What Will It Take To Get California Completely Out of Drought?

After two weeks of storms that have flooded thousands of homes and caused millions of dollars of destruction, you would think that California's drought woes would have been washed away.

Important reservoirs have seen huge rises in their water levels, and areas of "extreme drought" have disappeared following the deluges, with more wet weather set to hit the state this week.

But California's drought troubles aren't over yet, experts warn, as the storms may have brought too much rain at once, not enough snow that will melt into reservoirs in spring, and don't make up for the fact the past three years have been exceptionally dry.

'A Really Big Hole to Fill'

"The recent rains are very important in helping to prevent another dry year," Richard G. Luthy, a professor of civil and environmental engineering and water infrastructure expert at Stanford University, told Newsweek. "2020, 21 and 22 were exceptionally dry years. In 2022, Jan, Feb and Mar, normally wet months, were the driest since records were kept in the late 1800s."

"Lake Oroville and Shasta, the two biggest reservoirs, are still below average for this time of year. We have a really big hole to fill from three drought years in a row."

It will take a lot more rain to refill these surface reservoirs, let alone replenish the groundwater water stores.

But Jacob Petersen-Perlman, a water resources geography expert and assistant professor at East Carolina University, told Newsweek it's hard to say exactly how much rain would be needed due to the large number of variables involved.

"It's important to remember that timing and type of precipitation (rain vs. snow) is crucial for staying out of drought," Petersen-Perlman said. "Timing also matters—all the rain at once means that much of it will run off into the ocean instead of filling California's reservoirs. Second, if it continues to rain like it has been raining in California but not enough snow falls in the Sierras, drought may still persist."

'Too Much, Too Fast'

Petersen-Perlman said that if temperatures warm up too fast, much of the snowpack will melt too quickly and maintaining river flows for the summer will become much more difficult. Additionally, if the rains come too quickly and inconsistently, they may not refill California's aquifers sufficiently to relieve groundwater drought.

"Surface water levels are only part of the picture—groundwater levels will likely still remain chronically low, because (rain or no rain) we deplete more groundwater than is replenished," Aakash Ahamed, a hydrologist and co-founder of the Water Data Lab, told Newsweek.

"Over the last 25 years, we have lost more than 150 km3 of groundwater from California, which would take many many years of rain to replace, even if there were no consumptive use for municipal or agricultural purposes."

"Emptying underground groundwater reservoirs show the bigger picture, and we'd need 150 MAF [million acre-foot] of water (3x total storage capacity of 50MAF) to replenish them—that's unlikely to happen anytime soon because we pump groundwater faster than it replenishes every year," Rich Pauloo, a hydrogeologist and co-founder of the Water Data Lab, told Newsweek. "It's a huge problem, and we'll run out of groundwater in 100-400 years at business as usual rate depending on the location."

In a normal year California gets around 200 MAF of rain and snow, and it captures about 25% of this in surface reservoirs (50MAF combined capacity), Pauloo said.

"This year, statewide, currently we're 134% of normal for this time of year, but only 53% of normal for the full water year ending September 30, 2022 (we can still have dry Feb-May)," Pauloo said. "Our best hydro climate models still can't see more than a few weeks out—drought prediction remains an intractable scientific challenge. Surface reservoirs are at 78% average levels. Groundwater reservoirs are around 10% of normal across the state."

Despite the large amount of rain needed, the current rainfall can be used strategically to ensure maximum groundwater replenishment.

"One opportunity to address this problem is through managed aquifer recharge—diverting surface water to replenish groundwater when abundant surface reserves are available (like now)," Ahamed said.

Wettest Ever Stretch

December 26 to January 4 is now the record holder for the wettest 10-day stretch ever in San Francisco, and on December 31, 5.46 inches of rain fell in a single day in San Francisco.

"Nearly all of California has seen much above average rainfall totals over the past several weeks, with totals 400-600% above average values. This has resulted in nearly saturated soils and increasingly high river levels," said the National Weather Service in a statement on January 10.

This has helped bring down drought levels. U.S. Drought Monitor data shows the "exceptional drought" classification that covered 7 percent of the state as of December 27 has completely disappeared in the past fortnight.

Additionally, 2.07 percent of California is not classified as being under drought conditions, with some small slivers of "abnormally dry" land present in Del Norte County on the Oregon border, and Imperial County and Riverside County in the south.

On October 4, 2022, only 0.23 percent of the state was classified as "abnormally dry" rather than under the influence of drought. And more rain is forecast for the rest of the week across California.

'We Need More Big Storms'

"The hits keep coming in CA," tweeted the National Weather Service. "The next and most potent storm of the series will bring yet another round of heavy rain on already flooded rivers & saturated soils, high winds that may topple trees/power lines, and heavy snow on top of an enormous snowpack."

However, the outlook for the rest of the 2023 wet season is harder to predict: it might not rain as much as it has for months, putting the reservoirs and groundwater levels at risk of drying out again.

"We are hopeful that the reservoirs will be full at the end of this season, we just need several more big storms," Luthy said. "But it's hard to predict several months into the future. After a wet December in 2021, spring 2022 was a big disappointment."

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