San Francisco Bay

Evapotranspiration frequently increases during droughts

Nature Portfolio (Springer Nature) | October 27th, 2022

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce the moisture supply necessary for ET, limiting predictions of even the sign of ET anomalies. Drought-driven increases in ET (ET+drought) are of particular concern because they quickly deplete water resources, causing flash droughts and acute stress on ecosystems. Here, using a water balance approach, we show that ET+drought is globally widespread, occurring in 44.4% of drought months. The sign of ET’s drought response depends most on the magnitude of precipitation and total water storage anomalies, rather than its location. The Coupled Model Intercomparison Project Phase 6 Earth system models underestimate the ET+drought probability by nearly one-half, and more so in drier regions, primarily due to missing representations of soil structure effects on soil evaporation, as well as incorrectly parameterized plant and soil traits. These processes should be prioritized to reduce model uncertainties in the water–energy–food nexus.

Examining the causes and consequences of hybridization during Chinook salmon reintroductions: using the San Joaquin River as a restoration case study of management options

University of California, Davis (UC Davis) | June 15th, 2014

Successful salmonid restoration efforts depend upon an understanding of the evolutionary processes that historically shaped population diversity, as well as the realities

Successful salmonid restoration efforts depend upon an understanding of the evolutionary processes that historically shaped population diversity, as well as the realities of currently available, altered river systems. Habitat alterations over the past century have dramatically changed the ecological forces that shaped salmonid speciation and evolution, bringing formerly separate and distinct populations into contact and in some cases leading to hybridization. Hybridization can threaten the genetic diversity within salmonid species and may affect the outcomes of restoration efforts. Here we use the San Joaquin River Restoration as a case study to discuss some of the genetic challenges of Chinook salmon restoration in a newly reopened habitat. We discuss a range of genetic management strategies—from passive reintroduction to tightly managed, active reintroduction—and the strengths and weaknesses of each approach.

Examining the Contribution of the Observed Global Warming Trend to the California Droughts of 2012/13 and 2013/14

American Meteorological Society (AMS) | September 30th, 2014

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy se

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy season on record (1895–2014), while the 2012/13 season registered as the 45th warmest and 38th driest (Vose et al. 2014). The 2013 January–December calendar year was the driest on record (Water CA 2014). These consecutive below-normal seasons conspired with warm temperatures to reduce California’s snowpack to the second lowest level since 1960, when recording began, with snowpack at 24% of normal (Water CA 2014). Between January 2013 and January 2014, satellite observations documented dramatic snowpack-related land cover change (NASA Earth Observatory 2014): in 2014, the Cascade, Sierra Nevada, and Coastal ranges were almost completely devoid of snow. In February and March of 2014, air temperatures were extremely warm (NOAA NCDC 2014; HPRC 2014), and U.S. Geological Survey (USGS) observations indicated extreme or moderate hydrologic drought (USGS 2014) and high levels of vegetation stress (VegDRI 2014). The state declared a drought emergency (NIDIS 2014). While it is too soon to assess the full impact of the 2012/13 and 2013/14 California droughts, they seem likely to substantially impact the state’s ability to generate hydrologic power, support agriculture, reduce the risk of forest and bush fires, and protect fragile ecosystems (Huffington Post 2014). *Chapter 4, Explaining Extreme Events of 2013 from a Climate Perspective, Bull. Amer. Meteor. Soc., 95 (9)

Executive Order N-10-19

State of California | April 29th, 2019

Expert review of the sediment screening guidelines for the beneficial reuse of dredged material in San Francisco Bay, Workshop Summary Report

Publisher not available | March 17th, 2020

Exploring scientific and management implications of upper trophic level food webs in the Delta

Delta Stewardship Council (Delta Council) | April 17th, 2024

The Sacramento-San Joaquin Delta (the Delta) has complex and evolving ecosystems characterized by multiple food webs that vary in time and space. Here, food webs are defi

The Sacramento-San Joaquin Delta (the Delta) has complex and evolving ecosystems characterized by multiple food webs that vary in time and space. Here, food webs are defined as the network of species interactions (competition, predation) and interactions with their environment that are related through the flow of energy through the ecosystem (e.g., Paine 1980). Physical modifications, in addition to the introduction of non-native species and the changing climate, have significantly altered the structure and energetic pathways of the food webs for decades. The science clearly suggests that predicting the impacts of habitat restoration, fisheries, changes in environmental drivers (e.g., climate, changes in nutrient loading, invasive species) on the ecological carrying capacity and productivity of the Delta, as well as the bioaccumulation of contaminants on species or the ecosystem, requires an understanding of food web processes.

Exploring Water System Vulnerabilities in California's Central Valley Under the Late Renaissance Megadrought and Climate Change

American Geophysical Union (AGU) | April 24th, 2025

Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast

Nature Portfolio (Springer Nature) | July 3rd, 2017

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

Extreme California Rains During Winter 2015/16: A Change in El Niño Teleconnection?

American Meteorological Society (AMS) | January 25th, 2018

This is a story of two extreme events—one that was expected but failed to occur and the other that actually did occur but was not anticipated. The one that failed was

This is a story of two extreme events—one that was expected but failed to occur and the other that actually did occur but was not anticipated. The one that failed was extreme wetness over Southern California (SCAL) during winter 2015/16, which was predicted by seasonal forecasts. The extreme event that did occur was dryness whose considerable magnitude exacerbated one of the worst droughts on record over SCAL. *Chapter 10,  Explaining Extreme Events of 2016 from a Climate Perspective, Herring, S. C., N. Christidis, A. Hoell, J. P. Kossin, C. J. Schreck III, and P. A. Stott, Eds., 2018: Bull. Amer. Meteor. Soc., 99 (1), S1–S157.

Extreme hydrological changes in the southwestern US drive reductions in water supply to Southern California by mid century

Environmental Research Letters (IOP) | September 21st, 2016

The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of C

The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of California, which is the most populous and agriculturally productive in the United States, depends on an extensive arti cial water storage and conveyance system primarily for irrigated agriculture, municipal and industrial supply and hydropower generation. Here we take an integrative high-resolution ensemble modeling approach to examine near term climate change impacts on all imported and local sources of water supply to Southern California. While annual precipitation is projected to remain the same or slightly increase, rising temperatures result in a shift towards more rainfall, reduced cold season snowpack and earlier snowmelt. Associated with these hydrological changes are substantial increases in the frequency and the intensity of both drier conditions and ooding events. The 50 year extreme daily maximum precipitation and runoff events are 1.5–6 times more likely to occur depending on the water supply basin. Simultaneously, a clear de cit in total annual runoff over mountainous snow generating regions like the Sierra Nevada is projected. On one hand, the greater probability of drought decreases imported water supply availability. On the other hand, earlier snowmelt and signicantly stronger winter precipitation events pose increased flood risk requiring water releases from control reservoirs, which may potentially decrease water availability outside of the wet season. Lack of timely local water resource expansion coupled with projected climate changes and population increases may leave the area in extended periods of shortages.