San Francisco Bay

Water Year 2018 Hydrology

Delta Stewardship Council (Delta Council) | November 26th, 2018

Water Year 2021 Compound Precipitation and Temperature Extremes in California and Nevada

American Meteorological Society (AMS) | December 23rd, 2022

The most intense 22-yr drought in the western United States since 800 CE (Williams et al. 2022) was extended by compound dry and hot extremes in Water Year 2021 (October

The most intense 22-yr drought in the western United States since 800 CE (Williams et al. 2022) was extended by compound dry and hot extremes in Water Year 2021 (October 2020–September 2021). Compared to an instrumental record that dates to 1895, low precipitation (Fig. 1a) and high temperatures (Fig. 1b) were widespread across the western United States. The intense and prevalent drought has caused water delivery shortages (U.S. Bureau of Reclamation 2021), damaged ecosystems (Wlostowski et al. 2022), and contributed to extreme wildfires (e.g., Fu et al. 2021; Gutierrez et al. 2021; Abolafia-Rosenzweig et al. 2022). California and Nevada (CA–NV) were once again at the epicenter of drought and heat in Water Year 2021 (California Department of Water Resources 2021). This was the first time since 1895 that precipitation fell below –1.5 standardized departures and temperatures exceeded 1.5 standardized departures concurrently for the two-state average (Fig. 1c). Precipitation and temperatures were individually extreme as well, as the former was the second lowest since 1895 and the latter was the second highest. We examine whether the co-occurrence of anthropogenic climate change and La Niña, two principal climate drivers during Water Year 2021, altered the risk of unprecedented compound dry and hot extremes in CA–NV during Water Year 2021. Our assessment investigates the factors related to compound extremes that lead to heightened societal impacts compared to individual extreme events (e.g., AghaKouchak et al. 2020; Zscheischler et al. 2020; W. Zhang et al. 2021).

Waterline responses to climate forcing along the North American West Coast

Nature Portfolio (Springer Nature) | June 7th, 2025

Understanding waterline variability at seasonal to interannual timescales is crucial for predicting coastal responses to climate forcing. However, relationships between l

Understanding waterline variability at seasonal to interannual timescales is crucial for predicting coastal responses to climate forcing. However, relationships between large-scale climate variability and coastal morphodynamics remain underexplored beyond intensively monitored sites. This study leverages a newly developed 25-year (1997–2022) satellite-derived waterline dataset along the North American West Coast. Our results reveal distinct latitudinal patterns in seasonal waterline change, with excursions exceeding 25 m in the Pacific Northwest, decreasing to less than 10 m in Southern California and farther south. Waterline fluctuations strongly follow wave power in the Pacific Northwest (R = −0.78), northern California (R = −0.75), and Baja California (R = −0.62), while Baja California Sur aligns more with sea-level variations (R = −0.42). Interannually, waterline change exhibits latitudinal dependence: south of southern California, variability is low, with major erosion confined to strong El Niño-Southern Oscillation (ENSO) events, while northern regions show mixed responses. ENSO-driven storm track shifts modulate winter wave climate, resulting in enhanced (attenuated) erosion from southern California to Baja California Sur during El Niño (La Niña). However, further north, ENSO impacts are less consistent, reflecting a complex interplay of storm track displacement and intensification. These findings highlight the spatial complexity of ENSO-driven morphodynamics and provide a framework for assessing climate-induced coastal vulnerability.

Waterweed Invasions

Scientific American | October 1st, 1989

Populations of plants and animals ordinarily migrate and multiply slowly over time as a result of the natural interplay among many ecological factors: soils, waters,

Populations of plants and animals ordinarily migrate and multiply slowly over time as a result of the natural interplay among many ecological factors: soils, waters, glaciation, drought, the rise and fall of competitor species. Yet in some regions human activities have quickened the pace of change by dramatically altering the range and abundance of many species. Today plants and animals are shipped, sometimes accidentally, all over the globe to zoos and botanical gardens and for commercial and agricultural purposes. A small minority of the "alien," or introduced, species become ecological as well as economic disasters; although they may have been innocuous in their native region, these species are transformed into aggressive pests or weeds that invade and dominate their new environment.

West False River Drought Salinity Barrier Final EIR

California Department of Water Resources (DWR) | November 8th, 2024

With the proposed project, a temporary drought salinity barrier would be installed in West False River up to two times over 10 years, with each installation remaining in

With the proposed project, a temporary drought salinity barrier would be installed in West False River up to two times over 10 years, with each installation remaining in place for up to 20 months over two consecutive calendar years. The barrier would be installed if a drought were to occur during the 2026–2035 period and the drought conditions indicate that a barrier in West False River would be an effective tool to preserve upstream reservoir storage for health, safety, and regulatory releases, while preventing saltwater intrusion into the central and southern portions of the Sacramento–San Joaquin Delta (Delta). The drought salinity barrier would be constructed only if DWR, in cooperation with other State and federal agencies, determines that drought conditions have reduced water storage in Northern California reservoirs to critical levels, such that projected Delta outflow would be insufficient to control increased salinity intrusion into the Delta. 

West False River Drought Salinity Barrier Project Environmental Impact Report (Draft)

California Department of Water Resources (DWR) | July 7th, 2022

The California Department of Water Resources (DWR) proposes to the install the West False River Drought Salinity Barrier Project (proposed project). During drought condit

The California Department of Water Resources (DWR) proposes to the install the West False River Drought Salinity Barrier Project (proposed project). During drought conditions, water stored in upstream reservoirs may be insufficient to repel salinity moving upstream from San Francisco Bay. Without the protection of the drought salinity barrier in West False River, saltwater intrusions could affect more than 27 million Californians who rely on the Sacramento–San Joaquin Delta (Delta) for at least a portion of their water supply; could render Delta water unusable for agricultural needs; and could reduce the value of habitat for aquatic species. DWR installed emergency drought barriers in West False River in 2015 and 2021–2022 in response to drought conditions to protect water quality in the interior Delta. Installation of a drought salinity barrier in West False River has been shown to be an effective tool for reducing the intrusion of saltwater into the Central and South Delta based on these previous installations (see Section 1.2, “Project Background,” in Chapter 1; California Department of Water Resources 2019).

West Valley Watershed Assessment 2018: Baseline Ecological Condition Assessment of Southwest San Francisco Bay Creeks in Santa Clara County; Calabazas, San Tomas Aquino, Saratoga, Sunnyvale East and West

San Francisco Estuary Institute (SFEI) | May 1st, 2019

This report describes baseline information about the amount and distribution of aquatic resources, and evaluates the overall ecological conditions of streams using the Ca

This report describes baseline information about the amount and distribution of aquatic resources, and evaluates the overall ecological conditions of streams using the California Rapid Assessment Method (CRAM), for the West Valley watershed in Santa Clara County; consisting of Sunnyvale East and West Channels, Calabazas Creek, San Tomas Aquino and Saratoga creeks (subsequently referred to in this document as San Tomas-Saratoga), and many smaller tributaries. 

Western and Traditional Ecological Knowledge in ecocultural restoration

University of California, Davis (UC Davis) | October 1st, 2018

 The Delta Plan (DSC 2013) calls for “protecting and enhancing the unique cultural values” of California’s Sacramento–San Joaquin Delta, a 2,800-km2 (1,100 mi2)

 The Delta Plan (DSC 2013) calls for “protecting and enhancing the unique cultural values” of California’s Sacramento–San Joaquin Delta, a 2,800-km2 (1,100 mi2) region that was occupied by indigenous peoples for ~5,000 years. The legacies of Native Californians need to be included in the Delta Plan, especially Traditional Ecological Knowledge (TEK) of ways to gather, hunt, and fish for food; build shelters; prepare medicines; and perform ceremonies — along with ways to make tools, clothing, baskets, and shelters. Plants were not just collected but also tended, which involved planned burning, digging, planting, weeding, harvesting, and seed dispersal. Populations of plants that have cultural significance and unique values should be enhanced under the Delta Plan. While Western Ecological Knowledge (WEK) offers a strong foundation for restoration of species assemblages and ecosystems, TEK adds culturally-significant species to restoration targets and traditional management practices to achieve ecological resilience. We compare 11 attributes of WEK and TEK that aid ecological restoration; all are complementary or shared by these two ways of knowing. Both WEK and TEK emphasize adaptive approaches for managing natural resources, as mandated in the Delta Plan. We suggest that WEK–TEK restoration sites throughout the Delta can be linked (virtually) to honor cultural integrity and nurture a “Sense of Place” for Native Californians and others. At the same time, such a network could foster ways to achieve sustainability through the TEK ethic of reciprocity, which WEK lacks. A network of WEK–TEK sites could enhance unique cultural values while supporting passive recreation and attracting ecotourists. 

Wet Antecedent Soil Moisture Increases Atmospheric River Streamflow Magnitudes Nonlinearly

American Meteorological Society (AMS) | June 4th, 2025

Atmospheric rivers (ARs) drive most riverine floods on the U.S. West Coast. However, estimating flood risk based solely on AR intensity and duration is challenging becaus

Atmospheric rivers (ARs) drive most riverine floods on the U.S. West Coast. However, estimating flood risk based solely on AR intensity and duration is challenging because precipitation phase, antecedent conditions, and physical watershed characteristics (e.g., slope and soil depth) can influence the magnitude of floods. Here, we analyze how antecedent soil moisture (ASM) conditions contribute to variability in streamflow during AR events and how that changes across climatic regimes and physiography in 122 U.S. West Coast watersheds. We identify a robust nonlinear relationship between streamflow and ASM during ARs in 89% of watersheds. The inflection point in this relationship represents a watershed-specific critical ASM threshold, above which event maximum streamflow is, on average, 2–4.5 times larger. Wet ASM conditions amplify the hydrologic impacts of more frequent but weaker, lower moisture transport AR events, while dry ASM conditions attenuate the hydrologic impacts that stronger, higher moisture transport AR events could otherwise cause. Our research shows that watersheds prone to ASM-amplified streamflows have higher evaporation ratios, lower cold-season precipitation, lower snow-to-rain ratios, and shallower, clay-rich soils. Higher evaporation and lower precipitation lead to greater ASM variability during the cold season, increasing streamflow during wet periods and buffering streamflow during dry periods. Lower snow fraction and shallower soils limit the antecedent water storage capacity of a watershed, contributing to greater sensitivity of streamflow peaks to ASM variability. Incorporating ASM thresholds into hydrologic models in these regions prone to AR-amplified streamflow could improve forecasts and decrease uncertainty.

Wetland geomorphology and tidal hydrodynamics drive fine‑scale fish community composition and abundance

Environmental Biology of Fishes (Springer) | January 19th, 2024