SACRAMENTO — With the coming water year shrouded in uncertainty, California officials want to improve their ability to track “atmospheric river” megastorms and plan for them before they arrive.
But whether that would lead to faster decisions on water allocations for agriculture is itself uncertain.
The state Department of Water Resources is working with the National Aeronautics and Space Administration and the Scripps Institution of Oceanography to improve sub-seasonal and seasonal forecasting.
Developing accurate, long-range forecasting is “critical for our ability to plan for California’s highly variable weather,” DWR director Grant Davis said in a statement. But it would be of less help in determining water distribution, agency spokeswoman Erin Mellon said.
The State Water Project makes its initial allocation on Dec. 1 based solely on water in storage, then its updates during the winter are largely based on the snowpack that accumulates, Mellon explained. Improving precipitation forecasting helps more with reservoir management and drought planning, she said.
“It’s hard to say how allocations will shake out this year because again, weather is unpredictable,” Mellon said in an email. “However, the largest reservoirs in the state are at 120 percent of average for this time of year, so we’re certainly feeling much better than we did a few years ago in the middle of a drought.”
Central Valley growers complained earlier this year that they had to put off planting decisions or rely on guesswork as state and federal agencies took their time in determining water allocations even as the snowpack kept piling up amid record precipitation.
Federal officials have said they will make a greater attempt in future years to announce all their initial allocations in February after putting some of them off in the last two seasons to see how the snowpack developed.
For the state, which issued its final allocation on April 14, much of the delay was caused by repairs to the Oroville Dam’s spillways. Their near failure in February threatened a large portion of the Eastern Sacramento Valley’s $1.5 billion agriculture industry, including rice and tree crops and several major processors along the Highway 99 corridor between Chico and Yuba City, industry leaders said.
Lake Oroville is the main reservoir for the SWP, which irrigates more than 600,000 acres of Central Valley farmland and serves 20 million customers in the San Francisco Bay area and Southern California.
The water year that ended Sept. 30 saw an extraordinary number of “atmospheric rivers” that created high-water conditions, the DWR noted in a news release. The Feather River watershed received record runoff in January and February, which led to some of the highest inflows into Lake Oroville ever recorded, the release explained.
More accurate forecasting would have helped the DWR manage reservoir levels to deal with inflow in the days after the Feb. 7 discovery of erosion on the dam’s spillway and would also help determine the spillway’s reconstruction timeline, officials said.
The agency’s report comes as consensus is building among forecasters that this winter will feature weak La Nina oceanic conditions, which typically point storms toward the Pacific Northwest and far Northern California. AccuWeather predicted on Oct. 4 that the northwest will be inundated with snowfall but that a drier, less snowy season is in the offing for California.
Among other water-related developments:
• The first phase of Oroville’s $275.4 million repair and reconstruction project — work on the main spillway — is on track to be finished by Nov. 1, officials said. The 3,000-foot gated flood control spillway will handle flows of up to 1000,000 cubic feet per second.
Workers on the emergency spillway are also on schedule to finish building a cut-off wall by late December or early January.
“Nov. 1 is a major milestone for the Oroville reconstruction project but it is by no means a finish line,” said DWR project manager Jeanne Kuttel, noting the project will take two construction seasons to complete.
• The DWR announced that 99 percent of the state’s high- and medium-priority groundwater basins met a July 1 deadline to form local agencies to implement the 2014 Sustainable Groundwater Management Act.
The agencies will regulate pumping from aquifers through “groundwater sustainability plans” that must be completed by 2020 in the state’s 21 most critically overdrafted basins.