Why record rain hasn’t washed away California’s water woes

John Kennedy watched in frustration Tuesday as floodwaters pulsed through the Santa Ana River, past systems the Orange County, Calif., water manager uses to capture precious water and send it underground. For a second consecutive winter, rain is not just falling on once-parched California - it’s inundating the Golden State in record-setting volume, faster than it can be saved.

Parts of normally sunny Los Angeles saw a foot of rain in recent days, sending mud and debris flowing through neighborhoods. Weeks earlier, more than a month’s worth of rain swamped San Diego in a day. The disasters come within a year of atmospheric rivers that left California with one of its largest-ever snowpacks, one that miraculously pulled the state out of a perennial drought crisis and provided respite from red-alert fire seasons of the recent past.

[Los Angeles records nearly 400 mudslides during storm that has drenched Southern California]

But storms like these won’t be able to wash away California’s long-term water worries Kennedy and the rest of the state hold: whether there will be enough water to sustain the state for the future.

When so much rain falls in such a short span of time, it overwhelms the natural and man-made systems that try to contain it. Rather than filling up reservoirs or sinking slowly into the soil, the floodwaters surge across landscapes and rip through communities before finally washing out to sea.

Even as dry periods are becoming longer and more severe, climate change is making precipitation events warmer, wetter and more intense - enhancing their destructiveness and making it more difficult for people and ecosystems to capture the rainfall as a buffer against future drought.

This conundrum is yet another example of how human-caused warming is intensifying California’s climate of extremes and exacerbating its water challenges.

“When we do get these storm events, they’re going to be bigger and flashier, and we need to be better prepared to capture that water,” said Karla Nemeth, director of the state’s Department of Water Resources.

Achieving that is not a simple task. Assuming the wet trend continues, capturing more of the precious moisture will require major investments in a statewide system that is already highly engineered to get water from where it is most plentiful to massive population centers hundreds of miles away.

To confront the problem, California is exploring smarter ways to manage reservoir levels, husband precious snowpack and send more water from surface lakes and channels into sapped aquifers.

That’s because Californians know all too well that they have to take advantage of the precipitation while they can. At least for the next week, there is no sign of the stormy pattern resuming, said Julie Kalansky, a climate scientist at the Scripps Institution of Oceanography in San Diego.

“As quickly as that switch to wet weather goes on, it can switch back off,” she said.

Surges of rain are getting bigger

The state’s reservoir system alone cannot keep up with the recent surges of rain.

As the most recent storm approached, many California reservoirs were already near their capacity, forcing dam operators to release water from reservoirs to make room for the coming flows. By Tuesday, most were well ahead of historical averages, including the state’s largest reservoirs, lakes Oroville and Shasta.

Researchers and water managers have for years been studying whether they can hold more water in reservoirs by changing the rules that guide flood control releases. At one reservoir where they have tested a new strategy - using forecasts of precipitation and snowmelt to improve estimates of how much room in a reservoir is needed - they have managed to store as much as 19% more water by the end of the wet season, Kalansky said.

But because so much rain is coming in such massive storms, it can be hard to store more of it.

The state typically gets about half its annual precipitation from December through February, and many parts of Southern California exceeded that in just two days. Downtown Los Angeles received 49% of its annual average rainfall Sunday and Monday - with 7.03 inches over 48 hours, according to the National Weather Service.

The challenge ties back to global warming, and the physical reality that warmer air can hold more moisture. As climate change supercharges atmospheric rivers, research shows that it is also accelerating the intensity of the heaviest downpours and increasing the chance of multiple storms occurring in quick succession.

In studies she conducted as a doctoral student at Stanford University, civil engineer Corrine Bowers found that the highest intensity atmospheric river events are disproportionately likely to be sandwiched between other storms - overwhelming the landscape’s ability to absorb all the rain. Soils become saturated. Reservoirs approach capacity. Rivers reach - and then overtop - their banks.

If an atmospheric river occurs within five days of a prior storm, the associated damage can be as much as four times greater than if the event had happened in isolation. Such “super sequences” lasting at least two months could become two to three times more frequent by the end of the century, Bowers and her colleagues found.

‘We can’t rely on snowpack’ to store moisture

As California’s storms intensify, that can translate into a boom in snowpack, as was the case in 2023. Mild weather meant the massive melt extended well into the summer months.

But storms are also trending warmer, experts said. Rising temperatures in the mountains cause more precipitation to fall as rain, rather than snow, even at high elevations. This means snowpack is not as reliable a source of steady meltwater during the dry spring and summer months.

This winter, despite healthy rainfall, at 90% of normal for this point in the year, snowpack has lagged. The most recent storm pushed it to 72% of average for this point in the year, Nemeth said, though it is still less than half its normal total come April 1, when snow accumulation in the Sierra Nevada typically peaks.

“It really speaks to the need that California has to capture this water,” she said. “We can’t rely on snowpack in the future the way we once did.”

A race to capture water underground

With diminished snowpack and more intense yet brief storms, the difficult task of storing groundwater becomes even more important.

Last year, as mild weather allowed a record-tying snowpack to melt gradually, California officials reported moving 3.5 million acre feet of water through the State Water Project, a system of canals that carries water into reservoirs around the state.

But the state’s aquifers remain depleted. About a third of the 3,700 wells on the state’s live groundwater website remain below normal. More than 200 are at an all-time low.

Gov. Gavin Newsom (D) has a goal of increasing the amount of water the state sends back into aquifers by half a million acre feet. In places like the Westlands Water District, a Central Valley agricultural irrigation district that is the country’s largest, that was achieved through injection pumping into aquifers that were overpumped during drought years, Nemeth said.

Even with more water, that won’t be possible everywhere - overdraft has caused many aquifers around the state to collapse. But the state will need to find a way to take advantage of wet times as much as possible to reach its groundwater recharge goals, Nemeth said.

More places will have to develop robust programs to restore groundwater that provide multiple “access points” for surface water to seep into the aquifer, University of California Irvine civil engineer Brett Sanders said. Large basins serve as primary access points for groundwater to filter downward, holding large amounts of runoff and recycled wastewater that trickle into aquifers.

Communities also must add smaller green spaces to improve storage and prevent flooding by helping more water get into the ground, he said.

Without that, some communities will struggle to cope as precipitation surges. In Orange County, Kennedy’s district has one of the country’s most advanced groundwater recharge systems, which pulls the Santa Ana River’s flows as well as recycled wastewater into large basins, where the water can then trickle into the aquifer below. The system has allowed Orange County to almost halve its dependence on water imported from the Colorado River and the northern part of the state, insulating residents from the shortages plaguing much of the drought-stricken West.

But now, “there’s so much water coming down we’re not able to capture all of it,” Kennedy said. When the river is flowing so fast, it’s more difficult to divert into a recharge basin. Kennedy’s partners at the Army Corps of Engineers, which operates the Prado Dam upstream, are focused on managing the reservoir to prevent floods - which means they can’t hold back water for the district either.

When the storm is over, the Prado Dam operators will slowly release some remaining water back into the Santa Ana so that it can be directed into the Orange County recharge basins.

“But at the end of the day, with these large storms, some of the water is going to get past us,” Kennedy said.

- - -

Lauren Tierney contributed to this report.