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Melt from historic California snow may be less damaging than feared

Officials cite two reasons for the reduced risk: Luck with the weather combined with ongoing efforts to divert and manage the flood waters

Workers secure a levee near Corcoran, Calif., on May 1. In part due to the emergency work, officials no longer expect floodwaters to inundate the town this spring. (David Paul Morris/Bloomberg News)
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As California’s “big melt” nears its anticipated peak, officials on Monday painted a more optimistic picture of the potential for flooding from the record snowpack in the southern Sierra Nevada. Even as the once-dry Tulare Lake expands — expected to swell to more than 117,000 acres at the end of May — new modeling suggests that inundation will be less damaging than originally predicted, sparing the major towns in the lake basin.

Officials cite two reasons for the reduced risk: luck with the weather combined with ongoing efforts to divert and manage the floodwaters. But while the worst-case scenario for what could happen as California’s historic snowpack melts this spring may be averted, some risk remains, simply due to the amount of snow still remaining in the Sierra. If the weather turns, flood forecasts could shift.

“We’re trending in the right direction, but modeling is modeling and what comes down from the mountain can change if we have a warm streak or a hot storm comes through,” said Brian Ferguson, deputy director of crisis communications for the California Office of Emergency Services, at a briefing Monday. “We’re in significantly better shape with that peak water level than we were a few weeks ago.”

Tulare Lake, long ago drained for agriculture, has been dry for decades, only re-emerging during extremely wet or snowy years like 1969, 1983 and 1997.

California's Sierra Nevada has experienced upward of 12 feet of new snow over the first days of March passing historical milestones in some regions. (Video: John Farrell/The Washington Post)

As snowmelt accelerated this spring, the expanse of the lake reached about 103,000 acres (161 square miles) by May 8. The most likely scenario has the lake peaking on May 31 at just over 117,000 acres (183 square miles) and then shrinking to about 102,000 acres (159 square miles) by late July, according to the Department of Water Resources’ latest Tulare Lake modeling projections. In 1983, a similar flood footprint submerged farmland for nearly two years. Other scenarios, while less likely, have the lake growing even larger and peaking later in the summer.

Officials no longer expect floodwaters to inundate the town of Corcoran or the prison complex there, in part due to emergency work to raise the levees near the town. Similarly, the communities of Alpaugh and Allen, which flooded in March during atmospheric river storms, should be spared further flooding from snowmelt.

“We’ve gotten lucky so far,” said Daniel Swain, a climate scientist at UCLA, in an online briefing Monday. “We have had some significant heat waves, but they haven’t been super prolonged.”

Cooler-than-normal periods this spring have allowed reservoir operators to clear space to catch the more rapid melt during warmer spells.

And over the weekend, the Department of Water Resources began diverting some water south toward Los Angeles via the California Aqueduct, though the planned diversions are small compared to the total melt flowing into the Tulare basin. Officials are also working to divert water into groundwater basins.

Still, experts are warily eyeing the amount of snow left in the mountains and cautioning against taking too optimistic a view of the upcoming melt.

“They have done a very good job of taking advantage of the cooler weather,” said Jeffrey Mount, a senior fellow at the Public Policy Institute of California’s Water Policy Center. “But the volumes of water expected to come down are very large — much larger than the space available in the reservoirs — so this is going to be a tense situation for a couple of weeks.”

There is hope that the worst floods — the kind that would breach levees along the San Joaquin River, for example — will be averted if the weather stays cool in the coming weeks, as current outlooks suggest.

However, Swain said that serious flooding “could still happen if we get an exceptional heat wave or a late-season atmospheric river at any point in the next month.”

Although the unfolding melt so far has given officials and communities time to prepare, the forecast could shift quickly, particularly as extreme heat becomes more likely during the summer months.

“There will be high flows for weeks, not just a day, with very large volumes running off,” Mount said. “So, it is a bit premature to pop the champagne, I think.”