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."
What's kept some of the pain at bay so far has been the increasing use of groundwater in the state, especially among farmers.
That use, along with crop imports to the U.S., has also kept consumer prices from rising more than they might.
But like many of the surface water supplies that have dried up, groundwater supplies are in danger of disappearing.
"Groundwater demand is normally around 40 percent a year," said Doug Carlson, information officer at the California Department of Water Resources ( DWR). "Now it's at 60 percent demand."
Carlson explained that groundwater is layered in clay and sandstone. Removing the water, he said, not only depletes the resource but often creates dangerous conditions of the earth sinking in on itself, which has already happened in parts of the state.
"Once that subsidence (collapse) happens, it's lost forever and rainfall won't replace it," he said.