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Adaptation to climate change requires careful evaluation of infrastructure performance under future climatic extremes. This study demonstrates how a multidisciplinary approach integrating geotechnical engineering, hydrology, and climate science can be employed to quantify site-specific impacts of climate change on geotechnical infrastructure. Specifically, this paper quantifies the effects of changes in future streamflow on the performance of an earthen levee in Sacramento, California, considering multiple modes of failure. The streamflows for historical (1950–2000) and projected (2049–2099) scenarios with different recurrence intervals were derived from routed hydrological simulations driven by bias-corrected global climate models. The historical and future flood levels were then applied in a set of transient coupled finite-element seepage and limit equilibrium slope stability analyses to simulate the levee subjected to extreme streamflow. Variability in hydraulic and mechanical properties of soils was addressed using a Monte Carlo sampling method to evaluate and compare the probability of failure of the levee under different historical and future climate scenarios. Three individual modes (underseepage, uplift, and slope stability) along with lower and upper bounds for the combined mode of failure were examined. The results showed that incorporating future floods into levee failure analysis led to considerable reductions in the mean factor of safety and increases in the levee's probability of failure, suggesting that risk assessment based on historical records can significantly underestimate the levee's failure probability in a warming climate. Despite inherent uncertainties in future projections and substantial variability across climate models, evaluating infrastructure against projected extremes offers insights into their likely performance for the future. [ABSTRACT FROM AUTHOR]

The loss of biodiversity and biotic homogenization are on the rise in ecosystems around the world as a result of species invasions, habitat degradation, and the effects of climate change. In the Sacramento–San Joaquin Delta, nonnative species make up the majority of the fish community, and declines in native species have been well documented; however, little is known about whether these trends have resulted in biotic homogenization. In this study, we used data from a long-term beach seine survey to analyze regional beta diversity trends of nearshore fish assemblages in the Delta from 1995 to 2019. Overall, we found no evidence of regional biotic homogenization occurring over the study period. Regional beta diversity increased moderately over time and was significantly influenced by the high interannual variability of freshwater inflow. These beta diversity patterns were driven by the non-native Mississippi Silverside that has proliferated in the system in recent years, but also by a handful of native fish species such as the Sacramento Sucker, Tule Perch, and Splittail. Overall, our results offer a contrast to other highly invaded ecosystems around the world and suggest that despite the near extinction of some native fish species, there remain pockets of suitable habitat in the Delta that may play a key role in the conservation of remnant native fish diversity. [ABSTRACT FROM AUTHOR]

This paper is among the first to report on the full integration of basin-scale models that include projections of the demand and supply of water and energy for residential, commercial, industrial, and agricultural sector users. We link two widely used regional planning models that allow one to study the impact of rising climate variability on water and electricity use in Sacramento, California. Historic data combined with the current energy and water system configuration was used to assess the implications of changes in temperature and precipitation. Climate simulations suggest that electricity imports to the region would increase during hot dry spells, when regional power production is most constrained. In particular, regional imports of electricity would increase over 35 % in hot dry years, assuming a 4 °C increase in average temperature and a 25 % decrease in average precipitation. [ABSTRACT FROM AUTHOR]

Ecosystems in the Sacramento-San Joaquin Delta are changing rapidly, as are ecosystems around the world. Extreme events are becoming more frequent and thresholds are likely to be crossed more often, creating greater uncertainty about future conditions. The accelerating speed of change means that ecological systems may not remain stable long enough for scientists to understand them, much less use their research findings to inform policy and management. Faced with these challenges, those involved in science, policy, and management must adapt and change and anticipate what the ecosystems may be like in the future. We highlight several ways of looking ahead--scenario analyses, horizon scanning, expert elicitation, and dynamic planning--and suggest that recent advances in distributional ecology, disturbance ecology, resilience thinking, and our increased understanding of coupled human-natural systems may provide fresh ways of thinking about more rapid change in the future. To accelerate forward-looking science, policy, and management in the Delta, we propose that the State of California create a Delta Science Visioning Process to fully and openly assess the challenges of more rapid change to science, policy, and management and propose appropriate solutions, through legislation, if needed. [ABSTRACT FROM AUTHOR]

The Sacramento-San Joaquin Delta is an important region for bird conservation in California, particularly as part of a large, productive estuary on the Pacific Flyway. The Delta currently provides habitat to an abundant, diverse community of birds, but it is likely only a small fraction of what the Delta's bird community once was. Meeting the goal of restoring a healthy Delta ecosystem is legislatively required to include providing habitat for birds among the conservation goals and strategies in the Delta Plan, yet birds and their habitat needs are often not addressed in science syntheses, conservation planning, and large-scale restoration initiatives in the Delta. In this essay, we provide an avian perspective on the Delta, synthesizing recent scientific work to describe factors that contribute to the Delta's current importance for birds, and the conservation needs of the diverse array of bird species that call the Delta home. We also evaluate the potential for the Delta to become even more important for birds in the future, incorporating climate change effects, species range shifts, and changes to the composition and configuration of the Delta's landscape. Finally, recognizing the uncertainties about the Delta's future landscape and the complexity of this social-ecological system, we provide recommendations--aimed at a higher-level policy and planning audience--for integrating bird conservation with other goals in the Delta. To improve ecosystem integrity, conserve biodiversity, and provide benefits to local communities of people, we urge a focus on creating a more resilient Delta and employing a diversified portfolio of conservation strategies, both old and new. [ABSTRACT FROM AUTHOR]

Stress on California's salmon fisheries drives a need for effective temperature management in California's Sacramento River. Shasta Dam has a temperature control device that enables managers to provide cold discharge temperatures to the river that are required for downstream Chinook salmon spawning and rearing. An added stress to water temperature management is prolonged drought and associated high air temperatures. California experienced its worst drought in a century from 2012 to 2015, and these conditions may provide insight into future reservoir conditions, as climate change predictions suggest that droughts will be more frequent and intense. In this study, a two-dimensional hydrodynamic model of Shasta Reservoir was used to simulate: (1) alternative reservoir operations during 2015 aimed at sustaining the volume of cold water in the reservoir to provide downstream cold water habitat during the critical time for endangered winter-run Chinook salmon egg incubation; and (2) reservoir temperature conditions under potential climate change scenarios. Results suggest that, with climate change, water managers at Shasta Reservoir may have increasing difficulty maintaining adequate cold pool volume in the reservoir through November, and even extreme reductions in reservoir outflows may not be enough to mitigate this result. [ABSTRACT FROM AUTHOR]

The impact of drought on water resources in arid and semiarid regions can be buffered by water supplies from different source regions. Simultaneous drought in all major source regions — or perfect drought — poses the most serious challenge to water management. We examine perfect droughts relevant to Southern California (SoCal) water resources with instrumental records and tree‐ring reconstructions for the Sacramento and Colorado Rivers, and SoCal. Perfect droughts have occurred five times since 1906, lasting two to three years, except for the most recent event, 2012–2015. This number and duration of perfect droughts is not unusual in the context of the past six centuries. The modern period stands out for the relatively even distribution of perfect droughts and lacks the clusters of perfect drought documented in prior centuries. In comparison, perfect droughts of the 12th Century were both longer (up to nine years) and more widespread. Perfect droughts of the 20th and 21st Centuries have occurred under different oceanic/atmospheric patterns, zonal and meridional flow, and ENSO or non‐ENSO conditions. Multidecadal coherence across the three regions exists, but it has varied over the past six centuries, resulting in irregular intervals of perfect drought. Although the causes of perfect droughts are not clear, given the long‐term natural variability along with projected changes in climate, it is reasonable to expect more frequent and longer perfect droughts in the future. Research Impact Statement: Concurrent or perfect droughts, lasting up to nine years have occurred in the Sacramento and Colorado River Basins, and Southern California over the past nine centuries. [ABSTRACT FROM AUTHOR]

The Green Sturgeon is a long-lived anadromous fish known to spawn in only three locations. Southern Distinct Population Segment (DPS) Green Sturgeon spawn only in the Sacramento drainage, while the Northern DPS spawns in the Klamath and Rogue rivers. In 2011, a young of year (YOY) Green Sturgeon was captured in the Columbia River below Bonneville Dam, providing preliminary evidence of a fourth spawning location. In 2017, four additional Green Sturgeon YOY of similar size were captured in the Columbia River below Bonneville Dam. Genetic analysis of all YOY samples indicates that they belong to the Northern DPS, confirming that the Northern DPS actually spawns in at least three locations. The detection of Green Sturgeon spawning in the Columbia River only in years with relatively high spring flow (2011, 2017), combined with confirmed correlations between flow and spawning for other White and Green Sturgeon populations, suggests that appropriate spawning conditions may only exist above a specific flow threshold. The Columbia River has the potential to play an important role in Green Sturgeon climate change adaptation due to its location at the northernmost end of the species' reproductive range. We recommend future research to better quantify Green Sturgeon recruitment magnitude, frequency and dynamics in the Columbia River. [ABSTRACT FROM AUTHOR]

Changes in the position of the low salinity zone, a habitat suitability index, turbidity, and water temperature modeled from four 100-year scenarios of climate change were evaluated for possible effects on delta smelt Hypomesus transpacificus, which is endemic to the Sacramento-San Joaquin Delta. The persistence of delta smelt in much of its current habitat into the next century appears uncertain. By mid-century, the position of the low salinity zone in the fall and the habitat suitability index converged on values only observed during the worst droughts of the baseline period (1969-2000). Projected higher water temperatures would render waters historically inhabited by delta smelt near the confluence of the Sacramento and San Joaquin rivers largely uninhabitable. However, the scenarios of climate change are based on assumptions that require caution in the interpretation of the results. Projections like these provide managers with a useful tool for anticipating long-term challenges to managing fish populations and possibly adapting water management to ameliorate those challenges. [ABSTRACT FROM AUTHOR]

Deltas are pinnacles of life: they provide environmental wealth to support biodiversity, human population centers, and industrial and agricultural production. Land use, water diversion, flooding, subsidence, salt water intrusion, and ultimately levee failure threaten these complex ecosystems, and it is, therefore, important that dynamic approaches be taken to avoid disaster and sustain thriving Deltas. This report focuses on the Sacramento-San Joaquin Delta, but the lessons learned can be extended across the globe. The Sacramento-San Joaquin Delta is the primary water resource for California's urban and agricultural development. Sherman Island sits on the western edge of the Delta and is a critical geographic feature in balancing the flux of saltwater in the Delta. However, Sherman Island is at risk of catastrophic failure. Flooding, saltwater intrusion, and ongoing subsidence are current threats that become further exacerbated by global climate change. Through collaboration with industry representatives, inhabitants, academics, and local government officials, the environmental, social, and economic impacts of these issues were holistically addressed. The synthesis of stakeholder input with natural and engineered environments led to the design of an Adaptive Water Management and Agricultural Diversification System (AWMADS) composed of a levee enclosed flood storage and wetland habitat area that can dynamically support hydroponics (soil-less agriculture), aquaculture (concentrated production of aquatic species), and many other optional components over the system's life. Engineering, socio-economic, and environmental impact analyses, and exploration of mitigation strategies demonstrate the theoretical success of the system to protect against flooding, sequester carbon, restore habitats, and reinvigorate the local economy. [ABSTRACT FROM AUTHOR]

Changes in water temperatures caused by climate change in California's Sacramento-San Joaquin Delta will affect the ecosystem through physiological rates of fishes and invertebrates. This study presents statistical models that can be used to forecast water temperature within the Delta as a response to atmospheric conditions. The daily average model performed well ( R values greater than 0.93 during verification periods) for all stations within the Delta and San Francisco Bay provided there was at least 1 year of calibration data. To provide long-term projections of Delta water temperature, we forced the model with downscaled data from climate scenarios. Based on these projections, the ecological implications for the delta smelt, a key species, were assessed based on temperature thresholds. The model forecasts increases in the number of days above temperatures causing high mortality (especially along the Sacramento River) and a shift in thermal conditions for spawning to earlier in the year. [ABSTRACT FROM AUTHOR]