Tracking California’s sinking coast from space: Implications for relative sea-level rise

American Association for the Advancement of Science (AAAS) | July 31st, 2020

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, record

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, records of high-resolution vertical land motion rates are scarce due to sparse instrumentation, and hazards to coastal communities are underestimated. Here, we considered a ~100-km-wide swath of land along California’s coast and performed a multitemporal interferometric synthetic aperture radar (InSAR) analysis of large datasets, obtaining estimates of vertical land motion rates for California’s entire coast at ~100-m dimensions—a ~1000-fold resolution improvement to the previous record. We estimate between 4.3 million and 8.7 million people in California’s coastal communities, including 460,000 to 805,000 in San Francisco, 8000 to 2,300,00 in Los Angeles, and 2,000,000 to 2,300,000 in San Diego, are exposed to subsidence. The unprecedented detail and submillimeter accuracy resolved in our vertical land motion dataset can transform the analysis of natural and anthropogenic changes in relative sea-level and associated hazards.

Transboundary geophysical mapping of geological elements and salinity distribution critical for the assessment of future sea water intrusion in response to sea level rise

European Geosciences Union (EGU) | July 4th, 2012

Geophysical techniques are increasingly being used as tools for characterising the subsurface, and they are generally required to develop subsurface models that properly

Geophysical techniques are increasingly being used as tools for characterising the subsurface, and they are generally required to develop subsurface models that properly delineate the distribution of aquifers and aquitards, salt/freshwater interfaces, and geological structures that affect groundwater flow. In a study area covering 730 km2 across the border between Germany and Denmark, a combination of an airborne electromagnetic survey (performed with the SkyTEM system), a high-resolution seismic survey and borehole logging has been used in an integrated mapping of important geological, physical and chemical features of the subsurface. The spacing between flight lines is 200–250 m which gives a total of about 3200 line km. About 38 km of seismic lines have been collected. Faults bordering a graben structure, buried tunnel valleys, glaciotectonic thrust complexes, marine clay units, and sand aquifers are all examples of geological structures mapped by the geophysical data that control groundwater flow and to some extent hydrochemistry. Additionally, the data provide an excellent picture of the salinity distribution in the area and thus provide important information on the salt/freshwater boundary and the chemical status of groundwater. Although the westernmost part of the study area along the North Sea coast is saturated with saline water and the TEM data therefore are strongly influenced by the increased electrical conductivity there, buried valleys and other geological elements are still revealed. The mapped salinity distribution indicates preferential flow paths through and along specific geological structures within the area. The effects of a future sea level rise on the groundwater system and groundwater chemistry are discussed with special emphasis on the importance of knowing the existence, distribution and geometry of the mapped geological elements, and their control on the groundwater salinity distribution is assessed.

Trapping of Suspended Sediment by Submerged Aquatic Vegetation in a Tidal Freshwater Region: Field Observations and Long-Term Trends

Estuaries and Coasts (Springer) | July 14th, 2020

Widespread invasion by non-native, submerged aquatic vegetation (SAV) may modify the sediment budget of an estuary, reducing the availability of inorganic sediment requir

Widespread invasion by non-native, submerged aquatic vegetation (SAV) may modify the sediment budget of an estuary, reducing the availability of inorganic sediment required by marshes to maintain their position in the tidal frame. The instantaneous trapping rate of suspended sediment in SAV patches in an estuary has not previously been quantified via field observations. In this study, flows of water and suspended sediment through patches of invasive SAV were measured at three tidally forced, freshwater sites, all located within the Sacramento-San Joaquin Delta in California. An acoustic Doppler current profiler deployed from a roving vessel provided velocity and backscatter data used to quantify fluxes of both water and suspended sediment. Sediment trapping efficiency, defined as instantaneous net trapped flux divided by incident flux, was positive in 24 of 29 cases, averaging + 5%. Coupled with 3 years of measured sediment flux data at one site, this suggests that trapping averages 3.7 kg m−2 year−1. This estimate compares favorably with the mean mass accumulation rate of 3.8 kg m−2 year−1 estimated from dated sediment cores collected at the study sites. Long-term measurements made upstream reveal a strong negative trend (− 1.8% year−1) in suspended sediment concentration, and intra-annual changes in both suspended sediment concentration and percent fines. The large footprint and high spatial density of invasive SAV coupled with declining sediment supply are diminishing downstream suspended sediment concentrations, potentially reducing the resiliency of marshes in the Delta and lower estuary to future sea-level rise.

Unintended consequences of using maps to communicate sea-level rise

Nature Portfolio (Springer Nature) | June 26th, 2024

Unprecedented continental drying, shrinking freshwater availability, and increasing land contributions to sea level rise

American Association for the Advancement of Science (AAAS) | July 25th, 2025

Changes in terrestrial water storage (TWS) are a critical indicator of freshwater availability. We use NASA GRACE/GRACE- FO data to show that the continents have undergon

Changes in terrestrial water storage (TWS) are a critical indicator of freshwater availability. We use NASA GRACE/GRACE- FO data to show that the continents have undergone unprecedented TWS loss since 2002. Areas experiencing drying increased by twice the size of California annually, creating “mega-drying” regions across the Northern Hemisphere. While most of the world’s dry/wet areas continue to get drier/wetter, dry areas are now drying faster than wet areas are wetting. Changes in TWS are driven by high-latitude water losses, intense Central American/European droughts, and groundwater depletion, which accounts for 68% of TWS loss over non-glaciated continental regions. “Continental drying” is having profound global impacts. Since 2002, 75% of the population lives in 101 countries that have been losing freshwater water. Furthermore, the continents now contribute more freshwater to sea level rise than the ice sheets, and drying regions now contribute more than land glaciers and ice caps. Urgent action is required to prepare for the major impacts of results presented

Valuing Urban Nature – Implications for Flood Resilience

Stanford University | June 3rd, 2019

Sea-level rise and extreme weather events such as torrential rain storms are having devastating consequences in the United States and globally. Researchers, prac

Sea-level rise and extreme weather events such as torrential rain storms are having devastating consequences in the United States and globally. Researchers, practitioners, and policymakers are increasingly calling for the use of natural and nature-based approaches to protect urban areas from flooding which has increased in frequency and intensity as a result. Natural features can help stabilize shorelines and protect communities from river flooding while, providing other co- benefits for people and ecosystems. In a new study, scientists at the Natural Capital Project developed a framework for valuating urban nature and examined different factors cities must consider when making infrastructure and other investment choices. This brief is part of a series based on that research which looks at nature’s abilityto provide resilience to flooding and the various co-benefits associated with nature-based solutions.

Variable vertical land motion and its impacts on sea level rise projections

American Association for the Advancement of Science (AAAS) | January 29th, 2025

Coastal vertical land motion (VLM), including uplift and subsidence, can greatly alter relative sea level projections and flood mitigations plans. Yet, current projection

Coastal vertical land motion (VLM), including uplift and subsidence, can greatly alter relative sea level projections and flood mitigations plans. Yet, current projection frameworks, such as the IPCC Sixth Assessment Report, often underestimate VLM by relying on regional linear estimates. Using high-resolution (90-meter) satellite data from 2015 to 2023, we provide local VLM estimates for California and assess their contribution to sea level rise both now and in future. Our findings reveal that regional estimates substantially understate sea level rise in parts of San Francisco and Los Angeles, projecting more than double the expected rise by 2050. Additionally, temporally variable (nonlinear) VLM, driven by factors such as hydrocarbon and groundwater extraction, can increase uncertainties in 2050 projections by up to 0.4 meters in certain areas of Los Angeles and San Diego. This study highlights the critical need to include local VLM and its uncertainties in sea level rise assessments to improve coastal management and ensure effective adaptation efforts.

Vulnerability Assessments in Support of the Climate Ready Estuaries Program: A Novel Approach Using Expert Judgment, Volume I

U.S. Environmental Protection Agency (EPA) | January 1st, 2012

The San Francisco Bay estuary is highly vulnerable to climate - related changes including increased water temperatures, changes in precipitation and winds, and sea leve

The San Francisco Bay estuary is highly vulnerable to climate - related changes including increased water temperatures, changes in precipitation and winds, and sea level rise. Impacts such as increased inundation of coastal wetlands, changes in water availability and quality, and altered patterns of sedimentation and erosion are increasingly interacting with other human stressors such as extractive water uses and land use changes. Thus it is essential that estuary managers become ‘climate-ready’ by: assessing the vulnerability of natural resources to climate change; considering strategic choices among adaptation strategies in the near term; and engaging in longer term planning based on a range of plausible scenarios of future change. In an era of shrinking budgets coupled with increasingly complex decision-making needs—often taking place in a context of uncertainty and incomplete information— managing natural resources in the face of climate change will be challenging. There is a need for assessment methods that take advantage of existing scientific expertise to help identify robust adaptation strategies, weigh difficult trade-offs, and justify strong action, all in a timely and efficient manner. The purpose of this project was to carry out a pilot vulnerability assessment for the San Francisco Estuary Partnership’s (SFEP) natural resources using expert judgment, the results of which could be linked to adaptation planning. To this aim, EPA’s Office of Research and Development collaborated with SFEP and the San Francisco Bay Conservation and Development Commission on a novel expert elicitation exercise for ‘rapid’ vulnerability assessment. A trial exercise was carried out during a two-day workshop in which two groups of seven experts each focused on two key ecosystem processes: sediment retention in salt marshes and community interactions of shorebirds with their predators and prey (see Figure ES - 1). The exercise, which was based on formal expert elicitation techniques but tailored specifically for qualitative analysis of ecosystem processes, was designed to glean expert information on the sensitivities of ecosystem process components under future climate scenarios . This was followed by group discussions of the implications of the results for management in light of climate change, as well as feedback on the exercise itself.  

What Threat Does Sea-Level Rise Pose to California?

Legislative Analyst's Office (LAO) | August 10th, 2020

Among Its Other Challenges, California Continues to Face the Looming Impacts of Climate Change and Rising Seas. While the coronavirus disease 2019 (COVID‑19) pandemic a

Among Its Other Challenges, California Continues to Face the Looming Impacts of Climate Change and Rising Seas. While the coronavirus disease 2019 (COVID‑19) pandemic and resulting economic impacts have rightly drawn the focus of the Legislature’s and public’s attention since March 2020, other statewide challenges continue to approach on the horizon. Among these are the impending impacts of climate change, including the hazards that rising seas pose to California’s coast. Scientific estimates suggest the magnitude of sea‑level rise (SLR) in California could be at least half of one foot in 2030 and as much as seven feet by 2100. Moreover, storm surges, exceptionally high “king tides,” or El Niño events could produce notably higher water levels than SLR alone.