Search Results (94)

Against the backdrop of global climate change and rapid urbanization, understanding the spatiotemporal dynamics and driving mechanisms of vegetation net primary productivity (NPP) is critical for ensuring regional ecological security and achieving carbon neutrality goals. This study focuses on the Yangtze River Delta Urban Agglomeration (YRDUA) and integrates multi-source remote sensing data with socioeconomic statistics. By combining interpretable machine learning (XGBoost-SHAP) with multiscale geographically weighted regression (MGWR), and incorporating Theil–Sen trend analysis and Mann–Kendall significance testing, we systematically analyze the spatiotemporal variations in NPP and its multiscale driving mechanisms from 2001 to 2020. The results reveal the following: (1) Total NPP in the YRDUA shows an increasing trend, with approximately 24.83% of the region experiencing a significant rise and only 2.75% showing a significant decline, indicating continuous improvement in regional ecological conditions. (2) Land use change resulted in a net NPP loss of 2.67 TgC, yet ecological restoration and advances in agricultural technology effectively mitigated negative impacts and became the main contributors to NPP growth. (3) The results from XGBoost and MGWR are complementary, highlighting the scale-dependent effects of driving factors—at the regional scale, natural factors such as elevation (DEM), precipitation (PRE), and vegetation cover (VFC) have positive impacts on NPP, while the human footprint (HF) generally exerts a negative effect. However, in certain areas, a dose–response effect is observed, in which moderate human intervention can enhance ecological functions. (4) The spatial heterogeneity of NPP is mainly driven by nonlinear interactions between natural and anthropogenic factors. Notably, the interaction between DEM and climatic variables exhibits threshold responses and a “spatial gradient–factor interaction” mechanism, where the same driver may have opposite effects under different geomorphic conditions. Therefore, a well-balanced combination of land use transformation and ecological conservation policies is crucial for enhancing regional ecological functions and NPP. These findings provide scientific support for ecological management and the formulation of sustainable development strategies in urban agglomerations. Full article

Extreme climate events are becoming more intense, and how coastal mangroves respond to the alternating intense cyclones and severe droughts is less understood, which challenges the sustainability of the ecosystem services they provide to coastal communities. To address this, we analyzed spatiotemporal dynamics of coastal mangroves in a Caribbean island in response to major hurricanes in 2017, which followed a severe multi-year drought in 2014–2015, using multiple indices derived from multispectral optical images. We further explored the roles of hurricane forces, local hydro-geomorphic environment, and rainfall dynamics in the damage and the following recovery. In addition to the hurricane forces, such as gusty wind and rainfall, the local hydro-geomorphic environment largely determines the spatial variations of damage. Lower-lying, flatter, and wetter mangrove areas sustained more damage, possibly due to prolonged inundation susceptibility and tall canopy configurations. Recovery is mainly limited by the severity of damage. However, sufficient rainfall gradually becomes important to facilitate the recovery. While the pre-hurricane severe drought (2014–2015) largely degraded the mangroves at dry sites, the drought after the hurricanes exacerbated the hurricane damage and retarded the recovery. We also found that the spectral distance and the mangrove vegetation index revealed slower and more spatiotemporally heterogenous mangrove recovery than indices of greenness, implying they are better measures for monitoring mangroves’ response to disturbance. Six years after the disturbance, the greenness of mangroves near the hurricane landfall reached 84% of the pre-hurricane values. However, the mangrove vegetation index showed that healthy mangrove coverage was only 10%, in comparison to 76% before the disturbance. The sluggish recovery at this site with the severest damage may be associated with the loss of pre-established seedlings and the difficulty to have new ones established, thus human efforts are in need to restore the system. Full article

The post-storm beach recovery process exhibits variability. Understanding its mechanisms is crucial for advancing the study of beach morphodynamics. This study involved a 25-day continuous field observation on Dongdao Beach, Hailing Island, Yangjiang City, Guangdong Province, following the passage of Typhoon Cempaka. The evolution of beach morphology and the spatiotemporal variations in erosion and accretion were analyzed to explore the key influencing factors, response mechanisms, and recovery modes during the short-term recovery process. The post-storm evolution of beach profile structures is predominantly influenced by major geomorphic units such as berms and sandbars, whereas localized responses are characterized by adjustments of fine-scale features like micro-troughs. The width of the supratidal zone and the position of the berm crest continuously fluctuate, while the slope of the intertidal zone increases or decreases as the berm crest migrates landward or seaward. The erosion–accretion process was complex and occurred in distinct stages, with marked spatial heterogeneity. In some areas, the beach experienced multiple short-term cycles of alternating erosion and accretion. Beach slope plays a significant role in short-term recovery. Three types of response relationships between beach unit-width volume and changes in slope were observed, with flatter beaches being more sensitive to changes in unit-width volume. Based on this, four recovery modes in the post-storm short-term recovery process were explored from the perspective of beach slope. This study provides theoretical support for managing beaches after storms and recommends the implementation of zoned and phased management strategies based on different recovery modes to enhance the efficiency and resilience of coastal recovery. Full article

In a coastal engineering project, hydrodynamic models are used to study wave transformations and impacts on structures, while morphodynamic models are applied to calculate the response and evolution of sedimentary beaches. Conventionally, laboratory experiments and numerical modeling have been called to investigate beach changes, particularly those resulting in the formation of an embayed beach. The former is undertaken in a wave basin, necessitating a huge outdoor facility to fit a project with large dimensions, numerous instrumentations, and manpower, while the latter is performed by powerful numerical models on a desktop, requiring only the advent of computing power and professional skills. Conventionally, both approaches have successfully achieved the expected outcome, though differing in cost and time frame. On the contrary, an efficient empirical geomorphic model for headland-bay beaches has been available since 1989 for assessing the planform stability of a crenulated beach in static equilibrium. The model can readily produce a graphic display of the static bay shape aided by a supporting software within a shorter time frame (in a couple of minutes), instead of in hours or days in laboratory tests and numerical modeling. Several practical examples drawn by the software MeePaSoL for the empirical model are presented to complement the results of a morphodynamic model in a wave basin, as well as to guide the modeler to terminate the programming when equilibrium is reached. We believe this alternative approach could be helpful for the experimentalists and numerical modelers on large engineering projects associated with shoreline beach evolution and shore protection, especially for time-saving and reducing manpower and cost. Full article

Understanding the evolution of the sandbar–trough system under regular wave conditions is essential for revealing the dynamic responses of coastal morphology in non-extreme environments and provides a scientific basis for long-term beach stability assessments and coastal erosion management. This study conducted a three-day field observation on Ten-Mile Silver Beach, Hailing Island, China, to investigate the coupling relationships between hydrodynamic factors and bed elevation changes during the morphological evolution of the sandbar–trough system. The results indicate that gravity wave (>0.04 Hz) energy is a key driver of bed elevation changes. During the erosion phase, gravity wave energy increases, and the peak wave energy frequency shifts toward lower frequencies, accompanied by a contraction of low-frequency energy and an expansion of high-frequency energy. In contrast, the accretion phase exhibits the opposite pattern. As the sandbar–trough system developed, the explanatory power of hydrodynamic factors on bed elevation decreased by 41% in the trough region and increased by 3.7% in the sandbar region, indicating a spatially differentiated pattern characterized by weakened forcing in the trough and enhanced response over the sandbar. During the geomorphic adjustment process, the trough area exhibited increased sensitivity, with gravity wave energy, near-infragravity wave (0.01–0.04 Hz) energy, far-infragravity wave (0.004–0.01 Hz) energy, mean wave height, and significant wave steepness reversing their influence directions on bed elevation. In contrast, the sandbar area maintained a more stable hydrodynamic control mechanism, with only the influence pattern of significant wave steepness undergoing a shift. This study enhances the understanding of geomorphology–hydrodynamics coupling within nearshore sandbar–trough systems and provides theoretical insights and technical support for monitoring and evaluating coastal erosion and accretion processes under normal wave conditions. Full article

Episodic sedimentary processes with significant changes in sedimentation rate have occurred on the East Hainan Coast, the inner shelf of the South China Sea, since the Last Glacial Maximum. In particular, the early-Holocene (~11.5–8.7 ka) rapid sedimentation at a mean rate of ~4.90 m/ka is crucial to understand the processes of terrigenous input to the ocean, carbon cycling and climate control in coastal-neritic sedimentary evolution. However, the chronological framework and the detailed environmental evolution remain uncertain. In this study, core sediments collected from the East Hainan Coast (code: NH01) were used to revisit the characteristics of luminescence signals by comparing the dating results using the blue-light stimulated luminescence (blue-OSL) ages and previously published post-infrared blue-light stimulated luminescence (pIR-blue OSL) ages. The results showed that both the ages agreed with each other for the fine-grained quartz fraction. The refined chronology of the early-Holocene deposits on the East Hainan Coast with higher resolution suggested that the sedimentation rate was ~0.60 m/ka before 10.97 ka, while it increased abruptly to ~5.89 m/ka during the period of 10.97–9.27 ka. According to the refined OSL chronology and the high-resolution (~2.5 cm) titanium intensity using X-ray fluorescence (XRF) scanning, the rapid sedimentation during the early Holocene was likely controlled by increased terrigenous input. The variation in Ti flux reflected the differential response between two meltwater pulse (MWP) events under the combined effects of enhanced early-Holocene monsoons and localized freshwater input. These findings highlight the compound controls of global ice-volume change, monsoon dynamics and coastal geomorphic evolution on sedimentary processes. Full article

Sandy barrier systems are highly dynamic, with the most significant natural morphological changes to these systems occurring during high-energy storm conditions. These systems provide a range of economic and ecosystem benefits and protect inland areas from flooding and storm impacts, but the persistence of many coastal barriers is threatened by storms and sea-level rise (SLR). This study employed observations and modeling to examine recent and potential future influences of storms on a sandy coastal barrier system in Nauset Beach, MA. Drone-derived imagery and digital elevation models (DEMs) of the study area collected throughout the 2023–2024 winter revealed significant alongshore variability in the geomorphic response to storms. Severe, highly localized erosion (i.e., an erosional “hotspot”) occurred immediately south of the Nauset Bay spit as the result of a group of storms in December and January. Modeling results demonstrated that the location of the hotspot was largely controlled by the location of a break in a nearshore sandbar system, which induced larger waves and stronger currents that affected the foreshore, backshore and dune. Additionally, model simulations of the December and January storms assuming 0.3 m (1 ft) of SLR showed the system to be relatively resistant to major geomorphic changes in response to an isolated storm event, but more susceptible to significant overwash and breaching in response to consecutive storms. This research suggests that both very strong isolated storm events and sequential moderate storms pose an enhanced risk of major overwash, breaching, and possibly inlet formation today and into the future, raising concern for adjacent communities and resource managers. Full article

Anthropogenic activities and climate change have increased the stress on the world’s estuaries over the past decades. Limited knowledge exists about how estuarine receding responds to human interference, particularly the geomorphic dynamics of channels and sandbars. Here, we evaluate the topographic evolution of the upper Yangtze River Estuary (YRE), the largest branch reach with frequently shifting sandbars, from 1994 to 2019. Our results show that a net channel erosion of 9.59 × 10⁸ m³ occurred in the upper YRE, equivalent to an annual erosion depth of 8.67 cm. On the contrary, sandbars with a large area increased from 47.68 km² to 70.88 km², showing the opposite development of estuarine channels. Reduced riverine sediment supply may have been responsible for the estuarine channel erosion, and river engineering may have contributed to intense erosion in local areas. Also, the engineering projects were likely the main reason for the stability and growth of the sandbars. This study reveals the branching channel–sandbar system of the upper YRE in response to anthropogenic and climatic change forcing. The knowledge gained from this study can be applied to other similar estuarine systems around the world, helping develop sustainable strategies for the utilization and protection of the world’s estuaries and deltas. Full article

The operation of large reservoirs significantly modifies flow–sediment regimes, and the reaches immediately downstream of the dams are the first to undergo responsive channel adjustments. Considering that the geomorphological responses are directly related to the flood control safety, channel stability and other sustainable functions of rivers, this paper explores the similarities and dissimilarities of the channel adjustments in the two reaches with gravel–sand beds immediately downstream of the Xiangjiaba reservoir and the Three Gorges Dam, respectively. The results show that major erosion primarily occurred during the initial years of reservoir impoundment. And then with the prominent reduction in washable sediment on the riverbed, the erosion intensity further weakened. It takes 6 to 13 years for the two reaches to reach a new state of relative equilibrium. In comparison, after the equilibrium state has been achieved, the reach with significant tributary sediment inflows exhibits alternating erosion and deposition dynamics, while the other remains relatively stable. The tributaries that transport a large amount of sediment during floods are the main sources of sediment deposition in the downstream reaches of the Xiangjiaba reservoir. However, the tributary inflow of the Qing River with low sediment concentrations has little impact on the riverbed evolution of the reaches from Yichang to Zhicheng immediately downstream of the Three Gorges Dam. These findings contribute to a deeper understanding of geomorphic adjustments near dams in response to upstream damming. Full article

The Eastern Tianshan region, influenced by the far-field effect of northward compression and expansion of the Qinghai-Xizang block, features highly developed Late Quaternary active faults that exhibit significant neotectonic activity. Historically, the Barkol-Yiwu Basin, located to the north of the Eastern Tianshan, experienced two major earthquakes in 1842 and 1914, each with a magnitude of M7¹/₂. In contrast, the Hami Basin on the southern margin of the Eastern Tianshan has no historical records of any major earthquakes, and its seismic potential, mechanisms, and future earthquake hazards remain unclear. Based on satellite image interpretation and field surveys, this study identified a relatively recent and well-preserved seismic surface rupture zone with good continuity in the Liushugou area of the western segment of the Northern Margin Fault of the Hami Basin (HMNF), which is the seismogenic structure responsible for the rupture. The surface rupture zone originates at Kekejin in the east, extends intermittently westward through Daipuseke Bulake and Liushugou, and terminates at Wuzun Bulake, with a total length of approximately 21 km. The rupture zone traverses the youngest geomorphic surface units, such as river beds or floodplains and first-order terraces (platforms), and is characterized by a series of single or multiple reverse fault scarps. The morphology of fault scarps is clear, presenting a light soil color with heights ranging from 0.15 m to 2.13 m and an average displacement of 0.56 m, suggesting that this surface rupture zone likely represents the most recent seismic event. Comparison with historical earthquake records in the Eastern Tianshan region suggests that the rupture zone may have been formed simultaneously with the Xiongkuer rupture zone by the 1842 M7¹/₂ earthquake along the boundary faults on both sides of the Barkol Mountains, exhibiting a flower-like structural pattern. Alternatively, it might represent a separate, unrecorded seismic event occurring shortly after the 1842 earthquake. The estimated magnitude of the associated earthquake is about 6.6~6.9. Given that surface-rupturing earthquakes have already occurred in the western segment, the study indicates that the Erdaogou–Nanshankou section of the HMNF has surpassed the average recurrence interval for major earthquakes, indicating a potential future earthquake hazard. Full article

The resilience and resistance of vegetation are important indicators of the vegetation’s response to droughts. Owing to the uniqueness of the environment in humid karst areas, results from studies on other climatic zones may not necessarily present the status of vegetation resilience and resistance in humid karst areas. Herein, We calculated vegetation resilience and resistance by autoregressive modeling using Enhanced Vegetation Index (EVI), Total Water Storage Anomaly (TWSA), temperature (TA), precipitation (PRE) data, An analysis of variance (ANOVA) was then conducted to compare the differences in resilience and resistance of different vegetation types in the study area, as well as the differences in resilience and resistance of vegetation in different sub-geomorphic zones. Finally, natural factors affecting vegetation resilience and resistance were quantified using partial least squares structural equation modeling (PLS-SEM). The results demonstrate the following points. First, vegetation resilience, total-water-storage anomaly resistance, and vegetation resistance against precipitation anomalies were lower in karst areas of the study area than in non-karst areas of the study area (except for vegetation resistance against temperature anomalies). Second, vegetation resilience was the lowest in some sub-geomorphic zones within karst areas, and it was still comparable to that in semiarid areas. Third, precipitation and temperature were important factors that affected the resilience and resistance of vegetation in karst areas, and the geochemical indicators (CaO, MgO, and SiO₂) of soil parent material were major factors that affected the resistance and resilience of vegetation in non-karst areas. In summary, this study was undertaken to reveal the natural characteristics of vegetation resilience and resistance in humid karst regions. Our findings complement and expand the existing body of knowledge on vegetation resilience and resistance in other ecologically fragile zones limited by moisture. Full article

Coastal cliffs erode in response to short- and long-term environmental changes, but predicting these changes continues to be a challenge. In addition to a chronic lack of data on the cliff face, vegetation presence and growth can bias our erosion measurements and limit our ability to detect geomorphic erosion by obscuring the cliff face. This paper builds on past research segmenting vegetation in three-band red, green, blue (RGB) imagery and presents two approaches to segmenting and filtering vegetation from the bare cliff face in dense point clouds constructed from RGB images and structure-from-motion (SfM) software. Vegetation indices were computed from previously published research and their utility in segmenting vegetation from bare cliff face was compared against machine learning (ML) models for point cloud segmentation. Results demonstrate that, while existing vegetation indices and ML models are both capable of segmenting vegetation and bare cliff face sediments, ML models can be more efficient and robust across different growing seasons. ML model accuracy quickly reached an asymptote with only two layers and RGB images only (i.e., no vegetation indices), suggesting that these more parsimonious models may be more robust to a range of environmental conditions than existing vegetation indices which vary substantially from one growing season to another with changes in vegetation phenology. Full article

Beachrock is a type of coastal carbonate sedimentary rock developed in the sandy beach intertidal zone, widely distributed along the beach front, and the loss of beach sediment is the main cause of beachrock exposure. Based on the analysis of measured data of different exposure forms of beachrocks in profiles, this paper analyzes the main features and influences of non-dynamic factors, such as the exposure position and morphology, of beachrocks on the dynamic geomorphic processes of beaches. Studies have shown that (1) changes between beach energy dissipation bodies are significant features of coastal geomorphic processes under the influence of beachrocks. The first spatial mode of EOF analysis shows that the erosion position of beach-rock-exposed profiles is mainly concentrated in the protected and real sections of beachrock, and the first temporal mode indicates that the exposure of beachrock results in a lagged response of its profile to dynamic environmental changes. (2) The differences in the exposure forms of beachrocks determine the sand-holding space of the beach, and the differences in the lateral exposure positions of beachrocks determine the main areas where erosion occurs on the profile. Meanwhile, the geomorphic processes of their profiles show different degrees of feedback, and such geomorphic phenomena can serve as reference indicators for the stage-wise evolution process influenced by beachrocks. Full article

In recent decades, the interplay of several factors, including land use change (particularly urbanization) and global warming, has resulted in harsher flooding, often associated with geomorphic disruption. These events in Latin America are predominantly driven by the El Niño Southern Oscillation (ENSO) phenomenon. The Andalién River basin is no exception, with a notable incident occurring in July 2006. This reality points out the need to study the geomorphological behavior of rivers. Geomatic tools can contribute to address this issue, thereby improving the planning and management of water courses. This paper presents the assessment of the morphological evolution of the Andalién River, downstream to the city of Concepción in a period of 75 years (1945–2020), in response to changes in land use and anthropogenic interventions on the river itself. Based on temporal satellite imagery and historical aerial images (from 1945 to 2020) combined with digital elevation models (LiDAR and TamDEM-X data), morphological alterations are revealed, which were caused by urbanization and anthropogenic activities. We demonstrate how the South River Toolbox (SRT), an original GIS tool developing in QGIS (in-house), enables the extraction of key geomorphological features of a river and their analysis, including their time evolution. This retrospective analysis includes an innovative method and tool to measure the lateral migration rate of the active channel. Ultimately, this study provides valuable insights for future management strategies, offering a comprehensive basin-level analysis of the Andalién River and a cartographic framework to aid decision-making, planning, and management of the fluvial corridor. Full article

Synthesis of geologic and chronologic data generated from Holocene sedimentary sequences recovered along the inner continental shelf, shoreface, and modern coastal zone of the Georgia Bight reveal a synchronous sequence of paleoenvironmental events that occurred in response to rate of sea level rise tipping points. During the early Holocene (11.7–8.2 cal kyr BP), the paleoshoreline was overstepped and submerged by rapidly rising seas that averaged ~5 mm yr⁻¹. Rates of rise during the middle Holocene (8.2–4.2 cal kyr BP) averaged ~2 mm yr⁻¹ and this deceleration resulted in the formation of coastal environments and sedimentary sequences that were subsequently reworked as the shoreface continued its landward and upward migration. The modern coastal zone emerged commensurate with the late Holocene (4.2–0 cal kyr BP), when the rate of sea level rise averaged <1 mm yr⁻¹. Analysis of water level data collected at six NOAA tide gauge stations located along the Georgia Bight coast indicates the rate of relative sea level rise has increased from a historical average of 3.6 ± 0.2 mm yr⁻¹ (<1972 to 2022) to 6.6 ± 0.8 (1993 to 2022) and during the 21st century it has averaged 9.8 ± 0.3 mm yr⁻¹ (2003 to 2022). The current rate of sea level rise is nearly double the early Holocene rate of rise. Based upon a novel application of the principle of uniformitarianism (i.e., the past is the key to the future), the likely geomorphic trajectory of the Georgia Bight coastal zone under conditions of 21st century accelerating sea level rise will be one of increasing instability (e.g., coastal erosion) and flooding (e.g., overwash, breaching). Evidence of an emerging instability within the coastal zone has been previously reported throughout the region and supports the trajectory of geomorphic change proposed herein. This will ultimately result in the submergence of existing landscapes and replacement by estuarine and marine environments, which may hasten in pace and scale given the current rate of sea level rise is expected to continue accelerating throughout this century. These findings have not been previously reported and should be considered by coastal practitioners responsible for conceptualizing risk, as well as the formulation and implementation of adaptation action plans designed to mitigate threats to the built and natural environment induced by climate change. Full article