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Coastal erosion is a normal process of nature. However, the rate of coastal erosion, and the frequency and intensity of coastal flooding events, are now on the rise around the world due to the changing climate. Current responses to coastal erosion are primarily determined by site-specific factors, such as coastal elevation, coastal slope, coastal features, and historical coastline change rate, without a systematic understanding of the coastal-change processes in the context of climate change, including spatiotemporal changes in sea level, regional changes in wave climate, and sea ice coverage. In the absence of a clear understanding of the coastal-change processes, most of the current coastal responses have been built upon a risky assumption (i.e., the present-day coastal change will persist) and are not resilient to future climate change. Here, we conduct a literature review to summarize the latest scientific understanding of the coastal-change processes under climate change and the potential research gaps towards the prediction of future coastal erosion. Our review suggests that a coupled coastal simulation system with a nearshore wave model (e.g., SWAN, MIKE21, etc.) can play a critical role in both the short-term and long-term coastal risk assessment and protective measure development.

Understanding coastal hydraulic processes is essential for sustainable coastal planning and management, especially in semi-arid regions where data scarcity represents a significant challenge. This study sought to apply the Brazilian Coastal Modelling System (SMC-Brasil) to analyse the coastal hydraulic processes present on the Brazilian semi-arid coast in Rio Grande do Norte, seeking to understand its boundary conditions given the scarcity of data and limited monitoring network. The methodological procedures followed five main stages: data collection and processing, running the models, statistical analysis, and interpretation of the results. The simulations identified wave propagation and dissipation patterns influenced by local bathymetric features such as sandy banks and submarine canyons. The modelling indicated waves with an average Hs50% of 1.14 m, with dominant directions from ENE to ESE. Longitudinal flows ranged from 1 to 8 m3/h, with a predominance of east to west at medium and high tides. The modelling indicated spatial gradients of energy and sediment transport compatible with historical records and field observations. The results show that submerged relief irregularities play a central role in regional coastal dynamics, conditioning current flows and deposition. The application of SMC-Brasil has shown potential to fill monitoring gaps in regions with low infrastructure, offering affordable and effective technical support for adaptive coastal planning in the face of climate change impacts.

Presence of coastal structures usually causes significant impacts to adjacent shores, especially when they are composed of sand. Many times, these impacts are associated with inappropriate design due to inadequate consideration of hydromorphological processes and system interactions. As a result, excessive erosion and/or deposition of sediment is observed, which implies costly, and in some cases, continuous maintenance. The study presents an assessment and gives explanation of significant changes in the morphology of Asparuhovo Beach (Varna Bay, Bulgarian Black Sea coast) occurred immediately after the construction of the fishing port \"Karantinata\". In only two-year period, the beach adjacent to the facility increased several times in width, significant amount of sediments accumulated on the submerged slope in front of the port entrance, silting it up to such an extent that only the smallest vessels can access the port. The study elucidates the pattern of hydrodynamic and morphodynamic regime in the area influenced by the port, allowing the prediction of future changes in the hydromorphology of Asparuhovo Beach.

Jun, K.W.; Kin, S.D.; Lee, H.J., and Choi, J.H., 2020. Monitoring of morphological changes in an estuary based on time-series analysis of sediment discharge using a hydrophone. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 516–521. Coconut Creek (Florida), ISSN 0749-0208. The purpose of this study is to predict the littoral transport rate and morphological changes of estuaries by measuring the discharge of sediments from rivers into the sea in a time series using a hydrophone. To identify the problem of longshore sediments, an understanding of waves and currents is necessary. However, the runoff characteristics of sediments in river estuary that serve as the main source of sediments should be grasped first. It is important to predict the discharge of sediments from rivers into the sea and understand the coastal processes involved in the formation of sandbars in the estuary and the transport of sediments to coastal waters. The selected study area was the Gagok River located in the East Coast of Korea, where periodic estuary occlusion occurs due to the behavior of rivers and waves. This study investigated the morphological changes in the estuary according to the changes in sediment discharge. The sediment discharge was measured using a hydrophone capable of measuring the continuous sediment transport from the acoustic information based on the movement of the sediments. Based on this method, the hydrophone was applied to the field, and measurements of major rainfall events were taken to investigate the influence of changes in sediment discharge on the morphological changes in the estuary. In addition, to verify the results, the morphological changes in the estuary were linked to the ground LiDAR data measured over several years. The results of the survey confirmed that the occlusion phenomenon of the Gagok River estuary occurred according to the seasonal changes. Except for the flood season, there was a small amount of runoff through the river. As a result, a sand barrier developed in the estuary due to the influence of the sediments transported by the waves from the open sea.

Between the land and ocean, diverse coastal ecosystems transform, store, and transport material. Across these interfaces, the dynamic exchange of energy and matter is driven by hydrological and hydrodynamic processes such as river and groundwater discharge, tides, waves, and storms. These dynamics regulate ecosystem functions and Earth’s climate, yet global models lack representation of coastal processes and related feedbacks, impeding their predictions of coastal and global responses to change. Here, we assess existing coastal monitoring networks and regional models, existing challenges in these efforts, and recommend a path towards development of global models that more robustly reflect the coastal interface. Coastal systems are hotspots of ecological, geochemical and economic activity, yet their dynamics are not accurately represented in global models. In this Review, Ward and colleagues assess the current state of coastal science and recommend approaches for including the coastal interface in predictive models.

Climate change and intense anthropogenic activities have heightened the vulnerability of coastal areas globally. The intensification in the dynamism and uncertainty of coastal processes and change in the past few decades have led researchers and coastal managers to explore new tools with the capability of undertaking a rapid assessment of coastal resources at a relatively lower cost compared with the conventional in situ data collection. The latest advances in unmanned aerial vehicle (UAV) platforms and sensor technologies have made them useful environmental remote sensing tools due to the high temporal and spatial resolution and relatively inexpensive operating costs. This study reviews literature that explored UAV applications in five different areas of the coastal zone comprising the intertidal, coastal organisms and habitats, marine litter, coastal zone disaster management, and coastal zone land use and land cover mapping. The review provides evidence of the potentials and effectiveness of UAVs for coastal zone management (CZM). However, factors such as difficulty in imaging water, setting out ground control points (GCPs) for geolocation of images, and processing large volumes of data can pose a challenge to coastal managers. Extensive review shows the capabilities of current UAV technologies for monitoring and tracking changes in the coastal environment at high spatial and temporal resolution.

The interaction between physical drivers from oceanographic, hydrological, and meteorological processes in coastal areas can result in compound flooding. Compound flood events, like Cyclone Idai and Hurricane Harvey, have revealed the devastating consequences of the co-occurrence of coastal and river floods. A number of studies have recently investigated the likelihood of compound flooding at the continental scale based on simulated variables of flood drivers, such as storm surge, precipitation, and river discharges. At the global scale, this has only been performed based on observations, thereby excluding a large extent of the global coastline. The purpose of this study is to fill this gap and identify regions with a high compound flooding potential from river discharge and storm surge extremes in river mouths globally. To do so, we use daily time series of river discharge and storm surge from state-of-the-art global models driven with consistent meteorological forcing from reanalysis datasets. We measure the compound flood potential by analysing both variables with respect to their timing, joint statistical dependence, and joint return period. Our analysis indicates many regions that deviate from statistical independence and could not be identified in previous global studies based on observations alone, such as Madagascar, northern Morocco, Vietnam, and Taiwan. We report possible causal mechanisms for the observed spatial patterns based on existing literature. Finally, we provide preliminary insights on the implications of the bivariate dependence behaviour on the flood hazard characterisation using Madagascar as a case study. Our global and local analyses show that the dependence structure between flood drivers can be complex and can significantly impact the joint probability of discharge and storm surge extremes. These emphasise the need to refine global flood risk assessments and emergency planning to account for these potential interactions.

In this review we highlight the relevance of biodiversity that inhabit coastal lagoons, emphasizing how species functions foster processes and services associated with this ecosystem. We identified 26 ecosystem services underpinned by ecological functions performed by bacteria and other microbial organisms, zooplankton, polychaetae worms, mollusks, macro-crustaceans, fishes, birds, and aquatic mammals. These groups present high functional redundancy but perform complementary functions that result in distinct ecosystem processes. Because coastal lagoons are located in the interface between freshwater, marine and terrestrial ecosystems, the ecosystem services provided by the biodiversity surpass the lagoon itself and benefit society in a wider spatial and historical context. The species loss in coastal lagoons due to multiple human-driven impacts affects the ecosystem functioning, influencing negatively the provision of all categories of services (i.e., supporting, regulating, provisioning and cultural). Because animals’ assemblages have unequal spatial and temporal distribution in coastal lagoons, it is necessary to adopt ecosystem-level management plans to protect habitat heterogeneity and its biodiversity, ensuring the provision of services for human well-being to multi-actors in the coastal zone.

The brine‐seawater interface (BSI) is a unique type of groundwater‐seawater interface (GSI) characterized by the higher density of underground brine compared to seawater. This study focuses on characterizing the bay‐scale BSI morphology and identifying submarine‐groundwater discharge windows using a comprehensive in‐situ geophysical detection on the south bank of Laizhou Bay. Our findings reveal that the BSI forms an extensive mixing zone (15–20 km) without distinct contours between waters of varying salinities. The discharge windows for underground brine are located in nearshore areas with fine sand distribution and offshore pockmark areas. Hydraulic and salinity gradients drive the underground brine discharge through these windows. The aquitard window is the primary area for shallow and deep brine exchange, likely evolved from paleochannels, ancient tidal creeks, or ancient underwater barriers. These findings provide crucial modeling support for analyzing environmental evolution mechanisms and theoretical basis for planning the underground brine mining in similar coastal regions. Plain Language Summary This study investigates a unique interface where underground brine meets seawater, known as the brine‐seawater interface (BSI). Unlike regular groundwater‐seawater interfaces, the BSI features brine that is denser than seawater. The research focused on characterizing the BSI's morphology and identifying locations where brine discharges into the sea along the south bank of Laizhou Bay. By using advanced detection methods and analyzing samples, the study found that the BSI forms a broad mixing zone of about 15–20 km. There are no clear boundaries between water of different salinities within this zone. The study also identified specific areas near the shore with fine sand and offshore pockmarks where brine discharges occur. These areas are recognized by the presence of suspended fine sediment on the seabed. The movement of brine through these discharge areas is driven by differences in water pressure and salinity. The study suggests that ancient channels and barriers underwater play a significant role in these discharge processes. Understanding these dynamics can help us manage coastal environments and predict how changes in sea and land interactions may affect them. Key Points The bay‐scale brine‐seawater interface (BSI) is a long mixing zone with underground water salinity ranging from high to low from land to sea The nearshore seabed fine sand area and offshore pockmarked area are the main windows for underground brine discharge The BSI morphology and submarine groundwater discharge/exchange windows can be identified by comprehensive geophysical detection results

The late-glacial and post-glacial history of the development of the White Sea coastal zone in the area of the Varzuga River estuary is considered as a result of the interaction of endogenous and exogenous factors of coastal morpholithogenesis. Based on the geomorphological investigations, study of Holocene deposits by lithostratigraphic, diatom, and radiocarbon analyses, as well as collection and analysis of published data, new results on the development of relief of the area for ~13 cal ka have been obtained. The features of the regional hierarchical morphostructure and local post-glacial tectonics of the territory—the spatial relationships of blocks and the rate of vertical movements—were determined. The superimposed linear Nizhnevarzugskaya Depression, which determined the configuration of the Varzuga River estuary in the late-glacial and post-glacial periods, was identified for the first time. The influence of the spatial ratio of blocks and differentiated post-glacial uplift on the coastal morpholithogenesis was established. The course of changes in the relative sea level (RSL), development conditions, and morphodynamics of the open coast and the estuary of the Varzuga River were reconstructed, and new data on the rhythms of coastal geomorphologic  processes (coastal, estuarine, and eolian) were obtained. Three stages of development of the coastal zone were identified, which corresponded to regional rhythms of changes in the relative sea level and climate. They are (I) the Late Glacial transgression and Early Holocene regression (~12 to 9.8 cal ka BP), (II) the Middle Holocene Tapes transgression (7.8 to 4.9 cal ka BP), and (III) the Late Holocene regression (after 4.9 cal ka BP). The upper marine boundary of the Late Glacial transgression was traced at heights of ~54 or 55 m to the west of the Nizhnevarzugskaya depression, 39 or 40 m to its east, and 22 to 25 m a.s.l in the depression. The shores of lower morphostructural blocks up to ~10.2–9.8 cal ka BP were probably blocked by dead ice. During the Tapes transgression, the RSL reached a maximum (~20 m a.s.l.) of ~7.8 to 7.6 cal ka BP and slowly decreased to ~15 m a.s.l. in the interval of ~7.6 to 4.9 cal ka BP. The prevailing directions of sediment fluxes and the approaches of winds and waves became similar to those of today and have not changed significantly since that time. The main source of the coastal sediment supply was the erosion of glaciofluvial sediments and the input of sands from the seabed. In the interval of ~4.9 to 1.7 cal ka BP, the RSL decreased to ~5 m a.s.l. and then slowly approached the modern one. Activation of coastal (~5–1 cal ka BP) and channel (~4.9–4.7 to 3.6–3.4 cal ka BP) processes contributed to rapid filling of the estuary and formation of accumulative sand terraces on exposed banks. The sediment runoff of the Varzuga River became the main source of coastal sediment supply. After ~2.3 cal ka BP, several stages in the intensification of eolian processes were revealed.