The Sacramento-San Joaquin Delta Future

USGS scientists and academic colleagues have investigated how California’s interconnected San Francisco Bay and Sacramento-San Joaquin Delta (the Bay-Delta system) is expected to change from 2010 to 2099 in response to both fast and moderate climate warming scenarios. Results indicate that this area will feel impacts of global climate change in the next century with shifts in its biological communities, rising sea level, and modified water supplies. “The protection of California’s Bay-Delta system will continue to be a top priority for maintaining the state’s agricultural economy, water security to tens of millions of users, and essential habitat to a valuable ecosystem,” said USGS Director Marcia McNutt. “This new USGS research complements ongoing initiatives to conserve the Bay-Delta by providing sound scientific understanding for managing this valuable system such that it continues to provide the services we need in the face of climate uncertainty.”

The Sacramento-San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in northern California in the United States. The Delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and San Joaquin rivers and lies just east of where the rivers enter Suisun Bay (an upper arm of San Francisco Bay). The Delta is recognized for protection by the California Bays and Estuaries Policy. The city of Stockton is located on the San Joaquin River on the eastern edge of the delta.

The Sacramento-San Joaquin River Delta is an example of an inverted river delta, one of only a few worldwide. It is the largest estuary on the United States’ Pacific Coast. The fan-like area of the delta moves downstream, as the two rivers are forced to exit the Central Valley through the Coast Range via the narrow channel known as the Carquinez Strait, which leads to the San Francisco Bay and mainly the Pacific Ocean through the Golden Gate.

The new USGS study provides the first integrated assessment of how the Bay-Delta system will respond to climate change. Results show that the combined effects of increasing water temperature and salinity could reduce habitat quality for native species, such as the endangered Delta smelt and winter-run Chinook salmon, and intensify the challenge of sustaining their populations. The study indicates that water-resource planners will need to develop adaptation strategies to address potentially longer dry seasons, diminishing snow packs and earlier snowmelt leaving less water for runoff in the summer. The study also describes risk from flooding as sea-level rise accelerates and extreme water levels become increasingly common. Increased intensity and frequency of winter flooding could also occur as a result of earlier snowmelt and a shift from snow to rain.

The Delta provides drinking water to 25 million people and irrigation water to farmland producing crops valued at $36 billion per year. Intensive efforts are underway among the USGS, the Bureau of Reclamation, the Fish and Wildlife Service, NOAA, and the State of California to address what will be increasingly difficult decisions regarding allocations of water for human consumption and biological needs.

The report’s findings provide new information that can inform planning of next steps in collaborative initiatives such as the Bay Delta Conservation Plan and contribute to the science foundation underlying the Delta Stewardship Council’s Delta Plan.

Results of this study were recently published in the journal, PLoS ONE. The article, Projected Evolution of California’s San Francisco Bay-Delta-River System in a Century of Climate Change, is available online.

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Article by Andy Soos, appearing courtesy Environmental News Network.

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