It's Been At Least 500 Years Since California Had This Little Snowpack

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When California Governor Jerry Brown announced the state's first mandatory water restrictions in April, he did so from a brown patch of grass that is typically a snowy spot in the Sierra Nevada mountains in spring.

But for the first time since 1942, when scientists began measuring the state's snowpack, there was no snow to be found. In fact, throughout the whole range — running about 400 miles down the state's eastern side  — the snowpack was only five percent of its historical average, the lowest ever recorded by a full 20 percent.

Now, according to a new study published in the journal Nature Climate Change on Monday, we know how long it has been since the snowpack in the Sierra Nevada was that low — at least 500 years.

"It's an ominous sign of the severity of the California drought," said Valerie Trouet, an assistant professor at the University of Arizona and one of the study's authors. "When snowpack measurements for 2015 were announced, we realized we were in a position to use tree rings to put that number in a much longer context. But we did not expect to see a result like that."

Paleoclimatologists use tree ring records to examine Sierra Nevada snowpack: — NOAA NCEI Climate (@NOAANCEIclimate)September 14, 2015

California is closing in on its fifth year of a historic drought, the likes of which haven't been seen for at least 1200 years by one account, and experienced its hottest year on record in 2014 — more than 4 degrees Fahrenheit warmer than last century's average. Snowpack is essential to the state's residents and its economy, providing a third of the yearly water used by California's cities and farms and drinking water for about 23 million Californians.

Roughly two thirds of the state's total water originates as rain or snow in the Sierra Nevada, and the snowpack is critical to replenishing reservoirs naturally throughout the year. The state's Mediterranean climate — warm and wet in the winter, hot and dry in the summer — means it's especially important for the mountains to capture as much snow as possible during the few winter months.

"Snow is a natural storage system — in the winter it freezes, then it becomes available as temperatures rise in the spring and the water melts," Trouet said. "That way you have access to water during the hot summer season when there's hardly any precipitation."

Climate change, the study's authors note, will increase the likelihood of severe droughts, make snow melt sooner in the spring, and cause more of California's precipitation to fall as rain, not snow — which the state's water infrastructure is designed to best capture.

"A lot of the water resource management system in California is built on the assumption that there's going to be snow in the winter in the Sierra Nevadas. That might no longer be the case in the future," Trouet said. "That doesn't mean there won't be any water. There are ways to capture that rain and store it, but that kind of infrastructure needs to be developed."

Less snowpack in the winter has consequences later in the year, too. Combined with drought, it means the California soil dries earlier in the year, making the parched landscape perfect fuel for wildfires.

Related: As Scientists Debate the Causes, California's Drought Continues to Punish Farmers

Wildfire season in the United States is two and a half months longer than it was just a few decades ago. With more than 8 million acres burned this year, a swath larger than the state of Maryland, and 2015 is on pace to be the worst wildfire season on record. The only other six years when more than 8 million acres have burned have all come since the year 2004.

Over the weekend, the Valley Fire roared through 50,000 acres north of San Francisco in just 24 hours, killing at least one person. The fire wasn't moving with the winds; rather, it was creating its own weather, said Cal Fire's Chief of Operations Todd Derum, according to a tweet by the Lake County Office of Emergency Services. Derum called the fire's behavior "unprecedented."

According to a 2006 study, the increase in wildfires across the western United States was due to several factors, including hotter temperatures, less precipitation, and reduced snowpack that melted earlier in the year."

"Seeing these huge wildfires that are really hard to control, that are threatening the giant sequoias, demonstrates, once again, the link between snowpack and subsequent wildfires," Trouet said.

Watch the VICE News documentary Flooding Fields in California's Drought here:

Follow Darren Ankrom on Twitter: @darrenankrom