If California doesn't get rain this winter ...

Each year from October to the following September, California measures its rainfall and snow accumulation.

This past season didn't take much figuring. It turned out to be the fourth driest year ever for the state, as it only got around 60 percent of the average precipitation.

As California starts a new water measurement cycle—and faces a fourth year of severe drought—another dry winter could be a tipping point for the country's top agricultural producer.

"This year is crucial," said Michael Hanemann, professor and environmental economist at the W.P Carey School of Business at Arizona State University.

"A third winter of low rain would be extremely painful," he said. "If we have one or two dry winters we can get through that. But the lack of water this winter would have a significant economic impact on agriculture that hasn't been felt before."

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