Sensitivity Analysis on Sea Surface Drag Parameterization in Storm Surge Modeling

Unequivocal change in the climate system has put coastal regions around the world at increasing risk from climate-related hazards like storm surge flooding. With studies demonstrating an increase in the frequency of storm surges along the Northwest coast of Ireland, within the EU H2020 project SCORE (Smart Control of the Climate Resilience in European Coastal Cities) a numerical modelling approach has been undertaken using SHYFEM (System of HYdrodynamic Finite Element Model) to simulate the storm surges into 2100 for the NW of Ireland under different Climate scenarios.   Using the significant grid flexibility offered by the finite elements within SHYFEM, unstructured grids are implemented for two computational domains. One confined to the region of interest, specifically the Donegal Bay, namely the Limited Area Model (LAM) and the other extended to span the entirety of the North Atlantic Basin namely the Basin Scale Model (BSM). The two model applications are designed to capture the development of storm surges due to wind shear stresses and barometric pressure fluctuations associated with the passage of storm systems across the North Atlantic and to quantify the influence of the tides on the tide surge interaction. Given the large tidal excursion in the region, baroclinicity is neglected and the models are implemented in the barotropic mode. The LAM is forced with surface atmospheric forcing (pressure and winds) from ECMWF and sea surface height (SSH, including eleven tidal components) from CMEMS at its open boundary, whereas the BSM is solely forced with the atmospheric forcing. Extensive calibration of wind drag and bottom friction coefficients for the LAM and BSM using tidal gauge observations for 2020, shows high P. Corr and acceptable RMSE. Only negligible differences, around 3 cm, are seen in the surge magnitudes between the LAM and the BSM implying the negligible non-linear interaction of the tides on the storm surge dynamics in the Donegal Bay.  Thus, the BSM has been forced with atmospheric forcing obtained from CMIP6 climate models to predict the impact of climate changes on storm surge intensity and frequency under different climate scenarios up to 2100. Finally, by accounting for the tidal contribution, total water levels projections have been determined thus facilitating the generation of useful statistics (for instance Annual exceedance probabilities) and flood maps to inform relevant policies for coastal resilience. 

Based on Finite Volume Coastal Ocean Model (FVCOM), this study constructed a numerical model covering the Bohai Sea, Yellow Sea, and East China Sea. National Centers for Environmental Prediction’s Climate Forecast System Reanalysis (NCEP-CFSR) data were used to drive the model to simulate a large storm surge generated by Typhoon Chan-hom. The model was validated by multiple in situ observations of water levels taken at tidal gauge stations. The effects of the nonlinear terms and topography on the modeling of storm surges were then studied. First, the tide–surge interaction during the storm surge process was analyzed. The results show that the tide–surge interaction can suppress the storm surge at the climax of the astronomical tide and benefit the growth of the storm surge at the ebb of the astronomical tide. The tidal constituents M2, S2 and K1 were added to analyze the influences of the amplitudes and periods of tides on the nonlinear reaction. The results indicate that the nonlinear effect will be enhanced by an increased tidal height; additionally, the nonlinear interaction of semidiurnal tides is more significant than that of diurnal tides. The semidiurnal fluctuation that appears near the peak-value time is also attributed to the tide–surge interaction. Moreover, the tide–surge interaction can be influenced by the water depth and position of the area of interest. According to the numerical results, topography has a certain impact on the storm surge: The peak value of the storm surge will decrease with increasing slope. The existence of the Ryukyu Islands reduces the area influenced by the storm surge on the southeast coast of China but expands the high-value storm surge area.

OuJiang River estuary and WenZhou bay are located in the southeast coast of Zhejiang province, China. At OuJiang river estuary, the storm surges are usually accompanied with flood. In this paper, the one-dimensional and two-dimensional coupling flood and storm surge model of the OuJiang river estuary and East China Sea area is used to examine the flood and storm surge dynamics in the region. The one-dimensional model is used for simulating the flood of the upstream of OuJiang River, the unstructured two-dimensional finite volume model is used for simulating the storm surge. The one-dimensional model and two-dimensional model are coupling at the estuary. The storm surges caused by 199417, 199608 and 200505 typhoons are simulated and the surge elevations at the nearshore, estuary and river are compared with the field observation results, which show that the coupling model can be good simulated the flood and storm surge process.

An unstructured grid storm surge model of the west coast of Britain, incorporating a high-resolution representation of the Mersey estuary is used to examine storm surge dynamics in the region. The focus of the study is the major surge that occurred during the period 11–14 November 1977, which has been investigated previously using uniform grid finite difference models and a finite element model of the west coast of Britain. However, none of these models included the Mersey estuary. Comparison of solutions in the eastern Irish Sea with those computed with these earlier models showed that, away from the Liverpool Bay region, the inclusion of the Mersey estuary had little effect. However, at the entrance to the Mersey, its inclusion did influence the solution. By including a detailed representation of the Mersey estuary within the model, it was possible to conduct a detailed study of storm surge propagation in the Mersey, which had never previously been performed. This detailed study showed for the first time that the surge’s temporal variability within the estuary is influenced by surge elevation at its entrance. This varies with time as a function of spatial and temporal variations of wind stress over the west coast of Britain. Within the Mersey, calculations show that the spatial variability is mainly determined by changes in bottom topography, which had not been included in earlier finite difference models. However, since water depth is influenced by variations in tidal elevation, this, together with tide surge interaction through bottom friction and momentum advection, influences the surge. The ability of the finite element model to vary the mesh in near-shore regions to such an extent that it can resolve the Mersey and hence the impact of the Mersey estuary upon the Liverpool Bay circulation shows that it has distinct advantages over earlier finite difference models. In the absence of detailed measurements within the Mersey at the time of the surge, it was not possible to validate predicted surge elevations within the Mersey. However, significant insight into physical processes influencing the surge propagation down the estuary, its reflection and spatial/temporal variability could be gained.

Storm surges are causing widespread devastation, directly impacting coastal communities through injuries and fatalities, infrastructure damage, and the displacement of residents. Projections of future storm surges are vital for assessing these risks, especially under climate change that causes both the intensity and frequency of these extreme events to increase. The temporal and spatial resolution of global climate model simulations do not resolve the critical characteristics of the events: storm surge peaks such as daily maximum storm surge occur on the scale of hours, while global climate model simulations are often only available at daily time scales. The coarse resolution data include some information about the daily maximum water levels but does not exactly determine the maximum storm surge peaks. Instead, a range of daily maximum storm surge peaks are realistic under the same coarse conditions.Hydrodynamic and data-driven models often derive storm surge time series deterministically capturing the average outcome, but do not represent the range of outcomes given coarse-scale predictors. Probabilistic models can address this by generating ensembles of outcomes, each consistent with coarse-scale predictors. For future projections, where no observed storm surge exists for comparison, it can be beneficial to use individual ensemble members to provide more realistic storm surge scenarios.We implement a multivariate probabilistic model using normalizing flows to simulate time series ensembles of daily maximum storm surges, driven by climate data aggregated to daily means. We train and evaluate the model using ERA5 climate reanalysis data and storm surge time series from the hydrodynamic Global Tide and Surge Model in the time period 1979-2018 across five representative regions worldwide. Our findings indicate that individual ensemble members replicate key statistical features of storm surges more effectively than the ensemble means, given the limited temporal and spatial resolution of the predictors. The multivariate model effectively preserves spatial correlations within each individual ensemble member, making it a spatially realistic realization of storm surge. Probabilistic storm surge time series conditioned on coarse atmospheric predictors open up new possibilities beyond traditional hydrodynamic modeling. Its performance in settings with limited predictor resolution make it an effective tool for computing storm surge projections consistent with climate model outputs.

The effect of nonlinear factors on tide-surge interaction: A case study of Typhoon Rammasun in Tieshan Bay, China

The Odra River mouth area is a region of the Southern Baltic coastal zone especially prone to the influence of storm surges. In the present study, the height and extent of the Baltic storm surges, and temporal offsets of the respective maximum water level occurrences in the Odra River mouth area were explored using cross-correlation, cluster analysis and principal component analysis. The analyses were based on hourly water level readings retrieved from water gauging stations located along the lower Odra reaches and at the coasts of the Szczecin Lagoon and the Pomeranian Bay during storm surge years 2008/2009–2019/2020. The analysis of mutual relationships between water levels during storm surges indicated that the extent of marine influence on the lower Odra River and within the Szczecin Lagoon was variable during the studied surge events, and dependent on meteorological conditions (the strongest during the sustained occurrence of wind blowing from the northern sector), discharge from the Odra River catchment (the strongest at low discharge), ice conditions on the lower Odra (suppressing the storm surge propagation upstream), and general sea level in the Pomeranian Bay (stronger at high sea levels). The strongest correlation between sea levels at Świnoujście and water levels in the Szczecin Lagoon and the lower Odra was found at a 6–7 h offset. The extent of storm surges usually reached 100 km up the lower Odra channels, less frequently reaching 130 km away from the sea.

Estuaries and tidal rivers are highly dynamic transitional zones where marine and riverine processes interact, creating complex hydrodynamic environments. These regions are influenced by natural phenomena such as tidal oscillations, storm surges, and river flow, as well as human activities like water management, hydropower operations, flood protection, and navigation. Effective management of these environments relies on understanding and predicting their hydrodynamic behavior, particularly under extreme conditions such as flooding or abrupt water level changes.This study examines the microtidal Neretva River estuary in Croatia to investigate the interactions between tides, storm surges, and river discharge, and their impacts on water level variability. A modified non-stationary harmonic analysis, based on the NS_Tide model, was developed specifically for microtidal conditions. This model incorporates storm surge and river discharge, improving the predictive accuracy of water levels along the estuary, from tide-dominated downstream sections to discharge-influenced upstream areas. The new version of NS_Tide also allows for a more detailed decomposition of total water levels and tide-surge-river interactions.The results reveal that river discharge is the primary factor influencing water levels at most stations, while the impact of storm surge decreases upstream. Tide-river interactions were observed throughout the study area, whereas tide-surge interactions had minimal effects. The analysis showed that high-frequency discharge fluctuations caused by hydropower operations amplify the S1 tidal constituent in upstream river sections. These fluctuations also modulate the amplitudes of other tidal constituents in estuarine and tidal river regions, highlighting the complex influence of human activities on tidal dynamics.The proposed non-stationary harmonic model proved highly effective for the microtidal Neretva River, capturing the complex interactions between tidal and non-tidal forces under various conditions. Its adaptability to local conditions suggests it could also be applied to mesotidal and macrotidal systems, offering a practical tool for managing estuaries and tidal rivers across diverse environments.

A numerical model study of barotropic subtidal water exchange between estuary and subestuaries (tributaries) in the Chesapeake Bay during northeaster events

Bohai Bay is an semi-closed bay, the storm surge disaster is very serious in past. Now more and more large ocean engineering are built here, To study changes of storm surge induced by the construction of large-scale coastal engineering in Bohai Bay in present, 2D numerical storm surge model is established with large - medium - small model nested approach. The three most typical storms surges: 9216, 9711 and by cold wave in October 2003 are simulated in the condition of before and after implementation of planning projects in Bohai Bay. Changes of storm surge water level due to implementation of artificial projects are analysis in this paper.

Post‐tropical Hurricane Fiona generated a large storm surge that resulted in pronounced flooding and coastal erosion in Atlantic Canada in September 2022. In this study we apply a regional barotropic storm surge model in the Gulf of St. Lawrence, a semi‐enclosed sea, to demonstrate a method of evaluating different contributions to the total water levels. These include the surge generated over the ocean, the surge generated by the cyclonic winds over the gulf, and the tides. The results indicate that the highest storm surge occurred in the southeastern region, a combination of locally and remotely generated components. The surge that entered from the ocean was greater than the surge generated over the gulf; however, these were not in phase. To investigate the case where the local and remote surges are coincident, we shift the wind field relative to the timing of the boundary conditions and find the near “perfect storm” with significantly higher storm surge elevations. These findings highlight the importance of basin morphology and storm conditions in controlling the interactions of surge components, and this approach can be applied to simulate a range of storm‐driven hazard outcomes for future extreme events.

Typhoon-induced storm tides can cause serious coastal disasters and considerable economic losses. Understanding the mechanisms controlling storm surges helps the prevention of coastal disasters. Hangzhou Bay (HZB), a typical macro-tidal estuary, is located on the east coast of China, where typhoons frequently occur. The funnel-shaped topography makes this macro-tidal bay even more sensitive to storm tides. Super Typhoon Chan-hom was used as an example to study the characteristics and dynamic mechanisms of storm surges using a well-validated numerical model. The model considers the two-way coupling of waves and tides. The wind strength for the model was reconstructed using multi-source wind data and was refined by considering different rotating and moving wind fields. The Holland–Miyazaki model was used to reconstruct the local wind-field data with a good performance. The model results show that the total water level of HZB during typhoon Chan-hom was mainly dominated by tides, and the storm surge was closely related to the wind field. Surface flow was mostly influenced by winds, followed by tides. The spatial and temporal distributions of the significant wave height were controlled by the wind and local terrain. Wind stress was the largest contributor to storm surges (91%), followed by the pressure effect (15%) and the wave effect (5%). Both wind and wave-induced surges occurred during low slack waters. The tide-surge interaction changes (enhance or suppress) the surge by approximately 0.5 m during the typhoon, comprising approximately 50% of the total surge. Tides interacted with surges through various mechanisms, from the bay mouth (local acceleration and friction) to the bay head (friction and advection). The Coriolis force had a relatively minor effect. The findings of this study provide useful information for studies on sediment dynamics and coastal structures under extreme weather conditions.

<p>We present here a novel application of state-of-the-art surge modeling on a past climate of special interest. The Last Interglacial (LIG; 125,000 years ago) was the latest instance of a climate (slightly) warmer than present: for this reason its study can inform on the response of several climate components to a climate state with partial resemblance to possible futures. Climate variables like temperature and precipitation have been extensively studied for the LIG. Here, we calculate for the first time the implications of the altered LIG atmospheric circulation (both in mean state and extremes) for storm surges along the global coastline. This presents particular interest since it is often claimed that a warmer climate may imply enhanced storminess in some ocean basins. We use sub-daily results from simulations of the LIG and of the pre-industrial periods with the climate model CESM1.2 (equipped with atmosphere module CAM5, with ca. 1 degree horizontal resolution) to force the Global Tide and Surge Model (GTSM) for 30-years at climate equilibrium conditions. We analyze patterns of storminess and of storm surges, and report on the anomalies in those metrics between the LIG and the pre-industrial climate. These results can help contextualize proxy-based reconstructions of storms of the LIG, as well as projections of storm surges in a future warmer climate. Finally, we also reconstruct tides of the LIG, aiming to provide useful constrains to paleo sea-level reconstructions.</p>

Regional storm tidal levels of the South African coastline are investigated by means of a calibrated and validated numerical model. The model was developed utilizing the shallow water hydrodynamic model, Delft3D. This model was coupled (online) with a non-stationary spectral wave model (developed in the Simulating WAves in the Nearshore (SWAN) numerical code). A local, 4.4 km version of the Unified Model was applied as atmospheric forcing for the coupled system. The models presented in this study form part of the operational marine forecasts of the South African Weather Service, Wave and Storm Surge model. The operational protocol and model calibration and validation are presented via statistical correlations with measured water levels at six South African coastal locations. The main calibration parameters and thus physical drivers were winds, atmospheric pressure and waves. The validated numerical model is used to provide an experimental physical description of South African storm surge characteristics, per coastline. The dominant driver of South African storm surge is winds associated with mid-latitude cyclones. Further novelty in the present study is the quantification of the relative contribution of extreme storm wave set-up to the South African storm surge signal. This wave set-up contributes approximately 20% of the total surge signal in the southwest, with winds contributing approximately 55%. The importance of the continental shelves is also elucidated concerning the frictional shoaling effects of the long surge wave propagation.

Storm surge and concomitant waves induced by extreme weather systems can significantly modulate the marine dynamic environment. In this study, we used the Advanced Circulation-Simulating Waves Nearshore (ADCIRC-SWAN) coupled model to analyze spatiotemporal variation in dynamic processes during two types of weather systems, i.e., typhoons and extratropical storms, in the sea area near the Shandong Peninsula. The effects of waves on water level, water level change on wave height, and currents on wave height were investigated and quantified separately by performing sensitivity experiments. Our results showed that the interaction between water level change and waves occurred mainly in the nearshore zone. The wave-induced surge accounted for about 10–15% of the total storm surge. The water level change-induced significant wave height reached up to 0.9–1.3 m. Wave–current interaction occurred mainly in the offshore zone and was related to the relative angle between wave and current directions. The modulations of water level and wave height were strongly dependent on not only storm track and intensity but also topography and coastline shapes.