Experts weigh in on risk of 'ark storm' amid heavy rainfall
WALNUT CREEK - Among the people who study weather and water in our state, a lot of focus is on what some might call "the big one" when it comes to rainfall: The so-called "ark storm."
"This is the one that's going to be here Wednesday," said Jeffrey Mount, Senior Fellow at the PPIC Water Policy Center, pointing at an image of the west coast. "See how it's spinning counterclockwise, pulling all that moisture in from Hawaii? That's the key, warm air holds more wat
Watching the storm traffic stretch out over the Pacific, Mount has one initial thought.
"We are seeing a normal wet winter," he laughed. "This is what a normal wet winter looks like."
But like many in this field, he is working to better understand what an abnormal wet winter might look like in California. The kind of winter that's almost hard to imagine, even though it has happened before.
"It was 1861 and 1862," he explained"That is the true storm of record that we have here in California, when we were keeping, at least, reasonable records. It's nothing like that right now. That storm started raining in the fall, and they were literally measuring the rain in feet, not inches."
But that doesn't come with one storm, it's a lot of storms landing with virtually no break between them. Something that could easily overwhelm the flood control we've built since 1862.
"What happens in a real 'Ark Storm' is that they stack up on top of each other and you never get a chance to drain," Mount Said. "So all your reservoirs fill and lose all their capacity to manage flood control. The rivers are all full so all the new water goes out of the rivers and on to the floodplain. Your landscape is fully saturated so every drop it falls runs off. That's what happens in an ark storm. We just don't get those gaps where things can drain out and dry out."
And even if it's not a statewide disaster, this is something that can happen on a regional level.
"And we've had that here," he added. "1997, here in the central valley. 1982, and '83 in the bay area. We had flooding all over the place in the Bay Area. Think San Jose. Coyote Creek. Guadalupe Creek, San Francisquito Creek Creek. All those creeks, they're not designed to handle a series of storms stacked on top of each other."
So in terms of drought, the sequence of storms we're getting is good news. It's timing that makes the difference between beneficial and problematic. And the ark storm, or something like it, is really just a matter of odds, and time.
"But that's California, Mount said. "This is something I think most Californians don't really appreciate. We are the land of extremes. Extremely wet and extremely dry. That's why there's rarely a Goldilocks moment in California where we have average, or what we people refer to as normal. Average is hardly normal."
