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1. The 21st-Century Relative Sea Level Rise in Anne Arundel County, Maryland

   https://doi.org/10.1061/9780784484852.037  

   Ikiriko, Sotonye; Liu, Yi; Qian, Sean; Zhou, Xin (May 2023, American Society of Civil Engineers)

   The rate at which sea level is rising in recent years due to global warming has become a growing concern, most especially as it affects coastal areas of the world. The devastating impact of sea level rise (SLR) on coastal communities, ranging from coastal beach erosion, nuisance high tide flooding, and saltwater pollution of low-lying farmlands to loss of tidal wetlands is leading to a decline in social and economic activities especially in coastal areas. According to the National Oceanic and Atmospheric Administration (NOAA), 40% of the US population living on the coast is inevitably vulnerable to SLR. Therefore, the objective of this study is to project relative sea level rise (RSLR) for Anne Arundel County and to estimate the contribution of land subsidence to RSLR at this location. To project RSLR for Anne Arundel County, this study combines global mean sea level rise (GMSLR) scenarios with local land subsidence measured at GPS LOYF station in Annapolis, Anne Arundel County, Maryland. Current quadratic trend of RSLR in Anne Arundel County projects that by 2100, RSLR for the county will be approximately 1.2 m forecasting from 1992, which is 86% and 174% of the GMSLR intermediate-high and intermediate-low scenarios, respectively. Land subsidence significantly contributed to RSLR in the 20th century; however, since 2001 absolute sea level rise (ASLR) driven by climate change has significantly contributed to RSLR in this location. The results in this paper suggest considering the intermediate-high RSLR scenario for planning and decision-making in Anne Arundel County, Maryland, in relation to SLR. 

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2. Flooding Projections Due To Groundwater Emergence Caused by Sea Level Variability

   https://doi.org/10.1029/2025EF006270  

   Barnes, Austin T; Merrifield, Mark A; Bagheri, Kian; Levy, Morgan C; Davani, Hassan (July 2025, Earth's Future)

   Abstract Rising groundwater tables due to sea level rise (SLR) pose a critical but understudied threat to low‐lying coastal regions. This study uses field observations and dynamic modeling to investigate drivers of groundwater variability and to project flooding risks from emergent groundwater in Imperial Beach, California. Hourly groundwater table data from four monitoring wells (2021–2024) reveal distinct aquifer behaviors across soil types. In transmissive coastal sandy soils, groundwater levels are dominated by ocean tides, with secondary contributions from non‐tidal sea level variability and seasonal recharge. In this setting, we calibrated an empirical groundwater model to observations, and forced the model with regional SLR scenarios. We project that groundwater emergence along the low‐lying coastal road will begin by the 2060s under intermediate SLR trajectories, and escalate to near‐daily flooding by 2100. Over 20% of San Diego County's coastline shares similar transmissive sandy geology and thus similar flooding risk. Results underscore the urgency of integrating groundwater hazards into coastal resilience planning, as current adaptation strategies in Imperial Beach—focused on surface flooding—are insufficient to address infrastructure vulnerabilities from below. This study provides a transferable framework for assessing groundwater‐driven flooding in transmissive coastal aquifers, where SLR‐induced groundwater rise threatens critical infrastructure decades before permanent inundation. 

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3. Timing and amount of southern Cascadia earthquake subsidence over the past 1700 years at northern Humboldt Bay, California, USA

   https://doi.org/10.1130/B35701.1  

   Padgett, Jason S.; Engelhart, Simon E.; Kelsey, Harvey M.; Witter, Robert C.; Cahill, Niamh; Hemphill-Haley, Eileen (February 2021, GSA Bulletin)

   Abstract Stratigraphic, lithologic, foraminiferal, and radiocarbon analyses indicate that at least four abrupt mud-over-peat contacts are recorded across three sites (Jacoby Creek, McDaniel Creek, and Mad River Slough) in northern Humboldt Bay, California, USA (∼44.8°N, −124.2°W). The stratigraphy records subsidence during past megathrust earthquakes at the southern Cascadia subduction zone ∼40 km north of the Mendocino Triple Junction. Maximum and minimum radiocarbon ages on plant macrofossils from above and below laterally extensive (>6 km) contacts suggest regional synchroneity of subsidence. The shallowest contact has radiocarbon ages that are consistent with the most recent great earthquake at Cascadia, which occurred at 250 cal yr B.P. (1700 CE). Using Bchron and OxCal software, we model ages for the three older contacts of ca. 875 cal yr B.P., ca. 1120 cal yr B.P., and ca. 1620 cal yr B.P. For each of the four earthquakes, we analyze foraminifera across representative mud-over-peat contacts selected from McDaniel Creek. Changes in fossil foraminiferal assemblages across all four contacts reveal sudden relative sea-level (RSL) rise (land subsidence) with submergence lasting from decades to centuries. To estimate subsidence during each earthquake, we reconstructed RSL rise across the contacts using the fossil foraminiferal assemblages in a Bayesian transfer function. The coseismic subsidence estimates are 0.85 ± 0.46 m for the 1700 CE earthquake, 0.42 ± 0.37 m for the ca. 875 cal yr B.P. earthquake, 0.79 ± 0.47 m for the ca. 1120 cal yr B.P. earthquake, and ≥0.93 m for the ca. 1620 cal yr B.P. earthquake. The subsidence estimate for the ca. 1620 cal yr B.P. earthquake is a minimum because the pre-subsidence paleoenvironment likely was above the upper limit of foraminiferal habitation. The subsidence estimate for the ca. 875 cal yr B.P. earthquake is less than (<50%) the subsidence estimates for other contacts and suggests that subsidence magnitude varied over the past four earthquake cycles in southern Cascadia. 

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4. Living in the ‘Blue Zone’ of a sea-level rise inundation map: Community perceptions of coastal flooding in King Salmon, California

   https://doi.org/10.1016/j.crm.2024.100596  

   Richmond, Laurie; Kunkel, Kristina (January 2024, Climate Risk Management)

   As sea-level rise (SLR) inundation maps proliferate, it is important to study their politics – both how they are created and how they act upon and shape various lives and places. This paper uses the example of King Salmon, CA – a rural, low-income residential area projected to be one of the most at risk to SLR on the US West Coast – to examine how a community responds to external projections showing SLR risk to their homes and businesses. Through interviews with 17 King Salmon community members and observation of a county-hosted ‘communities at risk’ workshop, we examined the community’s social context, their past experiences with flooding, and their reaction to SLR projection maps including what next steps they would like to see taken. Residents expressed a strong connection to the place, noting that it is one of the few affordable places to live on the coast in California. We found that residents already live with regular flooding during larger tides of the year and have taken steps to adapt. We observed a strong generational component in responses to projection maps with many older respondents believing or hoping that the worst effects from SLR would not come until after they passed away. Residents expressed a lack of faith in government to address flooding concerns both at present and into the future, noting that general maintenance issues have gone unaddressed for decades. Many residents interviewed and observed seemed open or at least resigned to the possibility of relocation at a future undetermined time. This work reveals the power dynamics inherent in climate projections like SLR maps, which, due to their technical nature and mobility, can leave communities out of conversations related to potential futures. Findings also have implications related to climate and SLR work – highlighting the importance of understanding community context; contributing to equity considerations about how wealth and other demographic factors shape how communities interact with SLR planning; and spotlighting the need for sustained learning, engagement, and co-production with communities in the ‘blue zones’ of SLR inundation maps. 

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5. Planning for Sea Level Rise: An AGU Talk in the Form of a Co-Production Experiment Exploring Recent Science (Invited)

   Behar, D. H. (December 2017, AGU Fall Meeting 2017)

   Global sea level rise (SLR) may present the most urgent climate change adaptation challenge facing coastal communities today. The direction is clear, impacts are manifesting now, and the pace of rise is likely to accelerate. As a result, many coastal communities have begun planning their adaptation response and some are quite far along in the process. At the same time, evolving science provides new observations, models, and understanding of land-ocean dynamics that can increase clarity while also in many ways increase uncertainty about the scope, timing, and regional nature of SLR. The planning, design, and construction of water infrastructure has a relatively long timeline (up to 30 years), and thus the evolution of scientific knowledge presents challenges for communities already planning for SLR based on previous information. When does science become actionable for decision-makers? Are there characteristics or thresholds that could cause communities decide to move from one set of scenarios to another, or change approaches altogether? This talk focuses on two important studies different in kind but dominating the conversation about SLR adaptation planning today. First, DeConto and Pollard (2016) have suggested significantly higher upper end projections for Antarctic ice sheet melt, which increase both global and regional SLR above most previously assumed upper limits. Second, probabilistic projections using model output and expert elicitation as presented in Kopp et al (2014) are increasingly appearing in federal reports and planning-related documents. These two papers are pushing the boundaries of the science-to-planning interface, while the application of this work as actionable science is far from settled. This talk will present the outcome of recent conversations among our diverse author team. The authors are engaged in SLR planning related contexts from many angles and perspectives and include the aforementioned Kopp and DeConto as well as representatives of the City of San Francisco, Army Corps of Engineers, Environmental Protection Agency, and engineering consultant community. Attendees of this session will hear a presentation demonstrating co-production in process, including topics about which the authors have and have not agreed upon to date, with some attention to next steps in the process. 

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