California is being inundated with rain. Will it ease the drought?


A month ago, California’s Sonoma County came closer than ever to a water crisis: The level of its main reservoir sank to an all-time low after three grueling years of severe drought.

This week, as a parade of atmospheric rivers carrying torrents of rain pound much of the state, the county in the heart of wine country is grappling with the opposite problem: too much water, too fast.

But even in a time of plenty, when Lake Sonoma is slowly filling and the Russian River could soon overflow its banks, water managers and scientists aren’t ready to declare the drought over .

“We had such a big hole to dig to begin with,” said Grant Davis, CEO of Sonoma Water, as rain drenched Santa Rosa, the county seat. “We as water managers are dealing with something we call a bump, that means extremes on the dry end and extremes on the wet end.”

Californians prepared for another major winter storm on Jan. 4 by setting up sandbags and staying indoors. (Video: Julie Yoon/The Washington Post)

Scientists say the apparent paradox of dangerous flooding amid historic drought shows how climate change has amplified California’s intense weather, making dry periods drier and wet periods wetter, without either stations completely counteract each other’s effects.

While California has improved its water management system in recent years, it wasn’t built to handle such intense storms, experts say. Even if every drop can be captured and stored in a reservoir, it will take much more rain to erase the state’s years-long water deficit. And rain is only part of the equation.

“We’re in a flood emergency while we still have an active drought emergency,” Karla Nemeth, director of the California Department of Water Resources, said in an interview. “That pretty much says it all about the new normal we have with climate change.”

Human emissions of greenhouse gases, primarily from the burning of fossil fuels, have raised California’s average air temperature by about 2.5 degrees Fahrenheit, according to the state Environmental Protection Agency. These warmer conditions increase water evaporation from vegetation and soil and deplete the mountain snowpack on which the state depends for 30% of its water storage.

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According to the US Drought Monitor, there hasn’t been a week where some part of California wasn’t abnormally dry or worse since 2011. Last year was exceptionally bad: wells ran dry and cities became dependent on of bottled water, as the state saw it. the second driest year in history.

“We’re starting from a very serious deficit position,” said Noah Diffenbaugh, a climate scientist at Stanford’s Doerr School of Sustainability. “If you don’t get paid for a few months, and then your employer gives you a normal monthly check, most people won’t feel like their bank account is back to normal.”

When the rain falls, climate change has occurred Studies show that it is much more intense and destructive and, in turn, harder for water systems to absorb. The atmosphere holds 7% more moisture for every degree Celsius of temperature rise, meaning any storm will be much wetter in a warmer world.

If the forecasts for the next two weeks hold, 22 trillion liters of water could hit California in the next 15 days, according to meteorologist Michael Snyder’s calculations. That’s enough to more than double Lake Mead.

“We are now in a climate where we are much more likely to have severe water deficits marked by wet conditions,” Diffenbaugh said.

Rising temperatures mean more of this precipitation falls as rain rather than snow. Instead of pooling on mountaintops, where it gradually melts into waterways and ecosystems, the water immediately flows into rivers and streams. That can overwhelm water systems that weren’t designed to handle such sporadic and severe rainfall, Diffenbaugh said. In a 2019 study in the journal Water Resources Research, he and his colleagues found that flood risk gets exponentially worse as precipitation shifts from snow to rain.

In California this week, downpours soaked soils and caused drought-stressed trees to topple. Officials fear the newly scorched landscapes could melt into soggy debris flows. Water managers once worried about critically low reservoirs are now contemplating releases to avoid dangerous flooding.

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Although dangerous, the recent spate of storms has helped ease the state’s longstanding water shortage.

Sierra Nevada snowpack is nearly 180 percent of its normal volume at this point in the season, the highest level in 10 years. Scientists hope California’s climate won’t warm too quickly in the coming months. This would allow the snow to slowly melt and trickle down into communities well into the summer.

As of January 3, the US Drought Monitor classified the entire state as “abnormally dry”. California’s more than 200 reservoirs are about 33 percent below their historical average levels. Monitoring wells show that the state’s underground aquifers, which account for more than half of the state’s water supply during drought years, hold only two-thirds of their normal amount of water.

Now, parts of the state are seeing up to an inch of rain per hour. But instead of slowly percolating through ecosystems and soils, rain rushes over saturated ground in a destructive flood. Instead of replenishing depleted groundwater, the deluge exceeds the limited capacity of rivers and reservoirs, causing overflows.

This forces water managers in flood-prone areas into a delicate balancing act. Water is the state’s most precious resource, and managers must hold on to it as much as possible. But repeated heavy storms mean they also need to set aside space to absorb flood water.

Those facing the most severe drought conditions have other problems. In early December, Lake Sonoma’s narrative was painfully cut short, Davis said. The reservoir was below 40 percent of its capacity, just under 100,000 acre-feet of volume. As of this week, it was over 120,000, a good sign, but only about half of what the lake can comfortably hold.

Faced with unprecedented challenges, Davis said, however optimistic and that the state is “better prepared than ever” to face weather extremes. One source of their hope is a pilot program that uses improved forecasting and modeling to make decisions about withholding or releasing water from reservoirs.

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Sonoma has used the system, known as informed reservoir operations forecasting, in one of its smaller reservoirs, and Davis credited it with saving thousands of acre-feet of water.

“It’s going to be how water managers get through these extreme events,” he said.

Meanwhile, a wet December and early January doesn’t guarantee all that water will last until spring. Look no further than last year’s weather, said Ellen Hanak, director of the Water Policy Center at the Public Policy Institute of California. The state saw similar winter storms, before an unseasonably warm and dry stretch obliterated most of the snowpack.

“Last year wasn’t a good year, even though we got off to a wet start,” Hanak said.

California’s traditional rainy season runs from October to April, so there’s plenty going on in the coming months.

“We still have a few months left to play here,” Hanak said. “But that’s it a welcome start.”

A key factor in navigating long-term drought conditions, and ensuring the state’s well-being, will be finding new ways to harness floodwater from future megastorms, effectively using one climate disaster to mitigate another .

Hanak and other experts see promise in groundwater storage, which has been used in some parts of the state but could become increasingly popular as snowpack becomes less reliable.

Jane Dolan, the chairwoman of the Central Valley Flood Protection Board, has been pushing state and local governments to widen floodways and restore wetlands as a way to protect against heavy storms and recharge groundwater basins . The recent storms in California show the urgent need to do both, he said.

“We pay now to make things more resilient and protect people’s lives and property, or we pay later by fixing the massive damage that occurs,” Dolan said from Chico, the state’s largest city in the north of Sacramento, where it has happened. decades in local government.

“Water is the number one problem in California,” he said. “Or we have too much, or not enough.”


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