Campus experts say increased rainfall into new year could mark end of California drought

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California’s current La Niña period, characterized by highly unpredictable rainfall patterns, might mean the end of the statewide drought, according to UC Berkeley environmental experts.

If the rainfall continues further into the new year, most, if not all, of the state will likely see the end of the drought, according to assistant professor of water and climate Ted Grantham. Grantham said there are two definitions of a drought — the traditional meteorological drought is characterized by significantly below average rainfall. Another definition, however, also considers water supply in reservoirs.

Grantham explained that continued rainfall into the new year could mark the end of the drought, but the water supply in some parts of the state, especially in Southern California, is still not enough.

“Our reservoirs were extremely low, so it’s still going to take more rain to completely fill them up. We’ve had a lot of rain but it still may take a few more years,” Grantham said. “We’re still going to be experiencing the effects of drought even if the weather tells us that the drought is over.”

The U.S. Drought Monitor, which Grantham said is the primary authority on declaring droughts, indicates that most of Northern California is out of the drought. According to Grantham, Southern California’s coast currently faces the most severe impact of the drought, with reservoir levels at about 10 percent of where they should be.

In previous years, high-pressure zones in the atmosphere prevented rainfall over the state, Grantham said, but this year these zones dissipated and atmospheric rivers moved in. The atmospheric rivers, which Grantham described as “high moisture bands” delivered rain to the land across California.

Professor of geography Richard Walker believes that the state will just have to wait to see what rainfall will look like this year and the next before deciding the drought is over.

“Everyone wants to declare an end to the drought as soon as it rains — as if it didn’t rain at all for five years!” Walker said in an email. “Recall the large December storms last winter, after which it stopped raining and snowing for weeks. … Droughts don’t start and stop on a dime. These are longer patterns of sub or above-average precipitation.”

Walker said that in terms of water supply for humans, the drought will be over when the reservoirs are full. He added, however, that as long as humans put too much demand on the system, California will not see an end to the water shortage.

With climate change, Grantham said he foresees an increased frequency of droughts in California. Grantham explained that most ecosystems across the state have adapted to the drought, but high human demand continues to put pressure on California’s water supply.

“If you look at a history of California, droughts are a naturally recurring feature in this state — there’s nothing unnatural about droughts,” Grantham said. “It’s more about the 30 million people living in the state and having water to meet our competing demands.”

Contact Malini Ramaiyer at [email protected] and follow her on Twitter at @malinisramaiyer.