look to be on a downturn, she says we should not necessarily focus on filling that snow "bank" anymore—perhaps we should just change banks. 

"Maybe snowpack in the Sierra Nevada will no longer be a reliable source of water. So maybe a system that is more resilient to this type of drought should be thought of and designed and put in place, including maybe changing where the water is captured. If it's going to rain more than snow in the future, maybe we should capture that rain." And tomorrow's rains, she says, may not fall where today's reservoirs are. Something for policymakers in California to think about, if they want to keep their state above water. 

—Christopher Intagliata

[The above text is a transcript of this podcast.]

Scientific American is part of the Nature Publishing Group.