San Francisco Bay

Climate Change and the Delta: A Synthesis (Public Review Draft)

Delta Stewardship Council (Delta Council) | March 23rd, 2018

The Delta Reform Act of 2009 (Water Code Section 85066) requires that the Delta Stewardship Council adopt a Delta Plan (the Plan) to achieve the coequal goals of providin

The Delta Reform Act of 2009 (Water Code Section 85066) requires that the Delta Stewardship Council adopt a Delta Plan (the Plan) to achieve the coequal goals of providing a more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem (Water Code Section 85000). In the time since the Plan was adopted in 2013, a significant shift in State planning for Delta ecosystem protection, restoration, and enhancement has occurred, prompting review of the Delta Plan to  examine whether its strategies are still suited to achieve the ecological goals of the Delta Reform Act. As such, the Delta Stewardship Council (Council) is developing an amendment of the Plan’s Chapter 4, Protect, Restore, and Enhance the Delta Ecosystem. Council staff are reviewing the best-available science to inform amendment of Chapter 4 of the Delta Plan. To support this effort, Council staff have developed three science  synthesis papers. This paper focuses on the effects of climate change in the Delta and is accompanied by two other papers focused on the Delta ecosystem (terrestrial and  aquatic resources) and restoration. Climate change is of interest for the Chapter 4  amendment given recent rapid advancements in research on climate change and its  effects on the Delta ecosystem that have occurred since the Delta Plan was adopted in  2013 (Dettinger et al. 2016). Climate change has the potential to significantly affect the Delta ecosystem by raising  air and water temperatures, changing the timing and volume of flows into and through  the Delta, increasing tidal inundation with sea-level rise (SLR), and increasing salinity  intrusion into the Delta. Climate change is recognized as a global stressor in Chapter 4 of the 2013 Delta Plan, but the effects of climate change on Delta ecosystems are  discussed only briefly and with limited consideration of management strategies that address the issue. Chapter 4 of the Delta Plan identifies five key stressors to the Delta  ecosystem and core strategies for addressing each. Climate change has interrelated  effects on all five core strategy areas: Delta flows, habitat, water quality, non-native 28 species, and hatcheries and harvest management. The Delta Reform Act specifies consideration of “the future impact of climate change and sea-level rise” (Water Code Section 85066), and identifies a restoration timeline horizon of 2100 (Water Code Section 85302). More generally, Executive Order B-30-15, signed by Governor Brown in April 2015, requires that State agencies incorporate climate change into planning and investment decisions, and that they prioritize natural infrastructure and actions for climate preparedness.

Climate Change Impacts, Vulnerabilities, and Adaptation in the San Francisco Bay Area: A Synthesis of PIER Program Reports and Other Relevant Research

California Research Bureau (CRB) | July 31st, 2012

This paper synthesizes San Francisco Bay Area-focused findings from research conducted in 2010–2012 as part of the state’s Vulnerability and Adaptation study sponsore

This paper synthesizes San Francisco Bay Area-focused findings from research conducted in 2010–2012 as part of the state’s Vulnerability and Adaptation study sponsored by the California Energy Commission’s Public Interest Energy Research (PIER) Program. Historical observations of changes already evident are summarized, as well as projections of future changes in climate based on modeling studies using various plausible scenarios of how emissions of heat-trapping gases in the atmosphere may change. Studies synthesized here show how these climate changes increase risks to society and natural ecosystems in a number of ways. Sectors for which impacts, vulnerabilities, and adaptation options are presented include water, agriculture, energy supply and demand, transportation, ecosystems, public health, wildfire, and coastal resources. Results show that depending on the vulnerability of human and natural communities, and their abilities to respond to these growing risks through adaptive changes, the San Francisco Bay Area could experience either significant impacts or maintain its resilience in the face of a rapidly changing environment.

Climate change is increasing the likelihood of extreme autumn wildfire conditions across California

Environmental Research Letters (IOP) | August 20th, 2020

California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of stro

California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of strong offshore winds coincident with unusually dry vegetation enabled by anomalously warm conditions and late onset of autumn precipitation. In this study, we quantify observed changes in the occurrence and magnitude of meteorological factors that enable extreme autumn wildfires in California, and use climate model simulations to ascertain whether these changes are attributable to human-caused climate change. We show that state-wide increases in autumn temperature (~1 °C) and decreases in autumn precipitation (~30%) over the past four decades have contributed to increases in aggregate fire weather indices (+20%). As a result, the observed frequency of autumn days with extreme (95th percentile) fire weather—which we show are preferentially associated with extreme autumn wildfires—has more than doubled in California since the early 1980s. We further find an increase in the climate model-estimated probability of these extreme autumn conditions since ~1950, including a long-term trend toward increased same-season co-occurrence of extreme fire weather conditions in northern and southern California. Our climate model analyses suggest that continued climate change will further amplify the number of days with extreme fire weather by the end of this century, though a pathway consistent with the UN Paris commitments would substantially curb that increase. Given the acute societal impacts of extreme autumn wildfires in recent years, our findings have critical relevance for ongoing efforts to manage wildfire risks in California and other regions.

Climate change is increasing the risk of a California megaflood

American Association for the Advancement of Science (AAAS) | August 12th, 2022

Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. Here, we investigate the physical characteristics of

Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. Here, we investigate the physical characteristics of “plausible worst case scenario” extreme storm sequences capable of giving rise to “megaflood” conditions using a combination of climate model data and high-resolution weather modeling. Using the data from the Community Earth System Model Large Ensemble, we find that climate change has already doubled the likelihood of an event capable of producing catastrophic flooding, but larger future increases are likely due to continued warming. We further find that runoff in the future extreme storm scenario is 200 to 400% greater than historical values in the Sierra Nevada because of increased precipitation rates and decreased snow fraction. These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.

Climate change is narrowing and shifting prescribed fire windows in western United States

Nature Portfolio (Springer Nature) | October 3rd, 2023

Climate Change Risks Faced by the California Central Valley Water Resource System

California Energy Commission (CEC) | ?

Observed climate trends and projections of accelerated future change have motivated several studies of the impacts of climate change on water resources management in Cal

Observed climate trends and projections of accelerated future change have motivated several studies of the impacts of climate change on water resources management in California. This paper presents a methodology that improves on previous approaches, revealing fundamental climate change risks to one of the State of California’s key water resource systems — the integrated California Central Valley System (CCVS). By using a bottom-up decision scaling approach, starting with a systematic climate change stress test of the performance of the system to changes in temperature and precipitation, specific vulnerabilities to the system are identified. This study also improves on previous water resource vulnerability analyses by incorporating and evaluating a much wider range of inter-annual precipitation variability than has previously been used. By drawing from the 1,100-year (reconstructed dendrochronology) record of Sacramento and San Joaquin river flows, vulnerabilities to low frequency natural climate variability are analyzed in concert with expected potential climate changes. The results of this analysis provide a comprehensive summary of the sensitivity of the system to climate change. This paper provides results and discussion of select future system performance metrics at 2050. Results indicate that declines in almost every category (e.g., supply, storage, delta outflow) of system performance are likely. The likelihood of severely degraded future performance is especially high for north-of-Delta carryover storage and Delta exports. The results of this study are expected to provide water managers and decision-makers with more actionable science because they provide probabilistic results that can be used in more traditional risk management approaches to planning of climate change adaptation investment decisions.

Climate Change Scenarios for Air and Water Temperatures in the Upper San Francisco Estuary: Implications for Thermal Regimes and Delta Smelt

University of California, Davis (UC Davis) | June 10th, 2024

Climate Change Scenarios for the San Francisco Region

California Energy Commission (CEC) | July 31st, 2012

Climate model simulations were used to investigate possible changes in regional climate over California. To accomplish this, the model simulations were downscaled from th

Climate model simulations were used to investigate possible changes in regional climate over California. To accomplish this, the model simulations were downscaled from the coarse global climate model resolution (usually 150 kilometers [km] or greater horizontal grid spacing) to about 12 km horizontal grid spacing over the California region, using statistical techniques. The global model output was used in a statistical modeling scheme to produce sea-level projections for selected California coastal sites. Six global climate models and two greenhouse emissions scenarios, the medium-high emissions Special Report on Emissions Scenarios (SRES) A2 and the lower emissions SRES B1 were considered. By the end of the twenty-first century, the envelope of warming in the models projections, as an annual average, ranges from about 2°C to 6°C (about 3.5 °F to 11°F). On average, mean annual temperature of the A2 scenarios is about 1.5°C (about 3°F) greater than that of the B1 scenario. There is greater warming in summer than in winter. All simulations indicate that hot daytime and nighttime temperatures (heat waves) increase in frequency, magnitude, and duration from the historical period and during the projected period through the first half of the twenty-first century. Projected precipitation is marked by considerable variability between years and decades. In the southern half of California, the models show a decline in annual precipitation. Sea level, at hourly intervals for the historical through the projected twenty-first century, is estimated for selected tide gage sites along the California coast, with rises in the sample of simulations considered here ranging from 27 to 48 centimeters (cm) (11 to 19 in) over historical levels by 2050, and ranging from 77 cm to 140 cm (30 to 55 in) over historical levels by 2100. The rise of mean sea level would provoke an increase in extreme events, as gaged by exceedances above a relatively high or rare historical threshold. Such events become much more frequent and have longer durations than has been seen historically.

Climate Warming and Water Management Adaptation for California

Climatic Change (Springer) | June 10th, 2010

The ability of California’s water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate

The ability of California’s water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate scenario are examined with population and land use estimates for the year 2100 using a statewide economic-engineering optimization model of water supply management. Methodologically, the results of this analysis indicate that for long-term climate change studies of complex systems, there is considerable value in including other major changes expected during a long-term time-frame (such as population changes), allowing the system to adapt to changes in conditions (a common feature of human societies), and representing the system in sufficient hydrologic and operational detail and breadth to allow significant adaptation. While the policy results of this study are preliminary, they point to a considerable engineering and economic ability of complex, diverse, and intertied systems to adapt to significant changes in climate and population. More specifically, California’s water supply system appears physically capable of adapting to significant changes in climate and population, albeit at a significant cost. Such adaptation would entail large changes in the operation of California’s large groundwater storage capacity, significant transfers of water among water users, and some adoption of new technologies.

Climate-Altered Wetlands Challenge Waterbird Use and Migratory Connectivity in Arid Landscapes

Nature Portfolio (Springer Nature) | March 15th, 2019

Wetlands in arid landscapes provide critical habitat for millions of migratory waterbirds across the world and throughout their annual cycle. The scope and scale

Wetlands in arid landscapes provide critical habitat for millions of migratory waterbirds across the world and throughout their annual cycle. The scope and scale of understanding avian use of these wetlands in conjunction with changes in climate are daunting yet critical to address lest we lose continent-wide migratory pathways. Here, we assess changes in waterbird use of North America’s Pacific Flyway in the Great Basin by examining water availability and climate trends over the past 100 years. We found recent (1980–2015) climate warming has significantly reduced the amount and shifted seasonality of water flowing into wetlands. Further, we found remarkable changes in waterbird species composition over time. We propose that a reduced hydroperiod and lower water quality from reduction in water level and flow limits sites used by waterbirds. These factors reduce chick survivorship as they cannot metabolize saline water, which makes suitable freshwater conditions a limiting resource. Collectively, climate-induced changes in Great Basin wetlands suggest a major shift in freshwater ecosystems, resulting in degradation of a continental migratory route. This work illustrates the importance of examining multi-scale changes in critical regional resources to understand their impact across a hemispheric flyway and provides a model to examine other flyways.