Peter Moyle has had his ups and downs during fishing trips on the Sacramento-San Joaquin Delta.

The UC Davis biology professor has been catching, counting and releasing fish in the Delta for more than 35 years. He’s seen populations spike and fall, but mostly it’s been a downward trend, in particular for native species.

“The Delta itself is not a good place to be a fish these days,” Moyle said.

Global warming and an insatiable thirst driven by population growth are conspiring to put California’s water sources and the ecosystems that depend on them at risk.

The Delta, which supplies water for two-thirds of Californians — nearly 25 million people — has experienced a collapse in native fish species that scientists blame partially on diversions for agricultural and urban use. In the Sierra Nevada, global warming is changing the snowpack and runoff patterns, threatening another large source of the state’s water supply.

With so much at stake, the University of California has made water one of its top research priorities. As UC scientists study the effects of temperature change and human activity on the state’s key water supplies, they are exploring solutions for balancing population needs with the long-term health of California's unique ecosystems.

In the Delta, native fish species are declining; six are listed as endangered or threatened. For 50 years, water at the southern part of the Delta has been exported for agriculture in the Central Valley and for millions of users in Southern California and San Francisco Bay Area cities. Fish can be sucked into the gigantic pumps used to divert water, but scientists surmise that altered river flows, in combination with pollution and invasive species, also have damaged the Delta’s ecology, leading to the collapse in fish populations.

In addition, many of the levees that protect islands in the south and central Delta are in danger of failing due to age, poor construction and rising sea levels. Maintaining most of these levees is not cost-effective and is a poor way of managing land and water, according to recent research studies.

Peripheral canal revisited

All these factors lead some scientists, including a group of UC Davis researchers, to support building a peripheral canal that would take water from the Sacramento River and bypass the Delta on its way to end users. A plan for a peripheral canal was voted down in 1982, largely by Northern California residents concerned about a Southern California water grab.

An advisory panel on the Delta, convened by Gov. Arnold Schwarzenegger, called for restoring the ecosystem, creating a more reliable water supply, promoting conservation and establishing an oversight commission to manage the vast waterway.

Five bills with goals similar to those of the governor’s Delta Vision panel are making their way through the state Legislature. The legislation includes a proposal to create a Delta Stewardship Council, which would have the authority to pursue restoration projects, including a peripheral canal.

The best thing for fish and the environment would be to stop pumping and water diversions, according to a 2008 research report. “We figure that’s not going to happen,” said Moyle, co-author of the Public Policy Institute of California Public Policy Institute of California report that calls for the construction of a peripheral canal and for allowing some Delta islands to flood permanently.

Proponents of a canal have the governor on their side. But opponents say a canal could lead to salt water incursions that would hurt the environment, farmers fear their irrigation allotments will be cut and many landowners of islands that would be flooded aren’t keen on the idea.

“If you have to export water, you can’t do what you’re doing today,” Moyle said. “The peripheral canal is one of few options that seem to make some sense.”

A canal would remove the effect of the pumps and restore a more natural water flow. It is also the most cost-effective way to manage water in a way that provides for human needs and the environment, concluded the 2008 report, which was written by Moyle with Jay Lund, William Fleenor, William Bennett, Richard Howitt and Jeffrey Mount from UC Davis and Ellen Hanak from the Public Policy Institute.

“This is one of these things that the devil is in the details. You have to do it in a smart way,” said Moyle, who's also associate director for the Center for Watershed Sciences at UC Davis, which conducts problem-solving research in restoration and water resource management, principally within the Central Valley, Sierra Nevada, Coast Range and San Joaquin Delta.

Surveying the snowpack

Climate change is putting another source of state water at risk. In the Sierra Nevada, global warming causes snowpacks to melt earlier in the year, which leads to less water for reservoirs during the dry summer months, according to Roger Bales, director of the Sierra Nevada Research Institute at UC Merced.

“The big concern is how and where the transition from snow to rain occurs, when and where it’s going to occur with climate warming, and what are we going to do about it as far as the changing water cycle,” Bales said.

Since 2004, researchers from UC Merced and other UC campuses have used satellite data, modeling and on-the-ground observations to take precise measurements of the snowpack, giving scientists a better picture of how much water is in the Sierra.

“We’re finding that more of the runoff comes from the higher elevations and there’s more snow at higher elevations than previously thought,” Bales said, “which is good for water supplies because it’s colder at higher elevations.”

Is more water up there?

Snow at high altitudes is less vulnerable to global warming, but generally is not measured, and the research is finding new technology that can measure the amount of snow and runoff. The data help water agencies predict how much supply they will have, which is vital to California’s cities, farms and the entire economy, Bales said.

“We’re providing a blueprint for a new water information system and for how to measure water supply and make forecasts in future,” he said.