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Climate change is an existential threat to the environmental and socioeconomic sustainability of the coastal zone and impacts will be complex and widespread. Evidence from California and across the United States shows that climate change is impacting coastal communities and challenging managers with a plethora of stressors already present. Widespread action could be taken that would sustain California's coastal ecosystems and communities. In this perspective, we highlight the main threat to coastal sustainability: the compound effects of episodic events amplified with ongoing climate change, which will present unprecedented challenges to the state. We present two key challenges for California's sustainability in the coastal zone: 1) accelerating sea-level rise combined with storm impacts, and 2) continued warming of the oceans and marine heatwaves. Cascading effects from these types of compounding events will occur within the context of an already stressed system that has experienced extensive alterations due to intensive development, resource extraction and harvesting, spatial containment, and other human use pressures. There are critical components that could be used to address these immediate concerns, including comanagement strategies that include diverse groups and organizations, strategic planning integrated across large areas, rapid implementation of solutions, and a cohesive and policy relevant research agenda for the California coast. Much of this has been started in the state, but the scale could be increased, and timelines accelerated. The ideas and information presented here are intended to help expand discussions to sharpen the focus on how to encourage sustainability of California's iconic coastal region. [ABSTRACT FROM AUTHOR]

Tidal salt marshes offer crucial ecosystem services in the form of carbon sequestration, fisheries, property and recreational values, and protection from storm surges, and are therefore considered one of the most valuable and fragile ecosystems worldwide, where sea-level rise and direct human modifications resulted in the loss of vast regions of today's marshland. The extent of salt marshes therefore relies heavily on the interplay between upland migration and edge erosion. We measured changes in marsh size based on historical topographic sheets from the 1850s and 2019 satellite imagery along the Texas coast, which is home to three of the largest estuaries in North America (e.g., Galveston, Corpus Christi, and Matagorda Bays). We further distinguished between changes in high and low marsh based on local elevation data in an effort to estimate changes in local ecosystem services. Our results showed that approximately 410 km2 (58%) of salt marshes were lost due to coastal erosion and marsh ponding and nearly 510 km2 (72%) of salt marshes were created, likely due to upland submergence. Statistical analyses showed a significant relationship between marsh migration and upland slope, suggesting that today's marshland formed as a result of submergence of barren uplands along gently sloping coastal plains. Although the overall areal extent of Texas marshes increased throughout the last century (~100 km2 or 14%), economic gains through upland migration of high marshes (mostly in the form of property value (USD 0.7–1.0 trillion)) were too small to offset sea-level-driven losses of crucial ecosystem services of Texan low marshes (in the form of storm protection and fisheries (USD 2.1–2.7 trillion)). Together, our results suggest that despite significant increases in marsh area, the loss of crucial ecosystem services underscores the complexity and importance of considering not only quantity but also quality in marshland conservation efforts. [ABSTRACT FROM AUTHOR]

Expansive soils pose a significant challenge in geotechnical engineering, especially in coastal areas. While research has mainly focused on their elastic properties, this study explores the overlooked aspect of inelastic subsidence during prolonged droughts, utilizing decade‐long GPS datasets from the University of Houston Coastal Center. Our findings reveal substantial subsidence, approximately one to two dm, during the summer droughts of 2018, 2020, 2022, and 2023, due to compaction within the upper 4 m of expansive soils. Inelastic subsidence constitutes roughly 10% of the total subsidence, resulting in step‐like permanent land elevation loss over time. Notably, drought‐induced subsidence is prominent in open‐field areas with expansive soils but is minor in built‐up areas or in non‐expansive soil regions. The occurrence of inelastic subsidence challenges traditional assessments of relative sea‐level rise and coastal flooding, emphasizing the need to consider it in coastal infrastructure planning for enhanced resilience against climate uncertainties. Plain Language Summary: Expansive soils, often found in coastal regions, are known for causing issues like land shifts and unstable buildings. Our research adds a new dimension: prolonged droughts can lead to significant, irreversible sinking of expansive soils, permanently lowering the elevation of open land areas. Using a decade of GPS data, we found that during droughts, these soils can sink considerably and will not fully recover. Interestingly, in developed regions where pavement covers the soils, thereby minimizing moisture loss, this sinking is observed to be minimal. In the Galveston coastal area, drought‐induced sinking can reach one to two dm, with irreversible subsidence making up about 10% of the total subsidence. This becomes a growing concern as droughts become more frequent due to climate change, especially in coastal areas. Additionally, our results suggest that current methods for estimating sea‐level rise may be missing a key factor: we have underestimated the speed at which uninhabited coastal lands are sinking because we did not account for this irreversible sinking due to droughts. Key Points: Prolonged droughts cause up 2 dm of subsidence in shallow expansive soils (<4 m deep) in Galveston, TX, 10% of which is inelasticProlonged droughts lead to notable subsidence in open fields with expansive soils, but less in built‐up areas or non‐expansive soil areasRecurring droughts lead to permanent land elevation losses in open‐field coast, possibly skewing sea‐level rise and flood risk projections [ABSTRACT FROM AUTHOR]

Many barrier islands and spits (collectively, "barriers") throughout the world are highly developed. As low‐lying, sandy coastal landforms, barrier systems are naturally reshaped by processes associated with storms and sea‐level rise (SLR). The resulting landscape changes threaten development, and in response, humans employ defensive measures that physically modify barrier geometry to reduce relatively short‐term risk. These measures include the construction of large dunes, emplacement of beach nourishment, and removal of washover. Simulations conducted using a new coupled modeling framework show that, over decades to centuries, measures to protect roadways and communities alter the physical characteristics of barrier systems in ways that ultimately limit their habitability. We find that the pathway toward uninhabitability (via roadway drowning or community narrowing) and future system states (drowning or rebound) depends largely on dune management—because building dunes blocks overwash delivery to the barrier interior—and on initial conditions (barrier elevation and width). In the model, barriers can become lower and narrower with SLR to the point of drowning. The timing and occurrence of barrier drowning depends on randomness in the timing and intensity of storms and dune recovery processes. We find that under a constant rate of SLR, negative feedbacks involving storms can allow barriers that do not drown to rebound toward steady‐state geometries within decades after management practices cease. Plain Language Summary: Barrier islands and spits (collectively referred to as "barriers") can naturally keep up with sea‐level rise primarily through a process called overwash. During overwash, sand from the beach is washed landward past the dunes by storm waves, leading to increases in barrier height (elevation) and width. Tall dunes, built to protect roadways and oceanfront properties, prevent overwash from elevating the existing barrier landscape. Here we use a new model to show that over many decades to centuries, an unintended consequence of rebuilding tall dunes in the aftermath of storms, which then block future overwash, is the narrowing and lowering of barriers relative to sea level. In some cases, this leads to complete drowning of the barrier interior. In other cases, once humans stop rebuilding dunes, the landscape recovers in as little as a few decades. Key Points: Counterintuitively, with higher dune design heights and lower/wider initial barrier geometries, barriers become uninhabitable soonerRandomness in dune‐storm interactions dictates whether or not a barrier drowns after management ceasesSimulations suggest barrier systems can recover in height, width, and cross‐shore position quickly (within decades) after management ceases [ABSTRACT FROM AUTHOR]

Coastal erosion and flooding are projected to increase during the 21st century due to sea-level rise (SLR). To prevent adverse impacts of unmanaged coastal development, national organizations can apply a land protection policy, which consists of acquiring coastal land to avoid further development. Yet, these reserved areas remain exposed to flooding and erosion enhanced by SLR. Here, we quantify the exposure of the coastal land heritage portfolio of the French Conservatoire du littoral (Cdl). We find that 30% (~40%) of the Cdl lands owned (projected to be owned) are located below the contemporary highest tide level. Nearly 10% additional surface exposure is projected by 2100 under the high greenhouse gas emissions scenario (SSP5-8.5) and 2150 for the moderate scenario (SSP2-4.5). The increase in exposure is largest along the West Mediterranean coast of France. We also find that Cdl land exposure increases more rapidly for SLR in the range of 0–1 m than for SLR in the range 2–4 m. Thus, near-future uncertainty on SLR has the largest impact on Cdl land exposure evolution and related land acquisition planning. Concerning erosion, we find that nearly 1% of Cdl land could be lost in 2100 if observed historical trends continue. Adding the SLR effect could lead to more than 3% land loss. Our study confirms previous findings that Cdl needs to consider land losses due to SLR in its land acquisition strategy and start acquiring land farther from the coast. [ABSTRACT FROM AUTHOR]

Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea‐level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low‐elevation forests along the US mid‐Atlantic coast have survived despite undergoing relative sea‐level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi‐decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea‐level rise have yet to be realized. [ABSTRACT FROM AUTHOR]

This contribution to the Reflections section of Ocean Yearbook devoted to the memory of the late Professor Meinhard Doelle concerns the options available to coastal States in their responses to global sea level rise driven by anthropogenic climate change. These reflections seek to explore the main policy options and practical approaches based on physical interventions in this context and to assess the possible risks as well as benefits of those approaches. They also explore some of the more radical and cutting-edge technologies which are already being deployed. While addressing the physical intervention options and some of their practical and legal implications, this paper also addresses the importance of environmental impact assessments (EIAs) and capacity-building, both of which were key themes in Meinhard Doelle's work. [ABSTRACT FROM AUTHOR]

Jackson, K.; Wang, P.; Pluckhahn, T.J.; Rogers, J.A., and Thompson, V.D., 2023. Stratigraphic framework, paleoenvironments, and Indigenous terraforming of inshore estuarine subbasins in Tampa Bay, Florida, U.S.A. Journal of Coastal Research, 39(5), 779–815. Charlotte (North Carolina), ISSN 0749-0208. Tampa Bay is a karst-controlled estuary system on Florida's central peninsular Gulf of Mexico coast. Although previous work has reconstructed late-Pleistocene environments (ca. 20–11.5 kya) and early marine influence (ca. 8–5.5 kya) in deeper central portions of the bay, the estuarine development of the shallow inshore subbasins remains poorly understood. Across the late Holocene, Indigenous societies terraformed the coastal strand with large volumes of estuarine mollusk shell, and these anthropogenic landforms constitute coastal barriers that partially enclose marginal tidal bayous. This study integrates sediment coring and archaeological excavations to reconstruct the Holocene estuarine evolution of four inshore subbasins within Tampa Bay. This study synthesizes sedimentological, macrofossil, and archaeological data to describe and differentiate seven sedimentary facies and 18 subfacies representing weathered Miocene limestone at the base, overlain by late-Pleistocene freshwater wetland deposits, followed by Holocene estuarine sediments and late-Holocene shell-terraformed settlements. Four stratigraphic cross-sections and >100 radiocarbon assays are utilized to interpret the sequences of inshore estuary development, situate ancient shell-bearing Native settlements within a geologic and paleoenvironmental framework, and resolve elements of mid- and late-Holocene sea-level history. [ABSTRACT FROM AUTHOR]

Satellite‐derived shoreline observations combined with dynamic shoreline models enable fine‐scale predictions of coastal change across large spatiotemporal scales. Here, we present a satellite‐data‐assimilated, "littoral‐cell"‐based, ensemble Kalman‐filter shoreline model to predict coastal change and uncertainty due to waves, sea‐level rise (SLR), and other natural and anthropogenic processes. We apply the developed ensemble model to the entire California coastline (approximately 1,760 km), much of which is sparsely monitored with traditional survey methods (e.g., Lidar/GPS). Water‐level‐corrected, satellite‐derived shoreline observations (obtained from the CoastSat toolbox) offer a nearly unbiased representation of in situ surveyed shorelines (e.g., mean sea‐level elevation contours) at Ocean Beach, San Francisco. We demonstrate that model calibration with satellite observations during a 20‐year hindcast period (1995–2015) provides nearly equivalent model forecast accuracy during a validation period (2015–2020) compared to model calibration with monthly in situ observations at Ocean Beach. When comparing model‐predicted shoreline positions to satellite‐derived observations, the model achieves an accuracy of <10 m RMSE for nearly half of the entire California coastline for the validation period. The calibrated/validated model is then applied for multi‐decadal simulations of shoreline change due to projected wave and sea‐level conditions, while holding the model parameters fixed. By 2100, the model estimates that 24%–75% of California's beaches may become completely eroded due to SLR scenarios of 1.0–3.0 m, respectively. The satellite‐data‐assimilated modeling system presented here is generally applicable to a variety of coastal settings around the world owing to the global coverage of satellite imagery. Plain Language Summary: We present a computer model to predict shoreline change due to waves, sea‐level rise (SLR), and other local processes. We apply the model to the entire California coastline (approximately 1,760 km), much of which is not well monitored using traditional survey methods. Observations of historical shoreline position obtained from satellite images can be used in lieu of traditional shoreline survey data to estimate erosion/accretion trends as well as to calibrate and validate models. By 2100, the model estimates that 24%–75% of California's beaches may become completely eroded due to SLR scenarios of 1.0–3.0 m, respectively. Key Points: We assimilate a large‐scale, ensemble shoreline‐change model with observations of shoreline position derived from Landsat satellitesSatellite‐derived shoreline observations perform similarly to in situ observations for calibrating and validating shoreline modelsThe model estimates that, without interventions, 24%–75% of California's beaches may be completely eroded by 2100 due to future sea‐level rise [ABSTRACT FROM AUTHOR]

Future sea-level rise poses an existential threat for many river deltas, yet quantifying the effect of sea-level changes on these coastal landforms remains a challenge. Sea-level changes have been slow compared to other coastal processes during the instrumental record, such that our knowledge comes primarily from models, experiments, and the geologic record. Here we review the current state of science on river delta response to sea-level change, including models and observations from the Holocene until 2300 CE. We report on improvements in the detection and modeling of past and future regional sea-level change, including a better understanding of the underlying processes and sources of uncertainty. We also see significant improvements in morphodynamic delta models. Still, substantial uncertainties remain, notably on present and future subsidence rates in and near deltas. Observations of delta submergence and land loss due to modern sea-level rise also remain elusive, posing major challenges to model validation. There are large differences in the initiation time and subsequent delta progradation during the Holocene, likely from different sea-level and sediment supply histories. Modern deltas are larger and will face faster sea-level rise than during their Holocene growth, making them susceptible to forced transgression. Regional sea-level projections have been much improved in the past decade and now also isolate dominant sources of uncertainty, such as the Antarctic ice sheet. Vertical land motion in deltas can be the dominant source of relative sea-level change and the dominant source of uncertainty; limited observations complicate projections. River deltas globally might lose 5% (∼35,000 km2) of their surface area by 2100 and 50% by 2300 due to relative sea-level rise under a high-emission scenario. [ABSTRACT FROM AUTHOR]

Coasts are dynamic environments prone to the physical and social impacts of climate change. Examining the archaeological and environmental records of coastal areas can deepen our understanding of how humans respond to changing environmental conditions. In this article we consider how sea-level rise impacted coastal environments through time, and how these changes could pose opportunities or challenges to local indigenous populations. We present new findings of coastal zone transformations and past settlement patterns for Borikén, the largest island of the Puerto Rican archipelago, during the Holocene. We use paleogeographic modeling to reconstruct ecosystem availability for six discernible coastlines at 1000-year resolutions that accounts for past relative sea-level (RSL) heights and paleotidal ranges. We then compared ecosystem availability trends with the spatiotemporal distributions of available archaeological data to demonstrate the localized impacts of climate-related RSL rise across the island's coastal ecosystems and suggest a consideration of habitat availability in past decision-making strategies. We observe a strong presence of Archaic Period sites in the island's southwest coast where high coastal ecosystem availability and stability were present during this period. We also observe a significant expansion of intertidal ecosystems beginning at 3 kya for the north-central, north-eastern, south-central, and south-eastern coastlines that correspond to the appearance of materials associated with Early and Late Ceramic Periods cultures in these areas. This comparison of differential coastal transformations and site distributions conveys a deeper understanding of factors involved in past decision-making strategies and contributes to the emerging picture of human adaptations amidst changing environmental conditions. [ABSTRACT FROM AUTHOR]

The long‐term stability of coastal wetlands is determined by interactions among sea level, plant primary production, sediment supply, and wetland vertical accretion. Human activities in watersheds have significantly altered sediment delivery from the landscape to the coastal ocean, with declines along much of the U.S. East Coast. Tidal wetlands in coastal systems with low sediment supply may have limited ability to keep pace with accelerating rates of sea‐level rise (SLR). Here, we show that rates of vertical accretion and carbon accumulation in nine tidal wetland systems along the U.S. East Coast from Maine to Georgia can be explained by differences in the rate of relative SLR (RSLR), the concentration of suspended sediments in the rivers draining to the coast, and temperature in the coastal region. Further, we show that rates of vertical accretion have accelerated over the past century by between 0.010 and 0.083 mm yr−2, at roughly the same pace as the acceleration of global SLR. We estimate that rates of carbon sequestration in these wetland soils have accelerated (more than doubling at several sites) along with accelerating accretion. Wetland accretion and carbon accumulation have accelerated more rapidly in coastal systems with greater relative RSLR, higher watershed sediment availability, and lower temperatures. These findings suggest that the biogeomorphic feedback processes that control accretion and carbon accumulation in these tidal wetlands have responded to accelerating RSLR, and that changes to RSLR, watershed sediment supply, and temperature interact to determine wetland vulnerability across broad geographic scales. Plain Language Summary: Coastal wetlands provide critical ecosystem services but are thought to be increasingly vulnerable in the face of rising seas. Wetlands can build vertically and maintain elevation relative to sea level by forming new soil through the preservation of organic matter produced by marsh plants and the trapping of sediments delivered during tidal flooding if the rate of sea‐level rise doesn't exceed the accretion capacity. We measured rates of salt marsh vertical accretion and carbon accumulation at nine sites along the U.S. East Coast from Maine to Georgia that experience a range of local sea‐level rise and watershed sediment supplies. We found that rates of vertical accretion have accelerated over the past century in a manner very similar to the acceleration of global sea‐level rise. Our findings also indicate that the rate at which these coastal systems sequester carbon in marsh soils has likewise accelerated. The acceleration of accretion and carbon accumulation was found to be greater at sites with higher sea‐level rise, greater watershed sediment supplies, and lower temperatures. Acceleration in coastal wetland accretion provides further evidence of widespread response in Earth's biological systems to human‐induced climate change. Key Points: Coastal wetland vertical accretion and carbon accumulation were measured at nine sites along the U.S. East Coast from Maine to GeorgiaTidal wetland accretion has accelerated in a similar manner to the acceleration of global sea‐level riseThe acceleration of accretion and carbon accumulation was explained by relative sea‐level rise, availability of sediment, and temperature [ABSTRACT FROM AUTHOR]

Palaeoenvironmental analysis of Late Holocene stratigraphic sequences recovered from two southwest Florida archaeological sites reveal a synchronous evolution of events caused by natural processes (e.g. sea‐level rise) and human activity (e.g. construction of shell works). Basal mangrove peats indicate that a transition from a terrestrial to coastal landscape started ~4000 cal bp in conjunction with the Late Holocene sea‐level rise. Continued sea‐level rise ultimately submerged the area to create estuarine conditions. Commensurate with submergence was the construction of relatively large (0.5 to 1.0 km2) shell mounds from 1500 to 1050 cal bp. These activities started in the estuarine environment and over time produced emergent landscape features with significant local relief (>7 m). The overlap in radiocarbon ages of oysters collected from the estuarine interval and the overlying shell mounds suggests construction material was locally harvested. About 1120 cal bp and during the waning of an indigenous presence in the area, red mangrove forests re‐emerged along the margins of each site and within the adjacent estuary to create an expansive mangrove‐dominated landscape within which both shell works are now embedded. This palaeoenvironmental reconstruction contradicts the prevailing notion that the two sites were purposely constructed on the mainland and adjacent to tidally influenced rivulets. [ABSTRACT FROM AUTHOR]

Climate change is an issue of concern and is expected to cause various adverse impacts on human societies in the near and long-term future. Sea-level rise, which is caused by global warming and melting continental ice sheets, in combination with the rising global population and evolution of human activities in coastal areas, tends to make coastal societies more prone to coastal hazards. The Gulf of Corinth in Greece with its diverse coastal landforms and tectonic complexity makes the region unique when considering an assessment of coastal vulnerability. In this study we apply an Integrated Coastal Vulnerability Index (ICVI) to a potential sea-level rise for the southern coastline of the Gulf of Corinth (Greece) consisting of physical and socio-economic parameters. Among multiple different methodologies that have been developed over the recent years, we decided to apply two of the mathematical approaches we believe are best suited for the protection of human activities in our study area. The first one, ICVI_1, is based on the Coastal Vulnerability Index (CVI) by Thieler and Hammar-Klose (1999) with variables of equal relative importance, whereas the second one, ICVI_2, uses the Analytic Hierarchic Process (AHP) with the assignment of relative weight values to each parameter. The parameters were identified and ranked into a vulnerability index with a scale from 1 to 5. The results reveal that both approaches depict more or less the same coastal sections of high or very high vulnerability, but differ in the distribution of extreme values. ICVI_1 shows that 18.3% of the total coastline features very high vulnerability (score 5), while ICVI_2 shows 9.1%. The coastal sections with the highest scores of vulnerability are mostly represented in the eastern part of the studied coastline with low-lying regions of gentle slope and concentrated human activity. [ABSTRACT FROM AUTHOR]

Ongoing sea-level rise has brought renewed focus on terrestrial sediment supply to the coast because of its strong influence on whether and how long beaches, marshes and other coastal landforms may persist into the future. Here, we summarise findings of sediment discharge from several coastal rivers, revealing that infrequent, large-magnitude events have disproportionate influence on the morphodynamics of coastal landforms and littoral cells. These eventdominated effects are most pronounced for small, steep mountainous rivers that supply beach and wetland sediment along the world's active tectonic margins, although infrequent events are important drivers of sediment discharge for rivers worldwide. Additionally, extreme events (recurrence intervals of decades to centuries) that follow wildfires, earthquakes, volcanic eruptions, extreme precipitation or - most notably - combinations of these factors can redefine coastal sediment budgets and morphology. Some of these extreme events (e.g., wildfires plus rainfall) are increasing in magnitude and frequency under modern climate warming, with the likely result of increasing sediment flux to affected coastlines. Climate change is also altering watershed processes in both high latitudes and high altitudes, resulting in increased sediment supply to downstream catchments. We conclude that sediment inputs to coastal systems are highly variable with time, and that the variability and trends in sediment input are as important to characterise as long-term averages. [ABSTRACT FROM AUTHOR]

The coastal areas of the Mediterranean have been extensively affected by the transgressive event that followed the Last Glacial Maximum, with many studies conducted regarding the stratigraphic configuration of coastal sediments around the Mediterranean. The coastal zone of the Messolonghi area, western Greece, consists of low-relief beaches, containing low cliffs and eroded dunes, a fact that, in combination with the rising sea levels and tectonic subsidence of the area, has led to substantial coastal erosion. Coastal vulnerability assessment is a useful means of identifying areas of coastline that are vulnerable to impacts of climate change and coastal processes, highlighting potential problem areas. Commonly, coastal vulnerability assessment takes the form of an "index" that quantifies the relative vulnerability along a coastline. Here, the Coastal Vulnerability Index (CVI) methodology by Thieler and Hammar-Klose was employed, by considering geological features, coastal slope, relative sea-level change, shoreline erosion/accretion rates, and mean significant wave height as well as mean tide range, to assess the present-day vulnerability of the coastal zone of the Messolonghi area. In light of this, an impact assessment is performed under three different sea-level-rise scenarios. This study contributes toward coastal zone management practices in low-lying coastal areas that have little data information, assisting decision-makers in adopting best adaptation options to overcome the impact of sea-level rise on vulnerable areas, similar to the coastal zone of Messolonghi. [ABSTRACT FROM AUTHOR]

Coastal zones are experiencing rapid urbanization at unprecedented rates. At the same time, coastal cities are the most prone to climate-related vulnerability, including impacts of sea-level rise and climate-related coastal hazards under the present and projected future climate. Decision making about coastal urban climate adaptation can be informed by coastal climate services based on modeling tools. We develop a two-period coastal urban adaptation model in which two periods—the present and the future—are distinguished. In the model, a city agent anticipates sea-level rise and related coastal flood hazards with adverse impacts in the future period that, through damages, will reduce the urban income. However, the magnitude of future sea-level rise and induced damages are characterized by uncertainty. The urban planning agent has to make an investment decision under uncertainty: whether to invest in climate adaptation (in the form of construction of coastal protection) or not, and if so, how much. The decision making of the urban agent is derived from intertemporal maximization of expected time-discounted consumption. An exact solution in the closed form is derived for an analytically tractable particular case, for which it is shown that investment decisions depend discontinuously on the value of a single non-dimensional model indicator. When this indicator exceeds a certain threshold value, the urban agent discontinuously switches from the 'business-as-usual' (BaU) strategy when no adaptation investment is taken to a proactive adaptation. The role of coastal climate services in informing the decision making on adaptation strategies is discussed. [ABSTRACT FROM AUTHOR]

Evaluation of sea‐level rise (SLR) impacts on coastal landforms and habitats is a persistent need for informing coastal planning and management, including policy decisions, particularly those that balance human interests and habitat protection throughout the coastal zone. Bayesian networks (BNs) are used to model barrier island change under different SLR scenarios that are relevant to management and policy decisions. BNs utilized here include a shoreline change model and two models of barrier island biogeomorphological evolution at different scales (50 and 5 m). These BNs were then linked to another BN to predict habitat availability for piping plovers (Charadrius melodus), a threatened shorebird reliant on beach habitats. We evaluated the performance of the two linked geomorphology BNs and further examined error rates by generating hindcasts of barrier island geomorphology and habitat availability for 2014 conditions. Geomorphology hindcasts revealed that model error declined with a greater number of known inputs, with error rates reaching 55% when multiple outputs were hindcast simultaneously. We also found that, although error in predictions of piping plover nest presence/absence increased when outputs from the geomorphology BNs were used as inputs in the piping plover habitat BN, the maximum error rate for piping plover habitat suitability in the fully‐linked BNs was only 30%. Our findings suggest this approach may be useful for guiding scenario‐based evaluations where known inputs can be used to constrain variables that produce higher uncertainty for morphological predictions. Overall, the approach demonstrates a way to assimilate data and model structures with uncertainty to produce forecasts to inform coastal planning and management. Plain Language Summary: Bayesian networks provide a means for estimating the probability of various outcomes that depend on input conditions that also have a range of probabilities. They can, for example, predict the probability that a specific location is a suitable nesting site for shorebirds if provided information about the site. The information required can be obtained from mapping on‐the‐ground habitat conditions, or as is done here, be predicted from another BN. The methods for doing that, and the additional uncertainties introduced by using multiple networks, are discussed here. Key Points: Independent Bayesian networks (BNs) can be linked through probability distributions to predict sea‐level rise impacts on barrier island habitatUncertainty in predictions increased as additional BNs and output variables were considered in the frameworkLinked BNs offer a way to quantify uncertainty and scenario‐based predictions in complex geomorphic and ecological settings [ABSTRACT FROM AUTHOR]

Whilst climate change has been regarded as a growing concern in recent years due the disruptive and detrimental effects experienced across the globe, one of its most compelling and threatening evidence is Sea Level Rise (SLR). This phenomenon is more prominent in Small Island Developing States (SIDS) and such islands are already facing escalating associated environmental threats, causing social and economic disruptions as well as insecurities. Amongst the SIDS, the coastal areas of Mauritius are considered among the most vulnerable to SLR, where statistics showed that between the years 1987 and 2007, an annual increase of 2.1 mm in the sea level has been observed around Mauritius. Although SLR has various associated impacts, limited work has been undertaken to assess the coastal vulnerability of the impacts of SLR for Mauritius and to compute the Coastal Vulnerability Index (CVI) of the island. Taking cognizance of this limitation, the purpose of this paper is to quantify, prioritize and critically assess the vulnerability of key impacts of sea level rise on the coastal areas of Mauritius following computation of a CVI. In this process, five key research questions are answered towards calculating the CVI of the island to eventually conceptualize a framework with the aim to reduce the adverse impacts of SLR on coastal zones of Mauritius. Findings of this study aim at the advancement of resilience and increased sustainability of coastal areas to the impacts of SLR. [ABSTRACT FROM AUTHOR]

Economic costs due to operational downtime and wave overtopping under the RCP 8.5 scenario are evaluated at 7 Chilean ports. Wave statistics for a historical period (1985–2004), mid-century (2026–2045), and end-of-century projections (2081–2100) are computed with a Pacific-wide model, forced by wind fields from six General Circulation Models. Offshore waves are then downscaled to each port, where a proxy of downtime is computed by comparing wave heights with vessel berthing criteria. The difference in downtime between the historical and future projections is attributed to climate change. Results show that some ports would reduce and others increase downtime for mid-century projections due to local effects. However, by the end-of-century, all ports would experience a reduction in downtime. Additionally, by mid-century, overtopping would increase in northern ports as a combination of extreme waves and sea-level rise (SLR), while in southern ports, it is expected to be slightly reduced. By the end-of century, overtopping would increase in the whole region, mainly driven by SLR. However, overtopping is significantly altered by coseismic uplift/subsidence that may occur during the design-life of coastal works. Finally, a few practical suggestions aimed atimproving infrastructure management and operational conditions at the analyzed ports are outlined. [ABSTRACT FROM AUTHOR]

Faye, Y.; Ba, K.; Sedrati, M.; Diouf, I., and Diouf, M.B., 2024. Coastal risk assessment and management-related issues of sand spits on the southern coast of Senegal. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 1093–1098. Charlotte (North Carolina), ISSN 0749-0208. This study presents an assessment of the vulnerability of the Mbodiène-Joal coastal zone located along the Petite Côte in Senegal. The assessment integrates various indicators, including coastal characteristics (geomorphology, historical shoreline changes, coastal elevation, slope, and bathymetry), oceanographic factors (sea-level rise, mean tidal range, significant wave height), and socio-economic aspects (coastal population density and land use). Using this comprehensive approach, a coastal vulnerability index (CVI) for both erosion and flooding was established and mapped from Pointe Sarène (Mbodiène) to Pointe Finio (Joal). The results reveal that within the 24 kilometers of coastline studied, 17% (4 km) and 12.5% (3 km) respectively exhibit high to very high vulnerability indices. However, 33% (7 km) of the coastal area falls within the spectrum of moderate vulnerability, while 25% (5 km) and 12.5% (3 km) are classified as having low to very low vulnerability. This study demonstrates the potential of coastal vulnerability maps as effective decision support tools for identifying exposed coastal zones. Such maps are instrumental in preparing for and responding to the threats posed by sea-level rise, contributing to national climate action initiatives, disaster risk reduction efforts, and the pursuit of sustainable development goals. [ABSTRACT FROM AUTHOR]

Modelling and understanding shoreline response to sea-level rise over decadal to centennial timescales is crucial for managing sandy coasts. Globally, the Bruun Rule is one of the most common shoreline model applied to facilitate this. However, there are several limitations to the Bruun Rule, which can compromise coastal management decisions. Here, we provide a novel assessment of the suitability of the Bruun Rule for application in sandy coasts by applying it to hindcast and project shoreline change in three morphologically different sandy beaches over yearly and decadal timescales. We also compare the Bruun Rule predictions against associated observations, published predictions from a hybrid shoreline model, and historical shoreline changes. Results show that the Bruun Rule fails to accurately hindcast and provide realistic projections of future shoreline change in sandy coasts. We attribute this to the Bruun Rule's assumption of linearity between shoreline retreat and relative sea-level rise and its inability to account for nearshore circulation. We, therefore, recommend limiting the use of the Bruun Rule for informing policy and the management of sandy coasts. • We assess the Bruun Rule ability to model shoreline change in sandy coasts. • The Bruun Rule predictions are not physically and theoretically realistic. • Nearshore circulation has greater impact on shoreline change than sea-level rise. • We recommend limiting the use of the Bruun Rule for informing coastal management. [ABSTRACT FROM AUTHOR]

Recent observations and publications have presented the possibility of a high and accelerated sea-level rise (SLR) later this century due to ice sheet instability and retreat in Antarctica. Under a high warming scenario, this may result in a sea level in 2100 that is up to 2 m higher than present and 5 m in 2150. The large uncertainties in these projections significantly increase the challenge for investment planning in coastal strategies in densely populated coastal zones such as the Netherlands. In this paper, we present the results of two studies that were carried out within the framework of the Dutch Delta Programme. The first study showed that it is not only the absolute SLR that presents a challenge but also the annual rate of rise. The latter impacts the lifetime of constructions such as barriers and pumping stations. When the rate of sea-level rise increases up to several centimeters per year, the intended lifetime of a flood defense structure may be reduced from a century to several decades. This new challenge requires new technologies, experiments, strategies, and governance. The second study explored different strategies for the long term to adapt to high SLR (>1 m) and assessed the consequences thereof on adaptation and developments in the coming 2–3 decades. We believe that strategic choices have to be made regarding the permanent closure of estuaries, the pumping or periodic storage of high river discharges, agriculture in an increasingly saline coastal area, and the maintenance of the coastline by beach nourishments. These strategic choices have to be complemented by no-regret measures such as spatial reservations for future sand extraction (for beach nourishments) and future expansion of flood defenses, water discharge, and water storage. In addition, it is advised to include flexibility in the design of new infrastructure. [ABSTRACT FROM AUTHOR]

Naturally formed forest patches known as tree islands are found within lower-statured wetland matrices throughout the world, where they contrast sharply with the surrounding vegetation. In some coastal wetlands they are embedded in former freshwater marshes that are currently exposed to saltwater intrusion and mangrove encroachment associated with accelerating sea-level rise. In this study we resurveyed tree composition and determined environmental conditions in tree islands of the coastal Florida Everglades that had been examined two decades earlier. We asked whether tree islands in this coastal transition zone were differentiated geomorphologically as well as compositionally, and whether favorable geomorphology enabled coastal forest type(s) to maintain their compositional integrity against rising seas. Patterns of variation in geomorphology and soils among forest types were evident, but were dwarfed by differences between forest and adjacent wetlands. Tree island surfaces were elevated by 12–44 cm, and 210Pb analyses indicated that their current rates of vertical accretion were more rapid than those of surrounding ecosystems. Tree island soils were deeper and more phosphorus-rich than in the adjoining matrix. Salinity decreased interiorward in both tree island and marsh, but porewater was fresher in forest than marsh in Mixed Swamp Forest, midway along the coastal gradient where tropical hardwoods were most abundant. Little decrease in the abundance of tropical hardwood species nor increase in halophytes was observed during the study period. Our data suggest that geomorphological differences between organic tree island and marl marsh, perhaps driven by groundwater upwelling through more transmissive tree island soils, contributed to the forests' compositional stability, though this stasis may be short-lived despite management efforts. [ABSTRACT FROM AUTHOR]

This article addresses uses of heritage in urban planning projects that seek to adapt coastal landscapes to increasing risks of flooding, storm surges, and sea level rise. We interrelate concepts from recent research on the climate-heritage-nexus with contemporary coastal climate adaptation projects to reveal some of the complex realities and nuances that are apparent on the ground, and to raise heritage concerns for future practice. Questioning the role that heritage plays in specific climate adaptation projects from Denmark and the Netherlands, two low-lying countries with long coastlines facing climate risks, we show the wide range of roles that heritage can play in climate adaptation planning and we propose a framework to conceptualise heritage in this context. The study shows the important role that climate imaginaries (i.e. depictions, affect, and ways of apprehending the climate past) play in climate adaptation projects, and reveals national and local differences. Finally, we discuss the knowledge gained from climate adaption projects in terms of developing dynamic responses to climate change, of working with rather than against landscape processes, and the potential role of heritage in creating climate-resilient living environments. [ABSTRACT FROM AUTHOR]

In Humboldt Bay, tectonic subsidence exacerbates sea-level rise (SLR). To build surface elevations and to keep pace with SLR, the sediment demand created by subsidence and SLR must be balanced by an adequate sediment supply. This study used an ensemble of plausible future scenarios to predict potential climate change impacts on suspended-sediment discharge (Qss) from fluvial sources. Streamflow was simulated using a deterministic water-balance model, and Qss was computed using statistical sediment-transport models. Changes relative to a baseline period (1981–2010) were used to assess climate impacts. For local basins that discharge directly to the bay, the ensemble means projected increases in Qss of 27% for the mid-century (2040–2069) and 58% for the end-of-century (2070–2099). For the Eel River, a regional sediment source that discharges sediment-laden plumes to the coastal margin, the ensemble means projected increases in Qss of 53% for the mid-century and 99% for the end-of-century. Climate projections of increased precipitation and streamflow produced amplified increases in the regional sediment supply that may partially or wholly mitigate sediment demand caused by the combined effects of subsidence and SLR. This finding has important implications for coastal resiliency. Coastal regions with an increasing sediment supply may be more resilient to SLR. In a broader context, an increasing sediment supply from fluvial sources has global relevance for communities threatened by SLR that are increasingly building resiliency to SLR using sediment-based solutions that include regional sediment management, beneficial reuse strategies, and marsh restoration. [ABSTRACT FROM AUTHOR]

Changes in shoreline positions provide a historical record for identifying causal mechanisms and adaptive responses of coastlines to a wide spectrum of sea-level change that arises either from natural or anthropogenic disturbances. This paper presents a case study of coastal change during a period of the steady rise in sea level that is coupled with frequent storm events. Observations from multiple sources including field survey, topographic map, and series of satellite images were combined and analyzed to determine shoreline changes along the western coast of Calatagan, Batangas from 1979-2018. The Digital Shoreline Analysis System (DSAS) extension tool of ArcGIS was used to estimate magnitudes of shoreline changes, either erosion or accretion. Surface sediment samples were acquired in March and April 2010 to assess the predominant grain size and composition. Historical shoreline positions show that the western coast of Calatagan exhibits discrete erosion, but predominantly coastal accretion trend over a period of nearly 40 years. Both land progradation and the emergence of sand-gravel bars after 1992 occurred in a period of rising sea level across the South China Sea basin, including the West Philippine Sea. Land progradation is attributed to an increase in sediment input to the coast from agricultural activities in unconsolidated volcanic terrain. Notably, overlapping events of storms between 1993--1995 and the 1994 tsunami in the Verde Island Passage (VIP) may have emplaced and reworked a large amount of reef front material onto the reef flat forming emergent bars. Newly accreted lands and emergent bars were subsequently colonized by Avicennia and Sonneratia mangroves. This study highlights that in certain areas, local factors such as increased sediment supply from agricultural activities, storms, and possibly tsunami can modulate shoreline changes in response to modern-day sea-level rise. [ABSTRACT FROM AUTHOR]

The coastal vulnerability to multi-hazard study aims to assess the coastal zones of Andhra Pradesh that really are vulnerable to various oceanogenic hazards. Using high-resolution coastal elevation, the maximum extent of coastal inundation during extreme high waves of cyclones & tsunamis, shoreline change, and sea-level rise can be computed. Vulnerability impact up to the village level was assessed based on future projection (return period) of multi-hazard impact using a holistic approach with geospatial techniques. The current study results revealed that 706 villages and 8 towns that are completely falling under CMZ are at risk. A total of 9682 km2 of coastal zones of Andhra Pradesh coast are exposed and prone to inundation as recorded under CMZ. Krishna, Godavari, Guntur and Prakasham districts comprise 70% of the total CMZ area are large low-lying areas exposed to ocean hazards. CMZ area along Andhra Pradesh coast recorded a significant negative correlation of − 0.65 with coastal elevation and a positive correlation of 0.34 with coastal exposure index. Shoreline change assessed from 1972 to 2019 across the study area reveals the 7% under high erosion along the headland and low-lying area of Krishna-Godavari delta. The outputs and maps produced in this study provide vital input for coastal disaster management and necessary policy interventions. [ABSTRACT FROM AUTHOR]

Climate change has led to increased sea levels, which are caused by a complex interplay of the physical environment components from coastal areas, causing the rise in storm surge, erosion and flooding. In this scenario, the low-lying topography of the Mumbai region is highly susceptible to sea level-induced flooding and coastal erosion due to the increasing number of economic activities. The unsustainable urbanization, unplanned development, and huge land conversion lead to the destruction of this region lead to the destruction of mangroves and filled waterways with construction debris which makes the region more vulnerable to flooding due to inadequate drainage, overflow and absence of natural protectors. These human-induced factors and their impacts remain unknown. Therefore, the study uses four socioeconomic variables (CVI4) with five geological (CVI5) and three geological variables (CVI8; with integrating CVI5) to assess the role of developmental and socio-economic activities in overall coastal vulnerability (CVI12) analysis. To quantify the importance of the combined variables and understand the response, random forest (RF) model was also used. This study selected four different iterations with integrating the pixel-based differentially weighted rank values of all variables to determine the significant causes behind that have an impact on coastal vulnerability index (CVI). The results show that CVI5 and CVI8 contributed 7.8% and 36.9%, respectively, whereas CVI4 contributed 55.3% to the CVI12. The response curve shows that the influence of these variables is an increasing trend to CVI12 and the results of CVI12 are highly correlated with socioeconomic index variables (r = 0.84, p = 0.001) which indicates the socio-economic variables played a major role towards the coastal vulnerability of the region. It suggests that unsustainable urbanization, unplanned development and coastal erosion increasing pressure make Mumbai and Kurla region more vulnerable to flood. Accordingly, CVI12 results show 55.83 km of the shoreline surveyed, being very low vulnerable, a moderate vulnerability of 60.91 km, while a high vulnerability of 50.75 km is considered to be very high. The results may be used as a guide in formulating policies to mitigate and adjust the Mumbai coast as the rise in sea level is expected to cause more frequent coastal floods, etc. [ABSTRACT FROM AUTHOR]

Context: Coastal landscapes evolve in response to sea-level rise (SLR) through a variety of geologic processes and ecological feedbacks. When the SLR rate surpasses the rate at which these processes build elevation and drive lateral migration, inundation is likely. Objectives: To examine the role of land cover diversity and composition in landscape response to SLR across the northeastern United States. Methods: Using an existing probabilistic framework, we quantify the probability of inundation, a measure of vulnerability, under different SLR scenarios on the coastal landscape. Resistant areas—wherein a dynamic response is anticipated—are defined as unlikely (p < 0.33) to inundate. Results are assessed regionally for different land cover types and at 26 sites representing varying levels of land cover diversity. Results: Modeling results suggest that by the 2050s, 44% of low-lying, habitable land in the region is unlikely to inundate, further declining to 36% by the 2080s. In addition to a decrease in SLR resistance with time, these results show an increasing uncertainty that the coastal landscape will continue to evolve in response to SLR as it has in the past. We also find that resistance to SLR is correlated with land cover composition, wherein sites containing land cover types adaptable to SLR impacts show greater potential to undergo biogeomorphic state shifts rather than inundating with time. Conclusions: Our findings support other studies that have highlighted the importance of ecological composition and diversity in stabilizing the physical landscape and suggest that flexible planning strategies, such as adaptive management, are particularly well suited for SLR preparation in diverse coastal settings. [ABSTRACT FROM AUTHOR]

The predominant responses to rising sea levels are in situ adaptations. However, increasing rates of sea-level rise will render ex situ adaptations—in the form of relocations—inevitable in some low-lying coastal zones. Particularly small island states like the Maldives face this significant adaptation challenge. Here, government action is necessary to move vulnerable communities out of flood-prone areas. Yet, little empirical knowledge exists about the governance of relocations. While the literature often highlights risks and benefits of relocations, it remains unclear how governments organized relocations and what drove relocation policy. Therefore, we examined Maldivian relocation policies from 1968 to 2018 to explain government support of relocations. For this, we used a qualitative research design and extended the multiple streams approach with the theoretical lens of historical institutionalism. To gather data, we conducted semi-structured interviews (n = 23) with relocation policy experts and locals affected by relocations. Interview data was complemented with a desk review of relevant laws, historical records, and policy documents. We find 29 completed and 25 failed cases of relocations in the 50-year period. Key drivers of relocation policies are focusing events, socioeconomic development, and institutionalized island autonomy. We find that relocations were predominantly initiated as means to facilitate economic development, not as a response to rising seas or coastal risk. With current rapid economic development and strengthened democratic institutions, relocations are not considered as a policy option anymore. We conclude that implementing relocations proactively will face significant barriers in the future, which highlights the urgency of successful in situ adaptations in the Maldives. [ABSTRACT FROM AUTHOR]

• This article explores adaptation pathways to climate change in coastal areas. • Six territorial archetypes are defined to be representative of the French coastal territories. • The pathways identify different and common resources and levers for each archetype. • A rapid rise in sea level reduces adaptation capacities for structural changes. • An ambitious and early mitigation policy results in more robust adaptation pathways. The attractiveness and urbanisation of coastal zones increase their vulnerability to climate change and sea-level rise, in particular to flooding and marine erosion. In the face of the projected increase in losses and damages, the anticipation and measures needed for adaptation involve physical, socioeconomic and political dimensions at different governance levels and timescales. A large literature addresses these various issues, generally in a targeted way. Drawing on adaptive policy pathways approaches and on research results of the past decade in mainland France, this article proposes an interdisciplinary characterisation of long-term adaptation pathways in coastal areas. Among the different variables and processes of change that characterise coastal zones and their future, particular emphasis is placed on social and institutional dynamics. This work contributes to the debate about adaptive governance in a highly uncertain context as well as to recent work to explore pathways and tipping points in support of climate adaptation policies. [ABSTRACT FROM AUTHOR]

Bibliometric analysis is a quantitative evaluation method for scientific research aiming at measuring knowledge expressed as scientific publications in a given field. This paper proposes to analyze the worldwide scientific production on social vulnerability of coastal populations through six bibliometric indicators: typology, historical evolution, geographic distribution, main sources, relevant authors and publications and recurring keywords. The research theme was chosen given the continuous increase of studies related to climatic changes and their consequences to populations in coastal zones. In total, 191 indexed documents covering the period from 1991 to 2019 were selected from the Scopus database, after the examination of more than 900 entries, and analyzed through VOSViewer software and the Bibliometrix R package. The results obtained confirmed the exponential growth of scientific production on this subject. Most frequently impacts considered were coastal flooding and erosion triggered by extreme events and the majority of studies have been presented as academic articles published in scientific journals. Moreover, most documents identified were site-specific, based on secondary data and associated with authors from the USA and the UK, with an emerging production related to authors from developing economies in recent years. Among the 658 authors found, only nine have published three or more articles on the theme, with citations highly concentrated in only four publications. The analysis also revealed the evolution of preferred keywords over time and the lack of consensus in the use of terminology. Studies about coastal social vulnerability were initially mostly focused on the evaluation of risks and exposure to hazards, evolving over time such that the focus shifted to adaptation measures seeking to minimize impacts from climate change to coastal zones. [ABSTRACT FROM AUTHOR]

• Release of solid waste in coastal zones is a problem with a geological timescale. • Sea level rise will exacerbate risks of solid waste release from coastal landfills. • Three sites with contrasting range of coastal scenarios affecting landfills studied. • Erosion of solid wastes more of a problem than flooding and leachate release. • Lack of methods to assess risks of solid waste release limits remediation options. In England and Wales, there are at least 1700 coastal landfills in the coastal flood plain and at least 60 threatened by erosion, illustrating a global problem. These landfills are a major issue in shoreline management planning (SMP) which aims to manage the risks associated with flooding and coastal erosion. Where landfills exist, "hold the line" (requiring the building or upgrading of artificial defences to maintain the current shoreline) is often selected as the preferred SMP option, although government funding is not available at present. To investigate these issues in detail, three case-study landfills are used to examine the risks of future flooding and erosion together with potential mitigation options. These cases represent a contrasting range of coastal landfill settings. The study includes consideration of sea-level rise and climate change which exacerbates risks of erosion and flooding of landfills. It is fundamental to recognise that the release of solid waste in coastal zones is a problem with a geological timescale and these problems will not go away if ignored. Future erosion and release of solid waste is found to be more of a threat than flooding and leachate release from landfills. However, while leachate release can be assessed, there is presently a lack of methods to assess the risks from the release of solid waste. Hence, a lack of science constrains the design of remediation options. [ABSTRACT FROM AUTHOR]

In the recent decades, the 60-km coastal stretch of Vedaranyam swamp located in the southern coast of Tamil Nadu is identified as a major 'Vulnerable Hotspot', due to increased land-based infrastructures and associated episodic hazards including floods attributable to heavy rain, cyclones, storm surges, earthquakes and tsunami. In order to assess the impact of the land use/land cover changes (LULC) on the historical shoreline of this geographical area, vulnerability study between the periods 1978, 1998 and 2017 was attempted. The LULC change analysis from 1978 to 2017 indicated significant increase in aquaculture farms, salt pans and settlement areas upon conversion of crop lands, mudflats, coastal dunes and scrub lands especially along the coast. The end-point rate resulting from the shoreline analysis over the study period showed evidences of accretion and erosion ranging from 9.93 to − 2.28 m year−1 while the net shoreline movement transects about − 107.79 to 382.71 m, respectively. Changes in the land uses and shoreline dynamics of the study area were considered as key parameters for the vulnerability assessment of this coast. This analysis will help to create awareness among the people about impacts of land use changes and effects of natural hazards such as coastal erosion, inundation and their consequences which includes loss of life and properties. The stress driving vulnerability parameters, namely sea-level rise, relief, wave exposure, surge potential, were considered for calculating the vulnerability index of the 60-km coastline considered for the study. The outcome of the study indicates that about 6 km of the coast is very highly vulnerable, 45 km is highly vulnerable, and 9 km is moderate vulnerable to episodic natural hazards. [ABSTRACT FROM AUTHOR]

Resilience is defined as the ability to predict, prepare for, and adapt to every condition change and withstand, respond to, and recover rapidly from any disruptions. One of these upcoming changing conditions is sea-level rise in coastal cities with its severe impacts regarding coastal erosion. This dramatic environmental issue necessitates adaptation strategies for waterfront areas to be prepared for the future. Such strategies will help stakeholders to identify vulnerabilities, assess environmental and health risks of disasters. and track progress in improving recovery capacity. The research will focus on the northern wetland of Egypt. as it constitutes about one quarter of the wetland of the Mediterranean region. Port Said governorate will be the case study, as Port Said hosts Egypt's second largest harbor. Port Said Governorate is the most physically and socio-economically vulnerable area in the region and will be seriously threatened by sea-level rise as most of its land is low-lying. Several models predict an accelerated sea-level rise after 2040 to 2050 in response to increased melting of the West Antarctic ice shelf. The most expected serious impacts of this sea-level rise is the threat to recreational beach communities as well as to other activities in the coastal zone. This article presents four strategies for sea-level rise adaptation: protection, accommodation, retreat, and attack. A comparative analysis will be constructed for these strategies with respect to the governorate coastal zones to state the most efficient for each zone's conditions/constraints. Coastal development phasing will be introduced, addressing design guidelines to achieve these resilient strategies for urban development in Port Said city. [ABSTRACT FROM AUTHOR]

Watson, P.J., 2019. An assessment of the utility of satellite altimetry and tide gauge data (ALT-TG) as a proxy for estimating vertical land motion. Journal of Coastal Research, 35(6), 1131–1144. Coconut Creek (Florida), ISSN 0749-0208. Policy, planning, and adaptation responses to sea-level rise are being developed at increasingly localised scales, placing greater emphasis on sea-level studies to more accurately account for all vertical land motions (VLM) at tide gauge sites using technologies such as global navigation satellite systems (GNSSs). Although the spatial coverage and length of GNSS data records continues to increase in proximity to tide gauges, large tracts of the world's coastlines contain limited or no GNSS data. Various studies have investigated proxy methods of estimating VLM by trends from differenced altimetry–tide gauge techniques (ALT-TG). This study has concentrated on investigating the utility of ALT-TG techniques using so-called 'off the shelf' gridded satellite altimetry products (U.S. National Aeronautics and Space Administration Jet Propulsion Laboratory [NASA JPL] and Copernicus Climate Change Service [C3S]) for use in regional and local scale sea-level studies to estimate VLM. Twenty locations across the globe were analysed; these locations met specific data constraints designed to ensure the longest overlapping coverage of GNSS, altimetry, and tide gauge data, with the proximity of the GNSS record limited to within 1 km of the tide gauge. The utility of ALT-TG estimates was significantly improved by using gridded altimetry products no closer than 30 km from the open coast. When compared directly with measured GNSS solutions from NASA JPL, Systeme d'Observation du Niveau des Eaux Littorales (SONEL), and Nevada Geodetic Laboratory (NGL), both ALT-TG VLM estimates agree with the NGL GNSS solution for 19 of the 20 locations (95% confidence interval). This is significant given that the NGL estimates are derived over the longest timeframe available from all three key GNSS data repositories considered. If one considers the limitations of altimetry sea surface height measurements in the coastal zone, the results using gridded sea surface height anomaly products for ALT-TG derived estimates of VLM are extremely encouraging for sea-level research. [ABSTRACT FROM AUTHOR]

Future sea-level rise will likely expand the inland extent of storm surge inundation and, in turn, increase the vulnerability of the people, properties and economies of coastal communities. Modeling future storm surge inundation enhanced by sea-level rise uses numerous data sources with inherent uncertainties. There is uncertainty in (1) hydrodynamic storm surge models, (2) future sea-level rise projections, and (3) topographic digital elevation models representing the height of the coastal land surface. This study implemented a Monte Carlo approach to incorporate the uncertainties of these data sources and model the future 1% flood zone extent in the Tottenville neighborhood of New York City (NYC) in a probabilistic, geographical information science (GIS) framework. Generated spatiotemporal statistical products indicate a range of possible future flood zone extents that results from the uncertainties of the data sources and from the terrain itself. Small changes in the modeled land and water heights within the estimated uncertainties of the data sources results in larger uncertainty in the future flood zone extent in low-lying areas with smaller terrain slope. An interactive web map, UncertainSeas.com, visualizes these statistical products and can inform coastal management policies to reduce the vulnerability of Tottenville, NYC to future coastal inundation. [ABSTRACT FROM AUTHOR]

Understanding the sea-level change in the geological past is helpful for the future coastal protection. Information of sea-level changes has been documented in various archives in the coasts. In this study, the well-preserved peat in three representative Holocene ditches in Dayanghe Plain in the Yellow Sea China were investigated using radiocarbon dating and diatom analysis. The widely distributed buried peats at elevation of ca. 2-10 m above sea-level (a.s.l.) in Dayanghe Plain are classified as marsh and limnological peats, which were formed after seawater receding from the drowned ditches. The peat layers lower than 4 m a.s.l., overlain the marine sediments conformably, correspond to the late-Holocene regression. Timing of the highstand sea-level in North Coast of North Yellow Sea is limited to 6182- 5466 cal. a BP by radiocarbon dating. Shell banks at west of the Dagu Mountain which was at a 7-10 m height were thought not to be indicative of the Holocene highstand sea-level. [ABSTRACT FROM AUTHOR]

Coastal zones and many small islands are highly susceptible to sea-level rise (SLR). Coastal zones have a large exposed population and integrated high-value assets, and islands provide diverse ecosystem services to millions of people worldwide. The coastal zones and small islands affected by SLR are likely to suffer from submergence, flooding and erosion in the future. However, very few studies have addressed the heterogeneity in SLR changes and the potential risk to coastal zones and small islands. Here we used the mean sea level (MSL) derived from satellite altimetry data to analyse the trends and accelerations of SLRs along global coastal zones and small islands. We found that except for the Antarctic coastal zone, the annual MSL within 50 km of the coasts presented an increasing trend of 3.09 ± 0.13 mm a−1 but a decreasing acceleration of −0.02 ± 0.02 mm a−2 from 1993 to 2017. The highest coastal MSL trend of 3.85 ± 0.60 mm a−1 appeared in Oceania, and the lowest trend of 2.32 ± 0.37 mm a−1 occured in North America. Africa, North America and South America showed acceleration trends, and Eurasia, Australia and Oceania had deceleration trends. Further, MSLs around global small islands reflected an increasing trend with a rate of 3.01 ± 0.16 mm a−1 but a negative acceleration of −0.02 ± 0.02 mm a−2. Regional heterogeneity in the trends and accelerations of MSLs along the coasts and small islands suggests that stakeholders should take discriminating precautions to cope with future disadvantageous impacts of the SLR. [ABSTRACT FROM AUTHOR]

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Abstract: This paper provides for the first time an experimental study where the impact of sea‐level fluctuations and inland boundary head‐level variations on freshwater–saltwater interface toe motion and transition zone dynamics was quantitatively analysed under transient conditions. The experiments were conducted in a laboratory flow tank where various (inland and coastal) head changes were imposed to the system and the response of the key seawater intrusion parameters was analysed with high spatial and temporal resolution. Two homogeneous aquifer systems of different grain size were tested. The numerical code SEAWAT was used for the validation. The results show that in cases of sea‐level variations, the intruding wedge required up to twice longer time to reach a new steady‐state condition than the receding wedge, which thereby extend the theory of timescale asymmetry between saltwater intrusion and retreat processes in scenarios involving sea‐level fluctuations. The intruding and receding rates of the saltwater wedge were respectively similar in the scenario involving sea‐level and the freshwater‐level changes, despite change in transmissivity. The results show that, during the intrusion phase, the transition zone remains relatively insensitive, regardless of where the boundary head change occurs (i.e., freshwater drop or sea‐level rise) or its magnitude. By contrast, a substantial widening of the transition zone was observed during the receding phase, with almost similar amplitude in the scenario involving a rise of the freshwater level compared with that caused by a drop of the saltwater level, provided that an equivalent absolute head change magnitude was used. This transition zone widening (occurring during saltwater retreat) was greater and extended over longer period in the low hydraulic conductivity aquifer, for both freshwater‐level rise and sea‐level drop scenarios. The concentration maps revealed that the widening mechanism was also enhanced by the presence of some freshwater sliding and into the wedge during saltwater retreat, which was thereafter sucked upward towards the interface because of density difference effects. [ABSTRACT FROM AUTHOR]

The United States’ deeply racialized history currently operates below the surface of contemporary apolitical narratives on vulnerability mitigation and adaptation to sea-level rise. As communities, regulatory agencies, and policy-makers plan for rising seas, it is important to recognize the landscapes of race and deep histories of racism that have shaped the socio-ecological formations of coastal regions. If this history goes unrecognized, what we label colorblind adaptation planning is likely to perpetuate what Rob Nixon calls the “slow violence” of environmental racism, characterized by policies that benefit some populations while abandoning others. By colorblind adaptation planning, we refer to vulnerability mitigation and adaptation planning projects that altogether overlook racial inequality—or worse dismiss its systemic causes and explain away racial inequality by attributing racial disparities to non-racial causes. We contend that responses to sea-level rise must be attuned to racial difference and structures of racial inequality. In this article, we combine the theory of racial formation with the geographical study of environmental justice and point to the ways racial formations are also environmental. We examine vulnerability to sea-level rise through the process of racial coastal formation on Sapelo Island, Georgia, specifically analyzing its deep history, the uneven racial development of land ownership and employment, and barriers to African American participation and inclusion in adaptation planning. Racial coastal formation’s potential makes way for radical transformation in climate change science not only in coastal areas, but other spaces as situated territorial racial formations. [ABSTRACT FROM AUTHOR]

The flood hazard in New York City depends on both storm surges and rising sea levels. We combine modeled storm surges with probabilistic sea-level rise projections to assess future coastal inundation in New York City from the preindustrial era through 2300 CE. The storm surges are derived from large sets of synthetic tropical cyclones, downscaled from RCP8.5 simulations from three CMIP5 models. The sea-level rise projections account for potential partial collapse of the Antarctic ice sheet in assessing future coastal inundation. CMIP5 models indicate that there will be minimal change in storm-surge heights from 2010 to 2100 or 2300, because the predicted strengthening of the strongest storms will be compensated by storm tracks moving offshore at the latitude of New York City. However, projected sea-level rise causes overall flood heights associated with tropical cyclones in New York City in coming centuries to increase greatly compared with preindustrial or modern flood heights. For the various sea-level rise scenarios we consider, the 1-in-500-y flood event increases from 3.4 m above mean tidal level during 1970-2005 to 4.0-5.1 m above mean tidal level by 2080-2100 and ranges from 5.0-15.4 m above mean tidal level by 2280-2300. Further, we find that the return period of a 2.25-m flood has decreased from ~500 y before 1800 to ~25 y during 1970-2005 and further decreases to ~5 y by 2030-2045 in 95% of our simulations. The 2.25-m flood height is permanently exceeded by 2280-2300 for scenarios that include Antarctica's potential partial collapse. [ABSTRACT FROM AUTHOR]

Large parts of tropical coastlines are influenced by the presence of reefs that shape its coastline. Wave attenuation crossing reefs as they approach the coast results in accretionary coastal features developed in its shadow zones. With the aim of assessing the level of wave exposure of the coastline under different sea-level rise scenarios, numerical modeling experiments have been designed considering a coastline segment of approximately 450 km in northeast Brazil. Results show the distribution of wave power along the area of interest, with higher values being found in areas without reefs. However, when considering sea-level rise scenarios, it is behind the reefs where the maximum differences in wave power are observed. The increase in the free surface over the reef structures as a result of rising sea level reduces the wave attenuation effects caused by these structures. Thus, the waves hit the shore with greater force in the shadow zone protected by the reef. Here, we demonstrate that regions within the reef shadow zones are most strongly affected by sea-level rise with up to a 90% increase in the wave power, which will lead to increase in sediment transport and erosion processes. Such processes indicate a trend toward coastline flattening and alignment in response to less effective shadow zones. [ABSTRACT FROM AUTHOR]

The most recent Intergovernmental Panel on Climate Change reports conclude that for Australasia, without adaptation, further changes in climate, atmospheric CO2, sea-level rise and ocean acidity are projected to have substantial impacts on climate sensitive systems, sectors and populations. In the context of varying geographical, social, cultural and policy contexts, this paper reviews research contributions and activities concerning coastal adaptation to climate change in Aotearoa-New Zealand. It reflects on the insights derived from this emerging pool of scholarship and considers what lessons have been learned to help us address the future challenges of adaptation to climate change on our coasts and estuaries. In particular, future progress will require strong understanding of natural coastal systems, clearer national direction and guidance in balance with regional flexibility, and collaborative processes to help communities understand, implement and evaluate adaptation pathways for a sustainable and resilient future. [ABSTRACT FROM AUTHOR]