Climate change is increasing the frequency and severity of coastal hazards, with rising sea levels and intensifying typhoons accelerating coastal erosion worldwide. Although headland-bay beaches are widely regarded as topographically protected, they are not immune to substantial erosion during intense typhoons. However, their morphodynamic responses to extreme events-particularly sequential typhoon impacts-remain poorly quantified and mechanistically understood, largely due to the lack of high-resolution monitoring. Here we examine Dasha Beach in Zhejiang Province, China, using high-resolution UAV-derived topography to quantify morphological changes associated with two sequential typhoons, Hinnamnor and Muifa, in September 2022. Hinnamnor generated 9827 m3 of net erosion concentrated in the central beach, and Muifa caused an additional 6370 m3 of erosion, completely removing the remaining beach berm. Post-typhoon recovery deposited 7352 m3 of sediment, predominately reconstructing the northern beach berm, and restoring volumes to pre-Muifa but not preHinnamnor levels. Hydrodynamic analyses reveal pronounced cross-bay gradients in wave energy, with stronger forcing in the northern sector producing enhanced erosion during the typhoons and greater accretion during recovery. During typhoons, waves primarily drove cross-shore sediment transport. In the recovery phase dominated by obliquely incident waves, however, waves facilitated both cross-shore and longshore sediment transport. Swash processes (uprush and backwash) dominated sediment transport, while water-level variations controlled its spatial extent. Specifically, Muifa-induced high water levels combined with energetic waves led to severe berm erosion. The stable berm sediments, derived from well-sorted backshore and dune areas, exhibited minimal grain-size change under typhoon impact. The coarser sediments indicate that the depositional material during the recovery phase originated from the submarine seabed. Although Dasha Beach currently exhibits substantial short-term resilience, increasingly frequent and intense typhoons will pose escalating challenges. Therefore, the assessment of the need for human intervention on the beach and the design of appropriate beach nourishment schemes are among the key focuses for future research. Overall, these findings refine the processbased understanding of storm-driven morphodynamics, and provide a basis for safeguarding headland-bay beach stability.

Gravel beaches serve as natural defenses against wave energy, storm surges, and coastal hazards. Understanding their sediment dynamics requires analyzing gravel grain-size and grain-shape parameters, yet traditional field sampling, laboratory analysis, and transport-direction determination methods have long presented challenges. To overcome these limitations, this study proposes an integrated technical framework that employs machine learning algorithms to derive sediment characteristics and transport directions from multisource uncrewed aerial vehicle (UAV) datasets. Using spatial and spectral UAV datasets collected at the Fengmenkou gravel beach (Nantian Island, China), the framework derives four key grain-size and grain-shape parameters: mean grain size, sorting coefficient, skewness, and roundness. Results demonstrate that oblique quadrat images collected in the field can be orthorectified for reliable digital analysis, yielding grain-size and grain-shape parameters within acceptable error margins (mean grain-size errors <0.4 Phi; sorting coefficient errors <0.3 Phi). The four derived parameters exhibit consistently high accuracy on validation datasets (R-2 >0.80, root mean square error [RMSE] <0.04), enabling high-resolution and spatially continuous characterization of gravel beach sediments. The resulting spatially continuous parameter fields overcome discrete sampling constraints and substantially reduce field costs, while providing improved input data for the Gao-Collins model. Enhanced data resolution and reduced edge effects extend the applicability of the model for grain-size trend analysis on gravel beaches. In addition, a UAV elevation-based approach was developed to infer sediment transport directions from surface elevation changes. This independent analysis shows potential for identifying net sediment movement and provides complementary support for grain-size trend interpretations. Collectively, this work enables spatially explicit and cost-effective characterization of gravel beach sediment dynamics, thereby improving the assessment of coastal processes using UAV data.

Saltmarshes are undergoing rapid retreat worldwide, typically manifested as lateral erosion of marsh edges driven by a combination of continuous erosion and episodic mass failure. Observations resolved at weekly to seasonal intervals mask episodic failures, producing deceptively smooth retreat trends. Here, we present a non-contact Marsh Edge Monitor (MEM) observational framework that uses air-based ultrasonic distance sensing to provide the tidal-scale chronology of marsh-edge retreat. A stable–abrupt–stable distance signature in the time series provides an operationally robust indicator of irreversible failure events. During periods of rapid marsh-edge retreat at the study site, cumulative retreat is dominated (>70%) by discrete failure events, indicating that marsh-edge retreat is fundamentally organized as a sequence of discrete geomorphic events rather than a continuous process. Resolving failure timing at tidal scales enables these dominant failures to be aligned with their near-term, potentially triggering hydrodynamic conditions, highlighting the potential importance of short-term forcing (1–3 tides) relative to longer-term averages (7 tides). These results demonstrate that key marsh-edge retreat dynamics can only be resolved with observations of sufficient temporal resolution and continuity.

The sediment source-to-sink process is an important topic in marine sedimentology. However, how sedimentary signals evolve along source-to-sink path remains less clear. This study focuses on the southward shift of the Huanghe River course between AD 1128 and 1855, and the manifestation and variation of sedimentary signals in a natural diffusion system were investigated through sedimentological analysis of three spatially adjacent regions, the abandoned Huanghe Delta, the central coast of Jiangsu, and the Changjiang Delta. Laboratory analyses including Optically Stimulated Luminescence (OSL), geochemical element analysis, and grain size analysis, were conducted. The results show that sedimentary signals manifest in various forms, primarily manifested in two ways: grain size refinement and sedimentation rate acceleration. The fining of grain size is most pronounced in the abandoned Huanghe delta, followed by the central coast of Jiangsu, and is least pronounced in the Changjiang subaqueous delta. The response of the coastal system to the event was delayed by approximately 0-100, 100-300, and 300-500 years for the abandoned Huanghe Delta, the central coast of Jiangsu, and the Changjiang River Delta, respectively. These findings indicate that sediment transport processes exhibit sedimentary signal attenuation and response lag. This study not only highlights the variation along the source-sink path of coastal sedimentary signals but also illuminates the sedimentary record of drastic changes in sediment flux, which will help study the source-to-sink process given the variable changes in sedimentary fluxes.

Tropical cyclones (TCs) significantly influence coastal sedimentation, geomorphologic features, and morphodynamic processes through strong winds, heavy rains, and storm surges. These effects are particularly pronounced in the east China coastal ocean. However, the impacts of poleward and landward shifts in TC tracks on sedimentology, specifically sediment transport and erosion‐deposition processes, remain insufficiently understood. This study utilizes the Delft3D‐FM numerical model integrated with TC best track data and field measurements to investigate sediment transport patterns under historical TC tracks and to quantify erosion responses to poleward and landward track shifts. From the historical sediment transport pattern derived from the typical historical TC track, results reveal that sediment in waters shallower than 30 m is highly sensitive to TC activity, with four distinct zones where net sediment transport is sensitive to the change of typical historical TC tracks. Coastal erosion depth changes due to poleward and landward shifts of typical TC tracks during the peak TC intensity period are quantified as 0.24–1.63 cm°N −1 and 0.05–1.06 cm°E −1 , respectively. Under global warming scenarios, these values are projected to increase by 2.45%–8.00% and 4.71%–13.33%, respectively. Identifying the coastal areas more susceptible to TC‐induced sediment transport and quantitatively assessing the effects of poleward and landward track shifts are important for understanding local TC variability and supporting research on sedimentology during TCs and the future protection of coastal areas.

The transport processes of coastal sediments play a critical role in shaping coastal geomorphology, with sediment properties-such as grain size-being fundamental to understanding morphodynamics. However, the field collection and laboratory analysis of sediments are time-consuming and labour-intensive, posing great challenges for large-scale and rapid monitoring of sediment spatiotemporal variations. Unmanned aerial vehicle platforms, combined with machine learning techniques, offer a promising solution for efficiently capturing and analysing sediment characteristics. In this study, surface sediment samples were collected from Dasha Beach, a sandy beach located along the East China Sea, and a sediment type coding scheme was established to convert text-based sediment types into digitized codes. Using 10 spatial and spectral unmanned aerial vehicle datasets, along with machine learning models and traditional mathematical methods, we predicted five sediment characteristics: sediment types, sediment water content, mean grain size, sorting coefficient and skewness. Among the models tested, Random Forest demonstrated superior performance, achieving an overall accuracy of 95.65% and a Kappa coefficient of 0.78 for sediment type. For the other four continuous variables, the Random Forest model yielded an average R2 of 0.86 and 0.82 on the validation and test sets, respectively, significantly outperforming traditional multiple linear regression. The study revealed five key predictors: near-infrared, red edge, digital surface model, red and slope, underscoring the necessity of integrating spatial and spectral data for accurate predictions. In contrast, variables like intensity, green and NDVI were less relevant in predicting sediment characteristics, particularly in unvegetated areas like beaches. This study highlights an efficient and accurate approach to obtaining high-resolution sediment characteristics, addressing the limitations of traditional sampling and laboratory methods while significantly reducing labour and financial costs. Its application holds considerable potential in diverse coastal environments, including remote or inaccessible regions, offering a robust framework for future sedimentological studies.

Rivers are a primary source of sediment in continental shelf regions, and the identification of sediment provenance in river systems is crucial to understanding the transport processes, sediment flux, and changes in marine sedimentary environments. Detrital and clay mineral composition, along with geochemical elemental characteristics, serve as key tracers for sediment sources. This study compiles source-discrimination indicators from sediment samples of the Yangtze River (YZR) and Yellow River (YER). While qualitative comparisons between the two rivers show some consensus, discrepancies arise due to differences in studied components, grain size selections, and mineral-specific analyses. Additionally, quantifying riverine contributions to marine sediments remains a significant challenge. Future research should focus on characterizing detrital and clay minerals across grain-size fractions, integrated with advanced instruments and techniques to examine single minerals comprehensively (e.g., geochemistry, chronology, and isotopes). Such efforts will enhance the identification of end-member components of riverine sediments, estimate the specific contributions of terrestrial transport materials, and investigate their dispersion and distribution patterns in continental shelf regions. This research provides new insights into the source-to-sink processes of sediment in the East Asian marginal seas.

Anthropogenic climate warming is predicted to increase the intensity of global tropical cyclones (TCs) on decadal timescales, known as the ‘temperature-TC intensity’ paradigm. However, no proxy is currently available to directly quantify TC intensity in the northwestern Pacific region over centennial to millennial timescales. Here, we reconstruct the intensity of past TCs inferred from event-beds detected in two sedimentary systems in eastern China spanning approximately 1910 to 645 yr BP using an instrumental-calibrated technique, thereby encompassing a sufficiently wide range of temperatures to test the paradigm in the time domain. Intriguingly, our two intensity indices, based on flooding depth and wind speed, provide the initial quantitative evidence that TC intensity in eastern China has been anomalously weak since around 1485 ± 45 yr BP, with a reduction of approximately 30 ± 8% in intensity, despite no concurrent temperature shift. This reduction appears to have been pre-conditioned by a combined influence of a weaker El Niño-Southern Oscillation, a stronger Atlantic Meridional Overturning Circulation, and an increased level of Saharan dust. We suggest that the magnitudes of these factors may have crossed a tipping point and have not reverted to their pre-shift levels since that time, resulting in their impact on TC intensity exceeding that of temperature by triggering changes in the oceanic and atmospheric state within the tropical Pacific region where TCs originate.

Analyzing the spatial-temporal changes in tropical cyclone (TC) tracks in the east China coastal ocean (ECCO) to quantify the magnitude of poleward and landward migration of TCs is of significant importance for coastal disaster mitigation and planning due to its susceptibility to the impacts of TCs. In this study, the TCs that affected the ECCO from 1949 to 2022 are classified into three typical types of tracks using the k-means clustering method, mass moments, and track interpolation based on TC location, shape, and intensity information. Type 1 is a northwestward track, Type 2 is a northwest to northeast-turning track, and Type 3 is a northwest to northeastturning offshore track. Type 1 tracks mainly make landfall in southern China, while Type 2 predominantly makes landfall in eastern China. Moreover, the proportion of Type 1 decreases while their landfall percentage increases over time, and the proportion of Type 2 tracks is increasing. The probability of TC effects on the eastern and northern parts of the ECCO is increasing, and the boundary where the TC center reaches after landfall is shifting landward. During the period from 1994 to 2022, there has been a significant migration in TC tracks, with the mean centroid of the TCs affecting the ECCO shifting westward by 0.66 degrees in longitude and northward by 1.26 degrees in latitude, which means the magnitude of the poleward shift is about twice that of the landward shift. This migration appears to have been pre-conditioned by a combined influence of a weakening westward steering flow, reduced vertical wind shear, and warmer sea surface temperature Our findings provide valuable insights into the longitudinal and latitudinal migration of TC tracks and have important implications for disaster prevention, mitigation planning, and the adjustment of crucial coastal protection zones in the ECCO and similar regions around the globe.

A better understanding of how the vertical profile of suspended sediment concentration (SSC) is influenced by multiple factors is required to better understand the hydrodynamics and sediment dynamics of estuaries. Based on in situ measurements obtained during a spring-neap cycle in the estuarine turbidity maximum (ETM) of the Changjiang Estuary in January 2015, we investigate the intratidal evolution and controlling mechanisms of SSC profiles. The results show that during the dry season the ETM was characterized by periodic salinity stratification, low SSC, suspended sediments with reduced grain size, and low sediment availability for resuspension. Three types of SSC profiles were identified, i.e., profiles with two-layer, linear and quasi-uniform structures. The shapes of the SSC profiles varied with time and generally deviated from the equilibrium profile due to the highly variable hydrodynamic and sediment conditions. During ebbs of spring and intermediate tides, the SSC profiles generally evolved from a two-layer to a quasi-uniform structure via a linear structure. Analysis shows that the linear and quasi-uniform profiles occurred under the combination of vertically well-mixed salinity, negligible resuspension, low settling velocity associated with very fine grains, and shallow water depth. Such an evolution pattern can be well reproduced using a one-dimensional numerical model, with the diffusion coefficient being parabolically distributed in the water column and the four factors mentioned above. The findings reported here imply a high variability of SSC profiles in estuarine environments.

Green sea dykes, also known as ecosystem-based sea dykes, represent a novel type of coastal defense consisting of both traditional structural engineering and coastal ecosystems, designed to cope with the future trends of sea level rise and intensified storms. Here we focus on the mid-latitude mud coasts (eastern China in particular), which face the most prominent risks of storm surge, storm-induced giant waves, and shoreline erosion, and summarizes the scientific basis of green sea dykes and the current status of engineering practices. We show that the basic mechanisms of nearshore wave energy dissipation include bottom friction, sediment transport, and form drag. These explain the wave damping capacity of oyster reefs and salt marshes on mud coasts. In tidal flat environments, oyster growth increases frictional resistance and even causes wave breaking; the resuspension and transport of fine-grained sediments on salt marsh beds and the movement or resistance to hydrodynamic forcing of salt marsh vegetation stems effectively dissipate wave kinetic energy, and their efficiency increases with the elevation of the bed surface. Based on the wave damping capacity of oyster reefs and salt marshes on mud coasts, ecosystem-based sea dykes are being built in combination with traditional structured sea dykes. By utilizing natural tidal flats outside the dykes or implementing artificial modification projects, a certain scale of salt marshes and/or oyster reefs can be maintained, which serve to protect the sea dykes and enhance their wave resistance functions. From the perspective of system optimization, it is necessary to further improve the efficiency and sustainability of green sea dykes under constraints such as regional environment characteristics, ecosystem health, investment capacity, and ecological resilience. Related scientific issues include the theorization of the wave damping process of salt marshes, the niche and scale control of oyster reef and salt marsh ecosystems, the establishment of engineering standards and the design of the optimal form of sea dykes.

The tidal sand ridges in the southwestern Yellow Sea are unique in the world characterized by radial morphology, significantly higher elevation above low water level, and fine-grained sediment deposits. Using a numerical model, we examined the morphological evolution of the radial sand ridge system from 1979 to 2059. The model was calibrated and validated using hydrodynamic and sediment transport data, seabed topography, and grain size distributions from sediment cores. Our findings reveal that tidal force is the primary driver of the ridges' evolution, and they will continue to expand in response to sediment supply from the abandoned Yellow River delta and the Yangtze delta, with the latter contributing more. The ridges are mainly composed of fine sand and mud, with finer sediment dominating in the north and coarser sediment dominating in the south. Wind and waves sort sediment, depositing sand on ridges and fine sediment in channels, leading to erosion of higher elevated lands and filling of deep channels. Sea-level rise increases regional erosion, which has a large impact on areas with complex morphology. The 500-year morphological evolution of sand ridge systems, simulated through an idealized model, illustrated that the formation of radial sand ridges is dependent upon specific conditions such as the radial tidal regime, sufficient sediment sand, and the presence of cohesive sediment. This study deepens our understanding of the long-term prediction of coastal morphology and interpretation of seabed stratigraphy, and offers insights for effective coastal management.

There are concerns that intense tropical cyclones (TCs) are expected to become more frequent and powerful in warming climates. However, the long-term trend of TC activities, the spatiotemporal variability of such trends across different latitudes of the Western North Pacific (WNP), and the drives of the variability remain unclear. Here, we present a reconstruction of a 1600-year paleo-TCs activity using a sediment core taken in Li’an Lagoon located in southeastern Hainan Island, South China Sea. We used muti-dating methods (210Pb and AMS 14C dating) for age control and muti-proxy analysis (XRF geochemical element scanning and grain size analysis) for identifying periods of frequent intense TC activities. Based on an updated compilation of basin-wide paleo-TC records, we confirm that there exists a seesaw pattern of intense TC frequency between low and middle latitude in the WNP. Comparing with global and regional paleoclimate proxies, we propose that the basin-wide latitudinal TC activity variation in the WNP can be linked to the migration of Western Pacific Subtropical High (WPSH) and its associated high-latitude forcings (e.g., NAO) and low-latitude internal variability forcings (i.e., El Niño Southern Oscillation, sea surface temperature (SST)). More intense TC will occur at low latitudes in the future, though with less frequency.

Heavy metal pollutants in sediment greatly impact the estuarine environment and ecosystems, increasingly influenced by anthropogenic perturbations. Here, we examined the surface sediments of the Modaomen estuary in 2003, 2015, and 2021 to understand how human-induced changes influence the fate of heavy metals in the estuary's sediments. The potential ecological risk index (RI) suggests Cd should be the priority pollutant for environmental pollution control due to its high toxicity coefficient. In each sampling period, two main sources were identified through normalized heavy metals and PCA-MLR: natural and mixed anthropogenic sources (agricultural, industrial, and traffic activities), reflecting an increase in heavy metals pollution, later mitigated by successful environmental protection measures. Moreover, anthropogenic activities have not only impacted the sources discharge of heavy metals but have also influenced their spatial and temporal distribution through factors such as land reclamation, leading to sediment coarsening and reduced heavy metal content in specific areas.

Gravel beaches serve as both important recreational destinations and natural barriers against wave erosion. In the context of global climate change and sea level rising, the use of gravel for beach nourishment has become an increasingly favored option for soft shoreline protection solutions. However, sampling and analyzing the grain size of gravel have always been challenging in this field of research. This challenge not only hampers the accurate prediction of gravel beach morphodynamics but also adds uncertainty to designs of beach nourishment projects. Here, we present three recent progresses in grain size sampling and analysis of gravel sediments. (1) Minimum sampling mass for sieving method. By assuming a normal distribution and considering the standard deviation and the grain size of the coarsest particle, we derived a method for calculating the minimum sampling mass, for instance, a gravel sample with a standard deviation of 4.0 φ and the coarsest grain size of 64 mm would require a minimum sampling mass not exceeding 48 kg. (2) Digital photograph-based automatic grain size and shape analysis technique. We have developed hardwares for measuring gravel grain size and shape and have written corresponding software, namely the Gravel Grain Size and Shape Automatic Measurement System (GraSSAMS). This system caters to both laboratory and fieldwork requirements, enabling measurements of particles within the range of 1–330 mm. (3) Grain size parameter calculation for samples analysed with a comprehensive approach. When applying a comprehensive approach (combining laser and sieving methods) to analyze the grain size of gravel-sand-mud mixtures, we observed overlap between the results of the laser and sieving methods. To address this issue, we propose two algorithms, both of which yield highly consistent results. Finally, we discuss two questions: (1) Is there a standard technique for gravel grain size analysis? (2) How will technology for automated identification of gravel grain size and shape evolve in the future? Exploring these questions can help to better understand the morphology and evolution of gravel beaches.

Typhoon-induced storms surges and river flooding events represent two types of natural disasters that affect a wide range, occurring with high frequency and causing serious societal losses. Due to the limited duration of instrumental records, there is an inadequate understanding of the patterns and mechanisms underlying the variations in typhoons and floods. The interpretation of sedimentary records aptly compensates for these deficiencies in terms of the temporal scale, becoming a crucial medium for extending the temporal span of typhoon and flood records. Previous studies in this field have primarily focused on the identification of single types of extreme events. The Changjiang Estuary, particularly Chongming Island, is significantly affected by both typhoons and river floods, making it an excellent area for synchronous comparative studies of these two types of extreme events. Based on the analysis of a core sample, ZP02, collected from Chongming Island, in terms of chronological, sedimentological, and geochemical characteristics, specific tracing fingerprints for event deposits from typhoon and flood events are established. Sediments from typhoon events generally exhibit erosive contact surfaces, coarser grain sizes, and a tendency to become finer upwards, often featuring layers mixed with coarse sand and shell fragments. In contrast, flood event deposits vary in grain size, either coarser or finer, with abrupt contact surfaces compared to normal sediment layers, and are predominantly brownish-yellow in color. The fingerprint tracing results indicate that the typhoon event layers are characterized by high values in principal component 2 (PC2) of the elements, Zr/Fe and Sr/Fe ratios, with low values in principal component 1 (PC1) the elements and Ti/Ca ratio. Flood event deposits are marked by high values in PC1 and Ti/Ca ratio, low values in PC2 and Sr/Fe ratio, and an increase in Zr/Fe ratio in coarser flood layers but no significant change in finer layers. Based on these fingerprints, 19 layers of typhoon and the same number of flood events were identified in core ZP02, which correspond well with documentary records. The establishment of tracing fingerprints for typhoon and flood event deposits provides methodological support for the identification and interpretation of various extreme event deposits.

The main focus of studying sediment sources in marine areas is to determine the properties of clastic minerals originating from different rivers. Variations in the characteristics of clastic minerals occur due to differences in the types of source rocks within the watershed. Determining the source rock of clastic minerals in the marine area can improve the accuracy of provenance analysis. Electron probe microanalysis of 258 amphibole grains from six surface stations in the South Yellow Sea (SYS) was conducted to calculate the numerical and characteristic values of cations in the crystal structure. The results showed that amphibole in the SYS is mainly magnesiohornblende (52.2% ~ 81.4%) in the calcic amphibole subgroup, followed by tschermakite. The source rock types of amphibole are mainly different types of magmatic (ultrabasic, basic, and intermediate acidic) and metamorphic rocks. Amphibole derived from intermediate-acid intrusive rocks accounts for a large proportion (>40%). The genetic analysis of clastic amphibole in the SYS showed that most of the medium-acid invading amphibole belong to crust-mantle type, followed by mantle type. Most of the amphibole from metamorphic origins are of medium-low pressure type (± 80%). Combined with electron probe analysis of amphibole from the Huanghe River (the Yellow River, HH) and Changjiang River (the Yangtze River, CJ), the amphibole in the SYS exhibits characteristics inherited from these two rivers. The northern sea area has a strong resemblance to the sediments from the HH, while the southern area is more influenced by sediments supply from the CJ. The central area represents a mixed zone with a higher sediment supply from the HH. The clastic amphibole deduces the type of source rock in different watersheds, serving as a crucial link between the source rock, watershed, and marine area, providing a basis for provenance analysis.

Rip currents are narrow, powerful seaward currents that frequently occur on sandy shores, posing a significant hazard by quickly pulling swimmers into deeper waters, leading to numerous drowning incidents. As such, they are among the most dangerous natural threats in coastal zones. The Ω-RTR (dimensionless fall velocity-relative tide range) model is a widely recognised framework for classifying the geomorphic and dynamical states of beaches. Although this model does not explicitly predict the location, timing, and intensity of rip currents, it estimates the likelihood of rip currents forming at specific beach types. In this study, 33 representative touring beaches along the coasts of China were studied and the rip current risk of these beaches was evaluated with the Ω-RTR model. According to this classification, beaches can be categorised into eight types, seven of which are presented among the 33 Chinese beaches studied in this paper, and notably, the Ultra-Dissipative (UD) type is absent. The most common three beach types identified are Barred (B), Low Tide Bar/Rip (LTBR), and Non-Barred Dissipative (NBD). The former two are predominantly located in Shandong, Fujian, and Hainan provinces, while the latter is mainly found in Zhejiang, Fujian, and Guangxi provinces. The rip current risk across these beaches is primarily assessed as medium to high, with low-risk beaches primarily situated in Zhejiang, Fujian, and Guangxi provinces. There is minimal month-to-month variation in beach type and rip current risk along the Yellow Sea, Bohai Sea, the coast of Zhejiang Province, and the coasts of Hainan Island and Guangxi Province. However, notable seasonal variations in beach type and rip current risk are observed in Fujian Province. This study provides a comprehensive assessment of rip current risk across key coastal touring beaches in China. Additionally, it contributes to the expansion of data sources for the beach geomorphic-dynamical classification system. The findings offer valuable insights for enhancing the safety of beachgoers and promoting the sustainable development of China’s coastal tourism industry.

With sea level rise (SLR), tidal nuisance flooding has become a growing threat, especially around estuaries with large tidal amplitudes. This study investigated how sea level change affects tides in Hangzhou Bay, a macro-tidal estuary with high SLR rate. By downscaling climate projections to a regional hydrodynamic model, the amplitude of primary tidal constituent (M2) was predicted to increase by 0.25 m in the upper bay, where the amplitude of major diurnal tide (K1) was also predicted to increase by 15%. In addition, the sensitivity of tidal amplitude to mean sea level was examined by a set of numerical simulations with different SLR. It was found that the increase of tidal amplitude is nonlinear to SLR, and the tidal amplitudes almost cease to increase when SLR is over 1.5 m. Although predictions show less amplitude changes in the lower bay, Zhoushan Archipelago around the bay mouth strongly modulates the incoming tidal energy, thus affecting the tidal amplitude in the upper bay. Energy budget analysis revealed that the complex topography, such as narrow channels, in the archipelago area leads to strong horizontal shear, which dissipates approximately 25% of total tidal energy in the bay. On the other hand, around 60% of the energy is dissipated in the bottom boundary layer. However, the bottom dissipation decreases by 4% due to reduced friction, while horizontal dissipation increases by 10% due to enhanced horizontal shear with SLR. This suggests that the strong horizontal shear in the Zhoushan archipelago region can play a more important role in the tidal energy budget in the future.