California, particularly Northern California, was walloped by a major winter rain and snow storm last week and meteorologists expect that high levels of precipitation will continue for at least another week.

Despite some damage and at least one death from local flooding and tree-toppling high winds, the storm and the predictions of more to come are welcome relief from what had appeared to be a prolonged drought.

There are lessons to be learned from this watery wave, if Californians and the politicians they have elected pay attention, to wit:

• Despite great advances in technology and data collection, weather forecasting is still an imperfect science. Until the storm hit, meteorologists had expected that a phenomenon known as La Niña would continue to block Pacific fronts from reaching the state and thus continue the drought.

That said, there’s no guarantee that the 2022-23 season will be a wet one. A year ago we had a similar spurt of precipitation, but it did not continue into the spring.

• Erratic precipitation makes it very difficult for reservoir managers to decide how much water to release and how much to retain for future use. For example, Folsom Lake near Sacramento was scarcely a third full when the storm hit, but the Bureau of Reclamation tripled releases to 24,000 cubic feet a second, worried about the reservoir’s ability to absorb runoff in the American River’s Sierra watershed.

• Folsom’s increased releases are another indication that California lacks enough water storage to cope with precipitation cycles that are becoming less predictable due to climate change. If we had built the additional storage that water managers had long proposed – Auburn Dam upstream from Folsom, for example – it would have meant less guesswork when opportunities arose to capture water from heavy storms•.

Preliminary construction had begun on Auburn Dam when, during the 1970s, it was abruptly halted. Other storage projects have been on the drawing board for decades, such as Sites Reservoir on the west side of the Sacramento Valley. Were Sites a reality today, it would be absorbing excess flow from the Sacramento River, banking water for when it would be needed in the future.

• The “atmospheric river” now watering California underscores the state’s vulnerability to catastrophic flooding.

Last year, a massive study was released, suggesting that climate change creates an ever-increasing risk of megafloods that would cause untold death and destruction.

It is the latest update to studies that originated from the historic flooding that struck California during the winter of 1861-62, when California had been a state for scarcely a decade.

As the study noted: “This event, which was characterized by weeks-long sequences of winter storms, produced widespread catastrophic flooding across virtually all of California’s lowlands – transforming the interior Sacramento and San Joaquin valleys into a temporary but vast inland sea nearly 300 miles in length and inundating much of the now densely populated coastal plain in present-day Los Angeles and Orange counties.”

If such a prolonged deluge occurred again, researchers Xingying Huang and Daniel Swain, wrote, it “would likely produce widespread, catastrophic flooding and subsequently lead to the displacement of millions of people, the long-term closure of critical transportation corridors and ultimately to nearly $1 trillion in overall economic losses.”

Again, the American River’s situation illustrates the threat. Officials say that Folsom Lake’s capacity, nearly one million acre-feet, is too small to protect Sacramento from such a disaster. One rationale for Auburn Dam had been to provide another layer of flood protection.

Will politicians heed the lessons from the current period of prolonged precipitation or continue disengaged business as usual?

Dan Walters is a CalMatters columnist.

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