As part of its work to bring climate science into the CALFED Bay-Delta Restoration Program, in Jan 2003 CAP (Cayan and Dettinger) organized a special session at the 2003 CALFED Science Conference in Sacramento. Abstracts from the session are shown below. This session is, in a sense, sequel to the session that CAP organized for the first CALFED Science Conference in 2000. Click here for the session report from the 2000 conference.

A Special Session for the

2nd Biennial CALFED Science Conference

Sacramento, 13-16 January 2003

CLIMATE SCIENCE ISSUES AND NEEDS OF THE CALFED BAY-DELTA PROGRAM

Click here for PDF of AMS preprint: "Climate Science Issues and Needs of the CALFED Bay-Delta Program"

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 success of the Program depends, among other factors, on the robustness of its plans to the buffeting that California's variable climate will inevitably impose upon it. The Bay-Delta watershed is affected by both the wet-Southwest and dry-Northwest influences of the El Nino-Southern Oscillation, the Pacific Decadal Oscillation, and other climatic influences that are less understood. In addition, observed warming of winter-spring temperatures and associated streamflow-timing trends in the past 50 years threaten to unsettle crucial aspects of the State's water supply system by adversely impacting the State's snowpacks and snowmelt runoff. Recent studies of California's paleoclimate also provide worrying evidence that the erratic precipitation regimes that have been observed (and largely accommodated) during California's development have been-by and large-benign and small compared to precipitation variations over the past 1000 years. Thus, California's climate varies in ways that CALFED should be prepared to accommodate, on time scales from years to decades, as evidenced in its past and present climates as well as in projections of its future climate. These climate fluctuations need to be characterized (i.e., monitored, predicted, projected, or described probabilistically), and the resulting characterizations need to be communicated, in order to provide a basis for scientifically sound planning by the CALFED Program. Examples of research and monitoring options that CALFED may need to pursue will be discussed.

THE RECORD OF NATURAL CLIMATE VARIABILITY OVER THE CENTRAL VALLEY WATERSHED

Malcolm K. Hughes and David M. Meko
Laboratory of Tree-Ring Research, University of Arizona

Natural archives of climate variability, such as tree rings and geomorphic features, show that the 20th century was not a representative sample of climate variability in the Central Valley watershed in recent millennia. Certain general conclusions may be drawn on the basis of currently available information.

The first is that, in several respects, the region's 20th century climate was unusually benign. Droughts were less severe and less persistent than in earlier times, for example in the period before AD 1500. There is strong evidence from several sources for multidecadal extreme droughts between AD 400 and 1500 in the central and southern Sierra Nevada unlike any in the last few centuries. Single-year droughts like that of 1977 occurred four times as frequently in some centuries. Some of these, for example, 1580, were markedly more severe than the 1977 drought. There is evidence that the sustained but less extreme drought of the late 1980s and early 1990s was weaker than hundreds of other droughts in the last 8000 years.

Secondly, this variability is neither completely random in time, nor strongly cyclical, but it does have much temporal structure. Some of the most severe multidecadal droughts in the central Sierra Nevada (e.g., in the 10th-14th centuries) probably coincided with wetter than average periods in Oregon and Northern California. Thus it is necessary to develop geographically explicit "pictures" of the spatial gradients of moisture and temperature anomalies to fully appreciate the variability of the climate of the Central Valley Watershed

Terrestrial records and others from the Bay itself provide an opportunity to test the reliability of models linking conditions in the mountains of the Central Valley watershed with those in the Bay, under a markedly wider range of conditions than observed in the 20th century.

PALEOCLIMATE CHANGES IN SAN FRANCISCO ESTUARY AND ITS WATERSHED

B. Lynn Ingram ¹, Frances Malamud-Roam ¹, and Malcolm Hughes ^2
1 Department of Earth and Planetary Sciences, University of California, Berkeley, CA
² Laboratory of Tree-Ring Research, The University of Arizona, Tucson, AZ

An understanding of the range of climate changes that are possible in the San Frnacisco Bay Estuary and watershed both from natural causes and as a result of global warming is important as the state's population continues to grow, placing ever-greater pressure on natural ecosystems and water quality. This review describes various paleoclimatic records from both the San Francisco Estuary and its watershed, spanning the past several thousand years. The records include those that reflect its physical systems (sedimentation patterns, hydrology and water quality) and its biological systems (the Estuary's tidal wetlands), as well as reconstructions of precipitation and temperature throughout the watershed. Bay sediment core records indicate that, while sea level rise over the past 5,000 years has produced a gradual increase in salinity moving eastward in the Estuary, this gradual change has been punctuated by periods of higher and lower salinity that are attributable to changes in regional precipitation. Marsh sediment cores reveal how changes in water salinity in the Estuary affected vegetation patterns, linking the physical and the biological systems. Records collected from the Bay/Delta Estuary and from its greater watershed suggest that the range of natural variability in California climate has included periods of prolonged drought, lasting from several decades to centuries long. However, evidence for such droughts is present in some records from the Sierra Nevada and in the Bay Estuary, but is missing in others. The last 150 years of American occupation of California may have been an anomalously wet period, which has profound implications for management of water resources and growth. Recommendations are given for areas for further research.

GEOMORPHIC RECORD OF CLIMATE VARIABILITY IN LOWLAND RIVERS IN THE BAY-DELTA WATERSHED

Joan Florsheim
Department of Geology, University of California, Davis, CA

Climate change and variability affect geomorphic processes, morphology, and the sediment budget of lowland river and floodplain systems in the Bay-Delta watershed. A review of geologic evidence and historical data illustrates that these lowland fluvial systems are located such that they are affected by either climate changes influencing the upstream watershed hydrology or downstream sea levels and base levels. Fluctuations of these upstream and downstream controls are recorded in both past and modern river and floodplain sediment deposits. For example, Holocene sediment strata illustrate variations in magnitudes and geomorphic type, presumably, in response to climate fluctuations; however, the chronology of sediment deposition has not yet been correlated with available paleoclimate records. Modern deposits are affected by pervasive anthropogenic disturbances. The current rigid structural control of the lowland fluvial system has altered geomorphic processes and degraded functions in the once dynamic ecosystems, and analysis of the geomorphic response to climate change over the historic period is complicated by the land use changes that occurred during the same period. Nonetheless, understanding the effects of past, current, and potential future climate variations on fluvial processes, morphology, and the sediment budget of lowland rivers is critical to development of scientifically sound adaptive management plans and restoration strategies for Central Valley river systems. In order to be successful, programs to rehabilitate geomorphic processes must create and maintain balanced sediment budgets and dynamic morphology that sustain healthy ecosystems. Such programs also must accommodate potentially increased variability and greater ranges of flood magnitudes resulting from global warming.

CLIMATE VARIABILITY--A REGIONAL STRESS ON CALIFORNIA'S WATER AND POWER SYSTEMS

Dan Cayan, Mike Dettinger, Noah Knowles, Dave Peterson
U.S. Geological Survey, Scripps Institution of Oceanography
La Jolla, and U.S. Geological Survey, Menlo Park, CA

Climate fluctuations are an environmental stress that must be factored into our designs for water resources, power, and ecosystem restoration. Under California's Mediterranean climate, winter and summer climate fluctuations both have important consequences. Winter climatic conditions determine the rates of water delivery to the State, and summer conditions determine most demands for water and energy. Both are dictated by spatially and temporally structured climate patterns over the Pacific and North America. Winter climatic conditions have particularly strong impacts on Bay/Delta water quality because the large freshwater flows through the Delta then overwhelm seaward salinities and set the stage for salinities during much of the year. It is thus noteworthy that precipitation from winter storms in California is more variable than in neighboring regions. For example, annual discharge from the Sacramento-San Joaquin system has a coefficient of variation (standard deviation/mean) of 44% compared to 19% in the Columbia and 33% in the Colorado basins. Also, in California, multi-year droughts occur more often than would be expected by chance, but wet years do not exhibit such persistence. A crucial aspect of California's climate stresses is that they influence conditions over broad spatial scales. Climate patterns that cause the State's climate fluctuations typically reach well beyond its boundaries. This breadth affects California because much of the energy and water used here is supplied by distan parts of the State as well as from the Northwest and Southwest. When dry winters occur in the Sierra Nevada, they also tend to occur in the Columbia and Colorado basins. These regional scales, coupled with California's reliance on resources from an especially broad region, including power from the Columbia and Colorado basins and water from the Colorado, make the State especially vulnerableto climate fluctuations. These vulnerabilities are likely to grow as the State and Region's populations and demands for resources grow.

POTENTIAL EFFECTS OF GLOBAL WARMING ON THE SACRAMENTO / SAN JOAQUIN WATERSHED AND THE SAN FRANCISCO ESTUARY

Noah Knowles and Dan Cayan
U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla and Menlo Park, CA

California's primary hydrologic system, the San Francisco estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. An understanding of the potential impacts is necessary to prepare mitigation strategies. Projected temperature anomalies from a global climate model are used to drive a combined model of watershed hydrology and estuarine dynamics. By 2090, a projected temperature increase of 2.1ºC results in a loss of about 1/2 of the average April snowpack storage, with greatest losses in the northern headwaters. Consequently, spring runoff is reduced by 5.6 km2, with associated increases in winter flood peaks. The smaller spring flows yield spring/summer salinity increases in the estuary of about 5 psu, with larger increases in wet years. Mitigating the impacts of climate change is likely to be more difficult in wet years.

DISTRIBUTED CLIMATE CHANGE HYDROLOGIES FOR MODELING WATER MANAGEMENT IN CALIFORNIA

Tingju Zhu, Marion W. Jenkins, Jay R. Lund
Department of Civil and Environmental Engineering, University of California, Davis

Many studies exist of potential climate change in California, most focusing exclusively on streamflow changes, either macroscopically or on a few selected streams. While water management implications often are discussed and sometimes are modeled for fragments of California's complex inter-tied system, these studies have not prepared hydrologic estimates of sufficient breadth or detail for understanding how management of California's vast integrated surface and groundwater system might adapt to climate change. As part of a California Energy Commission study of adaptation to climate change in California, spatially disaggregated estimates of over 160 streamflow, groundwater, and reservoir evaporation locations have been created for 12 different climate change scenarios. These distributed fluxes are based on analysis of six index basins and the statewide temperature shifts and precipitation change ratios for twelve climate change scenarios developed by Lawrence Berkeley National Lab. The 12 distributed climate change hydrologies are being used for water management modeling using an economic-engineering optimization model for water in California (CALVIN) using forecast 2100 water demands. Most climate change studies indicate that California may endure wetter winters and drier summer over the next century. CALVIN modeling will indicate the ability of California's water system to adapt to such changes. Without such operation modeling, approximate changes in water availability have been estimated for the 12 climate change scenarios. These changes are compared with estimated changes in urban and agricultural water uses between now and 2100. The magnitudes of these climatic and water demand changes have potentially important implications for the long-term success and sustainability of CALFED water supply and environmental restoration programs.

YOGI BERRA WAS RIGHT: PREDICTING THE EFFECTS OF CLIMATE CHANGE ON THE SAN FRANCISCO ESTUARY

Wim Kimmerer
Romberg Tiburon Center, Tiburon, CA

Recent research has improved confidence in predictions of global change. Regional forecasts are less certain because of uncertainty in forecasts of regional responses to global effects, the influence of local anthropogenic effects, and compensating effects of different mechanisms. For example, a predicted shift toward earlier precipitation in the Sierra Nevada will affect seasonal patterns of river flow and estuarine salinity. However, total precipitation could either increase or decrease with increasing temperature. In addition, local human activities may affect the San Francisco Estuary more strongly and rapidly than those arising through global influences. Important human influences include a long-term reduction in sediment input, current and historical contaminant loading, invasive species, modification of freshwater flow patterns, and large-scale restoration. Urban population is likely to increase, accelerating the pace of these changes in the estuary.

Attempting to predict the net effect of all these changes on the estuarine ecosystem reveals several difficulties. For example, rising sea level combined with an increase in strong wind events and storm surges should increase resuspension, erosion, and turbidity. Conversely, the net sediment deficit should reduce turbidity, resulting in higher phytoplankton growth and nutrient uptake rates. However, unpredictable changes in the overriding influence of benthic filter-feeding may overwhelm these other effects on phytoplankton. Responses of higher trophic levels will probably be even more complex. Many species respond positively to flow, and could be adversely affected by reductions in spring flow. Others may be affected by multiple pathways, such as by changes in river and ocean temperature, timing of runoff, changes in management and hatchery practices, or habitat restoration. Without considering the multiplicity of causal pathways and uncertainties in each, predictions of even the sign of long-term changes in the estuarine ecosystem will remain elusive.

EFFECTS OF CLIMATE CHANGE ON FISH POPULATIONS OF THE SAN FRANCISCO ESTUARY

W.A. Bennett ^1,2
1 John Muir Institute of the Environment, ² Bodega Marine Laboratory, University of California, Davis

Evidence of broad fluctuations in recent and historical climate indicates the urgency for CALFED to develop management plans that anticipate the likely responses of fish populations to future changes. Climate induced effects can be difficult to identify in an estuary with highly variable environmental properties and more apparent human interventions (e.g. water exports, toxic chemicals). However, unless potential responses to changing climate are anticipated and recognized, they could undermine CALFED rehabilitation efforts. This calls for the development of a framework to characterize the diverse pathways in which climate change affects fishes. Two broad classes of effects are described: direct effects on individual physiology and behavioral ecology, as well as indirect effects arising from changes in ecosystem and food web dynamics. In general, direct effects on populations are more likely to be detected (easier to assess with monitoring data) than those associated with ecosystem and community-level functioning. Direct and indirect effects are described in the context of recent inter-annual (El Nino-Southern Oscillation) and inter-decadal (Pacific Decadal Oscillation) climate variability. Changes in water temperatures are directly linked to alterations in migration patterns, long-term decline, and recent resurgence of striped bass, as well as regulation of the delta smelt spawning season and subsequent year-class success. Indirect effects on fish populations can manifest through extremes in freshwater outflow (droughts and floods), rising sea-level, and establishment of invasive species that can regulate the persistence of estuarine habitats and reconfigure estuarine food web structure. These examples illustrate the importance of considering potential effects of climate change so that management and rehabilitation actions are applied accurately to fish populations.

CLIMATE CHANGE AND THE SCIENCE-POLICY INTERFACE-A CASE STUDY OF CALIFORNIA WATER POLICY

M.J. Kiparsky and P.H. Gleick
Pacific Institute for Studies in Development, Environment and Security, Oakland, CA

California was the subject of some of the first studies projecting the impacts of climate change on water resources fifteen years ago. Since then, the topic has been discussed in over 100 publications, which indicate the need for water managers to begin seriously considering possible consequences of climate change and ways of mitigating the worst impacts through better planning and management. We analyze both peer-reviewed and gray literature from a variety of disciplines. While uncertainties remain about the direction and magnitude of some impacts, both groups of literature paint a consistent picture of some of the projected impacts of climate change on the State's water resources. We document and analyze the response of policymakers to this information at the levels of state government and state and local agencies, including CALFED. Some impacts, such as earlier melting of the Sierra snowpack, indicate the clear need for better planning and for rethinking water resources operations statewide. Although policy-making bodies have been aware of these projections, policy responses have been slow to materialize. We discuss the implications of our findings for the science-policy interface