What California’s weird winter means for its water problems

The West just had a very wet winter. The snowpack at the top of the Rocky Mountains, which feed the Colorado River, a crucial water source for seven states and Mexico, has been replenished. The Great Salt Lake has risen a little more than three feet. Currently, the US Drought Monitor shows that almost all of California is out of a severe drought.

Now, spring temperatures are causing the snowpack on the Sierra Nevadas to melt and trickle down to California’s waterways. After enforcing steep cuts in some counties in 2021 and 2022, the state just granted more river water to millions of residents and agriculture. For farms in particular, this means they may not have to rely as heavily on groundwater, which is being rapidly depleted in some parts of the state.

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But scientists warn this one strange winter should be taken as that: extraordinary. To fully rid the West of its long-term megadrought, which research shows has been exacerbated by climate change, there would need to be several rainy and snowy winters in a row, says Wei Zhang, a climate scientist and assistant professor at Utah State University.

Zhang calculated how abnormal California’s precipitation was from December 2022 to February 2023 using data from the National Oceanic and Atmospheric Administration, and found it was about 52 percent higher than average. “It’s an extreme event—it happens every few decades,” he notes.

“This wet winter definitely is great news for the Colorado River because of the snowpack. That snow runoff from the mountains will drain into the Colorado River and increase the stream flow,” Zhang explains. “But that cannot solve the water problem in the Colorado River—that demand is still much larger than the supply.”

The Colorado River has been overused for decades. And thanks to the megadrought, which has caused increased evaporation and decreased snowfall, it’s also shrinking. The federal government plans to adopt a final decision this summer about how to best manage the parched river—and which states will lose acre-feet of water from the plan. 

Zhang is also digging into why this past winter was so wet in Western states. He says it’s unlikely it was caused by climate change, which would cause precipitation to fall more as rain than snow. He thinks it’s more likely tied to shifts in jet streams, or the upper level wind flows that drive the movement of winter storms. These new patterns could potentially be tied to changes in climate, but either way, scientists need more evidence before they can make a definitive conclusion about the reason behind all the snow this winter.

“This extreme event could be caused by some random [atmospheric] processes in the climate system, or it could also be forced by some sea surface temperature anomalies, or because of the background changes in the [Earth’s] climate,” Zhang says. “But it’s very difficult to build that causal relationship between one extreme winter or one extreme event and climate change.”

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Simon Wang, another climate scientist and professor at Utah State University, thinks that while climate change can contribute to the overall warming of the planet and increases in precipitation, it doesn’t regulate year-to-year patterns. 

Like Zhang, he’s cautious about how much impact one season can have. “Drought is a long-term problem that requires sustained water management and conservation efforts, as well as proactive measures to adapt to increasing aridification due to increased evaporation,” he writes in an email to PopSci. “While this wet winter has helped to alleviate some immediate concerns, it is not a solution to the diminishing water supply.”

Both Wang and Zhang emphasize that California and the rest of the West’s water woes have not yet waned. “Many people may think that we don’t have a water problem anymore. I don’t think that’s true,” Zhang says. “All the models are projecting a dryer and hotter western US [in the next decades]. I don’t think this event will overturn that trend.”

Correction (May 2, 2023): The article previous incorrectly stated that the Sierra Nevada snowpack feeds the Colorado River. It should be the Rocky Mountains.