Integrated Science Project Explores Bay-Delta Responses to Climate Change

As global warming continues over the next several decades, the ecological pressure on the San Francisco Bay and Sacramento-San Joaquin Delta will intensify, increasing the risk of extinction of some species, according to a first-of-its-kind study recently published.

The Delta Science Program supported study, Computational Assessments of Scenarios of Change for the Delta Ecosystem (CASCaDE), explored cascading effects of global climate change on the system-a “flash forward” to what the Bay and Delta could become by the end of this century.

This U.S. Geological Survey (USGS)-led project investigated how the Bay-Delta system could change from 2010 to 2099 in response to scenarios of fast and moderate warming by linking a wide range of models -- from climate to hydrology to sediment transport to habitat quality. Results indicate that the Bay-Delta system will experience effects of global climate change through shifts in its biological communities, rising sea level, and modified timing and amounts of river flows.

The study “provides the first integrated assessment of how the Bay-Delta system will respond to climate change,” according to a USGS statement. “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, flashier flows during winter, diminishing snow packs and earlier snowmelt, leaving less water for runoff in the summer.

“As we plan for the future, it is important to consider more than just global warming,” said the study’s lead author, USGS scientist Jim Cloern. “We also have to consider other drivers such as land-use changes and population growth. A comprehensive assessment of the future looks at responses to global warming in the context of all factors that will change the resources we value.”

CASCaDE also describes risk from flooding as sea-level rise accelerates and extreme water levels become increasingly common. According to the report, 270,000 people and $62 billion of development are at risk of flooding in the San Francisco estuary and watershed. Increased intensity and frequency of winter flooding could also occur as a result of earlier snowmelt and a shift from snow to rain.

In addition to providing future visions of the Bay-Delta system, this research provides “general lessons to guide development of adaptation strategies for coping with climate change in other coastal landscapes,” the USGS statement said. “Anticipation, flexibility, and adaptability will be the keys to the success of those strategies.”


“Anticipation, flexibility, and adaptability will be the keys to the success of [adaptation] strategies [to climate change].”

--U.S. Geological Survey


“This new USGS research complements ongoing initiatives to conserve the Bay-Delta [such as the Bay Delta Conservation Plan and the Delta Plan] 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,” said Marcia McNutt, USGS Director.

In the next phase of the study, CASCaDE II, recently funded by the Delta Science Program and USGS Priority Ecosystems Science, researchers propose to refine and extend the modeling capabilities from CASCaDE I to assess Delta ecosystem response to changes in climate and physical configuration. With a new state-of-the-art hydrodynamic and sediment model at its core, CASCaDE II will link models of climate, hydrology, hydrodynamics, sediment, geomorphology, phytoplankton, bivalves (e.g., clams), contaminants, marsh accretion, and fish.

The researchers’ goals are to apply these linked models to: 1) better understand Delta ecosystem function, 2) assess possible futures of the Delta under scenarios of climate and structural change, and 3) provide science-based information to support the Delta Stewardship Council in attaining its coequal goals of providing a more reliable water supply and protecting, restoring and enhancing the Delta ecosystem. The tools developed will provide an objective basis for anticipating and diagnosing Delta ecosystem responses to planned and unplanned changes. Experiments using the linked models are designed to address questions such as: How will climate change, together with new conveyance structures or increased wetland or flooded island habitat, alter water flow and drinking water quality? With projected changes in residence time, turbidity, temperature, and salinity, how will primary productivity, invasive bivalves, marsh processes, contaminant dynamics, and fish populations respond?

Results of the CASCaDE I 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 here.