Flooded California looks for new ways to deal with drought

It's early in the morning in the city of Fresno, central California, and water management expert Laura Ramos sounds relieved to hear the day's weather forecast.

"It's still sprinkling a bit, but it looks like it's going to pass quickly," she told DW. The huge storms that soaked the US state over most of the last month have passed, leaving behind at least 20 dead, breached levees, destroyed homes and at least $1 billion (€918 million) in damage.

Ramos, who works at California State University, said Fresno was largely spared the flooding, but other nearby communities to the north weren't so lucky.

"Their creeks have not been able to handle [the floodwaters,] and there's been a lot of flood damage to homes and businesses in some of those towns," she said.

And yet, despite the mega floods, wide swaths of California are still in drought. Water levels at five out of 12 major reservoirs are under average, and groundwater levels in more than 60% of wells across the state are historically low after decades of overpumping to supply farms and a growing population.

California is searching for ways to deal with its changing climate of longer, hotter dry periods followed by rarer bursts of intense rain and flooding.

Can't the state just capture and store excess flood water?

It's not so simple, said Caitlin Peterson, associate director of the PPIC Water Policy Center, a nonprofit think tank in San Francisco.

"One challenge is timing — these heavy rain and flood events tend to occur in big 'gulps,'" Peterson told DW. It's difficult to catch all that water if it falls over a short period.

Cycles of drought and rain have always been part of California's climate but these events are becoming more extreme as the world warms.

And climate change means the state's water infrastructure is no longer able to cope, said Ramos, the associate director of research and education at CSU's California Water Institute.

Water infrastructure built for 'different climate' 

"Our general water infrastructure was built in the 1950s and 60s, and so it was built for a different population and a different climate," said Ramos.

That infrastructure was built around runoff from a melting snowpack in the mountains, which would slowly percolate into the ground and recharge aquifers.

"Now we're getting the same amount of precipitation, but it's coming in the form of rain instead of snow," she said, adding that during periods of intense rainfall the ground becomes so saturated that the water just flows away. "There is no average, so it's hard to prepare."

Ramos said the state's aging water infrastructure has long needed an upgrade — not only more aboveground storage basins but also repairs to irrigation canals damaged by subsidence, reinforced levees and wider canal systems to bring water to places that no longer have a reliable supply.

But those are longer term, expensive projects, so water authorities are turning to a quicker, cheaper option to curb drought — one that involves allowing flooding in certain areas.

Capturing water with intentional floods

California's existing groundwater replenishment projects, common in the fertile Central Valley and the southern part of the state, generally use dedicated recharge basins. These basins look like large swimming pools or artificial lakes and collect water during wetter periods, said Peterson.

But older basins may not be built to handle such large flows of floodwater, and can require expensive maintenance and refurbishment.

Flood-managed aquifer recharge, however, often goes beyond these basins and involves allowing agricultural and open fields to be inundated. The water is left to soak into the natural underground reservoirs, where it is held back for later use.

In contrast to using dedicated recharge basins, this approach opens up groundwater replenishment to any suitable site — while at the same time helping to reduce the risk of flooding elsewhere. It also lessens the need for canals and other infrastructure to get the water to purpose-built basins.

"California is lucky to have a vast network of underground aquifers that can be actively managed to store water for dry years," said Peterson. "In fact, they can store much more than our surface reservoirs combined — due in part to all the space opened up by decades of overpumping."

An August 2022 government report said the state expects to invest $350 million (about €322 million) in local recharge projects by the end of 2023, funding more than 340 new projects "to harness the bounty of wet years to cope with dry years."

But will farmers be happy allowing their land to flood? 

Compared with purpose-built storage basins and dams, which can be expensive and take many years to approve and build, Ramos said refilling aquifers by allowing certain areas to flood is relatively straightforward. "But," she added, "it needs a lot of land."

Pilot projects have managed to convince farmers to allow their land to be used for this process, at least for part of the year.

"We know, for instance, that vineyards and some deciduous tree crops like almonds can handle having extra water on the ground in the off-season," said Peterson. As can certain fruit trees, and crops like alfalfa.

Some growers have also been choosing to flood land normally used for winter crops or choosing to plant crops they'd be willing to sacrifice to possible flooding, in the hope of retaining that water for more valuable summer crops.

The plan has seen financial and regulatory delays, and some farmers are worried about giving over land that could be otherwise used for planting.

"But I think they also see that if they don't have the water, then some of that land is going to come out of production anyway," added Peterson.

Aquifer recharge not enough to solve the problem

Apart from getting farmers on board, Ramos said the success of recharge projects also depends on soil quality and composition. Water flows easily through gravel and sand but not clay. It's important to prevent contaminants like pesticides and fertilizers from leaching into aquifers too. More research is needed, added Ramos.

Aquifer recharge also won't necessarily make up for the groundwater overdraft, especially in places like the Central Valley where use is high. More than a third of US vegetables and 75% of fruit and nuts are grown there.

Other water reclamation measures like usage restrictions, desalination plants and wastewater recycling will continue to play a major role, along with ongoing efforts to restore rivers and flood plains.

Still, when the rain began to fall in late December, Ramos said her first thought was whether the flood-managed aquifer recharge projects already in place were set to deal with the sudden deluge.

"Were we ready for all of this flood? Were we able to capture it?" she asked.

So far, the jury is out. "Everybody right now is just still dealing with the aftermath of the flood."

Edited by: Jennifer Collins