Published Aug 02, 2024

California faces a growing water crisis as climate change risks reducing supplies from the State Water Project by as much as 23 percent in 20 years, according to projections.

A new report, published on Wednesday by California's Department of Water Resources (DWR), states that a 23 percent decline in water supplies would be equivalent to around 496,000 acre-feet per year, enough to supply 1,736,000 homes yearly.

Karla Nemeth, the DWR's director, said in a statement: "The analysis released today underscores the need to modernize and upgrade our aging infrastructure so we can capture water supplies when it's wet.

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"The State Water Project service area amounts to the world's eighth-largest economy and includes more than 8 million Californians living in disadvantaged communities. Modernizing the State Water Project is critical to delivering on the human right to water in California."

The analysis, published in the "The State Water Project Delivery Capability Report 2023," looked at the impacts of a range of climate change factors and estimated that water supply through the SWP could be reduced by between 13 and 23 percent by 2043, according to the Los Angeles Times. This is a significant increase on the DWR's previous report in 2021, which estimated a projected supply reduction of 9 percent in 20 years.

The SWP is a massive network of canals, dams, reservoirs, pumping plants and power plants that provide water to around 27 million Californians and 750,000 acres of farmland.

Built in the 1960s, the system transports water from rivers in northern California to populous and water-scarce cities in the south. The network, which is under the supervision of the DWR, is the largest state-owned water and power generator in the country.

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The report states that under future climate conditions, California is likely to experience increasing "variability, frequency, and magnitude of floods and droughts."

More precipitation is likely to fall as rain instead of snow in winter months, creating higher patterns of flows into reservoirs during these periods. Droughts in summer are also likely to be more frequent, and rain is equally expected to fall in more intense bursts. These factors will make it more difficult to store water in reservoirs and increase the chance of existing infrastructure being overwhelmed.

"Increased flows during the winter months are not stored as effectively in reservoirs as inflows that occur later in the water year," the report states. "This is because storage during the winter months is subject to stricter flood control levels. These levels are set to mediate the risk of reaching critical operational thresholds in each reservoir."

It adds, "The ability to export these additional flows is constrained by infrastructure limitations, permitted capacity and regulatory constraints."

Separately, sea level rise is also expected to impact water supplies. When saltier water is forced into the delta, it increases the required outflow to meet salinity requirements. These are supported by greater reservoir releases, which contribute to "lower average annual reservoir storage levels."

The problem will also be exacerbated by continued population growth and water demand. The report states that California's population grew from around 30 million to 36 million between 1990 and 2005, and based on this trend it will likely reach more than 43 million by 2030.

Commenting on the impacts of climate change, John Yarbrough, the SWP's deputy director, said in a statement: "The SWP was designed for the climate of the 20th century when our precipitation fell as snow more reliably between October and May and we could capture that water effectively for future use.

"We need to continue to adapt and invest in the SWP, so that we can add flexibility and resilience for 21st century conditions and we can avoid these losses in reliability."

The SWP is developing a Climate Adaption Plan, which will include development strategies for the state and opportunities for new and expanded storage both above and below ground.

Among the projects being developed to tackle the issue is the new Sites Reservoir, which will cost an estimated $4 billion to construct and will hold up to 1.5 million acre-feet of water, enough to supply three million households per year.

California Governor Gavin Newsom is also pushing ahead with plans to build a water tunnel beneath the Sacramento-San Joaquin River Delta to store water during rainy periods. The project is expected to cost more than $20 billion, according to the Associated Press.

Angel S. Fernández-Bou, a Western States senior climate scientist at the Union of Concerned Scientists, told Newsweek that the findings of the study are "worrying" and that California's water crisis "will become even worse if we don't act."

He said there is not enough water in the state to maintain current practices, especially in agriculture, which uses about 80 percent of the state's developed water. "In the last decade, evapotranspiration (the water used by the plants) has gone up by 4.4 percent in the San Joaquin Valley alone, and the amount of that change represents the indoor water use of about 12 million Californians. In other words, to produce the same agriculture, it needs more water now than 10 years ago, and that difference could provide water for 30 percent of the indoor water use in the state," Fernández-Bou said. "Projections suggest that evapotranspiration will go up around 15 percent in a few decades."

Fernández-Bou added that climate extremes would also worsen, with predictions suggesting that acute droughts—such as those seen in 2012 to 2016 and 2020 to 2022—would be between three and 15 times more frequent because of climate change in the coming decades.

Commenting on what needs to change, he said that cropland repurposing could help achieve water sustainability while bringing new opportunities for agricultural communities. "The idea behind it is to transform part of the irrigated agriculture to less water-intensive uses, to habitat restoration, to green areas for disadvantaged communities, to local basins to artificially replenish aquifers, and other multi-benefit outcomes," Fernández-Bou said.

He said that replenishing local aquifers with surface water would help prevent water insecurity for disadvantaged communities, help farmers meet regulations for groundwater sustainability and help create habitat connectivity.

However, he also said that creating dams was "not an option anymore in California, since there are already 1,500 dams occupying the best locations, and the cost would be too high to be able to provide cheap water for agriculture."

Fernández-Bou added: "Surface water storage in dams and conveyance with canals have major losses to evaporation, and with climate change, evaporation will increase. That is why storing water in the ground, in our aquifers, is the best way right now. It is more equitable because it doesn't depend on surface conveyance from afar, and it can target local needs with multi-benefit projects."
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