This week’s rains pushed precipitation above average — but average isn’t enough

Donner Summit

UC Berkeley’s snow lab at Donner Summit is awash in snow. (Photo: Todd Lappin via Flickr)

As you might expect, with all the rain that has hit Northern California this week, things are looking up for California’s water picture.

A week ago, the state was a little on the parched side, but the passing through of what climatologists call an atmospheric river has dramatically altered things

Up at the UC Berkeley Central Sierra Snow Laboratory at Donner Summit, Randall Osterhuber needed until Friday morning to get the lab’s instruments dug out from 8.2 feet of fresh snow.

Just like that, the state’s never-ending thirst was slaked. For a moment.

“We pretty well got buried,” Osterhuber says. “In any year, it’s the big events that define the year, and this was one of the big ones.”

More than that, it was what Lake Tahoe-area skiers call “Sierra cement.” The snow was heavy with water, which is great for those who see snow as a resource for water, less so for those who see snow as something to ski atop.

Osterhuber says the level at the snow lab has risen slightly above normal for the season. The season’s hallway point comes in about two weeks, on Feb. 1, and typically, two of the wettest months are February and March.

That being said, Osterhuber warns that just being average isn’t all that great.

“A statistically average snowfall year here is almost inadequate for the water needs of California now,” Osterhuber says. “The demand is there, and, short of flooding, the demand will always be there.”

For four consecutive winters beginning in 2012, the rains stayed away. Each year was drier than the previous. Things got back to normal in 2016, and the winter of 2017 was a rain and snow monster. Last winter, precipitation was above average, but snowfall was below average. Water in the snowpack is what feeds rivers and reservoirs well into summer.

“All those dry years really led to depletion of the groundwater in the state,” Osterhuber says. “Groundwater isn’t a resource we see every day. We can see reservoirs fill up and rivers rise, but groundwater is important in a state where agriculture and firefighting depend on huge amounts of water.

“To replenish the groundwater, we need a lot of precipitation. To do it, we need to get to the point where the big aquifers and reservoirs and rivers can get us to the point where we aren’t needing to pump.”

Osterhuber adds that the long-term water issues aren’t going away. A decade ago, the average snowline in the Sierra sat at about 4,500 feet. Today it’s at 5,500 feet.

“That makes for potentially much less stream flow,” he says. “Mountains are mostly triangular, and as the snow level goes up, the drop-off in the amount of snow being held is real dramatic.”