Some weather experts are predicting heavy rainfall this year in California, thanks to an El Niño that many hope will put an end to the historic drought.
“This is the Godzilla EL Niño if it matures and comes to fruition,” Bill Patzert, a climatologist with NASA’s Jet Propulsion Lab, told NBC News last week.
A recent statement released by California’s state climatologist Michael Anderson sings a different tune.
“California cannot count on potential El Niño conditions to halt or reverse drought conditions,” he wrote. “Historical weather data shows us that at best, there is a 50/50 chance of having a wetter winter.”
So just how likely is it that this year’s El Niño will put an end to the drought?
Not very likely, experts told NBC Bay Area.
To start, storm prediction is tricky business. Weather forecasting models typically run about two weeks out, but winter -- and the impact of El Niño -- is still several months away.
As a result, it’s difficult to make an accurate prediction, said Jeanine Jones, Interstate Resources Manager at the California Department of Water Resources.
A look at data from past El Niño winters won’t help much either, says Jay Lund of the University of California, Davis’ Center for Watershed Sciences.
He says that data for Northern California shows very little correlation between El Niño and heavy rainfall.
“You’ll see that there are some very low and very high El Niño events that have a lot of precipitation and very little precipitation,” he added, referencing the graph below, which measures El Niño strength and corresponding streamflow.
There’s no evidence of a pattern there, Lund says.
In other words, El Niño could mean a lot of rain, or no rain at all in Northern California.
Southern California sees a greater correlation between the weather pattern and rainfall thanks to geographic proximity to El Niño.
“The strongest correlation geographically is up at the Pacific Northwest, and down into Southern California and into the Mexico coast,” said Jeanine Jones. “Where we are in Northern California is in sort of a gray zone that can go either way.”
That gray zone is exacerbated by a ridge of high pressure, called the Ridiculously Resilient Ridge, which buffers the Bay Area from stormy weather.
“If we have a strong high pressure ridge off the coast, we don’t get storms,” Jones said.
But even if the ridge doesn’t block El Niño, and fierce rainfall does arrive this winter, it still isn’t likely to end California’s drought.
“For some of the reservoirs, a half decent flood will fill them up pretty well,” said UC Davis’ Jay Lund. “Some of the larger reservoirs, it’ll take more than that.”
It could take decades or even a century to fill up some of those aquifers, Lund added.
While heavy rains would certainly help quench California’s thirst, the claim that a wet winter is a 50/50 proposition is true.