State worries about winter

October 3, 2017 10:47am

•  Concerned it might not result in enough rain and snow – or maybe too much

•  “Advancing accurate, even longer-range forecasting is critical”

The new state “water year” is just three days old but already the state is fretting about what Mother Nature might bring – or not bring – this winter in the way of snow and rain.

After five years of drought, last winter there was enough rain and snow to break the drought and refill the state’s reservoirs. There was so much water, that the spillways at Oroville Dam failed, forcing 180,000 people living downstream to flee to higher ground in a night of chaos.

The precipitation ranks second only to 1983 as California’s wettest year for statewide runoff.

The California Department of Water Resources says Tuesday that it is beginning water year 2018 “intent on narrowing the forecasting gap with improved sub-seasonal to seasonal forecasting.”

It says it is working with researchers at the National Aeronautics and Space Administration and the Scripps Institution of Oceanography to develop new technology to forecast land-falling atmospheric rivers.

“Current short-term forecasting for seven days out is 70 percent accurate, while the 14-day forecast is only 7 percent accurate,” says DWR Director Grant Davis. “That isn’t adequate for water management. Advancing accurate, even longer-range forecasting is critical for our ability to plan for California’s highly variable weather.”

The water year that ended September 30 saw an extraordinary number of atmospheric rivers that created high water conditions throughout the state. The Feather River watershed received record runoff in January and February, which led to some of the highest inflows into Lake Oroville ever recorded.

“More accurate forecasting would have helped DWR manage reservoir levels to deal with significant inflow in the days following the February 7 discovery of erosion on the main spillway at Lake Oroville,” it says.

“Better forecasting also would help inform the spillway’s reconstruction timeline based on predicted precipitation,” says DWR.

The record-setting precipitation in Northern California and above-average rainfall elsewhere contributed to flooding in several river systems. Fifty-two counties declared states of emergency due to the January storm sequence, and flood fight materials and specialists were pre-positioned in Merced, Butte, Stanislaus, Fresno, and San Joaquin counties based on the forecasts in anticipation that local agencies would request support.

Despite record-breaking rainfall in Northern California in water year 2017, drought impacts still linger.

Although a wet 2017 minimized the risk of subsidence in historically affected parts of the San Joaquin Valley, DWR is still paying for satellite- and aircraft-based radar monitoring of subsidence by NASA to support local implementation of California’s ground water management law.

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