As California drought retreats, threat of spring flooding rises
LOS ANGELES — Though California may be ending its winter with quenched reservoirs and near record snowpack, meteorologists are warning that the state will face increased flooding risk in the coming months as Sierra Nevada snowmelt fills rivers and streams.
On Thursday, the National Oceanic and Atmospheric Administration’s spring flood outlook reported that drought conditions will continue to improve in much of the state, but the potential for flooding will worsen in the face of heavy snowpack and elevated soil moisture.
“Approximately 44% of the U.S. is at risk for flooding this spring,” said Ed Clark, director of NOAA’s National Water Center. “California’s historic snowpack, coupled with spring rain, is heightening the potential for spring floods.”
The severity of that flooding remains to be seen, however, and depends on a variety of weather factors, experts say.
“It’s going to happen, and the question is whether it happens quickly versus slowly,” UCLA climate scientist Daniel Swain said. “Is it gradual snowmelt — in which case the flood concerns would be mostly minor — or is it more rapid … in which case we could be talking about something in the major flood territory.”
Potential triggers for rapid snowmelt could be an early season heat wave or another series of warm storms, Swain said, both of which could lead to “significant snowmelt flooding, particularly in the San Joaquin Valley and on some of the Sierra east-slope watersheds that drain in the Great Basin and into Nevada.”
The NOAA report forecast moderate flooding in the Central Valley and Sierra, and minor flooding in nearly all of Northern California and along the coast.
For a state that has endued three years of drought, only to be hammered by 11 atmospheric rivers since the start of the year, the prospect of clear sky flooding comes as a mixed blessing as some of that water is bound to soak into badly depleted aquifers.
But for communities that have suffered deaths and displacement as a result of being inundated, the forecast is alarming. Such communities include Pajaro, in Monterey County, which was flooded after a levee breached late Friday night.
The flooding displaced hundreds of people in the primarily migrant town, with no clear timeline for returning. It also raised significant concerns about crop yields in the heavily agricultural region this year.
A similar series of storms in January breached levees along the Cosumnes River near Sacramento, flooding low-lying fields and roadways and contributing to the deaths of at least three people.
State and federal officials who were contending with dwindling reservoirs just months ago are now making strategic releases from dams to make room for incoming flows.
Water managers are “making sure that the reservoir releases are coordinated as best as they can be — given the amount of snowpack — to minimize to the extent possible downstream impacts,” Jeremy Arrich, manager of the Division of Flood Management with the California Department of Water Resources, said during a briefing Wednesday.
“However, there’s a ton of snow above these watersheds, and we do expect a significant amount of flows coming through through the snowmelt season.”
Minor flooding is already occurring along the Sacramento, Salinas, Merced and San Joaquin rivers due to the recent storms, and “many rivers and streams along the Sierra Nevada foothills, especially in the San Joaquin Valley, will continue to run high through the next week from a combination of heavy rainfall and snowmelt,” the NOAA outlook said.
The latest round of storms saw a near-record crest on the San Joaquin River at Patterson, with water rising to less than a foot of its high-water mark from February 2017, according to the U.S.
Drought Monitor.
The Pajaro River at Chittenden reached its highest crest since February 1998, while the nearby Salinas River at Spreckels rose 3.89 feet above flood stage, second only to the record set in 1995. The Nacimiento River edged out its 1969 high-water mark by 1.51 feet.