Climate Science issues and needs of the CALFED Bay-Delta Program

To be presented at the 83rd American Meteorological Society (AMS) Annual Meeting, February 2003:
click here for PDF of AMS preprint, excerpts are below

Michael Dettinger¹, William Bennett², Daniel Cayan¹, Joan Florsheim³, Malcolm Hughes⁴, B. Lynn Ingram⁵, Noah Knowles¹, Frances Malamud-Roam⁵, David Peterson⁶, Kelly Redmond⁷, and Lawrence Smith⁸

¹ US Geological Survey, Scripps Institution of Oceanography, La Jolla, CA
² Bodega Marine Laboratory, University of California, Davis, CA
³ Department of Geology, University of California, Davis, CA
⁴ Laboratory of Tree-Ring Research, The University of Arizona, Tucson, AZ
⁵ Department of Earth and Planetary Sciences, University of California, Berkeley, CA
⁶ US Geological Survey, Menlo Park, CA
⁷ Western Regional Climate Center, Desert Research Institute, Reno, NV
⁸ US Geological Survey, Sacramento, CA

The San Francisco Bay/Sacramento-San Joaquin Delta system provides habitat for approximately 750 plant and animal species, drinking water for 22 million people, and irrigation supplies for at least $27 billion in agriculture. The CALFED Bay-Delta Program is developing comprehensive plans to accomplish four ambitious objectives:

1. Improve the reliability of water supplies in California,
2. Improve water quality in the Bay-Delta system,
3. Restore ecosystems within the Bay/Delta watershed, and
4. Stabilize Delta levee systems,

The San Francisco Bay/Sacramento-San Joaquin Delta system is the largest estuary on the West Coast and is central to California's water economy and ecosystem. The Delta encompasses 3000 km² of tidal to freshwater wetlands, agricultural lands, and river/estuarine channels at the confluence of the Sacramento and San Joaquin Rivers in central California (see figure below).

Shaded, raised relief view of cental California, looking eastward; the figure shows most of the watershed of the Bay-Delta watershed, with San Francisco Bay, the Delta, and the Central (Sacramento-San Joaquin) Valley in the middle, the Pacific Ocean and California's Coast Ranges in the forecground, the Sierra Nevada in the background.

Freshwater discharge through the Delta -- which captures 42% of California's runoff (Marandi 1998) -- feeds San Francisco Bay and partially flushes ocean salt from the estuary's waters. California's Mediterranean climate and its propensity to fluctuate on a wide range of time and space scales play a crucial role in establishing the variability of those discharges, salinities, and the state of the Bay and Delta's ecosystems and other resources.

The Bay-Delta system provides drinking wate for two-thirds of the State's population (22 million people), irrigation supplies for at least $27 billion in agriculture (45% of the Nation's produce), and is a primary water source for California's trillion-dollar economy (CALFED 2001). About 6 km ³/yr of freshwater are pumped from the Delta by the federal Central Valley Project and the State Water Plan to supply municipal and agricultural water demands in southern and central California (California Department of Water Resources 1993).

The success of the CALFED Program depends upon the robustness of its plans and actions to the considerable buffeting that California's highly variable climate will inevitably impose upon it. This watershed straddles the transition zone between the wet-Southwest and dry-Northwest influences of the El Niño-Southern Oscillation, as well as their interdecadal expressions in the Pacific Decadal Oscillation and other short- and (especially) long-term influences that are less understood (Cayan and Webb 1992, Mantua et al. 1997). Superimposed upon these climate fluctuations is a recent observed warming trend in winter-spring temperatures and associated streamflow-timing trends (Dettinger and Cayan 1995). These trends are either harbingers or analogs for future global warming effects in the State. Recent studies of California's paleoclimate also provide worrying evidence that the erratic precipitation regimes that have been observed during California's development have been -- by and large -- benign and small in comparison to natural precipitation variations over the past 1000 or more years (e.g., Meko et al. 2001).

Thus, California's climate has varied in the past in ways that CALFED must acknowledg and somehow accomodate on time scales from years to decades. The climate that CALFED faces during its planned 30-year lifetime and over the much longer period that it will eventually influence most likely will be some combination of the kinds of climate variability evidenced in California's paleoclimate proxies, in its historical period, and in recent climate-change projections (see below, left).

Conceptual diagrams of the intermingling contributions of past, present, and future climate variability to a realistic depiction of CALFED's climatic setting (left) and relative uncertainties regarding possible ranges of climatic variability as estimated from paleoclimatic sources, historical sources, and global-warming projections (right).

Some of the key climatic issues facing the CALFED Bay-Delta Program are:

Paleoclimates and CALFED

How has climate varied in the California region over the past several thousand years on seasonal, interannual, decadal, and centennial scales?

What effects did past climate changes have on energy, water, sediment, biogeochemical budgets and distributions throughout the Bay-Delta system?

What effects did past climate variability and physical effects of climate variability have on Bay-Delta and watershed ecosystems?

How could current water-supply operational programs, water quality, physical hazards, and ecosystem management have coped with past climate variations?

Historical Climate and CALFED

How does the estuary/watershed system vary in response to climate fluctuations? How much of the current Bay-Delta variability is due to climate?

What are the main linkages between climate variability and water-supply operations, water quality, sediment transport, and ecosystems?

How might climate forecasts, ranging from days to decades, be used to benefit and augment CALFED activities?

Climate Monitoring and CALFED

Is the existing climate-monitoring network in California sufficient, timely, and stable enough to provide CALFED's long-term informational needs?

Are all physical, chemical, and biological variables needed by CALFED being monitored at necessary temporal and spatial sampling resolutions? If climate changes, will its effects be evident in the current networks?

What technical and communication mechanisms are required to provide a sound climate-science basis for all parties in the CALFED decision making process, including the public?

Future Climate and CALFED

What are the full-plausible -- and most-likely -- ranges of climate variation, including sea-level rise, in California during the next 100 years?

How will climate changes vary within the watershed of the Bay-Delta?

How will future climate variations and changes affect energy, water, sediment, biogeochemical, and contaminant budgets and distributions within the Bay-Delta system?

How will likely future climate changes, and hydrologic and biogeochemical responses, affect wetlands, water quality, estuarine and riparian systems, and fish populations?

How will likely future climate changes, and hydrologic and biogeochemical responses, affect water-supply operations and reliability?

References

CALFED, 2001: Annual Report 2001. CALFED Bay-Delta Program, Sacramento, 78p.

California Department of Water Resources, 1993: Sacramento-San Joaquin Delta Atlas. The Resources Agency, Sacramento, 121p.

Cayan, D., and R. Webb, 1992: El Niño/Southern Oscillation and streamflow in the western United States, in Diaz, H.F., and V. Markgraf (eds.), El Niño: Historical and Paleoclimatic Aspects of the Southern Oscillation. Cambridge University Press, 29-68.

Dettinger, M., and D. Cayan, 1995: Large-scale atmospheric forcing of recent trends toward early snowmelt in California. J. Clim., 8, 606-623.

Mantua, N., S. Hare, Y. Zhang, J. Wallace and R. Francis, 1997: A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. American Meteorological Society, 78, 1069-1079.

Meko, D., M. Therrell, C. Baisan and M. Hughes, 2001: Sacramento River flow reconstructed to AD868 from tree rings. J. American Water Resources Association, 37, 1029-1040.