“The big melt is now here”: California braces for floods

The state’s high peaks stored historic amounts of snowfall this winter. Now, the state’s aging water management systems could be at risk.

A home surrounded by floodwaters of the reemerging Tulare Lake in on April 14, 2023 in Corcoran in California's Central Valley.

California’s water woes could soon get worse.

After weeks of nervous anticipation in California’s Central Valley, a massive pulse of snowmelt is expected to flow out of the Sierra Nevada this week, challenging levees and raising the risk of another round of damaging flooding. 

California’s high peaks stored historic amounts of snowfall this winter in the southern Sierra as more than a dozen atmospheric river storms battered the state with rainfall and caused billions of dollars in damage from landslides, avalanches and river flooding. Now, the water stored as mountain snow will begin to flow into saturated valleys and already swollen rivers. 

“The big melt is now here,” Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research, said during a recent briefing. “This week is going to be an exclamation point on the warming process.”

Parts of California saw more than 500 inches of snow during a historic wet winter season.

That snowfall means that there is a lot of frozen water currently in the mountains — more than 30 inches in some sections — that will melt when the weather warms.

When that snow melts, it will travel down rivers and lakes into the central valley.

Several important California cities are in the valley, including Fresno and Sacramento.

The increased water is already causing flooding in parts of the valley.

What could be an extreme melt-out will soon meet a familiar vulnerability in California: The state’s labyrinthine, patchwork and aging water management systems will be at risk if flows become extreme. 

And in some areas, like the already-flooded Tulare Lake bed where several rivers dead-end, there’s simply too much runoff to prevent it from damaging crops, homes and infrastructure in low-lying areas. 

A flood threat – in the form of a monster and now melting snowpack – could loom over parts of the Central Valley into July, disrupting growers in the nation’s food basket and leaving communities on edge for months.   

“We’re going to get wet somewhere. I don’t know where,” said Ron Caetano, of his community in the Island District of rural Kings County, near the growing Tulare Lake.   

California state climatologist Michael Anderson said he did not expect river flooding this month below dams that provide flood control and help manage the state’s water supplies. River flooding is more likely in May, he said, adding that it would likely be less significant in scale and impact when compared to the floods this winter.

Emergency planners and thousands of state personnel have readied to respond to flooding, according to Brian Ferguson, deputy director of crisis communications for the California Governor's Office of Emergency Services. Temperatures began to spike Wednesday, touching off what could be a long spring and summer of patching levees and fighting floods. 

California’s snowpack serves as a natural reservoir. In a typical year, it accounts for about a third of California’s water supply and helps the state through its dry season from roughly May to September. 

But this year, the mountains are simply storing too much snow in some parts of the state. In general, the height of peaks in the Sierra range increases from north to south, with more precipitation falling as snow rather than rain in the southern – and highest – reaches.

In the southern Sierra, the state has more than three times its typical snowpack – a record amount. Over the past several weeks, dam operators on snowpack-fed rivers have been releasing water to make more space to take on more water later in the season for flood control. 

The pace and timing of the snowpack’s melt will be determined by the angle of the sun and the air temperature. Swain and other experts think the melt out will begin to speed this week. 

Flooding in some parts of California – like the Sacramento River system – is driven by intense rainfall, usually in the winter months. These areas will likely avoid more trouble this season.   

Instead, flood worries are centered on the San Joaquin River system, the Tulare Lake Basin and some parts of the Eastern Sierra, which don’t have as much capacity to control flooding and are fed by the outsize, high-alpine snowpack in the central and southern Sierra.   

“In the southern Sierra, where we have the deepest snowpack, at some points we have about 5-6 feet of water sitting in the snowpack,” said Safeeq Khan, an assistant adjunct professor of civil and environmental engineering at the University of California, Merced. “Imagine 5 feet of water coming down within five or six weeks – how do you go about managing that water?” 

More than 76,000 acres are underwater already in the Tulare Lake Basin, according to estimates from the California State Department of Water Resources. Dams on the four rivers that historically dead end at the lake will help control flows as snow melts. But, scientists expect the lake – which was dried out for use as farmland decades ago – to grow in size. 

“They just can’t store all the water,” said Alan Haynes, the hydrologist-in-charge at the California Nevada River Forecast Center. “They’ve got to release it. It’s got nowhere else to go, except Tulare.” 

Rural communities in the San Joaquin River valley could see flooding, too, if protective levees fail. The network of levees that’s designed to channel water away from homes and provide irrigation access is in poor condition, Haynes said. Breaches are possible and the levees will need persistent maintenance.  

“It’s going to be a constant battle,” Haynes said. “It could impact homes and things, but we just don’t know exactly where.”

In Yosemite National Park – where the Merced River flows through alpine terrain – officials plan on Friday to temporarily close access to much of Yosemite Valley, the touchpoint for most park visitors. Park officials expect the river, which is unmanaged within the park’s boundaries, to exceed flood stage. High water could put visitors at risk. 

“If we don’t have bathrooms, running water, roads – it’s health, life and safety,” said Scott Gediman, a park spokesman, outlining potential impacts and reasons for closure. 

Californians throughout the Central Valley are keeping close watch on river gauge and dam outflow data. 

In Kings County, where water managers have told residents to protect their homes and make plans for what to do if the Kings River overtops its banks, Caetano said he already has his 53-foot van trailer loaded with belongings and ready to take off. 

“We know that mathematically it does not look good. Now the rest of it is going to depend on mother nature,” Caetano said. 

Graphics data sources:

National Operational Hydrologic Remote Sensing Center, Snow Data Assimilation System (SNODAS) data products at National Snow and Ice Data Center (NSIDC); National Weather Service; California Department of Water Resources.