Existing barrier evolution models only simulate storm impacts from landward-driven flows (overwash), neglecting the impacts of seaward-directed flows (outwash). Here, we modify an existing model to incorporate outwash processes. We find that outwash enhances barrier vulnerability (the tendency to drown) over decadal timescales by scarring the island interior, creating lower, narrower landforms. If outwashed sand stays nearshore, a wider beach and steeper shoreface facilitate dune recovery and closure of gaps, which are otherwise maintained by overwash. Importantly, faster (natural) dune growth means the barrier is less vulnerable to future outwash events, but potentially more vulnerable to back-barrier drowning from sea-level rise because dunes also limit building of interior elevation by overwash. Any changes in storm climatology could alter the balance between dune recovery and overwash making the future vulnerability of modern outwashed barriers difficult to assess.

Salt marshes are vital but vulnerable ecosystems. However, our understanding of disturbance-induced dieback and recovery processes in multi-specific marshes remains limited. This study utilized remote sensing data (2001-2021) to analyze a dieback event and subsequent recovery in the multi-specific San Felice marsh within the Venice lagoon, Italy. A significant dieback of Spartina maritima (Spartina) was identified in 2003, likely triggered by a drought event and heat stress. This resulted in a conversion of 4.6 ha of marsh predominantly colonized by Spartina (fractional cover of Spartina > 50%) in 2001 to bare soil in 2003. These bare areas were then gradually encroached by vegetation, indicating the occurrence of the recovery. Despite gradually gaining ground, Spartina only dominated 6.4 ha marshes in 2021, significantly lower than its pre-dieback area (21.3 ha). However, other species also encroached on the dieback area, such that the aboveground biomass returned to pre-dieback levels, indicating that the shift in marsh species composition that occurred as a consequence of the event compensated for this ecosystem service. Vegetation recovery, spanning from 1 yr to more than 18 yr, was found to be slowest in areas of lowest elevation. This study provides evidence that dieback and recovery can modify the species composition of multi-specific marshes over decades. These insights contribute to a better understanding of marsh resilience to drought and elevated temperature, both of which are likely to increase in the future.

Intertidal marshes are valuable geophysical systems, but their extent is rapidly declining globally. Marshes tend to keep up with sea-level rise through suspended-sediment and organic-matter deposition, up to a marsh-specific threshold rate of sea-level rise. Studies that explore marsh survival often assume that inorganic sediment deposition rates are directly linked to the density of marsh vegetation---coupling the inorganic and organic deposition processes. Here we examine the fluid-dynamics regulating sediment transport across a vegetated marsh and derive a framework for platform-wide sediment deposition. We demonstrate that sediment deposition rates are largely independent of vegetation density due to quasi-steady tidal propagation and vegetation-generated turbulence. Consequently, sediment deposition rates are primarily controlled by marsh size and tidal properties. Supported by extensive observations, these findings simplify modeling of long-term marsh dynamics by decoupling inorganic and organic deposition and offer insights into the processes that determine marsh resilience to accelerating sea-level rise.

Coastal wetlands are geomorphic systems highly sensitive to shifts in environmental forcings such as variations in fluvial sediment transport rates, sea level rise, subsidence rates, nutrient concentrations, temperature, and atmospheric CO2 levels. Despite these influences, the presence of vegetation growing on salt marshes significantly enhances their resilience. It mitigates surface and lateral erosion while fostering the accumulation of organic matter, which contributes to marsh soil accretion and the sequestration of organic carbon. Therefore, the characterization of vegetation properties, canopy biomass and species distribution, is crucial to provide a quantitative basis for bio-geomorphic modeling in coastal wetlands.This study aims to spatially characterize key parameters—such as vegetation species distribution and biomass production—through repeated observations utilizing drone, airborne, and satellite multispectral (MS) imaging. The chosen site for this investigation is North Inlet in South Carolina (USA), renowned for its extensive tidal marshes supporting diverse vegetation species. MS and field data acquisitions were conducted in summer (August 2022 and August 2023), coinciding with the period of maximum biomass, and in winter (February 2023), corresponding to the phase of lowest biomass.The application of a random forest (RF) approach proved highly effective in the unmixing process of halophytic vegetation species, enabling the retrieval of the percentage cover for each species. To train the algorithm, field observations were employed to classify drone-captured images within a limited section of the marshland. The random forest classification (RFC) algorithm achieves high accuracies in the classification of vegetation species based on the drone image, with a spatial resolution of about 0.02m and the overall accuracy of about 0.99. Based on this classification result, we applied the random forest regression (RFR) algorithm to unmix vegetation species using coarser-resolution WorldView2 data (pansharpened data with pixel of 0.5 × 0.5 m). Our results suggest that RFR achieves high accuracy in the unmixing process (0.80

Developed barrier systems (barrier islands and spits) are lowering and narrowing with sea-level rise (SLR) such that habitation will eventually become infeasible or prohibitively expensive in its current form. Before reaching this state, communities and other entities will make choices, in the face of changing climate conditions, to modify the natural and built environment to reduce relatively short-term risk. These choices will likely vary substantially even along the same developed barrier system as these landscapes are rarely uniformly managed alongshore. Building on the results from a companion paper, here we use a new modeling framework to investigate the complexities in barrier system dynamics that emerge as a function of alongshore variability in management strategies, accelerations in SLR, and changes in storm intensity and frequency. Model results suggest that when connected through alongshore sediment transport, barriers with alongshore variable management strategies – here, the construction of dunes and wide beaches to protect either roadways or communities – evolve differently than they would in the absence of alongshore connections. Shoreline stabilization by communities in one location influences neighboring areas managed solely for roadways, inducing long-term system-wide lags in shoreline retreat, even decades after nourishment ceases. Conversely, when barrier segments managed for roadways are allowed to overwash, this induces shoreline curvature system-wide, thus enhancing erosion on nearby stabilized segments. Feedbacks between dunes, storms, overwash flux, and alongshore sediment transport also affect the long-term outcome of climate adaptation measures. In the case of partial, early abandonment of roadway management (i.e., decades before the road is deemed untenable), we find that system-wide transitions to less vulnerable landscape states are possible, even under accelerated SLR and increased storminess.

Abstract 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.

Although coasts are frequently seen as at the frontline of near-future environmental risk, there is more to the understanding of the future of coastal environments than a simple interaction between increasing hazards (particularly related to global sea level rise) and increasing exposure and vulnerability of coastal populations. The environment is both multi-hazard and regionally differentiated, and coastal populations, in what should be seen as a coupled social-ecological-physical system, are both affected by, and themselves modify, the impact of coastal dynamics. As the coupled dance between human decisions and coastal environmental change unfolds over the coming decades, transdisciplinary approaches will be required to come to better decisions on identifying and following sustainable coastal management pathways, including the promotion of innovative restoration activities. Inputs from indigenous knowledge systems and local communities will be particularly important as these stakeholders are crucial actors in the implementation of ecosystem-based mitigation and adaptation strategies.

Whilst there is little argument that coasts are on the frontline when it comes to the impacts of near-future global environmental change, is there a need for yet another coastal journal? Emphatically ‘yes’. There is an unfilled niche here for a forum that promotes and presents cross-disciplinary research, from fundamental science to impact-orientated approaches. We wish to see a journal that informs pathways away from unsustainable practices towards more socially just and equitable futures for the world’s coastlines and their communities. We set out below some of the questions that arise when articulating this pathway, using the high-level categories in the journal’s topic map as some of the stepping stones that will be encountered along the way.

Street trees provide ecosystem services such as heat mitigation, improved community well-being, and biodiversity conservation. At the wildland–urban interface (WUI), high-flammability street trees also provide a conflicting ecosystem disservice, heightening risks of wildfire spread into urban areas. We addressed this service–disservice conflict by assessing shoot flammability patterns in 10 street tree species, to identify low-flammability species that can potentially mitigate wildfire risks at the WUI. We found significant differences among species in flammability attributes including time-to-flame (TTF), flame duration (FD), number of flaming events (nF), and flame temperature (FT), and identified low-flammability species for each attribute. Overall, species’ rankings from least to most flammable differed considerably across the four attributes. For example, native water gum (Tristaniopsis laurina) had the slowest TTF, but had the longest FD. Among nine shoot traits, we found that high leafing intensity was the most frequent trait correlated with flammability. In particular, high leafing intensity was significantly related to fast TTF and high FT. Lack of coordination among flammability attributes suggests that, in general, selection of low-flammability street tree species should consider how each flammability attribute differentially contributes to wildfire spread risk. Nonetheless, native Tuckeroo (Cupaniopsis anacardioides) emerged as a potential candidate for further exploration as a low-flammability street tree as it had comparatively long TTF, short FD, and low nF. We found no consistent evidence that exotic species were less flammable than native species, and suggest that native trees be the focus of further research to identify low-flammability street trees.

River-dominated deltas on Earth are composed of diverse shapes and patterns, ranging from small-scale bifurcations that create channel networks to large-scale deltaic lobes that build deltaic plains. Morphodynamic feedbacks among fluid flow, sediment transport, and bed elevation change are ultimately responsible for creating these shapes and patterns, and understanding how this morphodynamic feedback constructs deltaic landscapes will contribute to developing sustainable solutions for threatened deltaic environments. In this review, we explore what morphodynamic modeling approaches are commonly used to understand how deltas grow. We also explore what the community has learned by using these models and highlight key knowledge gaps to inspire new models and new questions about river-dominated deltas.

Researchers use models to understand and forecast morphodynamic evolution in a variety of coastal contexts: surf zone dynamics including the short-term evolution of the nearshore seabed and shoreline; the longer-term evolution of coastline planview shapes, and associated shoreline change; and the evolution of the cross-shore profiles of barrier and cliffed coastlines. Most models represent processes and interactions between processes in some way, with approaches ranging from simple analytical or geometric treatments to highly detailed numerical models that explicitly simulate fluid dynamics. Many numerical models fall in between these end members, synthesizing the effects that waves and currents have on sediment transport without explicitly simulating the fluid dynamics. In contrast to all these process-based modeling approaches, data-driven, phenomenological modeling approaches—including statistical and machine learning techniques—are increasingly being used to forecast morphological responses, such as shoreline changes related to wave or sea-level forcing scenarios. Important current developments and opportunities in coastal modeling include addressing couplings between planview and cross-shore-profile morphodynamics, couplings between ecological and physical processes, and couplings between human and natural coastal dynamics.

Coastal landforms can sometimes result in unique and visually mesmerizing spatially-organized patterns. Different spatial patterns develop over scales ranging from centimeters to tens of kilometers, and are observed at the shoreline (e.g., ripples, beach cusps, shoreline undulations), in the surf zone (e.g., crescentic or multiple sandbars) and even in the continental shelf (e.g., sand ridges, sand waves) where wind waves may play a minor role. Here, we provide a review of the characteristics of rhythmic patterns that develop in the nearshore and of some of their formative processes, a topic of ongoing debate within the research community.

The dynamics and morphological evolution of deltas and their channel networks involve interactions between many factors, including water and sediment discharge and cohesion from fine sediment and vegetation. These interactions are likely to affect how strongly vegetation influences deltas. Altering water or sediment discharge may affect channel mobility, magnitude of deposition and erosion events, and may result in the delta being less suitable for vegetation colonization. Using the numerical model DeltaRCM Vegetation, we explore how water and sediment discharge affects delta evolution and under which conditions vegetation exerts a stabilizing effect on the channel network. We propose new insights into delta evolution under different discharge conditions. First, we observe a regime shift in avulsion dynamics, driven by delta‐scale water surface slopes, with increasing water discharge: from a few active channels undergoing occasional complete, global avulsions (with low discharge) to many active channels experiencing frequent partial, local avulsions (with high discharge). Second, with vegetation, increased sediment discharge results in more frequent switching of the dominant channels but also prevents vegetation from establishing in non‐dominant channels, resulting in more frequent channel reoccupation and therefore greater stability in channel network planform. These insights have important implications for understanding the distribution of water, sediment, and nutrients on deltas in the face of future changes in climate and human modifications of fluxes of sediment and water to the coast, especially for restored or engineered deltas with controlled water or sediment discharges.

Coastal salt marshes are unique and complex geomorphological systems, which must accrete to keep pace with sea-level rise. Even though we know the importance of vegetation and organic matter accumulation in the marsh accretion process, we lack an understanding of spatially-distributed saltmarsh dynamics that include feedbacks with vegetation, especially for sites characterized by high species diversity. Remote sensing retrievals of wetland topography, spatial distribution of species, and vegetation biomass and productivity provide an ideal solution, providing observations over the wide range of scales of interest. Here we present the results obtained using LiDAR and hyperspectral data collected via Unmanned Aerial Vehicles (UAVs) on the San Felice saltmarsh (Venice lagoon, Italy). The selected study site hosts at least twelve species of halophytes grouped into five main associations. UAVs data were collected in September 2021, while a simultaneous field survey provided spatially-distributed georeferenced data and samples on the distribution of vegetation associations, above- and below-ground biomass, vegetation height, bulk density and organic carbon content of the soil. Results suggest that, for different plant associations, LiDAR data can be used to retrieve the aboveground biomass and estimate the belowground biomass (through allometric relations), hence providing a spatially-distributed assessment of the vegetation biomass across the marsh. Combining this information with the organic carbon content obtained by soil analyses, we estimate the combined above- and below-ground carbon stock of the salt marsh. The results obtained using hyperspectral data suggest that vegetation indexes defined on appropriate spectral bands correlate with the LiDAR biomass information and ground truth data. Using these results, observations from UAVs and satellites can be combined to bridge data from the plant to the wetland scale and beyond.

Sea level rise causes barrier islands to migrate landward. Coastal evolution modelling reveals a centennial-scale lag in island response time and suggests migration rates will increase by 50% within the next century, even if sea level were to stabilize.

On wave‐influenced river deltas, wave‐driven sediment redistribution affects river progradation, and therefore avulsions, while avulsions change where sediment is delivered to the coastline, affecting coastline shape. Coastline shape, in turn, affects sediment redistribution rates and patterns. Here we use a numerical model to investigate how the asymmetry of wave climates affects delta avulsion behaviors, which are coupled with delta shape evolution. Increasing wave‐climate asymmetry tends to reduce (increase) the curvature of updrift (downdrift) delta flanks, by increasing (decreasing) local shoreline diffusivity. In our model experiments, reduced shoreline curvature restricts the possible updrift post‐avulsion river mouth locations, while increased curvature expands the possible downdrift locations, favoring “downdrift avulsions.” However, under some wave climates, local diffusivity on the downdrift flank can become negative, leading to convexity and shoreline accretion, inhibiting downdrift avulsions. Increasing wave heights and decreasing superelevation threshold for avulsions both tend to reduce delta morphologic asymmetry, and therefore avulsion tendency.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Why Do Fluxes Near the Granular Bed Scale Differently Than Within the Transport Layer?AuthorsConnerLesteriDA. BradMurrayiDOrencioDuran VinentPhilippeClaudinBrunoAndreottiSee all authors Conner LesteriDCorresponding Author• Submitting AuthorDuke UniversityiDhttps://orcid.org/0000-0002-1622-0142view email addressThe email was not providedcopy email addressA. Brad MurrayiDDuke UniversityiDhttps://orcid.org/0000-0002-2484-9151view email addressThe email was not providedcopy email addressOrencio Duran VinentTexas A&M University College Stationview email addressThe email was not providedcopy email addressPhilippe ClaudinLaboratoire de Physique, ENS - PSL Research University, Université de Paris, CNRS, Sorbonne Université, Paris, Franceview email addressThe email was not providedcopy email addressBruno AndreottiUniversité de Paris - ENSview email addressThe email was not providedcopy email address

River deltas grow through repeated stacking of sedimentary lobes, the location and size of which are determined by channel avulsions (relatively sudden changes in river course). We use a model coupling fluvial and coastal processes to explore avulsion dynamics under a range of wave energies and sea-level-rise rates and find that the primary control on avulsion location and delta lobe size in our model is the critical superelevation ratio (SER), the amount of channel aggradation relative to the surrounding floodplain that is required to trigger an avulsion. The preferred avulsion location arises because of geometric constraints - a preferential avulsion node occurs at the break in floodplain slope that develops as the river progrades and/or sea level rises. This concavity develops in our model because the river profile aggrades and erodes via linear diffusion, whereas the diffusion of the floodplain topography is limited to episodic crevasse splays. These results are in contrast to recent modeling work, which was motivated by laboratory experiments and assumes a union between river channel and floodplain aggradation rates, and where avulsion nodes are driven by backwater hydrodynamics. The preferred avulsion length in our model scales well with laboratory, field, and model results without including hydrodynamic backwater effects. This work suggests an alternative mechanism to explain avulsion locations on deltas where floodplain topography aggrades and/or diffuses more slowly than the river channel profile, and it points to the need to elucidate river channel and floodplain connectivity over large space and time scales, and how the connectivity varies from one type of delta to another. Published by Elsevier B.V.

Leaf flammability is a functional trait that can vary widely among plant species. At present, however, the effects that increasing radiant heat flux have on variation in leaf flammability among species are not well understood. Yet, such effects could have important implications for wildfire models that take into account species' differences in flammability. We examined how five leaf flammability attributes spanning ignitibility (times to incandescence and flaming), sustainability (incandescence and flame durations) and combustibility (proportion of leaves entering flaming combustion) responded to increasing radiant heat fluxes (29.6 to 96.6 kWm-2 ) in 10 species of fire-prone woodlands. As radiant heat flux increased, times to incandescence and flaming became significantly faster and proportions of leaves entering flaming combustion became significantly higher. In contrast, incandescence duration became significantly shorter at high radiant heat flux. Differences among species in these flammability attributes decreased with increasing radiant heat flux, with species becoming significantly more similar to each other. Differences among species in flame duration, however, were not significantly affected by increasing radiant heat flux, with leaf flaming durations in each species remaining relatively fixed across the radiant heat flux gradient. Our findings show that leaf flammability is significantly affected by increasing radiant heat flux. We suggest that of the flammability attributes assessed in our study, flame duration is the most informative to include in wildfire models which explicitly consider species' flammability, given that differences among species in flame duration are maintained across a radiant heat flux gradient.