Extreme Storm Surge Events Research Articles

Integrating historical storm surge events into flood risk security in the Copenhagen region

Rapid urbanisation along the coasts of the world in recent decades has increased their vulnerability to storm surges, especially in response to mean sea level rise. The unique geographical and social conditions of Copenhagen, a major European coastal city, have prompted urban expansion along Køge Bay to the south of the city. However, this new urbanisation area is confronted with the common obstacle of developing a coastal defence strategy, i.e., the lack of long-term observational data required to determine a reliable storm surge protection level. This study aims to address this issue by developing a framework that integrates historical records of extreme storm surge events into coastal defence strategies, using Copenhagen as a case study. We propose a four-step work framework, including (1) Data collection and analysis: We collected and analysed data from neighbouring cities and used modelling and reanalysis data sets. By combining these sources, we aim to reconstruct historical time series for the study site dating back to 1836. This extended information set enhances our understanding of past storm surge events. (2) Statistical modelling and forecasting: Using Bayesian statistical methods, we fitted the historical storm surge data to appropriate probability distributions. This enabled us to generate probabilistic forecasts of storm surge magnitudes, providing insight into the likelihood of future events and their potential impacts on the coastal area. (3) Sensitivity analyses: We performed sensitivity experiments using Markov chain Monte Carlo (MCMC) methods to identify the most influential parameters, such as thresholds, that affect storm surge levels. This analysis improved our understanding of the key drivers of storm surge events and their uncertainties, further informing coastal defence strategies. (4) Expert judgement and risk management: Expert judgements are implemented to establish the necessary security level to manage flood risks in the city. This helps to ensure that high-impact, low-probability events are adequately considered in risk management efforts. Following this framework, we can develop a comprehensive understanding of storm surge risks in the urbanised region south of Copenhagen and use historical data to inform coastal defence strategies. This study emphasises the importance of incorporating long-term observational data and expert insights to improve the resilience of coastal cities facing the challenges of urbanisation and climate change.

Extreme Storm Surge Events and Associated Dynamics in the North Atlantic

AbstractStorm surges events are investigated using the ECHAR method, which identifies and quantifies the different dynamical structures of a typical storm surge event. In the North Atlantic, analysis of 65 tide gauges revealed that storm surge events display two major and two minor structures, each of them corresponding to specific ocean dynamics. The two major structures refer to a slow‐time Gaussian structure, lasting around 24 days, associated with the impact of the atmospheric pressure and a fast‐time Laplace structure, lasting around 1.4 days, mainly wind‐driven. The absence of the Gaussian structure along the North America coasts is explained by storms of smaller spatial extension, compared to Europe. Concerning the minor structures, a negative surge of around 6 cm just after the peak surge is observed over North America only. Such a sudden drop of the sea level is explained by the turning winds during the storm event, favored by the smaller spatial extension of storms. Finally, high frequency oscillations, with amplitude typically of 3 cm and up to 25 cm, are observed at some tide gauges. These oscillations refer to tide‐surge interactions and they are often maximum at a specific phase of the tide and/or enhanced because of resonant basins.

Quantifying future changes of flood hazards within the Broadland catchment in the UK

Flooding represents the greatest natural threat to the UK, presenting severe risk to populations along coastlines and floodplains through extreme tidal surge and hydrometeorological events. Climate change is projected to significantly elevate flood risk through increased severity and frequency of occurrences, which will be exacerbated by external drivers of risk such as property development and population growth throughout floodplains. This investigation explores the entire flood hazard modelling chain, utilising the nonparametric bias correction of UKCP18 regional climate projections, the distributed HBV-TYN hydrological model and HEC-RAS hydraulic model to assess future manifestation of flood hazard within the Broadland Catchment, UK. When assessing the independent impact of extreme river discharge and storm surge events as well as the impact of a compound event of the two along a high emission scenario, exponential increases in hazard extent over time were observed. The flood extent increases from 197 km2 in 1990 to 200 km2 in 2030, and 208 km2 in 2070. In parallel, exponential population exposure increases were found from 13,917 (1990) to 14,088 (2030) to 18,785 (2070). This methodology could see integration into policy-based flood risk management by use of the developed hazard modelling tool for future planning and suitability of existing infrastructure at a catchment scale.

Investigation of historical severe storms and storm tides in the German Bight with century reanalysis data

Abstract. Century reanalysis models offer a possibility to investigate extreme events and gain further insights into their impact through numerical experiments. This paper is a comprehensive summary of historical hazardous storm tides in the German Bight (southern North Sea) with the aim of comparing and evaluating the potential of different century reanalysis data to be used for the reconstruction of extreme water levels. The composite analysis of historical water level extremes, underlying atmospheric situations and their uncertainties may further support decision-making on coastal protection and risk assessment. The analysis is done based on the results of the regional hydrodynamic model simulations forced by atmospheric century reanalysis data, e.g. 20th Century Reanalysis Project (20CR) ensembles, ERA5 and UERRA–HARMONIE. The eight selected historical storms lead either to the highest storm tide extremes for at least one of three locations around the German Bight or to extreme storm surge events during low tide. In general, extreme storm tides could be reproduced, and some individual ensemble members are suitable for the reconstruction of respective storm tides. However, the highest observed water level in the German Bight could not be simulated with any considered forcing. The particular weather situations with corresponding storm tracks are analysed to better understand their different impact on the peak storm tides, their variability and their predictability. Storms with more northerly tracks generally show less variability in wind speed and a better agreement with the observed extreme water levels for the German Bight. The impact of two severe historical storms that peaked at low tide is investigated with shifted tides. For Husum in the eastern German Bight this results in a substantial increase in the peak water levels reaching a historical maximum.

Seasonal Shift of Storm Surges in the Yangtze Estuary, China

This study explores storm floods in the Yangtze Estuary to investigate how extreme sea levels and storm surges change in the context of global warming. Previous studies focused on the long-term variations in amplitude or frequency of storm surges, with limited research conducted on the timing of extreme storm surge events. Based on the methods of non-stationary extreme value theory, we explored the last 33-year tidal levels at Xuliujing Station and found that the annual extreme water level has exhibited a slight downward trend, which is directly attributed to the decrease in mean sea level resulting from reduced upstream river flow. The storm surge season of the Yangtze Estuary experienced a significant lag in the period 2005–2018, which is not restricted to the Yangtze Estuary but is rather a large-scale climate characteristic of a broad oceanic region. The reason for this shift is the sustained increase in the intensity of the western Pacific subtropical high in the last 15 years, leading to the appearance of low-pressure channels in the East China Sea in September and October and thus causing more typhoons to enter the East China Sea during the later period of the storm surge season.

Insights on the Extreme Storm Surge Event of the 22 November 2022 in the Venice Lagoon

The Italian Institute for Environmental Protection and Research (ISPRA) manages the national sea state real time monitoring system for Italy, which consists of the National Sea Level Network (RMN), the North Adriatic and Venice Lagoon Sea Level Network (RMLV), the National Wave Networks (RON), and a marine weather forecasting system. These systems are particularly deployed to monitor and predict storm surges that affect the northern part of the Adriatic Sea and the Venice Lagoon, usually causing damages and morphological impacts over the highly anthropized coastal areas. On 22 November 2022, an extreme storm surge event occurred in the northern Adriatic Sea, producing severe damages on its coastline. Venice and the surrounding urban settlements have been protected from flooding thanks to the operation of the Mo.S.E. (Modulo Sperimentale Elettromeccanico) system, a set of artificial barriers built to isolate the lagoon from the sea in case of extreme high tides. Coastal flooding prevention measures, such as storm-surge barriers, are indeed being widely adopted globally because of the accelerating rise in sea levels. An analysis of this extreme event is presented here to highlight the functionality and the usefulness of the ISPRA sea state monitoring system. In particular, the analysis of the as-if scenario reproducing the natural tide propagation within the lagoon, neglecting the operation of the Mo.S.E. system, can only be pursued by using hydrodynamic models forced using extensive observed data. Results highlight that the “not-regulated” sea level would have exceeded 200 cm above the reference datum at Chioggia, a threshold never recorded in the Venice Lagoon since sea level monitoring systems have been operational.

Unstructured Grid-Based River–Coastal Ocean Circulation Modeling towards a Digital Twin of the Seto Inland Sea

As computational techniques advance, the scope of digital twins (DTs) is expanding to encompass entire cities, oceans, or even the Earth. Digital twins of oceans can provide highly comprehensive insights and predictions, thus enabling better-informed decision-making regarding ocean-related activities and management. Here, a numerical model of the Seto Inland Sea (SIS), Japan, was built as a basis to establish a digital twin of the SIS. Spatially varying filtering parameters and grid resolutions were applied to facilitate the robust and accurate simulation of coastal and oceanic processes even under varying extreme conditions. The modeling results were validated using observational datasets from forty-two tidal stations, one mooring system, and thirteen water thermometers. The results represented tidal variations, with NRMSE values below 0.15 and R2 values exceeding 0.87 at all tidal stations. The NRMSE and R2 values for currents were approximately 0.14 and 0.76, respectively. The model reproduced the extreme storm surge event causing a sea level rise of 1.5 m near Osaka City resulting from Typhoon Jebi in 2018. The model was shown to enable analyses of complex circulations and hazards in the SIS by accurately replicating barotropic and baroclinic processes. After additional modules are added, this model will serve as a basis for constructing a digital twin of the SIS.

RCP8.5-projected changes in German Bight storm surge characteristics from regionalized ensemble simulations for the end of the twenty-first century

This study investigates climate-induced changes in height, frequency and duration of storm surges in the German Bight. The regionally coupled climate model system MPIOM-REMO with a focus on the North Sea has been utilized to dynamically downscale 30 members of the global climate model system MPI-ESM1.1-LR for the historical period 1950–2005 and a continuation until 2099 with the RCP8.5 scenario. Results of all members have been collected into the historical (1970–1999) and the rcp85 (2070–2099) data pools amounting to 900 years of the corresponding climate state. The global mean sea level rise was not considered. Nevertheless, the mean ensemble German Bight SSH trend amounts to about 13 ± 1 cm/century (PI control: 3 cm/century) due to adaptation of the ocean circulation to the changing climatic conditions. Storm surges were defined as SSH above mean high tidal water plus 1.5, 2.5, 3.5 m for “regular”, heavy, extreme storm surges, and then clustered to events. Our simulated storm surge events show a clear location-dependent increase in frequency (6–11%), median duration (4–24%), and average duration (9–20%) in the German Bight. Only along the central German Bight coast (Cuxhaven), longer lasting events gain more relevance. Heavy storm surge events show also a strong increase in frequency (7–34%) and average duration (10–22%). Maximum sea levels during storm events increase strongest and most significant along the northern German Bight and Danish coasts with more than 30 cm/century for the 60-year return period at Hörnum and 10–15 cm/century for shorter return periods. Levels of return periods shorter than a few years significantly increase everywhere along the southern German Bight coasts (around 5 cm/century for the 2-year return period). Highest SSH maxima do not change, and consequently, extreme storm surge events show hardly any response to climate change. Furthermore, our results indicate a shift of seasonality from the last to the first quarter of a year. As the main driver for the encountered alteration of German Bight storm surge characteristics, we identified a change in wind conditions with a pronounced increase of frequency of strong westerly winds.

On the generation of high‐resolution probabilistic design events capturing the joint occurrence of rainfall and storm surge in coastal basins

AbstractCoastal areas are subject to the joint risk associated with rainfall‐driven flooding and storm surge hazards. To capture this dependency and the compound nature of these hazards, bivariate modelling represents a straightforward and easy‐to‐implement approach that relies on observational records. Most existing applications focus on a single tide gauge–rain gauge/streamgauge combination, limiting the applicability of bivariate modelling to develop high‐resolution space–time design events that can be used to quantify the dynamic, that is, varying in space and time, compound flood hazard in coastal basins. Moreover, there is a need to recognize that not all extreme events always come from a single population, but can reflect a mixture of different generating mechanisms. Therefore, this paper describes an empirical approach to develop design storms with high‐resolution in space and time (i.e., ~5 km and hourly) for different joint annual exceedance probabilities. We also stratify extreme rainfall and storm surge events depending on whether they were caused by tropical cyclones (TCs) or not. We find that there are significant differences between the TC and non‐TC populations, with very different dependence structures that are missed if we treat all the events as coming from a single population. While we apply this methodology to one basin near Houston, Texas, our approach is general enough to make it applicable for any coastal basin exposed to compounding flood hazards from storm surge and rainfall‐induced flooding.

Long-term trends in storm surge climate derived from an ensemble of global surge reconstructions

We address the challenge, due to sparse observational records, of investigating long-term changes in the storm surge climate globally. We use two centennial and three satellite-era daily storm surge time series from the Global Storm Surge Reconstructions (GSSR) database and assess trends in the magnitude and frequency of extreme storm surge events at 320 tide gauges across the globe from 1930, 1950, and 1980 to present. Before calculating trends, we perform change point analysis to identify and remove data where inhomogeneities in atmospheric reanalysis products could lead to spurious trends in the storm surge data. Even after removing unreliable data, the database still extends existing storm surge records by several decades for most of the tide gauges. Storm surges derived from the centennial 20CR and ERA-20C atmospheric reanalyses show consistently significant positive trends along the southern North Sea and the Kattegat Bay regions during the periods from 1930 and 1950 onwards and negative trends since 1980 period. When comparing all five storm surge reconstructions and observations for the overlapping 1980–2010 period we find overall good agreement, but distinct differences along some coastlines, such as the Bay of Biscay and Australia. We also assess changes in the frequency of extreme surges and find that the number of annual exceedances above the 95th percentile has increased since 1930 and 1950 in several regions such as Western Europe, Kattegat Bay, and the US East Coast.

Lost in the North Sea-Geophysical and geoarchaeological prospection of the Rungholt medieval dyke system (North Frisia, Germany).

We performed geophysical and geoarchaeological investigations in the Wadden Sea off North Frisia (Schleswig-Holstein, Germany) to map the remains and to determine the state of preservation of the medieval settlement of Rungholt, especially its southern dyke segment, called the Niedam dyke. Based on archaeological finds and historical maps, Rungholt is assumed to be located in the wadden sea area around the island Hallig Südfall. During medieval and early modern times, extreme storm events caused major land losses, turning cultivated marshland into tidal flats. Especially the 1st Grote Mandrenke (or St. Marcellus' flood), an extreme storm surge event in 1362 AD, is addressed as the major event that flooded and destroyed most of the Rungholt cultural landscape. Cultural traces like remains of dykes, drainage ditches, tidal gates, dwelling mounds or even plough marks were randomly surveyed and mapped in the tidal flats by several authors at the beginning of the 20th century. Due to the tidal flat dynamics with frequently shifting tidal creeks and sand bars, the distribution of cultural remains visible at the surface is rapidly changing, making it hard to create a comprehensive map of the cultural landscape by surveying. Today, the Niedam dyke area is fully covered by tidal flat sediments, depriving any remains from further archaeological investigation. Since little is known about the precise location or state of preservation of these remains, our investigation aimed at the rediscovery of the medieval dyke system and associated structure with modern and accurate geophysical, geodetical and geoarchaeological methods. Magnetic gradiometry revealed a large part of the medieval dyke, confirming two tidal gates and several terps connected inland with the dyke, providing a detailed example of a Frisian medieval dyke system. Based on our results, the so far inaccurate and incomplete maps of this part of Rungholt can now be specified and completed. Beyond that, seismic reflection profiles give a first depth resolving insight in the remains of the dyke system, revealing a severe threat to the medieval remains by erosion. The site is exemplary for the entire North Frisian coast, that was influenced by multiple flood events in the middle ages to modern times.

Simulating major storm surge events in a complex coastal region

Climate change and increased coastal urbanization are causing low-lying coastlines to become increasingly susceptible to the threat of extreme water levels and coastal flooding. Robust decision-making on adaptation in the coastal zone, based on reliable ocean-modelling tools, is therefore crucially contingent on accurate assessments of current and future storm surge hazards. This accuracy relies considerably on the quality of the wind forcing used in the ocean models. In this paper, we use a high-resolution, regional 3D ocean model (HBM) covering the North Sea and Baltic Sea to simulate extreme water levels during three extreme storm surge events with different dynamics and patterns, in order to assess their impacts along Denmark’s coastlines, which are of varying levels of complexity. We demonstrate that the model is able to reproduce the observed extreme high-water levels accurately, indicating that the system is well suited for producing simulations of present and future projections of extreme storm surges with high resulting impacts and damage potentials. Additionally, we quantify the level at which acknowledged deficiencies in the otherwise most suitable atmospheric forcing data set influence the results of the storm surge simulations. We found that reducing the temporal resolution of the forcing data – that is, replacing two out of every six time stamps with linearly interpolated values – is preferable to using the original forcing data set when recurring noise is present in these time stamps. As a result, for given storm surge events, and depending on the stage reached in the storm’s evolution, mean absolute errors can be reduced by 4.5cm. This emphasizes the importance of considering such model fluctuations when coupling high-resolution atmosphere and ocean models.

Dynamical Downscaling of Coastal Dynamics for Two Extreme Storm Surge Events in Japan

Graphical AbstractStudy domains and model setup (up-left), Sea Surface Height results validation (up-right), Sea Surface Salinity results validation (down-left) and impact of the two storm surge events to the associated coastal dynamics variables (down-right).

A GIS-based screening method to identify climate change-related threats on road networks: A case study from Sweden

Extreme weather-related events are likely to increase in both frequency and intensity if current emission rates continue. Particularly vulnerable to the potential effects of climate change is the transportation sector, which fully relies on the uninterrupted accessibility of the road network. With the Swedish Government adopting a National Adaptation Strategy in 2018, creating a coordinated cross-disciplinary strategy underpinned by international frameworks, new ambition levels regarding climate change adaptation efforts have been established. Identifying particularly vulnerable parts of the road network is an essential step for National Road Authorities (NRAs) in early planning stages to prioritize adaptation efforts around high-risk areas to safeguard the road network. By utilizing both publicly and commercially available climate-related data, as well as applying and assessing new terrain analysis techniques, a large-scale vulnerability assessment is carried out for Halland County in southwestern Sweden by assessing three climate-adjusted extreme weather events (a 100-year pluvial flood event, a 100-year fluvial flood event, and an extreme coastal storm surge event) projected to exacerbate in the region. The study demonstrates how a GIS-based screening method, specifically adapted for NRAs or similar stakeholders, may provide quick overviews of potentially at-risk areas along road networks through a simple vulnerability index assigned to individual road segments. Further studies are recommended to compare modeled results to recorded flood events if available and incorporate updated climate change trajectories from upcoming IPCC reports.

Modeling of Future Extreme Storm Surges at the NW Mediterranean Coast (Spain)

Storm surges are one of the main drivers for extreme flooding at the coastal areas. Such events can be characterized with the maximum level in an extreme storm surge event (surge peak), as well as the duration of the event. Surge projections come from a barotropic model for the 1950–2100 period, under a severe climate change scenario (RCP 8.5) at the northeastern Spanish coast. The relationship of extreme storm surges to three large-scale climate patterns was assessed: North Atlantic Oscillation ( N A O ), East Atlantic Pattern ( E A W R ), and Scandinavian Pattern ( S C ). The statistical model was built using two different strategies. In Strategy #1, the joint probability density was characterized by a moving-average series of stationary Archimedean copula, whereas in Strategy #2, the joint probability density was characterized by a non-stationary probit copula. The parameters of the marginal distribution and the copula were defined with generalized additive models. The analysis showed that the mean values of surge peak and event duration were constant and were independent of the proposed climate patterns. However, the values of N A O and S C influenced the threshold and the storminess of extreme events. According to Strategy #1, the variance of the surge peak and event duration increased with a fast shift of negative S C and a positive N A O , respectively. Alternatively, Strategy #2 showed that the variance of the surge peak increased with a positive E A W R . Both strategies coincided in that the joint dependence of the maximum surge level and the duration of extreme surges ranged from low to medium degree. Its mean value was stationary, and its variability was linked to the geographical location. Finally, Strategy #2 helped determine that this dependence increased with negative N A O .

The limited role salt marshes may have in buffering extreme storm surge events: Case study on the New Jersey shore

The hybrid hurricane and storm event dubbed “SuperStorm Sandy” of October 2012 was the most costly natural disaster to hit the US Atlantic coast, and the second most costly to affect the United States. This extreme weather event presented an excellent opportunity to assess the effectiveness of tidal salt marshes and maritime forests in buffering adjacent development from storm-related damage. To address this question of how well did or under what conditions did coastal ecosystems buffer adjacent human development, we undertook to quantify the incremental monetary value that a hectare or linear extent of fronting salt marsh and/or maritime forest had on protecting the built environment of the back-bay communities in the Barnegat Bay region of New Jersey, USA. Statistical modeling was used to estimate the relationship between the spatial extent and characteristics of fronting coastal wetlands with the various damage metrics derived from the Federal Emergency Management Agency National Flood Insurance Program payout and Preliminary Property Modeling Task Force damage data at the scale of the individual housing unit. While salt marshes may be effective in diminishing wave energies and buffering adjacent development under normal conditions, in the case of SuperStorm Sandy, we find no evidence that New Jersey's extensive coastal marshes significantly buffered and thereby reduced NFIP payouts on the majority of back-bay residential properties. The extreme conditions of this storm event with storm surges upwards of 2 m, effectively flooded these marshes diminishing their protective capacity. The bulk of the residential properties damaged in our study area were located in lagoonal communities that are built directly adjacent to tidal water and are thereby highly vulnerable to storm surge-related flooding whether or not they are buffered by adjacent marshes. The results of this study should not be misconstrued in concluding that salt marshes do not have a positive value in protecting coastal properties; rather, their protective buffering capacity for extreme storm events is limited and that lagoonal-style developments remain highly vulnerable to sea level rise and future storms.

Storm surge and seiche modelling in the Adriatic Sea and the impact of data assimilation

In this research we present a modelling study of storm surges influenced by pre‐existing seiches in the Adriatic Sea. The natural oscillation modes – seiches – of the Adriatic Sea can be easily excited by wind, due to the particular marine bathymetry and coastal orography. Moreover, such oscillations can interact with newer wind‐induced storm surges or with other sea‐level components. This paper first considers modelling issues in the seiche reproduction, using a simplified approach, and then analyses the reproduction with the model of two extreme storm surge events, influenced by pre‐existing seiches. In order to investigate the impact of assimilating sea level data, these events are simulated without and with a data assimilation system, based on an Ensemble Kalman Filter. Results show that, while the formulation of the bottom shear stress does not influence the seiche period, the seiche decay time is correctly estimated with a hybrid linear‐quadratic formulation. We found also that non‐linear interactions of bottom currents, caused by different sea level components, can modify the decay time. However, the two events are poorly reproduced by the model, even with a correct modelling set‐up, because of wind deficiencies. Therefore we considered the issue and found that the assimilation of tide‐gauge residual sea level has a strong positive impact, lasting several days, despite the errors in the atmospheric forcing. This is mainly due to the persistence of the seiche oscillations in the Adriatic Sea.

A simplified hindcast method for the estimation of extreme storm surge events in semi-enclosed basins

Human presence, coastal erosion, and tourism activities are increasing the attention to coastal flooding risk. To perform risk assessments, long time series of observed or hindcast wave parameters and tide levels are then necessary. In some cases, only a few years of observation are available, so that observed extreme data are not always representative and reliable. A hindcast system aimed to reconstruct long time series of total tide levels may be of great help to perform robust extreme events analysis and then to protect human life, activities as well as to counteract coastal erosion by means of risk assessments. This work aims to propose a simplified method to hindcast storm surge levels time series in semi-enclosed basins with low computational costs. The method is an extension of a previous work of some of the authors and consists of a mixed approach in which the estimation of storm surge obtained by using the theory of linear dynamic system is corrected by using a statistical method. Both steps are characterized by low computational costs. Nevertheless, the results may be considered reliable enough also in view of the simplicity of the approach. The proposed method has been applied to the Manfredonia case study, a small village located in the Southern Adriatic Italian coast and often prone to coastal flooding events. The comparison of extreme events estimated on the basis of hindcast levels time series is satisfactorily similar to those estimated on the basis of observed tide series.

Dune ridge progradation resulting from updrift coastal reconfiguration and increased littoral drift

Coastal dune ridges are prominent morphological features of many barrier islands. To investigate the environmental controls on coastal dune ridge formation 38 samples from prominent coastal dune ridges on the barrier island of Fanø in the Wadden Sea were dated by the optically stimulated luminescence (OSL) technique. Multiple samples were recovered from each dune ridge to test the internal consistency of the ages and to establish the last time the ridges were active. The OSL ages range from 4 ± 1 yr to 318 ± 27 yr and the average age of the dune ridges from 255 ± 30 to 6 ± 2 yr. The results show that Fanø prograded between 1000 and 1500 m in the last 250 to 300 years with an average long-term progradation rate of 4 to 5 m yr−1. We argue that dune ridge formation was favoured by normal regressive conditions resulting from increased sediment supply after an extreme storm surge event in 1634, induced by a combination of regional-scale morphological changes in the updrift coastal configuration and erosion and deposition resulting from reorientation of the barrier shoreline. Increased storminess during the Little Ice Age does not appear to be directly responsible for dune building at Fanø or in the Danish Wadden Sea but may have contributed to an overall increased sediment supply along the coast. In a regional context, dune ridge building was controlled by the inherited morphology of the shoreline that forms a large-scale embayment favouring sediment surplus and regressive conditions in the inner part to the embayment and sediment deficit and transgressive conditions along protruding parts of the embayment. It is further argued that increased marine sediment supply due to changes in local to regional scale coastal morphology and changes in climatic drivers can be equally important controlling dune ridge formation.

Assessment of long-term impact of storm surges around the Korean Peninsula based on a large ensemble of climate projections

This study assesses the long-term impact of storm surges due to typhoons around the Korean Peninsula (KP) resulting from climate change. Long-term projection is conducted based on the large ensemble experiments on so-called d4PDF for the past and +4 K future climate conditions over 5000 years by a single atmospheric global climate model developed by the Meteorological Research Institute of Japan. The use of a large ensemble is to enable one to obtain probabilistic future changes in low-frequency of extreme storm surge events. The properties of typhoons which may directly and indirectly have an effect on the KP in terms of past and future climate conditions is extracted from d4PDF. These are employed as the driving force in the projection of future storm surges around the KP. The storm surge heights (SSH) around the KP are projected to increase in the future climate except for around some areas in the south coast. The magnitude of future change of SSH varies spatially. The maximum variation was estimated to be 0.36 m (9.9%) with a 100-year return period in the west area of the southeastern coast of the KP. The locations of the areas vulnerable to storm surge shift to the north area of the western region and to the west area of the southern regions in the Korean Peninsula under the future climate. The characteristic of future change to areas where high SSHs will occur coincides with that of the typhoon tracks.