Global warming has already left its mark on the backbone of California’s water supply, and represents a growing threat to its first developed agricultural region, state experts have warned in a new study. 

The Sacramento-San Joaquin Delta fuels California’s $3 trillion economy, including its $50 billion agricultural industry, sustains more than 750 plant and animal species and supplies 27 million people with drinking water. 

But global warming is likely to destabilize the landscape that made the delta a biodiversity and agricultural hotspot, according to a study released late last month by a state agency charged with preparing the region for the climate crisis.

The sprawling island-studded delta, about an hour’s drive northeast from San Francisco, is fed by a network of streams and tributaries as intricate and life-sustaining as the veins that carry blood to the heart, making the estuary a critical ecological resource for diverse wildlife populations.

It’s also the linchpin of the state’s water supply. Starting in the 1930s, federal and state agencies built a massive maze of dams, reservoirs, pumping stations, levees and canals to transfer the state’s most coveted resource from the water-rich north to farms and cities in the thirsty southern reaches of the state.

But climate change threatens to drain California’s lifeblood as it pummels the delta with more frequent and more extreme heat waves, prolonged droughts, air-polluting wildfires and severe flooding, reported the Delta Stewardship Council, a California agency established in 2009 to ensure water supply reliability for the state and ecosystem resiliency for the delta.

The law mandated the council to consider “the future impact of climate change and sea level rise” in restoring an ecosystem transformed by agricultural and urban development. Its Delta Adapts report provided the first in-depth analysis of the potential risks climate change may pose to the region’s natural and agricultural resources.

“This report is a quantum leap forward,” said Letitia Grenier, resilient landscapes program director for the San Francisco Estuary Institute, who did not contribute to the report. “Finally, we have a comprehensive look at the issues with climate change for the delta.”

Climate change is on track to disrupt nearly every aspect of delta life, the council’s expert panel of scientists, planners and engineers concluded. 

The delta’s $1.7 billion agricultural industry will face serious threats from extreme heat, temperature-related water stress, drought and flooding. 

Farmers will also see yield losses from a less predictable water supply, warmer winters that rob fruit and nut trees of their required chilling hours and longer periods of extreme heat and flooding, particularly toward the latter half of the century. Warmer temperatures may also expand the range, survival and abundance of crop pests and pathogens.

Crops in different regions of the delta will show variable responses to these stressors, said Kaylee Griffith, an environmental scientist who led the synthesis of climate impacts on agriculture for the Delta Stewardship Council. “But in general, higher temperatures will stress out plants and may change the yield of crops. Plus fruit and nut trees are really sensitive to heat changes.”

Beyond coping with changing heat and precipitation patterns like the rest of the world, the delta also faces the dual threat of rising sea level and sinking land, Griffith said. 

“More than a thousand miles of levees protect islands and tracts that are often subsided below sea level,” Griffith said. “And these levees are at risk of overtopping from high flood levels.” 

Within the next three decades, more than a third of the delta’s 415,000 farmland acres could be submerged under floodwaters due to sea level rise, heavy storms and altered stream flows, costing farmers more than $150 million. 

Flooding helped shape the vast wetlands that supported native fish and millions of migratory birds before European settlers started converting marshes and woodlands to farms in the 1850s.

Reshaping the region turned the delta into the largest swath of prime farmland in California. But it also destroyed most of the tidal wetland habitat that supported the region’s natural resilience to shifting climatic conditions. 

The delta once covered half a million acres of freshwater inland marsh. Delta rivers harbored salmon runs so thick that the fish touched each other. Grizzly bears feasted on the spawning hordes as elk grazed in the marsh. 

The region sustained a remarkably productive food web. “I’ve called it the refrigerator of California,” Grenier said.

“Tidal marshes rank as one of the most valuable ecosystems on earth. They’re also incredibly valuable to people.”

These marshes provide coastal flood protection, enhance water quality by processing nutrients in wastewater, produce biodiverse food webs and sequester carbon. Yet 98 percent of this extraordinary inland freshwater marsh is gone. 

When you lose such a productive floodplain, Grenier said, “you lose all the services that went along with it.”

Recognizing Historic Harms

The delta may look nothing like the vibrant marshland of the past, but it’s still the largest freshwater estuary on the West Coast. It’s also California’s most crucial water source, supplying two-thirds of the state’s cities and millions of acres of farmland with drinking and irrigation water. 

But the human engineering that harnessed the delta’s bounty for cities and farms has contributed to its current fragility and challenges, Grenier said. 

Three years ago, a growing recognition of that fragility inspired the Delta Stewardship Council to assess the region’s vulnerability to climate impacts and develop a plan to mitigate them by restoring its resilience. 

Council staff worked with technical advisors and community groups to study different emissions scenarios through the end of the century. That allowed them to identify the delta’s most vulnerable regions as a first step toward helping policymakers craft climate adaptation plans. 

“Half a million people or more who live in the region will experience the local impacts of  flooding, sea level rise, water quality concerns and harmful algal blooms, along with the heat and wildfire smoke that impacts the whole state,” said Jessica Rudnick, an environmental social scientist with the Delta Stewardship Council. 

Figuring out how to restore ecosystems to mitigate these impacts will require unprecedented coordination among different agencies and levels of government, Rudnick said. “There’s going to be tension there.”

Grenier added that any effective climate change plans will require recognizing that agriculture and ecology are intimately connected. “Accepting that and dealing with that are what we all need to do,” she said.

That starts with understanding how transforming the landscape has eroded the very foundation of the region’s agriculture.

Draining the tidal marshlands that sustained “California’s refrigerator” gave farmers access to exceptionally fertile soil. The region’s peat soils, which formed as freshwater plants in the wetlands decayed, produce nearly 50 percent higher yields per acre than the state average.

But the soils that produce that bounty are disappearing. 

Freshwater floodplains are classic agricultural places for people all over the planet because they create such fertile farmland, Grenier said. 

Unfortunately, they were built on peat soils, which lose carbon dioxide and elevation as they dry out, she said. “That’s bad for climate change because it’s actually putting greenhouse gases into the atmosphere. It’s also really bad for people and property because those lands are sinking.”

The islands have lost half their soil since the 1850s. Some have sunk 25 feet or more below sea level. Many delta islands are now lower than the levees around them, making crops and remnant freshwater wetlands highly vulnerable to rising seas and saltwater intrusion. 

Within the next three decades, more than 42,000 residents and 148,000 farmland acres and local businesses could be inundated, threatening more than $10 billion in infrastructure such as hospitals, natural gas pipelines and canals, and $2 billion in revenues. 

By 2085, the council team warned, those figures will double and nearly two-thirds of delta farmland will be at risk of flooding.

Weighing Crop Risks

The delta will probably see only modest increases in annual precipitation. But more of it will be packed into a narrower window, with much more falling as severe rainstorms rather than as snow that stores water in the mountains. 

These changing precipitation patterns will overload state water systems’ ability to capture and store overflows, increasing the risk of flooding in the winter and early spring and of shortfalls during normally dry summers and droughts.

California has always bounced between episodes of drought and heavy rains. But multiyear droughts and water scarcity are likely to  become more common, jeopardizing water deliveries to farms, cities and industries. 

Severe droughts like the unprecedented drought from 2012 to 2016 will be five to seven times more likely to occur by 2050, causing widespread economic losses. The last two years alone of that unprecedented drought caused $3.8 billion in statewide agricultural losses, according to a 2018 study in the Journal of Water Resources and Management. 

Droughts often bring severe heat, which decreases yields by affecting plant growth, reducing produce quality and increasing plants’ susceptibility to pests and pathogens.

“One of the most prominent challenges for delta agriculture will be figuring out how to lessen those effects and whether crops should be switched to accommodate the new regime,” said Griffith.

Droughts also upset the balance between fresh and saltwater, which flows in from San Francisco Bay as stream levels drop. Models predict that sea level in San Francisco Bay will likely rise two-and-a-half feet by 2100, making saltwater intrusions far more challenging to control. 

Winners and Losers

As a changing climate disrupts delta life, vulnerable communities will be hit hardest.

There are a number of vulnerable populations in the southern regions, particularly near the city of Stockton and in some of the small rural towns throughout the delta, Rudnick said. Communities that are spread out have fewer resources and less capacity to adapt,  and already have more exposure to environmental contaminants, such as air pollution.

Sixty-five percent of residents who face a high risk of flooding live in communities with lower levels of education and income, lower English proficiency and fewer resources to prepare for and respond to an emergency.

“We need to be thinking about solutions that really protect the people who are most vulnerable and who are going to feel the worst of the impacts,” Rudnick said.

History shows that the impacts of drought are not distributed equally. Most of the delta’s small drinking water systems and wells are considered at lower risk of drought and water shortages compared to the state as a whole. But delta counties also include communities that fall into the top ten percent of at-risk groups in the state due to declining groundwater levels or poor water quality.

And farmworkers, who are already highly exposed to extreme conditions, will face even more health risks as the globe warms, Rudnick said. “They are most vulnerable to extreme heat and poor air quality days and more chemical exposure as we need more inputs to sustain high productivity.”

It’s important to identify regions where farm laborers will be most vulnerable, Rudnick said, and what type of crops may present the greatest health risks for them.

The future for delta agriculture is not entirely bleak. The region might become a refuge for crops that can no longer be grown in other parts of the Central Valley that heat up by midcentury.

And hotter, longer delta summers might boost yields of some crops, though those gains  might come at the expense of quality.

No Time to Wait

While scientists consider how climate change may alter the delta in the future, farmers are already feeling the impacts, Rudnick said. “They’re on the frontlines facing these climate threats and are very aware of how they might impact their businesses.”

Research suggests that emphasizing the on-farm benefits of adopting different climate-smart practices is more effective than trying to motivate farmers based on what will reduce the most greenhouse gas emissions, she said. 

The state offers technical assistance and grants to help farmers reduce their carbon footprint by increasing irrigation efficiency, using cover crops to build healthy soils and absorb carbon and creating habitat for pollinators, birds and native predators to replace harmful chemicals with natural pest control.

Creating a resilient delta will require working together and moving beyond the old fights over water flows for farms versus endangered fish and between preserving land for agriculture versus wetland restoration, Grenier said. 

“This report shows that actually, given the challenges we face, we all are aligned in needing a more functional and resilient ecosystem,” Grenier said. “Because there isn’t a future for water supply or endangered fish or agriculture or restoration unless we coordinate better at the large scale and make these more functional, healthy ecosystems.”

Agency officials are keenly aware of the threats climate change presents, Griffith said, but conflicting missions among different agencies have made them slow to act. “We’re hoping that this report is going to bring together a united vision for what needs to be done.”

Rudnick believes that government agencies will feel growing pressure to act from delta residents who increasingly feel the impacts of climate change.

“We all lived through a horrible fire season in 2020,” said Rudnick, who pointed to studies showing that when people have personal experience of climate’s impacts they’re more likely to push for government action.

“So I do anticipate that we’ll see more calls on our government as more and more people become impacted by climate extremes.”