Ocean floor formed at intermediate spreading ridges typically consists of volcanic effusion products (80-90%) and regularly-spaced normal fault scarps (10-20%) that shape elongated abyssal hills. This fabric forms over millions of years as the divergence of two tectonic plates induces discrete events of magmatic intrusion and fault slip at the ridge axis, which can last from several seconds to several months. Little is known, however, on how the repetition of such events ultimately shapes the partitioning of tectonic and magmatic strain that is encoded in the morphology of the seafloor. To address this, we quantify the amount of fault slip and magmatically-accommodated extension during the early days of the April 2024 rifting event that took place on the Southeast Indian Ridge at 37°S, and was documented by the OHA-GEODAMS seismo-geodetic observatory (Royer et al. EGU26-GD5.1). Using elastic dislocation modelling in a Bayesian framework, we find that the rifting event accounted for 2–4 m of horizontal extension, of which ∼85% involved the emplacement of a magmatic fracture that propagated along the axis within less than 2 hours. We attribute the remainder of the extension to dominantly aseismic slip on axial valley bounding faults. This "instantaneous" fraction of magmatic extension is strikingly similar to that revealed by bathymetric analyses (M∼90%), which quantify deformation averaged over hundreds of thousands of years. We therefore propose that the long-term "M-fraction" that characterizes intermediate-spread seafloor could be determined at the scale of individual rifting events, possibly by static stress transfers between a propagating dike and adjacent faults. At the Southeast Indian Ridge, such events likely recur every ∼50 years and are separated by periods of seismic quiescence, as mid-ocean ridge normal faults may primarily grow when triggered by magmatic activity.

The Surface Water and Ocean Topography (SWOT) satellite altimetry mission, with its high spatial resolution and global coverage, offers unprecedented opportunities for studying coastal environments. Although primarily designed for observing open ocean and inland water bodies, recent studies have demonstrated its ability to capture intertidal topography at low tide. One key challenge in such applications lies in separating intertidal pixels from water ones, as current SWOT classification lacks a dedicated intertidal class. This study introduces a standalone methodology that relies exclusively on SWOT level-2 High Resolution (HR) pixel cloud dataset. Intertidal pixels are identified using a simple approach based on the probability distribution function (PDF) of sea surface height anomalies relative to a nearby reference open water point. This method was applied to the macro-tidal, geographically complex coastal region of Pertuis Charentais along the French Atlantic coast. Validation against airborne LiDAR topography shows good agreement, with Root Mean Square Error (RMSE) below 30 cm for both single-cycle and temporally stacked SWOT observations. Performance was consistent across different bottom types, with highest accuracy over low slope (<1 degrees) muddy and sandy bottoms and moderate degradation over rocky bottoms. Elevation profile analysis suggests that SWOT has a potential for detecting spatiotemporal morphological evolution in highly dynamic environments. While single-cycle observations are limited by inherent interferometric noise, annual stacks show promises in resolving long-term changes. These findings highlight SWOT's potential to fill key observational gaps in intertidal mapping, supporting coastal morphodynamic studies, hydrodynamic modeling and climate resilience efforts in data-sparse or rapidly evolving environments.

Abstract. Atoll reef islands are highly vulnerable to climate change because of their low elevation, exposure to ocean swells, and dependence on coral reef health. However, Sea Surface Height (SSH) and Significant Wave Height (SWH) variability across large atolls remain poorly documented due to limited in-situ observations. Satellite altimetry offers strong potential for monitoring these environments. In particular, the Surface Water and Ocean Topography mission (SWOT), through its Ka-band Radar Interferometer (KaRIn), enables two-dimensional observations of SSH and SWH at unprecedented resolution, offering new opportunities to investigate the barrier-reef lagoon dynamics of atoll islands. Yet, the performance of SWOT observations in such complex coastal settings must first be assessed. In this study, we compare KaRIn measurements with wave buoy, tide gauge, and in-situ Global Navigation Satellite System (GNSS) data collected over the Rangiroa atoll in 2025. Results show that KaRIn measures lagoon SWH with a bias of 10–30 cm and a centered root mean square error (CRMSE) of 10–13 cm, outperforming the global wave model currently used to estimate Sea State Bias (SSB) in current SWOT Level-2 products. Recomputing SSB using KaRIn SWH improves SSH agreement with in-situ observations by up to 3 cm. Spatial comparisons with GNSS-derived SSH also show that KaRIn captures strong SSH gradients near the main pass and northern atoll. Finally, improved SSH anomaly fields using time-averaged KaRIn SSH reveal differences of up to 50 cm between lagoon and ocean water levels driven by wave and tidal forcing.

Abstract Intertidal zones of the Ganges‐Brahmaputra (GB) delta are among the most active coastal environments worldwide, and quantifying their morphological evolution remains challenging due to rapid change and scarce in situ observations. This study presents a satellite‐based direct quantification of intertidal sediment volume change in the Meghna Estuary of the GB delta using the Surface Water and Ocean Topography (SWOT) altimetry mission. Originally designed to observe fine‐scale ocean dynamics and inland hydrology, SWOT also allows accurate mapping of intertidal topography. Using SWOT‐based intertidal topography, this study assesses elevation change and associated sediment erosion and accretion volume over a 1‐year interval (2024–2025). The analysis reveals a net sediment change of 70.32 ± 0.12 Megatonnes with distinct island‐scale and local‐scale sediment redistribution patterns. Consistent spatial patterns observed from overlapping different SWOT passes support the robustness of the derived changes, demonstrating a powerful approach for monitoring rapidly evolving intertidal changes across the world's coastline.

The volume of tide gauge data available to the sea level community has grown substantially, with information distributed across numerous global, national, and institutional data centres. As a result, the main challenge is no longer accessing data, but identifying the most relevant dataset for a given application. Currently, more than 15 global data centres provide sea level information, each tailored to different users and use cases (e.g., real-time monitoring, delayed-mode analysis, monthly means). For users unfamiliar with tide gauge data, selecting the appropriate source can be difficult. Tide Gauge CATalog (TGCAT) is a software tool developed to address this challenge. It helps users discover where specific tide gauge data are available and assists data providers and centres in identifying inconsistencies, such as misreferenced stations or discrepancies in metadata. TGCAT collects metadata from global and national sea level data centres to produce intercomparable catalogues. It also allows visualisation of data availability timelines across multiple sources. Written entirely in Python and linked to an online dashboard ( www.sonel.org/tgcat ), TGCAT is designed as an open, community-based platform. Its goal is to improve data discoverability, support better referencing practices, and help users navigate the complex landscape of tide gauge data portals.

The Amazon estuary is the eastern terminal connection of this hydrosystem, linking the Amazon watershed to the open ocean. At Óbidos, the upstream limit of the estuary, the 2021 May-June flood was recorded as the highest flood in 12 years, with a peak discharge of 257,661 m3.s−1. The impact of this record flood has not been yet quantified along the estuary. This study aims to quantify its signature on estuarine hydrodynamics, using a cross-scale hydrodynamic model of the Amazonian estuarine continuum based on SCHISM. It turns out that the 2021 discharge anomaly (10

The magnitude and temporality of the yearly maxima water levels are key parameters for the characterization of the riverine flooding hazard and its impacts. Although the Amazon estuary, that conveys the largest river discharge to the world ocean, exhibits marked events of maxima of the water level every year, the contribution of the natural drivers to these yearly extreme water levels is not well quantified. In this study, we investigate the contributing factors to the yearly maxima water level events along the Amazon estuary using a high-resolution cross-scale hydrodynamic model that has been extensively validated against comprehensive in situ and satellite datasets. Our study shows that the oceanic tide plays a crucial role in the genesis of the yearly maxima, whose influence decays from the downstream part (accounting for 85

The sudden 2018 volcanic eruption offshore Mayotte, in the western Indian Ocean, demonstrated, once again, the crucial need for means to monitor telluric activity occurring on the seafloor and threatening coastal zones. In the Mayotte case, on-land GNSS stations were of primary importance to detect the subsidence induced by the emptying of a deep magma chamber (Peltier et al. 2022), however they are not adequate to properly characterize and monitor the deformation created by further offshore or shallower processes.Ocean bottom pressure (OBP) records can be used to monitor seafloor motion. However, detecting small or slow deformation is challenging due to instrumental drift and oceanic variations at different timescales. New Ambient-Zero-Ambient (A0A) pressure systems allow the estimation of the instrumental drift in situ by periodic venting from ocean pressures to a reference atmospheric pressure (Wilcock et al., 2021) and therefore allow access to the accurate monitoring of slow deformation. A A0A drift-controlled pressure gauge has been deployed since 2020 (four successive deployments) to monitor the seafloor vertical deformation on the flank of Mayotte island. The deployment site is located within a seismically active circular-shape zone, called the proximal cluster (Lavayssière et al., 2022). During the last deployment (2022-2023), an additional reference instrument was installed outside the proximal cluster, to allow for differential deformation analysis.Beside volcanic activity monitoring, the objective of this study is to assess the performance of these new A0A pressure gauges and our ability to reduce the oceanic “noise” in corrected OBP records and characterize seafloor deformation in the Mayotte region. We investigate the use of numerical models, including available global ocean circulation reanalyses (OGCMs) and barotropic simulations, to account for the different oceanic processes contributing to the seafloor pressure variations and therefore limiting our ability to identify crustal deformation in the integrated pressure records.We also use temperature and salinity profiles from repetitive glider transects to validate OGCMs in the region and quantify the contribution of unresolved fine-scale processes to OBP records. Our results provide valuable insights into the feasibility of using numerical modeling for improving the accuracy of OBP-based monitoring at different timescales, in the context of the Mayotte seismic crisis as well as for other seafloor deformation monitoring. Finally, we present a preliminary work on the combination of sparse regional altimetric data with the glider observations to compute a seafloor pressure series to be compared to the recorded data. Current altimetry spatio-temporal coverage is limited, however, newcoming SWOT observations are likely to provide new perspectives in seafloor geodesy.Our results bring insights for future A0A deployments, especially in the perspective of the planned MARMOR seafloor cabled observatory offshore Mayotte.

Since the late 1990s, the hydrological cycle linking the Andes, the Amazon and the Atlantic Ocean has been intensifying. The Amazon estuary is the eastern terminal connection of this hydrosystem, linking the Amazon watershed to the open ocean. At Obidos, the upstream limit of the estuary, the 2021 May-June flood was recorded as the highest flood in 12 years, with a peak discharge of 260,000 m3.s-1. The impact of this record flood has not been yet quantified along the estuary. This study aims to quantify its signature on estuarine hydrodynamics, using a cross-scale hydrodynamic model of the Amazonian estuarine continuum based on SCHISM. It turns out that the 2021 discharge anomaly (10 % above the seasonal climatology) has a prominent influence on the Amazon River from 800 km to 380 km inland, inducing water level maxima typically 0.3 m higher than during a normal flood year, and about 1 m higher than during a weak flood year. Analysis of the various hydrodynamic factors conducive to the water level maxima along the estuary (i.e. discharge, oceanic tide and atmospheric forcing) shows that this is largely due to the discharge contributing twice as much in 2021 as in a normal year. In contrast, from 380 km inland to the oceanic mouth, both in the north-western arm (the North Channel) and in the south-eastern arm (the Para) of the estuary, the 2021 flood has no significant impact on the water level maxima dynamics, as the variability is dominated by the oceanic tide.

Ocean bottom pressure (OBP) records are an important source of information for monitoring seafloor motion due to tectonic and magmatic processes, such as earthquakes and volcanic eruptions, at a centimeter-level precision. Although centimeter-level resolution is commonly accessible with high-resolution sensors; monitoring seafloor deformation of a few centimeters through time with OBPs is challenging due to the instrumental drift and the existence of oceanic variations at different timescales.In the context of the Mayotte volcanic crisis, which occurred in the western Indian Ocean in 2018 and was characterized by a series of more than 10,000 small-magnitude earthquakes and a subsidence of tens of centimeters (Peltier et al., 2022), three RBR Ambient-Zero-Ambient (A0A) drift-controlled pressure gauges were consecutively deployed in 2020, 2021 and 2022 for seafloor vertical deformation monitoring. The A0A system allows the in-situ estimation of the instrumental drift by periodic venting from ocean pressures to a reference atmospheric pressure (Wilcock et al., 2021). Since no significant vertical ground displacements are recorded by ground GNSS stations since 2020, the overall objective of this study is to assess the calibration method of these innovative pressure gauges, reduce the oceanic “noise” in corrected OBP records and thus discuss our ability to observe any seafloor deformation in the Mayotte region.To do so, we investigated the use of numerical models, including available global ocean circulation reanalyses (OGCMs) and barotropic simulations, in order to better understand the relative influence of each processes evolving at different timescales, to reduce the oceanic “noise” in drift-corrected OBP records and thus improve our ability to derive accurate estimates of seafloor motion in the Mayotte region. In addition, we exploited temperature and salinity collected by repetitive glider transects to validate OGCMs in the region and quantify the contribution of unresolved fine-scale processes, such as sub-mesoscale eddies, to OBP records. Our results provide valuable insights into the feasibility of using numerical modeling for improving the accuracy of OBP-based monitoring in the context of the Mayotte seismic crisis as well as for other seafloor deformation monitoring. It also has important implications for future A0A deployments and in the perspective of the planned MARMOR seafloor cabled observatory.References Peltier, Aline, et al. "Ground deformation monitoring of the eruption offshore Mayotte." Comptes Rendus. Géoscience 354.S2 (2022): 1-23.Wilcock, W. S., Manalang, D. A., Fredrickson, E. K., Harrington, M. J., Cram, G., Tilley, J., ... & Paros, J. M. (2021). A thirty-month seafloor test of the A-0-A method for calibrating pressure gauges. Frontiers in Earth Science, 8, 600671.

Today, monitoring the evolution of sea level in coastal areas is of importance, since almost 11 % of the world's population lives in low-lying areas. Reducing uncertainties in sea level estimates requires a better understanding of both altimetry measurements and local sea level dynamics. In New Caledonia, the Nouméa lagoon is an example of this challenge, as altimetry, coastal tide gauge, and vertical land motions from global navigation satellite systems (GNSSs) do not provide consistent information. The GEOCEAN-NC 2019 field campaign addresses this issue with deployments of in situ instruments in the lagoon (GNSS buoy, pressure gauge, etc.), with a particular focus on the crossover of one Jason-series track and two Sentinel-3A missions tracks. In this study, we propose a method to virtually transfer the Nouméa tide gauge at the altimetry crossover point, using in situ data from the field campaign. Following the philosophy of calibration and validation (Cal/Val) studies, we derive absolute altimeter bias time series over the entire Jason and Sentinel-3A periods. Overall, our estimated altimeter mean biases are slightly larger by 1–2 cm compared to Corsica and Bass Strait results, with inter-mission biases in line with those of Bass Strait site. Uncertainties still remain regarding the determination of our vertical datum, only constrained by the three days of the GNSS buoy deployment. With our method, we are able to re-analyse about 20 years of altimetry observations and derive a linear trend of −0.2 ± 0.1 mm yr−1 over the bias time series. Compared to previous studies, we do not find any significant uplift in the area, which is more consistent with the observations of inland permanent GNSS stations. These results support the idea of developing Cal/Val activities in the lagoon, which is already the subject of several experiments for the scientific calibration phase of the SWOT wide-swath altimetry mission.

The Amazon River exports the largest volume of fresh water to the ocean worldwide. Although previous studies have revealed the spatiotemporal tidal variability of the estuary, its hydrodynamics is still poorly understood. Here we evaluate the seasonal and interannual variability of the tide from ' Obidos (800 km upstream) to the Atlantic Ocean and show how it is affected by the hydrological regime of the Amazon River. A high-resolution 2D hydrodynamic model was applied in this region at the scale of the whole estuary. The tide model is validated using data from 14 water level stations and shows an average complex error of 16 cm in the low flow season and 23 cm in the high flow season. The semi-diurnal tide is highly variable at seasonal timescales, and the seasonality of the discharge affects the tidal amplitude, the geographic extent of tidal influence, the tidal wave celerity, and the tidal flow reversal. Notably, the tidal influence on water level remains detectable up to ' Obidos during the low flow season while during the high flow season it extends from the ocean to only 300 km downstream of ' Obidos. On the other hand, the upstream limit of the domain where the tide induces a periodic flow reversal is different from the limit of tidal influence on the water level. The upstream limit of this flow reversal is shifted by 170 km (from 500 km to 670 km downstream of ' Obidos) along the year due to the seasonality of the discharge. At interannual scale, anomalous hydrological discharges affect the tidal amplitude by up to 30% in the central reach of the estuary. Our findings open unprecedented opportunities to understand biogeochemical and geomorphological processes, help navigation, and assess flooding hazards.

Le golfe du Bengale, au nord-est de l'océan Indien, est le siège tristement célèbre des cyclones tropicaux parmi les plus meurtriers de l'Histoire. Dans sa partie nord baigne le delta du Bengale, plus vaste région deltaïque de la planète. Malgré des avancées récentes, la morphologie et l'hydrodynamique complexes de ce grand delta, combinées au coût numérique de la modélisation hydrodynamique, ont empêché la prévision des surcotes marines sur cette région très vulnérable. Nous présentons ici un système de prévision des surcotes cycloniques fondé sur la plateforme de modélisation Schism-WWM, qui est à la fois efficace numériquement, cohérente physiquement et utilisable en temps réel avec des ressources informatiques limitées. Ce système de modélisation a permis de simuler en temps quasi réel le cyclone Amphan en mai 2020. The Bay of Bengal is a well-known birth region to some of the deadliest cyclones in history. In its northern part lies the largest deltaic region, the Bengal delta. Despite recent advancements, the complex morphology and hydrodynamics of this large delta and the associated modeling computational costs impede the storm surge forecasting in this highly vulnerable region. Here we present a proof of concept of a physically consistent and computationally efficient storm surge forecasting system tractable in real-time with limited resources. With a state-of-the-art wave-coupled hydrodynamic numerical modeling system, we forecast the 2020 super-cyclone Amphan in real-time.

In this data paper, the sea level time series at Socoa (Saint-Jean-de-Luz, southwestern France) is extended through a data archaeology exercise. We conducted a comprehensive study of national and local archives to catalogue water level records stored in ledgers (handwritten record books) and charts (marigrams from mechanical float gauges), along with other associated documents (metadata). A dedicated effort was undertaken to preserve more than 2000 documents by archiving them in digital formats. Using this large set of rescued documents, the Socoa time series has been extended back to 1875, with more than 58 station-years of additional data. The final time series has hourly sampling, while the raw dataset has a finer sampling frequency of up to 5 min. By analysing precise levelling information, we assessed the continuity of the vertical datum. We also compared the new century-long time series to nearby tide gauge data to ensure its datum consistency. While the overall quality of the time series is generally good, siltation of the stilling well has occasionally affected certain parts of the record. We have successfully identified these impacted periods and flagged the corresponding data as doubtful. This extended high-resolution sea level time series at Socoa, spanning more than 100 years, will be valuable for advancing climate research, particularly when studying the decadal-scale variations in the North Atlantic and investigating the storminess and extreme events along the French Basque coast. The raw digitized water level, the processed dataset, metadata, and the python notebooks used for processing are available at https://doi.org/10.5281/zenodo.7438469 (Khan et al., 2022).

&lt;p&gt;The Lagoon surrounding New Caledonia is a site of high interest for satellite altimetry, both for classical nadir missions and for the new SWOT wide swath mission, with dedicated calibration/validation (Cal/Val) experiments planned in 2023 during its 1-D repeat orbit.&lt;/p&gt; &lt;p&gt;This poster provides updated results from the 3-weeks campaign GEOCEAN-NC 2019, where various geodetic sea-level observing systems were deployed in the Lagoon (e.g. GNSS Buoy, pressure sensor, CalNaGeo GNSS towed carpet). By combining these data, we reconstruct the dynamics of the lagoon at a point of interest where 3 altimetric tracks intersect (i.e. 1 Jason and 2 Sentinel-3a tracks), and then virtually transfer the Noumea tide gauge records at this particular location. &amp;#160;&lt;/p&gt; &lt;p&gt;With this approach, we reconstruct two long sea-level time series (i.e. in-situ and altimetry) in the heart of the Lagoon, enabling us to compute altimetry biases and inter-mission biases comparable to those of historical Cal/Val sites for the whole Jason 1/2/3 period and for Sentinel-3a. This update of our results allows us to extend the comparison with new data from year 2022, and consolidate the vertical reference frame used to link our sensors. It is also an opportunity to try to reconcile sea-level rise trends with vertical land movements of permanent GNSS stations, which remains an issue in this area.&lt;/p&gt;

Abstract Coastal water level measurements represent one of the earliest geophysical measurements and allow an assessment of historical sea level rise and trends in tides, river flow and storm surge. However, recovery and digitization of archival tidal records have been much less widespread and systematic than, for example meteorological records. In this contribution, we discuss data rescue efforts and lessons learned in France, the United States and the United Kingdom, countries with early and extensive tide gauge networks by the mid‐19th century. We highlight the importance of (a) cataloguing the historical gauge records, as a first step towards locating them; (b) locating data in archives, and then recovering and saving data by any means necessary, including photographs and scanning; (c) obtaining metadata, including both quantitative survey records, gauge checks and clock data, but also qualitative records such as gauge notes, letters and reports; and (d) quantitative statistical analysis of data and datum quality, using both standard data‐entry checks but also tools that leverage the unique predictability of tide measurements. Methods for digitizing original analogue records are also discussed, including semi‐automatic, computer‐based methods of digitizing tidal charts (marigrams). Although the current best practice is described, future improvements are desirable and needed to make the more than estimated 10,000 station years of unused, undigitized records available to the scientific community.

Abstract. Spanning over a century, a traditional way to monitor sea level variability by tide gauges is – in combination with modern observational techniques like satellite altimetry – an inevitable ingredient in sea level studies over the climate scales and in coastal seas. The development of the instrumentation, remote data acquisition, processing and archiving in last decades allowed for extending the applications towards a variety of users and coastal hazard managers. The Mediterranean and Black seas are an example for such a transition – while having a long tradition for sea level observations with several records spanning over a century, the number of modern tide gauge stations are growing rapidly, with data available both in real-time and as a research product at different time resolutions. As no comprehensive survey of the tide gauge networks has been carried out recently in these basins, the aim of this paper is to map the existing coastal sea level monitoring infrastructures and the respective data availability. The survey encompasses description of major monitoring networks in the Mediterranean and Black seas and their characteristics, including the type of sea level sensors, measuring resolutions, data availability and existence of ancillary measurements, altogether collecting information about 236 presently operational tide gauge stations. The availability of the Mediterranean and Black seas sea level data in the global and European sea level repositories has been also screened and classified following their sampling interval and level of quality-check, pointing to the necessity of harmonization of the data available with different metadata and series at different repositories. Finally, an assessment of the networks’ capabilities for their usage in different sea level applications has been done, with recommendations that might mitigate the bottlenecks and assure further development of the networks in a coordinated way, being that more necessary in the era of the human-induced climate changes and the sea level rise.

Abstract Southern Asia experiences some of the most damaging climate events in the world, with loss of life from some cyclones in the hundreds of thousands. Despite this, research on climate extremes in the region is substantially lacking compared to other parts of the world. To understand the narrative of how an extreme event in the region may change in the future, we consider Super Cyclone Amphan, which made landfall in May 2020, bringing storm surges of 2–4 m to coastlines of India and Bangladesh. Using the latest CMIP6 climate model projections, coupled with storm surge, hydrological, and socio‐economic models, we consider how the population exposure to a storm surge of Amphan's scale changes in the future. We vary future sea level rise and population changes consistent with projections out to 2100, but keep other factors constant. Both India and Bangladesh will be negatively impacted, with India showing >200% increased exposure to extreme storm surge flooding (>3 m) under a high emissions scenario and Bangladesh showing an increase in exposure of >80% for low‐level flooding (>0.1 m). It is only when we follow a low‐emission scenario, consistent with the 2°C Paris Agreement Goal, that we see no real change in Bangladesh's storm surge exposure, mainly due to the population and climate signals cancelling each other out. For India, even with this low‐emission scenario, increases in flood exposure are still substantial (>50%). While here we attribute only the storm surge flooding component of the event to climate change, we highlight that tropical cyclones are multifaceted, and damages are often an integration of physical and social components. We recommend that future climate risk assessments explicitly account for potential compounding factors.

Storm-surge-induced coastal inundation constitutes a substantial threat to lives and properties along the vast coastline of the Bengal delta. Some of the deadliest cyclones in history made landfall in the Bengal delta region claiming more than half a million lives over the last five decades. Complex hydrodynamics and observational constraints have hindered the understanding of the risk of storm surge flooding of this low-lying (less than 5 m above mean sea level), densely populated (> 150 million) mega-delta. Here, we generated and analysed a storm surge database derived from a large ensemble of 3600 statistically and physically consistent synthetic storm events and a high-resolution storm surge modelling system. The storm surge modelling system is developed based on a custom high-accuracy regional bathymetry enabling us to estimate the surges with high confidence. From the storm surge dataset, we performed a robust probabilistic estimate of the storm surge extremes. Our ensemble estimate shows that there is a diverse range of water level extremes along the coast and the estuaries of the Bengal delta, with well-defined regional patterns. We confirm that the risk of inland storm surge flooding at a given return period is firmly controlled by the presence of coastal embankments and their height. We also conclude that about 10 % of the coastal population is living under the exposure of a 50-year return period inundation under current climate scenarios. In the face of ongoing climate change, which is likely to worsen the future storm surge hazard, we expect our flood maps to provide relevant information for coastal infrastructure engineering, risk zoning, resource allocation, and future research planning.

The Amazon yields the largest freshwater discharge to the world ocean, outflowing on a shallow, macro-tidal shelf. Its plume dynamics is complex and the impact of the discharge on the tidal properties on the adjoining shelf remains poorly understood. Through a series of numerical modelling experiment, we investigate the interaction between the Amazon discharge and the tide over the Amazonian shelf. We find that the runoff is responsible for a rise of the M2 tidal amplitude of ten cm in the embayment between Cabo Norte and Cabo Cassipore. The runoff also induces a rise of the mean sea level there, of 10 cm as well. Such a one-to-one sensitivity of the tidal amplitude and of the mean sea level over this region is quite unique among the world coastline. The modulation of the bottom friction by the thickness of the water column as well as by the vertical density stratification in the Amazon plume appears to be the main forcing factor of this response. Our numerical sensitivity experiments suggest that the seasonal variability of the Amazon discharge has little impact on the temporal variability of the tidal characteristics over the Amazonian shelf.