Rising seas in California: An update on sea-level rise science

California Ocean Protection Council | April 22nd, 2017

Key findings of this report: Scientific understanding of sea-level rise is advancing at a rapid pace. Projections of future sea-level rise, especially under high emiss

Key findings of this report: Scientific understanding of sea-level rise is advancing at a rapid pace. Projections of future sea-level rise, especially under high emissions scenarios, have increased substantially over the last few years, primarily due to new and improved understanding of mass loss from continental ice sheets. These sea-level rise projections will continue to change as scientific understanding increases and as the impacts of local, state, national and global policy choices become manifest. New processes that allow for rapid incorporation of new scientific data and results into policy will enable state and local agencies to proactively prepare. The direction of sea level change is clear. Coastal California is already experiencing the early impacts of a rising sea level, including more extensive coastal flooding during storms, periodic tidal flooding, and increased coastal erosion. The rate of ice loss from the Greenland and Antarctic Ice Sheets is increasing. These ice sheets will soon become the primary contributor to global sea-level rise, overtaking the contributions from ocean thermal expansion and melting mountain glaciers and ice caps. Ice loss from Antarctica, and especially from West Antarctica, causes higher sea-level rise in California than the global average: for example, if the loss of West Antarctic ice were to cause global sea-level to rise by 1 foot, the associated sea-level rise in California would be about 1.25 feet. New scientific evidence has highlighted the potential for extreme sea-level rise. If greenhouse gas emissions continue unabated, key glaciological processes could cross thresholds that lead to rapidly accelerating and effectively irreversible ice loss. Aggressive reductions in greenhouse gas emissions may substantially reduce but do not eliminate the risk to California of extreme sea-level rise from Antarctic ice loss. Moreover, current observations of Antarctic melt rates cannot rule out the potential for extreme sea-level rise in the future, because the processes that could drive extreme Antarctic Ice Sheet retreat later in the century are different from the processes driving loss now. Probabilities of specific sea-level increases can inform decisions. A probabilistic approach to sea-level rise projections, combined with a clear articulation of the implications of uncertainty and the decision support needs of affected stakeholders, is the most appropriate approach for use in a policy setting. This report employs the framework of Kopp et al. (2014) to project sea-level rise for three representative tide gauge locations along the Pacific coastline: Crescent City in northern California, San Francisco in the Bay area, and La Jolla in southern California. These projections may underestimate the likelihood of extreme sea-level rise, particularly under high emissions scenarios, so this report also includes an extreme scenario called the H++ scenario.  The probability of this scenario is currently unknown, but its consideration is important, particularly for high-stakes, long-term decisions. Current policy decisions are shaping our coastal future. Before 2050, differences in sea-level rise projections under different emissions scenarios are minor but they diverge significantly past midcentury. After 2050, sea-level rise projections increasingly depend on the trajectory of greenhouse gas emissions. For example, under the extreme H++ scenario rapid ice sheet loss on Antarctica could drive rates of sea-level rise in California above 50 mm/year (2 inches/year) by the end of the century, leading to potential sea-level rise exceeding 10 feet. This rate of sea-level rise would be about 30-40 times faster than the sea-level rise experienced over the last century. Waiting for scientific certainty is neither a safe nor prudent option. High confidence in projections of sea-level rise over the next three decades can inform preparedness efforts, adaptation actions and hazard mitigation undertaken today, and prevent much greater losses than will occur if action is not taken. Consideration of high and even extreme sea levels in decisions with implications past 2050 is needed to safeguard the people and resources of coastal California.

Risk-Informed Future Climate Scenario Development for the State Water Project Delivery Capability Report

California Department of Water Resources (DWR) | August 24th, 2023

This report introduces and documents an extensive effort undertaken by the California Department of Water Resources (DWR) to develop risk-informed future climate scenario

This report introduces and documents an extensive effort undertaken by the California Department of Water Resources (DWR) to develop risk-informed future climate scenarios for the State Water Project (SWP) Delivery Capability Report (DCR), a report issued by the SWP every two years. These reports present DWR’s analysis of the SWP system and planning information for users of SWP water. The analysis provides information about how climate change, regulatory, and operational considerations affect SWP delivery capability. Specifically, the report must provide “…under a range of hydrologic conditions, the then existing overall delivery capability of the project facilities and the allocation of that capacity to each contractor. The range of hydrologic conditions shall include the historic extended dry cycle and long-term average.” (Settlement Agreement 2003).

Risks and Options to Reduce Risks to Fishery and Water Supply Uses of the Sacramento/San Joaquin Delta

California Department of Water Resources (DWR) | January 1st, 2008

Assembly Bill (AB) 1200 (Laird, Chapter 573, Statutes of 2005) highlighted the complex Delta water issues, and directed the Department of Water Resources (DWR) and the De

Assembly Bill (AB) 1200 (Laird, Chapter 573, Statutes of 2005) highlighted the complex Delta water issues, and directed the Department of Water Resources (DWR) and the Department of Fish and Game (DFG) to report to the Legislature and Governor on the following: • Potential impacts of levee failures on water supplies derived from the Sacramento-San Joaquin Delta due to future subsidence, earthquakes, floods, and effects of climate change • Options to reduce the impacts of these factors • Options to restore salmon and other fisheries that use the Delta estuary The State is currently involved in four major planning efforts to evaluate ecosystem and water supply issues and consider options for improvements: 1. The Delta Risk Management Strategy (DRMS) is evaluating Delta issues primarily from the perspective of the risks from levee failures and ways to reduce those risks 2. The CALFED Ecosystem Restoration Program (ERP) Conservation Strategy is identifying restoration opportunities within the Delta and Suisun Marsh ecological restoration zones based on existing elevations, soil types, habitats and natural process requirements of pelagic organisms and other native fish species 3. The Delta Vision will develop a durable vision for sustainable management of the Delta with the goal of managing the Delta over the long term to restore and maintain identified functions and values that are determined to be important to the environmental quality of the Delta and the economic and social well being of the people of the state 4. The Bay Delta Conservation Plan (BDCP) is evaluating Delta issues primarily for the goal of obtaining permits for water supply operations through a comprehensive conservation plan for the Delta designed to protect and restore at-risk species. Since each process has only prepared initial findings at this point in time, this document reports on progress made to define the risks and options to reduce risks for the Delta as requested by the Legislature.

Risks of ocean acidification in the California Current food web and fisheries: ecosystem model projections

Wiley | January 12th, 2017

The benefits and ecosystem services that humans derive from the oceans are threatened by numerous global change stressors, one of which is ocean acidification. Here, we d

The benefits and ecosystem services that humans derive from the oceans are threatened by numerous global change stressors, one of which is ocean acidification. Here, we describe the effects of ocean acidification on an upwelling system that already experiences inherently low pH conditions, the California Current. We used an end‐to‐end ecosystem model (Atlantis), forced by downscaled global climate models and informed by a meta‐analysis of the pH sensitivities of local taxa, to investigate the direct and indirect effects of future pH on biomass and fisheries revenues. Our model projects a 0.2‐unit drop in pH during the summer upwelling season from 2013 to 2063, which results in wide‐ranging magnitudes of effects across guilds and functional groups. The most dramatic direct effects of future pH may be expected on epibenthic invertebrates (crabs, shrimps, benthic grazers, benthic detritivores, bivalves), and strong indirect effects expected on some demersal fish, sharks, and epibenthic invertebrates (Dungeness crab) because they consume species known to be sensitive to changing pH. The model's pelagic community, including marine mammals and seabirds, was much less influenced by future pH. Some functional groups were less affected to changing pH in the model than might be expected from experimental studies in the empirical literature due to high population productivity (e.g., copepods, pteropods). Model results suggest strong effects of reduced pH on nearshore state‐managed invertebrate fisheries, but modest effects on the groundfish fishery because individual groundfish species exhibited diverse responses to changing pH. Our results provide a set of projections that generally support and build upon previous findings and set the stage for hypotheses to guide future modeling and experimental analysis on the effects of OA on marine ecosystems and fisheries.

River Floods Under Wetter Antecedent Conditions Deliver Coarser Sediment to the Coast

American Geophysical Union (AGU) | April 13th, 2025

Increasing hydrologic volatility—more extreme rain, and larger variations between wet and dry years—has become apparent in some regions, but few data exist to determi

Increasing hydrologic volatility—more extreme rain, and larger variations between wet and dry years—has become apparent in some regions, but few data exist to determine how intensifying hydrologic extremes affect sedimentary systems. Using uniquely high-resolution records of fluvial suspended sediment and coastal morphology, we quantify sedimentary responses from a steep, 357-km2 watershed in California under extreme wet and dry hydrologic conditions. In years with multiple 2- to 10-year floods, fluvial sediment coarsened significantly as the wet season progressed, with late-season floods delivering dominantly sand-sized material to the coast. Greater and coarser sediment supply under wetter antecedent conditions affected nearshore geomorphic evolution for 4–5 years. The watershed and coastal changes we documented point to an increasing role of sediment-related hazards (flooding and hillslope erosion) and resources (nearshore accretion) as wet seasons intensify.

River Meandering

American Geophysical Union (AGU) | January 1st, 1989

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 12. River channel pattern comes in three flavors: straight, meander

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 12. River channel pattern comes in three flavors: straight, meandering, and braided. Of these, meandering is perhaps the most common, but at the same time the most mysterious: it is strikingly rich in pattern, yet is encumbered with neither the sterile order of its straight cousin, nor the undecipherable disorder of its braided relative. Consider Figures 1 and 2 herein. The former is of the artificially straightened Naka River, Shikoku, Japan. Thwarted in its quest for a meandering planform, the river has, nevertheless, generated of its own the precursor known as alternate bars. In the latter photograph, a pair of images of the East Nishnabotna River, Iowa, USA, illustrate the elegance of the sinuous river, and the inexorable migration and deformation of bends so characteristic of freely meandering streams.

River-Aquifer Interactions, Geologic Heterogeneity, and Low-Flow Management

U.S. Geological Survey (USGS) | ?

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard mater

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard materials beneath the river. Low flows are often important ecologically. Numerical simulations were used to assess how textural heterogeneity of an alluvial system influences river seepage and low flows. The Cosumnes River in California was used as a test case. Declining fall flows in the Cosumnes River have threatened Chinook salmon runs. A ground water–surface water model for the lower river basin was developed, which incorporates detailed geostatistical simulations of aquifer heterogeneity. Six different realizations of heterogeneity and a homogenous model were run for a 3-year period. Net annual seepage from the river was found to be similar among the models. However, spatial distribution of seepage along the channel, water table configuration and the level of local connection, and disconnection between the river and aquifer showed strong variations among the different heterogeneous models. Most importantly, the heterogeneous models suggest that river seepage losses can be reduced by local reconnections, even when the regional water table remains well below the riverbed. The percentage of river channel responsible for 50% of total river seepage ranged from 10% to 26% in the heterogeneous models as opposed to 23% in the homogeneous model. Differences in seepage between the models resulted in up to 13 d difference in the number of days the river was open for salmon migration during the critical fall months in one given year.

Rivers of California

Pacific Gas & Electric Company (PG&E) | July 1st, 1962

Rivers that Depend on Aquifers: Drafting SGMA Groundwater Plans with Fisheries in Mind

Golden Gate University (GSU) | April 12th, 2018

In California, surface waters have historically been regulated as if they were unconnected to groundwater. Yet, in reality, surface waters and groundwater are often hydro

In California, surface waters have historically been regulated as if they were unconnected to groundwater. Yet, in reality, surface waters and groundwater are often hydrologically connected. Many of the rivers that support fisheries such as salmon and trout are hydrologically dependent on tributary groundwater to maintain instream flow. This means that when there is intensive pumping of tributary groundwater the result can be reductions in instream flow and damage to fisheries. For this reason, stakeholders concerned about adequate instream flows for fisheries in California’s rivers, streams and creeks need to be effectively engaged in the implementation of California’s Sustainable Groundwater Management Act (SGMA). Consider the Scott River in Northern California, part of the larger Klamath River Basin. Nearby groundwater contributes to the Scott River. When high volumes of groundwater are extracted from nearby wells, it depletes the Scott River’s instream flow with adverse impacts on salmon and steelhead trout. As discussed further in Section VI of this guidebook, this has led to litigation over the application of California public trust law to groundwater extraction affecting Scott River instream flows, and efforts to use SGMA to ensure that groundwater pumping near the Scott River is compatible with the instream flow needs of fisheries. Situations similar to the Scott River surface and groundwater basin are unfolding throughout California. On a statewide basis, how pervasive is the effect of groundwater pumping on surface water flows? Research by Maurice Hall of the Environmental Defense Fund, utilizing the California Department of Water Resources Central Valley Groundwater Surface Flow Model, provides us with some sense of the magnitude of the problem. In a May 2018 presentation, Hall reported: What the model showed us is that early in the 1900s, 1940s and 1950s, the Sacramento River received a net inflow from the groundwater of something like 1 million acre feet a year…Since that time, the groundwater levels have gone down, and the amount of water that has flowed into the Sacramento River from the surrounding groundwater has gone down accordingly to the point that when we were doing this modeling around 2010, it appeared that on average, the Sacramento River lost just about as much as it gained from the surrounding groundwater in the valley floor. This is the Sacramento River and all of its tributaries upstream of the Sacramento…So the net effect over that period is there was roughly on average 900,000 acre-feet per year less water showing up in the  Sacramento River at Sacramento.” (Hall and O’Brien). SGMA was enacted in 2014. Pursuant to SGMA, by June 2017 a groundwater sustainability agency was required to be designated for each groundwater basin in California. Each groundwater sustainability agency in high and medium priority basins must prepare and adopt a Groundwater Sustainability Plan (SGMA Groundwater Plan) by 2020 if the basin is deemed to be in a critical state of overdraft or 2022 for all remaining high and medium priority basins. Each SGMA Groundwater Plan must detail how the groundwater basin will be managed to avoid overdraft conditions and, importantly for fisheries, to avoid adverse impacts on hydrologically connected surface waters. Although groundwater sustainability agencies and fishery stakeholders recognize that the groundwater-surface water connection needs to be addressed in SGMA Groundwater Plans, at present there is limited guidance on how to do this. That is, what are the specific types of information, modeling, monitoring, and pumping provisions that should be included in SGMA Groundwater Plans to ensure that groundwater extraction does not cause significant adverse impacts on fisheries? The purpose of this guidebook is to provide such guidance.

Role of Science and Engineering in Decision-Making Within the State and Regional Water Boards

California State Water Resources Control Board (SWRCB) | December 16th, 2005

The primary purpose of State Water Resources Control Board and the nine Regional Water Quality Control Boards is to preserve and protect the beneficial uses of all waters

The primary purpose of State Water Resources Control Board and the nine Regional Water Quality Control Boards is to preserve and protect the beneficial uses of all waters of the State. This includes all ground water, more than 1.6 million acres of lakes, 211,000 miles of rivers and streams, more than 1.3 million acres of bays and estuaries, 1,609 miles of coastline, and the first three miles of ocean off of our coastline. The California legislature found that “activities and factors which may affect the quality of the waters of the State shall be regulated to attain the highest water quality that is reasonable . . . (and) that the state must protect the quality of waters in the state from degradation inside or outside the boundaries of the state.” How we use water, or expect to use water in the future determines its beneficial uses. A designated beneficial use determines the quality of water that must be maintained for that use. Protecting water quality and preventing degradation in order to preserve beneficial uses of water relies heavily on science and engineering. Protecting water quality also depends on an equitable system for allocating water resources, which is carried out by the State Water Resources Control Board’s water rights program. This report discusses the role of science and engineering (technology) in decision-making at the water boards in implementing federal and state laws along with their implementing regulations, and water board plans and policies.