Historic California snowpack heightens risk of springtime flooding, officials say

It’s been a wet winter in California, one that’s brought record-breaking precipitation to many parts of the state. Now, state officials say it’s time to prepare for springtime runoff to come from now-historic levels of snowpack. 

Snowmelt season in California typically begins in April and ends sometime in July, but it’s hard to say exactly how quickly snowmelt will occur. Water from the snowpack could melt and trickle down slowly throughout the season, as state officials hope, but warm rainfall could make it melt more quickly than expected. 

“How this year plays out will depend on the weather and how quickly we warm up,” said Michael Anderson, the state climatologist. 

Jenny Fromm, chief of the water management section of the U.S. Army Corps of Engineers, said officials will be looking at a variety of factors when determining how best to manage runoff throughout the season. 

“We're constantly talking about what's the weather forecast, what's the precipitation forecast, what's the inflow to the reservoir forecast,” said Fromm. “That all informs what our operation is.”

During periods of heavy precipitation or runoff, reservoir operators will release water in controlled amounts to reduce potential flooding. Fromm said runoff coming from the historic levels of snowpack brought on by this past winter will likely require careful management in some flood-prone areas. 

“We anticipate larger releases near or at channel capacity throughout the spring, and in some locations this summer, in order to create the space in the reservoir for the projects in the San Joaquin and Tulare watersheds,” she said. 

California officials identified some areas, like the San Joaquin Region and Tulare Lake Basin, as particularly vulnerable to springtime flooding. Nicholas Pinter, a UC Davis professor in the Department of Earth and Planetary Sciences, said that’s because communities in those areas are living in what was naturally once a seasonal lake, making it more prone to flooding. 

“That lake is doing this year what it has done in the past after wet winters, and that is refill with water,” he said. 

Pinter said Tulare Lake is an extreme example of a more widespread issue in California, where communities are built in flood-prone areas. 

“We often say in the planning world, every flooding disaster is a past planning mistake,” he said. “And that [phrase] is just about siting houses, infrastructure and whole communities in places at risk of flooding.” 

Pinter said there’s two major components at play when it comes to planning communities in California: The first is climate change, which is worsening extreme weather, and the second is the fact that California weather is already extreme and highly variable year to year. 

“It's like California is trying to build its housing and communities as sandcastles on the beach,” he said. “We want to push those sand castles as close to the limit, as close to the waterline as possible, ignoring that there are waves that come up and down, and those are wet years in our dry years.” 

He said this past winter is a good example of this cycle. Although the winter has been among the wettest in California history, he said it’s not unprecedented. However, he said the state needs to prepare for more extreme weather in its future. 

State officials said people living in flood-prone areas should have an idea of potential evacuation routes and also sign up for emergency alerts in coming months in case of local flooding.