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Glaciologist Rob DeConto's research on polar climate change, specifically focusing on glaciers and ice sheets, is discussed in this article. DeConto explains the differences between Antarctica and Greenland and the challenges of understanding how the Antarctic ice sheet will behave in a warmer world. He also discusses the potential dangers of marine ice sheet instability and the impact of melting ice shelves on sea-level rise. The article emphasizes the uncertainties surrounding the rate of sea-level rise and the need for further research in this area. It highlights the term "deep uncertainty" used by the Intergovernmental Panel on Climate Change (IPCC) to describe the situation and the conservative nature of current projections. The author emphasizes the need for action to address the melting of ice sheets, as it poses a threat to infrastructure worldwide. [Extracted from the article]

Disentangling the effects of cyclical variability in environmental forcing and long-term climate change on natural communities is a major challenge for ecologists, managers, and policy makers across ecosystems. Here we examined whether the vertical distribution of rocky intertidal taxa has shifted with sea-level variability occurring at multiple temporal scales and/or long-term anthropogenic sea-level rise (SLR). Because of the distinct zonation characteristic of intertidal communities, any shift in tidal dynamics or average sea level is expected to have large impacts on community structure and function. We found that across the Northeast Pacific Coast (NPC), sea level exhibits cyclical seasonal variability, tidal amplitude exhibits ecologically significant variability coherent with the 18.6-year periodicity of lunar declination, and long-term sea-level rise is occurring. Intertidal taxa largely do not exhibit significant vertical distribution shifts coherent with short-term (monthly to annual) sea-level variability but do exhibit taxa-specific vertical distribution shifts coherent with cyclical changes in lunar declination and long-term SLR at decadal timescales. Finally, our results show that responses to cyclical celestial mechanics and SLR vary among taxa, primarily according to their vertical distribution. Long-term SLR is occurring on ecologically relevant scales, but the confounding effects of cyclical celestial mechanics make interpreting shifts in zonation or community structure challenging. Such cyclical dynamics alternatingly amplify and dampen long-term SLR impacts and may modify the impacts of other global change related stressors, such as extreme heat waves and swell events, on intertidal organisms living at the edge of their physiological tolerances. As a result, intertidal communities will likely experience cyclical periods of environmental stress and concomitant nonlinear shifts in structure and function as long-term climate change continues. Our results demonstrate that consistent, large-scale monitoring of marine ecosystems is critical for understanding natural variability in communities and documenting long-term change.

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.

This study aims to analyze the impact of sea-level rise and tropical cyclones on mangroves in the context of global climate change from 1993 to 2023, and to explore the development status, co-operative relationships and future trends in this research field. In order to analyze future research directions for mangroves in the context of climate, this study also provides an important basis and reference for the development of research related to the mitigation of natural disasters. Using CNKI and the Web of Science as data sources, this study employs the bibliometric tool CiteSpace 6.3 R1 to conduct a quantitative and visual analysis of the research field. The research findings indicate the following: (1) The volume of publications in this field has been increasing year by year; especially since 2010, the rate of increase has accelerated, indicating an increased academic interest in this area. (2) From the authorship maps of the two data sources, it can be observed that the collaboration network is dense, indicating the existence of co-operative relationships among researchers. (3) From the analysis of the keywords, it is evident that, with the rise of artificial intelligence, the focus of keywords has gradually shifted from traditional mangrove mechanism research and ecosystem studies to research on mangroves that integrates big data, artificial intelligence, and high-resolution remote sensing data. (4) As time has progressed, areas of research interest have been shifting from the study of disturbances and damage to mangrove vegetation to the study of mangrove resilience and vulnerability in the context of natural disasters, their carbon sequestration capabilities, and their protective functions against wind and waves. The use of remote sensing technology for the monitoring and conservation of mangroves has emerged as a key area of focus for future research. In future research, there will be a focus on the adaptive capacity of mangroves to varying degrees of sea-level rise and the increasing frequency of tropical cyclones, as well as on what measures can be taken to enhance the resilience of mangrove ecosystems. Quantitative and visual analysis of the development trends in this field can provide a reference for the construction of a disaster monitoring platform for mangroves affected by sea-level rise and tropical cyclones, and can aid the development of research aimed at mitigating the impacts of natural disasters. Furthermore, the integration of remote sensing technology and ecological models can facilitate more detailed research, offering more effective tools and strategies for the conservation and management of mangroves. This approach also provides a reference point for developing a monitoring platform for mangrove disasters associated with sea-level rise and the impact of tropical cyclones. [ABSTRACT FROM AUTHOR]

Arctic shorelines are vulnerable to climate change impacts as sea level rises, permafrost thaws, storms intensify, and sea ice thins. Seventy-five years of aerial and satellite observations have established coastal erosion as an increasing Arctic hazard. However, other hazards at play--for instance, the cumulative impact that sea-level rise and permafrost thaw subsidence will have on permafrost shorelines--have received less attention, preventing assessments of these processes' impacts compared to and combined with coastal erosion. Alaska's Arctic Coastal Plain (ACP) is ideal for such assessments because of the high-density observations of topography, coastal retreat rates, and permafrost characteristics, and importance to Indigenous communities and oilfield infrastructure. Here, we produce 21st-century projections of Arctic shoreline position that include erosion, permafrost subsidence, and sea-level rise. Focusing on the ACP, we merge 5 m topography, satellite-derived coastal lake depth estimates, and empirical assessments of land subsidence due to permafrost thaw with projections of coastal erosion and sea-level rise for medium and high emissions scenarios from the Intergovernmental Panel on Climate Change's AR6 Report. We find that by 2100, erosion and inundation will together transform the ACP, leading to 6-8x more land loss than coastal erosion alone and disturbing 8-11x more organic carbon. Without mitigating measures, by 2100, coastal change could damage 40 to 65% of infrastructure in present-day ACP coastal villages and 10 to 20% of oilfield infrastructure. Our findings highlight the risks that compounding climate hazards pose to coastal communities and underscore the need for adaptive planning for Arctic coastlines in the 21st century. [ABSTRACT FROM AUTHOR]

Reduced riverine sediment supply and sea-level rise (SLR) threaten land building and ecosystem in deltas. However, the sediment-morphodynamic processes in a channel-shoal complex are not well understood. Here, based on bathymetry and the Delft3D model, geomorphic changes and suspended sediment budgets in the South Passage, Nanhui and Jiuduansha Shoal in the mega-Changjiang Delta were examined. Results reveal that with riverine suspended sediment concentration (SSC) decreased by 75%, the net sediment deposition rate was reduced from 4.20 cm/yr in 1979–1990 to 3.21 cm/yr in 1990–2003, and further declined to 2.21 cm/yr in 2003–2013 and 0.40 cm/yr in 2013–2020. Severe erosion occurred along the upper South Passage and extended toward the mouth bar. Strong accretions accumulated in the Nanhui and Jiuduansha Shoal. After river SSC declined from 0.53 kg/m3 to 0.35 kg/m3, 0.16 kg/m3, and 0.12 kg/m3, net suspended sediment deposition was lowered by 3.13%, 7.35% and 8.67%, respectively. Moreover, SLR of 5 cm, 15 cm, 25 cm, and 50 cm resulted in a further 1.11%, 4.18%, 4.16%, and 14.79% reduction in sediment trapping efficiency. Our findings highlight the strong likelihood that reduced river sediment input, SLRs and intensified anthropogenic effects will exacerbate sediment deficit and erosion in mega fluvial-tidal deltas. [ABSTRACT FROM AUTHOR]

Communities need to implement adaptation strategies to prepare for the challenges posed by rising sea levels. In the U.S., federal funding will be required to support coastal communities’ adaptation, yet little is known about what the general public thinks about different sea-level rise adaptation strategies. In two studies, we investigated how support for different broad categories of adaptation strategies (managed retreat, resistance, accommodation, rebuilding in place) varied among Americans. We hypothesized that perceiver characteristics (e.g., political ideology) and the framing of community characteristics (risk and resilience) would predict support for adaptation. In Study 1 (N = 368), we asked participants to report their strategy preferences for a community in their own locale, then randomly assigned them to read about a hypothetical community which varied in terms of risk and resilience. People were much more willing to support adaptation strategies in high-risk communities. Strategy support was predicted by political ideology, eminent domain beliefs, and climate change concern. In Study 2 (N = 1048), we sought to extend our findings by collecting data from a nationally representative sample. We manipulated community framings of social capital and resources, but these framings related to resilience had little effect on strategy support. However, perceiver characteristics mattered, for instance, eminent domain endorsement predicted support for managed retreat. Across both studies, participants supported adaptation and opposed rebuilding without changes. We describe the ways these findings might be used by policymakers, and the implications of the research for communicators. [ABSTRACT FROM AUTHOR]

Estuaries worldwide have been altered by anthropogenic modifications including land clearing, dredging, and land reclamation, which impact sediment routing and accumulation on tidal flats. Numerous studies have explored tidal flat and marsh vulnerability to submergence or "drowning" under accelerating sea-level rise, but recent work along the Oregon coast suggests estuaries are maintaining positive accretionary balances (at least in marshes) despite ongoing sea-level rise. In this study, accretion rates (sediment accumulation rates) were evaluated from 210Pb profiles at eight sites on broad intertidal flats in Coos Bay, one of the largest estuaries on the U.S. West Coast and a site of substantial development and logging since the mid-1800s. Based on the century-scale record of sediment accretion represented by 210Pb profiles, tidal flats have been accreting at rates of ~ 1–3 mm/yr with little spatial relationship to relative sea-level rise or patterns of tectonic uplift. Thus, accretion is generally not accommodation- or supply-limited, and therefore likely not regulated by sea-level rise. Peaks in sediment accretion are well-preserved from the last 30 years, and accretion rates averaged over this more modern time span tend to be four times greater than rates averaged over the whole-core (century-scale) 210Pb records. It is unclear whether the higher, more modern rates represent a real change in estuarine accretion patterns over the past decades or a Sadler effect (i.e., an apparent but not real increase in accretion in younger sediments). The results highlight the spatial variability in accretion rates within a single estuary, the potential resiliency of this tectonically active estuary to sea-level rise (in the form of a positive accretionary balance), and raise the issue of whether management decisions are best made based on century-scale accretion rates or multi-decadal accretion rates. [ABSTRACT FROM AUTHOR]

Sea-level rise is accelerating globally and will continue for centuries under all shared socio- economic pathways. Although sea-level rise is a global issue, its impacts manifest heterogeneously at the local scale, with some coastal communities and infrastructure considerably more vulnerable than others. Aotearoa New Zealand is poorly prepared to deal with sea-level rise impacts, and some places are already approaching the limits of adaptation, short of relocation. Maladaptive choices threaten Aotearoa's ongoing ability to adapt going forward. Development of climate-resilient pathways requires an immediate adoption of non-partisan, long-term, system-scale approaches to governance and decision making (from local to national), that integrate effective adaptation and emissions mitigation. This also requires proactive and collective action underpinned by indigenous and actionable knowledge (e.g., NZ SeaRise projections) designed for our unique circumstances. There is still time to put in place sustainable, equitable and effective solutions, but funding and governance models need urgent attention. [ABSTRACT FROM AUTHOR]

Leaf litter in coastal wetlands lays the foundation for carbon storage, and the creation of coastal wetland soils. As climate change alters the biogeochemical conditions and macrophyte composition of coastal wetlands, a better understanding of the interactions between microbial communities, changing chemistry, and leaf litter is required to understand the dynamics of coastal litter breakdown in changing wetlands. Coastal wetlands are dynamic systems with shifting biogeochemical conditions, with both tidal and seasonal redox fluctuations, and marine subsidies to inland habitats. Here, we investigated gene expression associated with various microbial redox pathways to understand how changing conditions are affecting the benthic microbial communities responsible for litter breakdown in coastal wetlands. We performed a reciprocal transplant of leaf litter from four distinct plant species along freshwater‐to‐marine gradients in the Florida Coastal Everglades, tracking changes in environmental and litter biogeochemistry, as well as benthic microbial gene expression associated with varying redox conditions, carbon degradation, and phosphorus acquisition. Early litter breakdown varied primarily by species, with highest breakdown in coastal species, regardless of the site they were at during breakdown, while microbial gene expression showed a strong seasonal relationship between sulfate cycling and salinity, and was not correlated with breakdown rates. The effect of salinity is likely a combination of direct effects, and indirect effects from associated marine subsidies. We found a positive correlation between sulfate uptake and salinity during January with higher freshwater inputs to coastal areas. However, we found a peak of dissimilatory sulfate reduction at intermediate salinity during April when freshwater inputs to coastal sites are lower. The combination of these two results suggests that sulfate acquisition is limiting to microbes when freshwater inputs are high, but that when marine influence increases and sulfate becomes more available, dissimilatory sulfate reduction becomes a key microbial process. As marine influence in coastal wetlands increases with climate change, our study suggests that sulfate dynamics will become increasingly important to microbial communities colonizing decomposing leaf litter. [ABSTRACT FROM AUTHOR]

To increase the resilience of salt marshes subject to sea‐level rise impacts, managers can focus on interventions within current marsh footprints or in adjacent uplands to facilitate landward marsh migration. The latter approach may be more appropriate when degradation is severe and in situ intervention options are limited. Strategies for facilitating marsh migration include removing artificial barriers, soil grading to reduce steep topography, and manipulating adjacent upland vegetation that can hinder migration, but experiments testing the effectiveness of these activities are limited. We therefore conducted a field experiment to determine if physically removing three upland vegetation types (forest, shrub, and Phragmites australis) adjacent to a Rhode Island salt marsh facilitates short‐term marsh migration. Upland vegetation removal led to increased ambient light in all habitats, significantly enhanced marsh plant cover, extent, and elevation in shrub habitat, and declines in total bird abundance in forest and shrub habitats. Enhanced migration did not occur in forest or Phragmites habitats, and in shrubs, marsh plants only colonized where Baccharis halimifolia, common in upper marsh borders, had been removed. Five years after removal, all upland habitats and associated vegetation were indistinguishable from initial conditions. Our study suggests that upland plant removal might provide a limited window for facilitating salt marsh migration and that more intensive methods may be needed for sustained, longer‐term benefits. It also demonstrates that there may be ecological trade‐offs to consider when altering upland habitats to enhance landward marsh migration. [ABSTRACT FROM AUTHOR]

Practitioners at the local and regional scale are under increased pressure to reduce risks to people and property posed by the threats of sea‐level rise (SLR) and associated impacts. To achieve this, a dialog between practitioners and scientists is imperative. Current research documents impacts of SLR, evaluates local SLR adaptation activities, identifies barriers to action, and works to assess local adaptive capacity. Despite this work, there has been little qualitative assessment of practitioners' needs when it comes to translating SLR science into local changes. To fill this gap, we used a combination of semi‐structured interviews and surveys. The interviews revealed practitioners' needs, the tools they use, the challenges they face, and the contexts in which they make decisions. The survey allowed practitioners to rank potential interventions according to the level of impact they believed it would have on coastal adaptation planning. In total our study includes the perspectives of 142 practitioners from 24 states, Puerto Rico, the Mariana Islands, and Barbados. Corroborating earlier work, we find that resources broadly and funding specifically is the largest barrier faced by practitioners. We find that practitioners need more localized information and models supported by on the ground monitoring, decision support resources that allow for comparison of different scenarios, and communication tools that will enable them to engage with key audiences. These needs suggest a critical shift toward building trusted relationship between scientists and local practitioners and the need to bolster organizations that can support a bridge between these two contexts. Plain Language Summary: We describe the needs of practitioners to build resilience in their communities to sea‐level rise (SLR). They are concerned about how SLR will interact with existing natural coastal challenges. These challenges include storm surge, habitat loss, saltwater intrusion, and erosion. Practitioners continue to face challenges related to resources such as lack of funding and lack of staff capacity. They also face social and institutional challenges in the areas of information, commitment, and political environments. As one participant, who is responsible for building resilience in their community said: "Fundamentally, we're relying on the science, but there is a huge gap between scientists and people who are trying to get things done." This quote highlights the challenge of translating SLR science into local actions, such as building a sea wall or restricting development. It points to a need for many to help create a bridge between pure SLR science and those working as coastal planners, sustainability professionals, natural system managers, and other allied professions. Through interviews, we shed light on 38 specific needs in three categories—information, decision support, and communication tools/education opportunities—that would enable practitioners to build resilience in their communities. Based on our survey, we find that very specific information is needed to enable practitioners to build resilience. They need local scale data, on‐the‐ground monitoring, locally calibrated models about increased risks, and information about the relative effectiveness of nature‐based solutions. Practitioners are also looking for communication tools that translate the impacts of SLR into economic values. We recommend a series of interventions that could support practitioners in their work to build resilience to SLR. Key Points: We identified 38 specific needs in three categories—information, decision support, and communication tools/education opportunitiesPractitioners need local scale data, on‐the‐ground monitoring, and locally calibrated models for compound flooding and increased riskThey also need decision‐support resources including information about the effectiveness of solutions and translation into economic values [ABSTRACT FROM AUTHOR]

As global climate change alters the magnitude and rates of environmental stressors, predicting the extent of ecosystem degradation driven by these rapidly changing conditions becomes increasingly urgent. At the landscape scale, disturbances and stressors can increase spatial variability and heterogeneity — indicators that can serve as potential early warnings of declining ecosystem resilience. Increased spatial variability in salt marshes at the landscape scale has been used to quantify the propagation of ponding in salt marsh interiors, but ponding at the landscape scale follows a state change rather than predicts it. Here, we suggest a novel application of commonly collected surface elevation table (SET) data and explore millimeter-scale marsh surface microtopography as a potential early indicator of ecosystem transition. We find an increase in spatial variability using multiple metrics of microtopographic heterogeneity in vulnerable salt marsh communities across the North American Atlantic seaboard. Increasing microtopographic heterogeneity in vulnerable salt marshes mirrored increasing trends in variance when a tipping point is approached in other alternative stable state systems — indicating that early warning signals of marsh drowning and ecosystem transition are observable at small-spatial scales prior to runaway ecosystem degradation. Congruence between traditional and novel metrics of marsh vulnerability suggests that microtopographic metrics can be used to identify hidden vulnerability before widespread marsh degradation. This novel analysis can be easily applied to existing SET records expanding the traditional focus on vertical change to additionally encapsulate lateral processes. [ABSTRACT FROM AUTHOR]

Coastal wetlands surrounding urban environments provide many important ecosystem services including protection from coastal erosion, soil carbon sequestration and habitat for marine and terrestrial fauna. Their persistence with sea-level rise depends upon their capacity to increase their soil surface elevation at a rate comparable to the rate of sea-level rise. Both sediment and organic matter from plant growth contribute to gains in soil surface elevation, but the importance of these components varies among sites and with variation in climate over long time scales, for which monitoring is seldom available. Here, we analysed variation in surface elevation, surface accretion and mangrove tree growth over 15 years in Moreton Bay, Queensland, Australia, a period that spans variation in the El Niño/La Niña (ENSO) cycle, which strongly influences rainfall and sea level in the region. Piecewise structural equation models were used to assess the effects of biotic (tree growth, plant cover and bioturbation by invertebrates) and environmental factors on annual surface elevation increments throughout this period. Our model for mangroves identified that surface accretion and tree growth were both positively influenced by rainfall, but surface elevation was not, and thus, higher levels of compaction of the soil profile in high rainfall/high sea level years were inferred. In contrast, our saltmarsh model found that rainfall positively influenced surface accretion and elevation gains. Declines in surface elevation in the mangroves were influenced by the species composition of the mangrove, with higher levels of elevation loss occurring in mangrove forests dominated by Avicennia marina compared to those with a higher proportion of Rhizophora stylosa. Decadal-scale variation in ENSO affected mangrove tree growth, but surface elevation trends were more strongly influenced by variation in environmental conditions than by tree growth, although effects of biotic factors (mangrove species composition and bioturbation) on surface elevation trends were observed. Further research into tipping points with extreme ENSO events (either La Niña with high rainfall and high sea level or El Niño with low rainfall and low sea levels) will help clarify the future of mangrove and saltmarsh distribution within Moreton Bay. [ABSTRACT FROM AUTHOR]

The capacity of coastal wetlands to maintain their position within a tidal frame is a key indicator of resilience to climate change. A range of techniques can be used to assess this capacity, but few studies have focussed on describing wetland elevation dynamics across timescales. In this study, annual-scale wetland elevation dynamics within intertidal coastal wetlands located at different tidal positions in south-eastern Australia were quantified using both shallow and deep rod surface elevation tables and marker horizon (rSET-MH) techniques. This was supplemented by analyses of sediment accumulation rates across the decadal-centurial timescale using 210Pb dating techniques. The rSET-MH technique indicated slight variation in surface elevation change between sub-sites and processes contributing to surface elevation gain was a product of processes occurring over the full substrate volume. This included sediment (both mineral and organic) accretion on the surface and belowground substrate expansion in tidal positions where accommodation space and inundation frequency were higher (i.e. in the mangrove). 210Pb data provided the means to consider sedimentation and wetland elevation trends over decadal timescales over which relative sea-level rise has been operating. Sedimentation responded to localised accommodation space processes, exceeding sea-level trends lower in the tidal frame, but corresponded to rates of sea-level rise where accommodation space was increasingly limited (i.e. higher in the tidal frame). We demonstrate that anticipated sea-level rise will create new accommodation space for wetland vegetation and that where sea-level rise is not matched by an equivalent increase in surface elevation, coastal wetlands will either die, retreat landwards, or transition to lower tidal positions that support mangroves. [ABSTRACT FROM AUTHOR]

Tidal marshes build elevations by below- and aboveground organic and mineral soil processes. Marsh elevation and accretion data can be used to determine if marshes are keeping pace with sea-level rise. Using a network of 54 deep rod surface elevation tables with paired feldspar marker horizon plots, we tracked elevation and accretion trends across 16 marshes in California, USA. All sites had overall positive gains across years that included severe drought conditions and extreme rain events. Marsh elevation relative to tidal datum (z*) was the key predictor for elevation and accretion rates, with higher change rates at lower z* sites. Marsh sites are clustered into three regional groups (Northern California, San Francisco Bay area, and Southern California), primarily defined by maximum temperature and annual rainfall differences. Elevation, accretion, and shallow subsidence rates were not significantly different between clusters, but their explanatory variables did vary. High-temperature days were a key predictor for elevation, accretion, and shallow subsidence rates in the state-wide analysis and San Francisco Bay regional analysis. The largest elevation gains were observed in the San Francisco Bay-Delta and some of the smallest in Humboldt Bay, with Morro Bay having the lowest accretion rate overall. Central and Southern California marshes were keeping pace or out-pacing sea-level rise, while none of the Humboldt Bay marshes were keeping pace. Marsh surface elevation data can inform management intervention and be a leading indicator for sea-level rise vulnerability. Long-term monitoring across geomorphic settings can help inform management and anticipate marsh change. [ABSTRACT FROM AUTHOR]

In the face of accelerating climate change and rising sea levels, quantifying surface elevation change dynamics in coastal wetlands can help to develop a more complete understanding of the implications of sea-level rise on coastal wetland stability. The surface elevation table-marker horizon (SET-MH) approach has been widely used to quantify and characterize surface elevation change dynamics in coastal marshes and mangrove forests. Whereas past studies that utilized the SET-MH approach have most often quantified rates of surface elevation change using simple linear regression analyses, several recent studies have shown that elevation patterns can include a diverse combination of linear and non-linear patterns. Generalized additive models (GAMs) are an extension of generalized linear models (GLMs) that have previously been used to analyze a variety of complex ecological processes such as cyclical changes in water quality, species distributions, long-term patterns in wetland area change, and palaeoecological time series. Here, we use long-term SET data to demonstrate the value of generalized additive models for analyzing non-linear patterns of surface elevation change in coastal wetlands. Additionally, we illustrate how the GAM approach can be used to effectively quantify rates of elevation change at both landscape- and local site-level scales. [ABSTRACT FROM AUTHOR]

Australian tidal wetlands differ in important respects to better studied northern hemisphere systems, an artefact stable to falling sea levels over millennia. A network of Surface Elevation Table-Marker Horizon (SET-MH) monitoring stations has been established across the continent to assess accretionary and elevation responses to sea-level rise. This network currently consists of 289 SET-MH installations across all mainland Australian coastal states and territories. SET-MH installations are mostly in mangrove forests but also cover a range of tidal marsh and supratidal forest ecosystems. Mangroves were found to have higher rates of accretion and elevation gain than all the other categories of tidal wetland, a result attributable to their lower position within the tidal frame (promoting higher rates of accretion) higher biomass (with potentially higher rates of root growth), and lower rates of organic decomposition. While Australian tidal marshes in general show an increase in elevation over time, in 80% of locations, this was lower than the rate of sea-level rise. High rates of accretion did not translate into high rates of elevation gain, because the rate of subsidence in the shallow substrate increased with higher accretion rates (r2 = 0.87). The Australian SET-MH network, already in many locations spanning two decades of measurement, provides an important benchmark against which to assess wetland responses to accelerating sea-level rise in the decades ahead. [ABSTRACT FROM AUTHOR]

Twenty years of surface elevation table and marker horizon monitoring at three sites along the Fire Island (New York, USA) barrier island indicates that rates of marsh surface elevation change (Watch Hill, 4.4 mm year−1; Hospital Point, 3.5 mm year−1; Great Gun, − 0.3 mm year−1) were lower than the rate of monthly mean sea-level rise during the 2002–2022 monitoring period (5.1 mm year−1, NOAA Sandy Hook, NJ, water level station). The Great Gun monitoring site, with an elevation deficit relative to sea-level rise, shallow subsidence (surface accretion > marsh elevation rate), low elevation capital, prolonged marsh surface flooding, and declining vegetation cover, displays characteristics common to deteriorating marshes. The submergence trend was not as evident at the other monitoring sites, but with low tidal range (0.4 m) and projections of accelerated sea-level rise, sustainability is questioned if marsh elevation change continues to lag behind the local rate of relative sea-level rise. Hurricane Sandy occurred during the monitoring period (October 2012), creating a new inlet located about 300 m from one of the monitoring sites. Surprisingly, no immediate signals of deposition or erosion were noted from the marker horizon sampling. Overwash sand deposits on the marsh surface were extensive along Fire Island, although not reaching the monitoring sites, and will likely provide opportunities for future salt marsh growth, as will the flood-tide delta created by the inlet. Projecting the future of barrier island salt marshes under a regime of accelerated sea-level rise and episodic storms requires knowledge of marsh elevation and accretion processes and geomorphic dynamics. [ABSTRACT FROM AUTHOR]

Threats to coastal wetlands, including sea-level rise and subsidence, led the National Wildlife Refuge (NWR) System to protect over 500,000 hectares of coastal wetlands during the twentieth century, with approximately 20% occurring in the South Atlantic geography. This effort has involved systematic long-term monitoring of changes in marsh elevation using surface elevation tables and marker horizons at 20 sites across 19 NWRs in the southeastern coastal USA. From 2012 to 2021, the rates of change in surface elevation (−9.3 to 7.1 mm/year), accretion (−0.3 to 17.5 mm/year), and net vertical elevation change (−14.3 to 3.1 mm/year) were highly variable among monitoring sites and varied with coastal wetland type (oligohaline marsh, salt marsh, pocosin, or forested wetland), land surface elevation, and estuarine salinity and geomorphology (i.e., tidally influenced or embayed). Of 20 sites included in our study, only six were gaining elevation at a rate that was equal to or greater than the long-term rates of sea-level rise and therefore considered resilient. Only Waccamaw and Currituck NWRs, both located in oligohaline marshes, were gaining elevation at a rate that exceeded sea-level rise by 1 mm/year. These results support the mounting evidence that many coastal wetlands, particularly in the South Atlantic geography of the USA, will undergo ecological transformations in the next several decades. The NWR System and other coastal management entities will need to use strategic decision-making frameworks to identify management actions that can mitigate the loss of coastal wetlands to support the conservation of coastal wetland–dependent and obligate species. [ABSTRACT FROM AUTHOR]

Coastal wetlands adapt to rising seas via feedbacks that build soil elevation, which lead to wetland stability. However, accelerated rates of sea-level rise can exceed soil elevation gain, leading to wetland instability and loss. Thus, there is a pressing need to better understand regional and landscape variability in rates of wetland soil elevation change. Here, we conducted a regional synthesis of surface elevation change data from mangrove forests and coastal marshes in the iconic Greater Everglades region of south Florida (USA). We integrated data from 51 sites in which a total of 122 surface elevation table-marker horizon (SET-MH) stations were installed. Several of these sites have been periodically monitored since the 1990s and are among the oldest SET-MH datasets in the world. Rates of surface elevation change ranged from −9.8 to 15.2 mm year−1, indicating some wetlands are keeping pace with sea-level rise while others are at risk of submergence and conversion to open water. Vertical accretion rates ranged from 0.6 to 12.9 mm year−1, and subsurface change rates ranged from −13.5 to 8.6 mm year−1. Rates of surface elevation change were positively related to subsurface change but not vertical accretion. There were no significant relationships between rates of surface elevation change and elevation (NAVD 88) or rates of sea-level rise. Site-specific examples indicate that hurricanes, plant productivity, hydrologic exchange, and proximity to sediment and nutrient inputs are critical but confounding drivers of surface elevation change dynamics in the Greater Everglades region. Collectively, our results reinforce the value of long-term SET-MH data that incorporate spatial variability for advancing understanding of surface elevation change dynamics in coastal wetlands. [ABSTRACT FROM AUTHOR]

We estimate the economic benefits of avoiding reductions in drinking water quality due to sea level rise accruing to North Carolina (NC) coastal tourists. Using stated preference methods and responses from recent coastal visitors, we find that tourists are 2%, 8%, and 11% less likely to take an overnight trip if drinking water tastes slightly, moderately, or very salty at their chosen destination. The majority of those who decline a trip would take a trip to another NC beach without water quality issues, others would take another type of recreational trip, with a minority opting to stay home. Willingness to pay for an overnight beach trip declines with the salty taste of drinking water. We find evidence of attribute non‐attendance in the stated preference data, which impacts the regression model and estimates of the willingness to pay for trips. Combining economic and hydrological models, annual aggregate benefit losses due to low drinking water quality could be as high as $232 million by 2040. Key Points: We estimate the benefits to North Carolina coastal tourists of avoiding reductions in drinking water quality due to sea level riseWillingness to pay for an overnight beach trip declines with the salty taste of drinking waterAnnual aggregate benefit losses due to low drinking water quality could be as high as $232 million in 2040 [ABSTRACT FROM AUTHOR]

Nature-based solutions (NbSs) of biodiversity conservation and ecosystem restoration have been paid increasing attention as an essential approach to slow down climate change. However, to what degree an NbS approach will contribute to the combined effects of human intervention and climate change has not been well studied. From a habitat quality perspective, we set four NbS scenarios to analyze whether the NbS—mangrove restoration in particular—will be enough for climate change in Xiamen Bay of Fujian Province, China. The habitat quality module of the InVEST model (InVEST-HQ) and the Sea Level Affecting Marshes Model (SLAMM) were used to simulate the spatial-temporal changes in habitat types and habitat quality. Results show that (1) rising sea levels will cause coastal squeeze effects, impacting habitat quality due to erosion and inundation in the study area; (2) mangrove restoration is an effective way to mitigate climate change effects and to increase habitat quality; and (3) further analysis of the effectiveness of mangrove restoration shows that the consideration of mangrove fragmentation effects and sea-use impacts are necessary. The findings in this study will enrich the international discussion of NbSs to climate change in coastal areas. [ABSTRACT FROM AUTHOR]

Sea-level rise is particularly concerning for tidal wetlands that reside within an area with steep topography or are constrained by human development and alteration of sedimentation. Sediment augmentation to increase wetland elevations has been considered as a potential strategy for such areas to prevent wetland loss over the coming decades. However, there is little information on the best approaches and whether adaptive management actions can mimic natural processes to build sea-level rise resilience. In addition, the lack of information on long-term marsh characteristics, processes, and variability can hamper development of effective augmentation strategies. Here, we assess a case study in a southern California marsh to determine the nature of the pre-existing sediments and variability of the site in relation to sediments applied during an augmentation experiment. Although sediment cores revealed natural variations in the grain size and organic content of sediments deposited at the site over the past 1500 years, the applied sediments were markedly coarser in grain size than prehistoric sediments at the site (100% maximum sand versus 76% maximum sand). The rate of the experimental sediment application (25.1 ± 1.09 cm in ~2 months) was also much more rapid than natural accretion rates measured for the site historically. In contrast, post-augmentation sediment accretion rates on the augmentation site have been markedly slower than pre-augmentation rates or current rates on a nearby control site. The mismatch between the characteristics of the applied sediment and thickness of application and the historic conditions are likely strong contributors to the slow initial recovery of vegetation. Sediment augmentation has been shown to be a useful strategy in some marshes, but this case study illustrates that vegetation recovery may be slow if applied sediments are not similar or at a thickness similar to historic conditions. However, testing adaptation strategies to build wetland elevations is important given the long-term risk of habitat loss with sea-level rise. Lessons learned in the case study could be applied elsewhere.

The impacts associated with global climate change (e.g., sea-level rise, tropical storms, and warming temperatures) are expected to alter predator–prey interactions, foundation species, and plant community structure in coastal ecosystems. While the complex dynamics of these habitats have been examined under future climate predictions, few ecosystem models incorporate influences from fauna, such as the diamondback terrapin, the only estuarine turtle native to North America. This review examines the impacts of climate change on diamondback terrapins (Malaclemys terrapin) and the role that terrapins play as higher trophic level predators and keystone species in driving the dynamics of these ecosystems. We also review the potential implications of changes to terrapin populations on coastal ecosystems as a conservation challenge and suggest solutions to advance our understanding of those complex systems. Because of their role as a keystone and area-sensitive species that helps maintain healthy coastal habitats by foraging on herbivorous periwinkle snails, alterations to terrapin life history from climate change are expected, which could have significant impacts to the conservation of coastal habitats. Life history alterations could occur due to individual stressors, such as warming temperatures altering terrapin sex ratios. However, because of the complexity of these coastal systems, these stressors could also act additively or synergistically. Inclusion of faunal taxa such as the diamondback terrapin in modeling efforts examining climate change impacts to coastal ecosystems would better represent the complexity of these habitats thereby providing a more comprehensive evaluation of the entire ecosystem, resulting in more effective conservation strategies. [ABSTRACT FROM AUTHOR]

Introduction: Disrupted weather patterns are associated with climate change. Between 2001 and 2018, nearly 74% of disasters were water-related, including floods and cyclones. Such water-related cataclysmic events increase the risk of drowning. We aimed to map evidence on the impact of climate change on water-related physical events, associated human migration, and drowning burden in India. MATERIALS AND METHODS: We searched electronic databases, government reports, and relevant websites to map evidence on water-related physical events (including but not limited to sea-level rise, glacier bursts, lake bursts, floods, rainfall, cyclones, and droughts) and consequent human migration using narrative review approach, while drowning burden through scoping review approach. We summarized the results narratively. Results: Evidence from 48 studies and seven reports suggest that India will witness the greatest sea-level rise, significantly impacting poor coastal communities. An increase in droughts, cyclonic rainfall, storms, and floods, with increasing surface rainwater and streamflow water, due to melting glaciers is expected. Climate change–triggered migration is expected notably in northeast and south India, making farmers, drivers, street vendors, women, and youth most vulnerable. No direct evidence was identified on the impact of climate change, water-related disasters, meteorological events, or seasonal variations on drowning from India. Conclusion: Our study highlights a significant gap in the availability of context-specific and localized data to improve disaster response and strengthen public health systems, especially for areas most vulnerable to climate change. There is an urgent need to generate new knowledge and understanding of climate change, water-related or meteorological events, and seasonal variations’ impact on drowning burden as the level of risk remains unknown.

Bayhead deltas form at the interface between fluvial and estuarine systems. As such, they are sensitive to processes operating in both the fluvial catchment and the marine realm, including past relative sea‐level changes. The Nakdong valley is a small and confined incised valley containing a bayhead delta that provides a record of fluvial sediment input and accommodation changes. Based on a facies analysis that included 833 sediment textures and 118 optically stimulated luminescence and radiocarbon ages within five cores up to 70 m long, this study reconstructed the development of a fully filled bayhead delta in response to relative sea‐level changes through the early to late Holocene. Sixteen facies are defined and grouped into eight facies associations: alluvial plain; fluvial channel and floodplain; oxidized fluvial channel; tidal flat; tidal bar; central basin and bayhead prodelta; bayhead delta front; and bayhead delta plain. The sequence stratigraphy of the Nakdong valley fill can be divided into three systems tracts: a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Overall sedimentary analyses suggest six depositional stages corresponding to variations between sediment inputs and sea‐level rise of the developing bayhead delta in the Nakdong valley. The depositional model tracks relative sea‐level rise in the Nakdong valley after 12 ka during the early to late Holocene. These analyses on the Nakdong bayhead delta succession illustrate the balance between sediment inputs and periods of accelerating and decelerating relative sea‐level rise during the Holocene. The architecture of the valley fill also records two abrupt disequilibrium events from 9 to 8 ka and 5 to 3 ka, likely resulting from rapid sea‐level rise during the deglacial outburst flooding of the early Holocene and decreased sediment inputs during regional climatic changes associated with the middle Holocene, respectively. [ABSTRACT FROM AUTHOR]

Coastal hazards threaten properties, infrastructure, and cultural sites around Aotearoa New Zealand's (hereafter Aotearoa) coastline and sea-level rise (SLR) will escalate this problem. At present it is unclear how archaeological sites will be affected by future coastal erosion and inundation. In this paper we combine national-scale archaeological and environmental datasets to provide a first-pass overview of archaeological heritage at risk in Aotearoa. Two key national-scale datasets are utilized: (1) coastal sensitivity index (CSI) developed by the National Institute of Water and Atmospheric Research; and (2) ArchSite, Aotearoa's archaeological site database. The integrated datasets produce insights into the sensitivity of coastal archaeology to SLR and associated hazards, which are vital to planning for the loss of coastal archaeological sites. More than half (∼55%) of recorded coastal archaeological sites around Aotearoa are midden (n = 4938) and about 25% (n = 2271) are earthworks. In total, ca. 12% (9054) of all known archaeological sites are within 1000 m of soft shore shorelines. Of this total, only about 3% (302) of sites are burials, but the loss of these 302 burial sites would have very high cultural impact. Coastal erosion is a particularly important threat to archaeology as it would permanently remove sites, whereas the risk of site removal by coastal flooding inundation is lower. Our results show that about 22% (1954) of coastal archaeological sites are located on landforms that are sensitive to SLR-driven erosion: 29% (2660) of archaeological sites are located on foredune barrier beaches, 23% (2059) on foredune barrier plains, 14% (1283) on beaches, and 9% (808) on beach ridge barriers. This work draws attention to the scale of coastal archaeology in Aotearoa that needs adequate documentation, preservation, and potentially protection in the face of SLR. Robust coastal erosion and inundation datasets are needed to more deeply understand potential SLR-driven impacts on coastal archaeology and provide a scientific foundation for considering future adaptation options. [ABSTRACT FROM AUTHOR]

Atlantic White Cedar (Chamaecyparis thyoides) (AWC) anchors a globally threatened ecosystem that is being impacted by climate change, as these trees are vulnerable to hurricane events, sea-level rises, and increasing salinity at the forest–marsh ecotone. In this study, we determined the current amount and distribution of AWC in an area that is experiencing sea-level rises that are higher than the global average rate. We used a combination of a field investigation and aerial photo interpretation to identify known locations of AWC, then integrated Sentinel-1 and 2A satellite data with abiotic variables into a species distribution model. We developed a spectral signature of AWC to aid in our understanding of phenology differences from nearby species groups. The selected model had an out-of-bag error of 7.2%, and 8 of the 11 variables retained in the final model were derived from remotely sensed data, highlighting the importance of including temporal data to exploit divergent phenology. Model predictions were strong in live AWC stands and, accurately, did not predict live AWC in stands that experienced high levels of mortality after Hurricane Sandy. The model presented in this study provides high utility for AWC management and tracking mortality dynamics within stands after disturbances such as hurricanes. [ABSTRACT FROM AUTHOR]

Here, we describe a dataset of two-dimensional (2D) XBeach model files that were developed for the Coastal Storm Modeling System (CoSMoS) in northern California as an update to an earlier CoSMoS implementation that relied on one-dimensional (1D) modeling methods. We provide details on the data and their application, such that they might be useful to end-users for other coastal studies. Modeling methods and outputs are presented for Humboldt Bay, California, in which we compare output from a nested 1D modeling approach to 2D model results, demonstrating that the 2D method, while more computationally expensive, results in a more cohesive and directly mappable flood hazard result. Dataset:  https://doi.org/10.5066/P9048D1S. Dataset License: CC0 [ABSTRACT FROM AUTHOR]

The Sundarbans is the world's largest contiguous mangrove forest with an area of about 10,000 square kilometers and shared between Bangladesh and India. This world-renowned mangrove forest, located on the lower Ganges floodplain and facing the Bay of Bengal, has long served as a crucial barrier, shielding southern coastal Bangladesh from cyclone hazards. However, the Sundarbans mangrove ecosystem is now increasingly threatened by climate-induced hazards, particularly tropical cyclones originating from the Indian Ocean. To assess the cyclone vulnerability of this unique ecosystem, using geospatial techniques, we analyzed the damage caused by past cyclones and the subsequent recovery across three salinity zones, i.e., Oligohaline, Mesohaline, and Polyhaline. Our study also examined the relationship between cyclone intensity with the extent of damage and forest recovery. The findings of our study indicate that the Polyhaline zone, the largest in terms of area and with the lowest elevation, suffered the most significant damage from cyclones in the Sundarbans region, likely due to its proximity to the most cyclone paths. A correlation analysis revealed that cyclone damage positively correlated with wind speed and negatively correlated with the distance of landfall from the center of the Sundarbans. With the expectation of more extreme weather events in the near future, the Sundarbans mangrove forest faces a potentially devastating outlook unless both natural protection processes and human interventions are undertaken to safeguard this critical ecosystem. [ABSTRACT FROM AUTHOR]

We study how environmental risks induced by the potential inundation associated with sea‐level rise affects firms' financial structure decisions. We find that firm leverage decreases with inundation risks associated with sea‐level rise. To establish causality, we consider firms' relocation of their headquarters, a propensity score matching estimator, and a difference‐in‐differences estimator around the release of the documentary "An Inconvenient Truth" and find that our results are robust. The negative relation between inundation risks due to sea‐level rise and financial leverage is more pronounced for firms with more geographically concentrated operations, firms with more close rivals, and firms that are non‐investment grade. SLR risk‐affected firms shift more towards equity and away from debt in their capital raising efforts and have a relatively higher weight of their leverage in short‐term debt. Our findings highlight firms' proactive adjustment and adaptation to long‐term environmental risks. [ABSTRACT FROM AUTHOR]

The increase in natural disaster frequency, intensified by climate change, poses one of the greatest threats to coastal systems and low-lying areas worldwide. It is estimated that the Global Mean Sea Level (GMSL) could rise by approximately 2 m in the twenty-first century, alongside intensifying cyclonic events. Consequently, in Brazil, coastal natural disasters are likely to become more frequent and intense, especially in the southern region. Thus, this study aims to identify, map and discuss coastal natural disasters in municipalities exposed to the open ocean belonging to the coastal zone of Santa Catarina (SC), Brazil, between 1998 and 2020. A review and dating of coastal natural disasters were conducted using four official databases: The Civil Defense of Santa Catarina website, Integrated Disaster Information System (S2ID), Santa Catarina Atlas of Natural Disasters, and the Brazilian Atlas of Natural Disasters. The data were organized into spreadsheets and mapped using QGIS 3.16.0 software. The results and main conclusions indicate: (1) More coastal disasters occurred in the north, central-north, and central sectors of SC between 1998 and 2020; (2) the period between 2010 and 2020 was more impactful; (3) the municipalities with the most records of coastal disasters were Balneário Barra do Sul, Itapoá and Florianópolis (considering only Ilha de Santa Catarina), respectively; (4) the three fastest-growing sectors are the north, central-north, and central; and (5) the seasons of autumn, spring, and winter, respectively, are more impacting for the study area. [ABSTRACT FROM AUTHOR]

ABSTRACT: Introduction: Disrupted weather patterns are associated with climate change. Between 2001 and 2018, nearly 74% of disasters were water-related, including floods and cyclones. Such water-related cataclysmic events increase the risk of drowning. We aimed to map evidence on the impact of climate change on water-related physical events, associated human migration, and drowning burden in India. Materials and Methods: We searched electronic databases, government reports, and relevant websites to map evidence on water-related physical events (including but not limited to sea-level rise, glacier bursts, lake bursts, floods, rainfall, cyclones, and droughts) and consequent human migration using narrative review approach, while drowning burden through scoping review approach. We summarized the results narratively. Results: Evidence from 48 studies and seven reports suggest that India will witness the greatest sea-level rise, significantly impacting poor coastal communities. An increase in droughts, cyclonic rainfall, storms, and floods, with increasing surface rainwater and streamflow water, due to melting glaciers is expected. Climate change–triggered migration is expected notably in northeast and south India, making farmers, drivers, street vendors, women, and youth most vulnerable. No direct evidence was identified on the impact of climate change, water-related disasters, meteorological events, or seasonal variations on drowning from India. Conclusion: Our study highlights a significant gap in the availability of context-specific and localized data to improve disaster response and strengthen public health systems, especially for areas most vulnerable to climate change. There is an urgent need to generate new knowledge and understanding of climate change, water-related or meteorological events, and seasonal variations' impact on drowning burden as the level of risk remains unknown. [ABSTRACT FROM AUTHOR]

Durant, D. and Kernéïs, E., 2024. Investigating the farm resilience of polder environments after seawater flooding: Results from Storm Xynthia (2010). Journal of Coastal Research, 40(5), 887–900. Charlotte (North Carolina), ISSN 0749-0208. Climate forecasts predict that global warming will cause sea-levels to rise and will increase the frequency of storms in the future, thus also increasing the risk of submersion of coastal agricultural areas. Yet very few studies examine the consequences of seawater flooding, from either an agricultural or an environmental point of view. This study therefore investigates the resilience of coastal farming systems through the case study of the Saint Laurent de la Prée research farm hit by the Storm Xynthia in 2010. Two aspects of resilience are analysed here: (i) the soil characteristics of the system (indicators: salinity, sodicity and structural stability) after the submersion, and the system's ability to recover its productive capacity on croplands (crop yields) and on permanent grasslands (fodder production); and (ii) the ecological resilience of permanent grasslands (indicators: species richness and diversity). Results showed that the system recovered its productive capacity in 2012, so after two years, when the research farm engineers recorded a return of the crops and grasslands to a production level that they considered satisfactory. For crop soils, there was a quick recovery of salinity levels, but the structural stability after the storm was largely degraded and had not totally recovered by 2012. On grasslands, the farm suffered two successive years of low grassland productivity, partially due to a temporary shift in plant species' composition. Finally, two dimensions of resilience are discussed here: (i) the speed of recovery; and (ii) the ability to learn from the storm, in view of the increasing risks of coastal submersion in the future. As it appears that flood protection policy must consider local and long-term impacts of seawater flooding on agricultural lands, this study can provide useful information for further research on the foresight scenarios and adaptive strategies required. [ABSTRACT FROM AUTHOR]

Salt marshes have ecological and economic value, but shoreline development, the increasing rate of sea-level rise, and other human impacts have caused significant loss of salt marshes. As a result, restoration of these ecosystems is widespread. For restoration and management to be effective, it is imperative to improve our understanding of marsh-building plants that serve as the ecological foundation of these habitats. Given the observed differences in characteristics between populations of smooth cordgrass, Spartina alterniflora, restoration plantings may impact the biodiversity and resilience of restored ecosystems. Understanding differences in the structural and functional outcomes of active planting of restoration sites will enable the long-term success of restoration efforts to be improved. Natural and restored salt marshes in Long Island Sound were studied in 2021–2022 for S. alterniflora genetics, biomass, stem morphology, and faunal community composition. The average genotypic diversity of S. alterniflora was more than 4 times higher in restored than in natural marshes, and differentiation between each restored site and natural sites decreased with time. No difference was observed in live S. alterniflora belowground biomass; however, mean dead belowground biomass in natural marshes was more than 3 times greater than in restored marshes. Marsh platform invertebrates differed between the restored and natural sites, with natural marsh edge habitats having 9 times higher density of Geukensia demissa and 3 times as many crab burrows than in restored marshes, but there was no detected difference in species richness or abundance of nekton at high tide. With restoration practitioners seeking resilient, self-sustaining ecosystems, it is important to evaluate whether restored marsh characteristics are consistent with those goals and modify restoration planning accordingly to incorporate genetics, structure, and function. [ABSTRACT FROM AUTHOR]

Freshwater lenses and their freshwater–saltwater transition zones are affected by climate change. Both sea-level rise and groundwater recharge influence freshwater volume and transition zone thickness. This study used a semi-generic approach to investigate climate change effects on freshwater lenses: a hypothetical island cross-section was combined with real-world boundary conditions. Sea-level projections including tides and storm surges, annual mean sea-level rise data, and monthly recharge projections of several climate models of the German barrier island Norderney in the North Sea were used to evaluate changes in freshwater lens and transition zone size between 1971–2000 and 2071–2100. Firstly, impacts of sea-level and recharge boundary conditions were investigated on islands of different widths. Secondly, a multi-parameter study was conducted focussing on variations of several relevant hydrogeological parameters. Results showed that it is very likely but not certain that freshwater lens volume and depth will decrease and transition zone thickness increase as a consequence of climate change. Model predictions revealed a strong dependency on the employed climate models and to a lesser extent on the hydrogeological parameters, at least for the parameter ranges used in this study. Of all hydrogeological parameters tested, the largest effects were caused by the hydraulic conductivity and its anisotropy. Furthermore, the study showed that boundary conditions have larger impacts on smaller islands. These results illustrate the importance of using projections from climate models in a sufficiently high resolution. Furthermore, their uncertainties and changes in variability of boundary conditions should be considered in studies about climate change impacts on freshwater lenses. [ABSTRACT FROM AUTHOR]

Recent Greenland ice-sheet melt constitutes a considerable contribution to global sea-level rise. Observations indicate an approximate zero mass balance of the ice sheet until the late 1990s, after which a strong increase in melting occurred. This cannot be attributed linearly to gradually-increasing global warming. Instead the abrupt shift has been linked to atmospheric circulation changes, although causality is not fully understood. Here we show that changes of atmospheric waves over Greenland have significantly contributed to the shift into a strong melting state. This is evident after having applied a newly-developed methodology effectively decomposing atmospheric flow patterns into parts associated with waves of different scales such as Rossby waves and smaller perturbations. The onset of a westerly-flow reduction, consistent with anthropogenic Arctic warming, affected transports by atmospheric waves and led to a decrease in precipitation and an increase in surface warming, contributing to ice-sheet mass loss, in particular over the southwestern regions. As such, the Greenland ice-sheet melt is an example of a climate response non-linearly coupled to global warming. [ABSTRACT FROM AUTHOR]

A policy subsystem is a system of relations between actors within the context of a specific, territorially bounded policy issue. Mature policy subsystems feature well‐established, easily distinguishable, confrontational coalitions. Recent literature has explored the behavior of nascent subsystems, which emerge in response to novel policy challenges and feature developing, rather than fully fledged, coalitions. However, as yet, we lack an empirical approach to identify and analyze the structural characteristics of nascent subsystems and assess their implications for theoretical and subsystem development. How do we recognize a nascent policy subsystem when we see one? What are the drivers of its nascent coalitional structure? We answer these questions using social network analysis in the empirical case of the governance network of adaptation to sea‐level rise in the San Francisco Bay Area, using original data collected in 2018. We find that the network portrays a nascent subsystem developing out of pre‐existing coalitions focused on two facets of environmental advocacy: environmental protection and environmental justice. We conclude with recommendations for future research on policy subsystem development. [ABSTRACT FROM AUTHOR]

Southeast Australian saltmarshes are endangered ecological communities under threat from various anthropogenic factors including climate change. As climate change drives sea‐level rise mangrove encroachment and saltmarshes are squeezed at their landward edge, our lack of knowledge of the ecological interactions and any associations between saltmarsh vegetation and fauna becomes concerning, especially given the importance of saltmarsh for fisheries and as a blue carbon habitat. This study investigated the association of saltmarsh vegetation and the abundance and movement of gastropods in a typical coastal saltmarsh at Patonga, New South Wales, Australia. Densities of the gastropods including Phallomedusa solida, Ophicardelus spp. and Littoraria luteola were significant in vegetated Salicornia quinqueflora and least in unvegetated saltmarsh and areas where mangroves had encroached. Experiments that translocated Ophicardelus spp. and manipulated cover revealed that these patterns were actively maintained by Ophicardelus spp., which dispersed up to 40 cm and 1.4 m after 3 and 24 h, respectively, away from unvegetated saltmarsh and mangroves. The results of this study suggest that both habitat and cover influence the abundance and movement of gastropod dynamics in southeastern saltmarsh. Given future anticipated saltmarsh loss, further investigations are needed on the unknown functional role of gastropods in saltmarsh ecosystems. [ABSTRACT FROM AUTHOR]

In the context of climate change, coastal flood risk is intensifying globally, particularly in China, where intricate coastlines and frequent tropical cyclones make storm surges a major concern. Despite local government's efforts to initiate coastal monitoring networks and qualitative risk guidelines, there remains a gap in detailed and efficient quantitative assessments for combinations of multiple sea‐level components. To address this, we develop the Tropical Cyclone Storm Surge‐based Flood Risk Assessment under Combined Scenarios (TCSoS‐FRACS). This framework integrates impacts of storm surges, high tides, and sea‐level rise using a hybrid of statistical and dynamic models to balance reliability and efficiency. By combining hazard, exposure, and vulnerability, it incorporates economic and demographic factors for a deeper understanding of risk composition. Applying TCSoS‐FRACS to Hainan Island reveals that the combined effects of storm surges, high tides, and sea‐level rise significantly amplify local coastal flood risk, increasing economic losses to 4.27–5.90 times and affected populations to 4.96–6.23 times. Additionally, transitioning from Fossil‐fueled Development (SSP5‐8.5) to Sustainability (SSP1‐1.9) can reduce the risk increase by approximately half. The equivalence in flood hazard between current high tides and future sea level under a sustainable scenario boosts confidence in climate change adaptation efforts. However, coastal cities with low hazard but high exposure need heightened vigilance in flood defense, as future risk could escalate sharply. Our study provides new insights into coastal flood risk on Hainan Island and other regions with similar profiles, offering a transferable and efficient tool for disaster risk management and aiding in regional sustainable development. Plain Language Summary: Climate change is intensifying coastal flood risk worldwide. We developed TCSoS‐FRACS, a framework that assesses flood risk from storm surges, high tides, and sea‐level rise, using a combination of dynamic and statistical models. This framework evaluates hazard, exposure, and vulnerability to predict affected populations and economic losses across various land uses. When applied to Hainan Island, it shows that the combination of storm surges, high tides, and rising sea levels significantly increases flood risk. However, transitioning from a Fossil‐fueled Development Path to a Sustainability Path can reduce this increased risk almost by half. The study also finds that, on Hainan Island, current high tide hazards may be comparable to future sea‐level rise hazards under a sustainable scenario, boosting confidence in adaptation efforts. Coastal cities with low hazard but high exposure need greater vigilance, as their future flood risk could rise sharply. Our research offers valuable insights and tools for managing coastal flood risk in Hainan Island and similar regions, supporting sustainable development and effective disaster management. Key Points: Design a flood risk framework for TC storm surges combined with high tides and sea‐level rise using hybrid dynamic and statistical modelsEquivalence in flood between current high tides and future sea level under a sustainable scenario boosts confidence in adaptation effortsCoastal cities with low hazard but high exposure need heightened vigilance in flood defense as future risk could dramatically escalate [ABSTRACT FROM AUTHOR]

Fresh coastal groundwater is a valuable water resource of global significance, but its quality is threatened by saltwater intrusion. Excessive groundwater abstraction, sea‐level rise (SLR), land subsidence and other climate‐related factors are expected to accelerate this process in the future. The objective of this study is to (a) quantify the impact of projected climate change and (b) explore the role of individual hydrogeological boundaries on groundwater salinization of low‐lying coastal groundwater systems until 2100 CE. We employ numerical density‐dependent groundwater flow and salt transport modeling for this purpose, using Northwestern Germany as a case. Separate model variants are constructed and forced with climate data, that is, projected SLR and groundwater recharge, as well as likely ranges of other hydrogeological boundaries, including land subsidence, abstraction rates and drain levels. We find that autonomous salinization in the marsh areas, resulting from non‐equilibrium of the present‐day groundwater salinity distribution with current boundary conditions, is responsible for >50% of the salinization increase until 2100 CE. Sea‐level rise, land subsidence and drain levels are the other major factors controlling salinization. We further show that salinization of the water resources is a potential threat to coastal water users, including water suppliers and the agrarian sector, as well as coastal ecosystems. Regional‐scale uplifting of drain levels is identified as an efficient measure to mitigate salinization of deep and shallow groundwater in the future. The presented modeling approach highlights the consequences of climate change and anthropogenic impacts for coastal salinization, supporting the timely development of mitigation strategies. Plain Language Summary: Our study focuses on fresh groundwater near coastlines, which is crucial for drinking water, agriculture, and natural ecosystems, but is at risk of becoming salty due to mixing with saline groundwater. We investigate how climate change, including sea‐level rise, changing groundwater recharge and subsiding land surfaces, might make this problem worse by 2100 CE. Northwestern Germany, located at the North Sea, is used as a case, and numerical groundwater models are employed to simulate the groundwater development in the study area. We find that the current groundwater salinity distribution is not at equilibrium with present‐day boundary conditions, which is a primary reason for an expected salinity increase by 2100 CE. Rising sea‐levels and the design of the marsh drainage system are other key factors. We show that raising mainland drainage levels would be an effective way to reduce future salinization in both deep and shallow groundwater. The methods applied in this study could help other coastal areas to understand the implications of future groundwater salinization. Key Points: We show that autonomous salinization is a key process driving salinization of low‐lying coastal groundwater systemsWe find that sea‐level rise and land subsidence are other major factors amplifying future groundwater salinizationWe describe how salinization of coastal fresh groundwater impacts different water users [ABSTRACT FROM AUTHOR]

Sea‐level rise (SLR) poses a severe threat to the coastal environment through seawater intrusion into freshwater aquifers. The rising groundwater table also exacerbates the risk of pluvial, fluvial, and groundwater flooding in coastal regions. However, current Earth system models (ESMs) commonly ignore the exchanges of water at the land‐ocean interface. To address this gap, we developed a novel land‐ocean hydrologic coupling scheme in a state‐of‐the‐science ESM, the Energy Exascale Earth System Model version 2 (E3SMv2). The new scheme includes the lateral exchange between seawater and groundwater and the vertical infiltration of seawater driven by the SLR‐induced inundation. Simulations were performed with the updated E3SMv2 for the global land‐ocean interface to assess the impacts of SLR on coastal groundwater under a high CO2 emission scenario. By the middle of this century, seawater infiltration on the inundated areas will be the dominant component in the land‐ocean coupling process, while the lateral subsurface flow exchange will be much smaller. The SLR‐induced seawater infiltration will raise the groundwater levels, enhance evapotranspiration, and increase runoff with distinct spatial patterns globally in the future. Although the coupling process is induced by SLR, we found topography and warming temperature have more control on the coupling impacts, probably due to the relatively modest magnitude of SLR during the selected future period. Overall, our study suggests significant groundwater and seawater exchange at the land‐ocean interface, which needs to be considered in ESMs. Plain Language Summary: As ocean levels rise, seawater threatens to intrude into coastal freshwater aquifers that millions of people depend on for drinking water and irrigation. While regional studies have examined the impacts of sea‐level rise (SLR) on coastal groundwater systems, current Earth system models (ESMs) overlook the exchange of water between ocean and groundwater. Our work addresses this gap by developing a water exchange process between ocean and land components in a state‐of‐the‐science ESM. This coupling scheme includes lateral exchanges between seawater and groundwater, as well as vertical seawater infiltration resulting from oceanic inundation. We used this new coupled model to assess SLR impacts on the global coastal groundwater table under a higher CO2 emission scenario. We found that SLR will raise groundwater levels and intensify the hydrological cycle by midcentury mainly due to increased seawater infiltration. Further, while SLR triggers this increased seawater infiltration, topography and warming temperature play more significant roles in determining its magnitude. Key Points: A novel land‐ocean coupling scheme is developed and implemented in Energy Exascale Earth System Model version 2 to evaluate the hydrologic exchange at the land‐ocean interfaceThe impact of land‐ocean coupling on the groundwater table is dominated by seawater infiltration, while lateral exchange is negligibleFuture sea‐level rise will induce significant seawater intrusion into the coastal groundwater system [ABSTRACT FROM AUTHOR]

Coastal backwater effects on low-gradient coastal plain rivers extend well upstream of the head of the estuary and propagate upstream as sea-level rises. Hydrological, geomorphological, and ecological indicators can serve as sentinels of the upriver encroachment. Analyzing the along-river spatial distribution of these indicators as a space-for-time substitution allows the prediction of sequential changes. Interpretation of results from 20 rivers in Virginia and the Carolinas shows that backwater effects at the leading edge result in higher river stages, increasing floodplain inundation, and raising water tables. Lower slopes and flow velocities reduce sediment transport, reducing river sediment input and floodplain deposition. This inhibits natural levee development, reducing bank heights. These factors combine to increase the frequency and duration of inundation, resulting in semi-permanently flooded wetlands. Anaerobic conditions limit organic decomposition, and ponding allows transported and suspended organic matter to settle, leading to organic muck and peat floodplain soils. This accumulation, coupled with general valley-filling, buries alluvial terrace remnants. Finally, vegetation changes driven by salinity increases occur, resulting in swamp conversions to brackish marsh. Backwater encroachment is strongly controlled by channel bed slope, with relatively steeper channels experiencing slower rates of tidal extension. With accelerating sea-level rise (SLR), the lowest-sloping channels could experience encroachment rates of >1 km yr−1. Hydrological changes associated with SLR are most rapid at the leading, upriver end—averaging 71 km upstream of the head of the estuary in the study rivers at present—and at the lowermost, downstream end of the fluvial-estuarine transition zone. [ABSTRACT FROM AUTHOR]

Reduced riverine sediment supply and sea-level rise (SLR) threaten land building and ecosystem in deltas. However, the sediment-morphodynamic processes in a channel-shoal complex are not well understood. Here, based on bathymetry and the Delft3D model, geomorphic changes and suspended sediment budgets in the South Passage, Nanhui and Jiuduansha Shoal in the mega-Changjiang Delta were examined. Results reveal that with riverine suspended sediment concentration (SSC) decreased by 75%, the net sediment deposition rate was reduced from 4.20 cm/yr in 1979–1990 to 3.21 cm/yr in 1990–2003, and further declined to 2.21 cm/yr in 2003–2013 and 0.40 cm/yr in 2013–2020. Severe erosion occurred along the upper South Passage and extended toward the mouth bar. Strong accretions accumulated in the Nanhui and Jiuduansha Shoal. After river SSC declined from 0.53 kg/m3 to 0.35 kg/m3, 0.16 kg/m3, and 0.12 kg/m3, net suspended sediment deposition was lowered by 3.13%, 7.35% and 8.67%, respectively. Moreover, SLR of 5 cm, 15 cm, 25 cm, and 50 cm resulted in a further 1.11%, 4.18%, 4.16%, and 14.79% reduction in sediment trapping efficiency. Our findings highlight the strong likelihood that reduced river sediment input, SLRs and intensified anthropogenic effects will exacerbate sediment deficit and erosion in mega fluvial-tidal deltas.

Abstract Practitioners at the local and regional scale are under increased pressure to reduce risks to people and property posed by the threats of sea‐level rise (SLR) and associated impacts. To achieve this, a dialog between practitioners and scientists is imperative. Current research documents impacts of SLR, evaluates local SLR adaptation activities, identifies barriers to action, and works to assess local adaptive capacity. Despite this work, there has been little qualitative assessment of practitioners' needs when it comes to translating SLR science into local changes. To fill this gap, we used a combination of semi‐structured interviews and surveys. The interviews revealed practitioners’ needs, the tools they use, the challenges they face, and the contexts in which they make decisions. The survey allowed practitioners to rank potential interventions according to the level of impact they believed it would have on coastal adaptation planning. In total our study includes the perspectives of 142 practitioners from 24 states, Puerto Rico, the Mariana Islands, and Barbados. Corroborating earlier work, we find that resources broadly and funding specifically is the largest barrier faced by practitioners. We find that practitioners need more localized information and models supported by on the ground monitoring, decision support resources that allow for comparison of different scenarios, and communication tools that will enable them to engage with key audiences. These needs suggest a critical shift toward building trusted relationship between scientists and local practitioners and the need to bolster organizations that can support a bridge between these two contexts.