NH5.4

EDI
Natural hazards and climate change impacts in coastal areas

Coastal areas are vulnerable to erosion, flooding and salinization driven by hydrodynamic hydro-sedimentary and biological processes and human interventions. This vulnerability is likely to be exacerbated in future with, for example, sea-level rise, changing intensity of tropical cyclones, increased subsidence due to groundwater extraction, tectonics, as well as increasing socio-economic development in the coastal zone. This calls for a better understanding of the underlying physical processes and their interaction with the coast. Numerical models therefore play a crucial role in characterizing coastal hazards and assigning risks to them. Drawing firm conclusions about current and future changes in this environment is challenging because uncertainties are often large, such as coastal impacts of likely and unlikely (also called high-end) sea-level changes for the 21st century. Furthermore, studies addressing coastal impacts beyond this century pose new questions regarding the timescale of impacts and adaptation activity. This session invites submissions focusing on assessments and case studies at global, regional and local scales of potential physical impacts of tsunamis, storm surge, sea-level rise, waves, and currents on coasts. We also welcome submissions on near-shore ocean dynamics and also on the socio-economic impact of these hazards along the coast.

Convener: Renske de WinterECSECS | Co-conveners: Joern Behrens, Luke JacksonECSECS, Goneri Le Cozannet, Nicoletta Leonardi
vPICO presentations
| Tue, 27 Apr, 15:30–17:00 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Renske de Winter, Luke Jackson, Nicoletta Leonardi
15:30–15:35
Extreme Sea Level
15:35–15:37
|
EGU21-638
Kwang Ik Son, Woochang Jeong, and Seboong Oh

Many extreme sea level rise events, such as tsunami and surges, caused by abnormal climate change results sea level rise to frequent and serious flooding at coastal basins. The Typhoon Mamie resulted 200M US dollars property damage, 3 thousand family refugees, and 14 victims at Changwon city in 2003.  Furthermore, it is expected that the extreme sea level rise events due to abnormal climate change might be getting frequent and serious as times go by.

In this study, a numerical simulation and analysis of flood inundation in a small-scale coastal area had been carried out. The applied numerical model adopts two-D finite volume method with a well-balanced HLLC(Harten–Lax–Van Leer contact) scheme. The calibration was performed with comparison between simulation results and real inundated records of Changwon city during the typhoon “Maemi” in September 2003.

The model was developed to provide overflow simulation capability of parapet wall along coastal line as boundary conditions. Inundation scenarios were simulated with various parapet wall heights and analyzed the efficiency of disaster prevention measures from inundation due to sea level rise.

Numerical inundation simulation study showed efficiency of parapet walls along coastal line as one of the structural measures. It was found that the inundation volume could be reduced with respect to non-parapet wall by providing parapet wall along coastal line. In addition, the economic analysis between damages due to inundation and construction cost for parapet wall was performed for optimal disaster prevention design.

Acknowledgement: This work was supported by Korea Environment Industry & Technology Institute(KEITI) though Water Management Research Program, funded by Korea Ministry of Environment(MOE)(79608). and Korean NRF (2019R1A2C1003604)

How to cite: Son, K. I., Jeong, W., and Oh, S.: Numerical Simulation for Coastal Area Inundation and its Application , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-638, https://doi.org/10.5194/egusphere-egu21-638, 2021.

15:37–15:39
|
EGU21-7564
|
ECS
Ariadna Martín, Angel Amores, Alejandro Orfila, and Marta Marcos

Every year the Caribbean Sea faces the passage of powerful tropical cyclones that generate coastal extreme sea levels with potential strong and hazardous impacts. In this work we simulate the storm surges and wind-waves induced by a set of over 1000 tropical cyclones over the Caribbean Sea that are representative of the present-day climate and that have been extracted from a global database of synthetic hurricanes spanning a 10,000-year period. The atmospheric forcing fields, built from the synthetic tropical cyclones, are used to feed a fully coupled hydrodynamic-wave model with high resolution (~1 km) along the continental and island coasts. Given the large number of events modelled, the outputs allow detailed statistical analyses of the magnitude and mechanisms of coastal extreme sea levels as well as the identification of most exposed areas to both storm surges and large wind-waves.

How to cite: Martín, A., Amores, A., Orfila, A., and Marcos, M.: Coastal extreme sea levels in the Caribbean Sea induced by tropical cyclones, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7564, https://doi.org/10.5194/egusphere-egu21-7564, 2021.

15:39–15:41
|
EGU21-8839
Jani Särkkä, Jani Räihä, Mika Rantanen, and Kirsti Jylhä

In the Baltic Sea, the short-term sea level variation might be several meters, even if the tides in the Baltic Sea are negligible. The short-term sea level fluctuations are caused by passing wind storms, inducing sea level variation through wind-induced currents, inverse barometric effect and seiches. Due to the shape of the Baltic Sea with several bays, the highest sea levels are found in the ends of bays like the Gulf of Finland and the Bothnian Bay. The sea level extremes caused by the large-scale windstorms depend strongly on the storm tracks. Within the natural climatic variability during the past centuries, there have most likely been higher sea level extremes than the extreme values found in the tide gauge records.

To study this variability of sea levels, induced by varying tracks of the passing windstorms, we construct an ensemble of synthetic low-pressure systems. In this ensemble, the parameters of the low-pressure systems (e.g. point of origin, velocity of the center of the system and depth of the pressure anomaly) are varied. The ensemble of low pressure systems is used as an input to a numerical sea level model based on shallow-water hydrodynamic equations. The sea level model is fast to calculate, enabling a study of a large set of varying storm tracks. As a result we have an ensemble of simulated sea levels. From the simulation results we can determine the low-pressure system that induces the highest sea level on a given location on the coast. We concentrate our studies on the Finnish coast, but the method can be applied to the entire Baltic coast. 

How to cite: Särkkä, J., Räihä, J., Rantanen, M., and Jylhä, K.: Extreme sea levels at the Finnish coast due to large-scale wind storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8839, https://doi.org/10.5194/egusphere-egu21-8839, 2021.

15:41–15:43
|
EGU21-16214
|
ECS
Aleksandra Cupial and Witold Cieslikiewicz

One of the most dangerous aspects of the observable climate change is an increase in frequency of severe weather events. This is true especially for the coastal regions, that are particularly vulnerable to strong winds and high waves, such as Baltic Sea which lies at the end of one branch of North Atlantic storm track, which is said to have changed in recent decades. Statistical analysis of past events can reveal whether these storms have any common characteristics which might allow for more precise prediction of occurrence of sea storms and better mitigation of storm effects.

The Gulf of Gdańsk (Southern Baltic Sea) is a heavily populated sea area with commercial harbours and long peninsula which strongly affects wave propagation and wave energy distribution. The main aim of this work was to confirm whether weather patterns, responsible for extreme storms observed in the last half-century in the Gulf of Gdańsk, have common characteristics, as was indicated by our preliminary research.

Two hindcast datasets are analysed in this work. The first one is the 44-year long reanalysis of meteorological data produced with the atmospheric model REMO (REgional MOdel; Jacob and Podzun 1997). The second dataset is wave data produced with the wave model WAM. For the modelling of waves over the Baltic Sea, a subset of gridded REMO data was extracted. Both datasets are the result of an EU-funded project HIPOCAS (Cieślikiewicz & Paplińska-Swerpel 2008).

To better distinguish similar patterns, long-term stochastic characteristics of some basic meteorological parameters (e.g. atmospheric pressure) and wind wave fields (e.g. significant wave height (Hs)) were estimated. The preliminary analysis confirmed a strong anisotropy of wind directions over the entire Baltic Sea area which seems to be stronger for stronger winds. A number of extreme storms, critical for a few chosen regions were selected based on Hs time series. For those events, a number of parameters were examined: the overall evolution of atmospheric pressure and wind velocity fields, wind direction resulting in the highest values of Hs and differences in spatial distribution of Hs. Careful examination of storm depressions’ tracks as well as location of the pressure centre during the peak of the storm was conducted. The Empirical Orthogonal Functions (EOF) method was applied to the wind velocity vector fields and pressure fields to enrich our understanding of long-term storm characteristics of these meteorological parameters.

This analysis confirmed our preliminary research results and showed two distinct metrological conditions that cause extreme storms in the Gulf of Gdańsk. Cyclones moving along the east side of the Baltic Sea are associated with strong northerly winds, which cause extremely high waves in the Gulf. On the other hand, cyclones travelling east in the zonal direction over the northern Baltic bring strong westerly winds. They significantly raise Hs,although not to the extent observed for the northerly winds.

References

Cieślikiewicz, W. & Paplińska-Swerpel, B. (2008), Coastal Engineering, 55, 894–905.

Jacob, D. & Podzun, R., (1997). Meteorol. Atmos. Phys., 63, 119–129.

How to cite: Cupial, A. and Cieslikiewicz, W.: Analysis of meteorological regimes resulting in severe storms in the Gulf of Gdańsk  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16214, https://doi.org/10.5194/egusphere-egu21-16214, 2021.

15:43–15:45
|
EGU21-11077
|
ECS
Daria Smirnova, Igor Medvedev, Alexander Rabinovich, and Jadranka Šepić

Two hazardous typhoons, Maysak and Haishen, in September 2020 produced extreme sea level oscillations in the Sea of Japan. These typhoons generated three different types of sea level variations: 1) storm surges (with typical periods from several hours to 1.5 days), 2) extreme seiches (with periods from a few minutes to several tens of minutes), and 3) storm-generated infragravity waves (with periods up to 3-5 min). The data from eleven tide gauges on Russian, Korean, and Japanese coasts were used to examine the properties of these oscillations. The relative contribution of the three separate sea level components and their statistical characteristics (duration, wave heights, and periods) were estimated. The periods of the main eigen modes of individual bays and harbours in the Sea of Japan were estimated based on spectral analysis of longterm background records at the corresponding sites. The results of wavelet analysis show the frequency properties and the temporal evolution of individual sea level components. We found that high-frequency sea level oscillations at stations Preobrazheniye and Rudnaya Pristan have a “white noise” spectrum, caused by the dominance of infragravity waves. A high correlation was detected between the variance of high-frequency sea level oscillations at these stations and the significant wind wave height evaluated from ERA5 for this water area.

How to cite: Smirnova, D., Medvedev, I., Rabinovich, A., and Šepić, J.: Extreme sea level oscillations in the Sea of Japan caused by typhoons Maysak and Haishen in September 2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11077, https://doi.org/10.5194/egusphere-egu21-11077, 2021.

15:45–15:47
|
EGU21-4602
|
ECS
Krešimir Ruić, Jadranka Šepić, Maja Karlović, and Iva Međugorac

Extreme sea levels are known to hit the Adriatic Sea and to occasionally cause floods that produce severe material damage. Whereas the contribution of longer-period (T > 2 h) sea-level oscillations to the phenomena has been well researched, the contribution of the shorter period (T < 2 h) oscillations is yet to be determined. With this aim, data of 1-min sampling resolution were collected for 20 tide gauges, 10 located at the Italian (north and west) and 10 at the Croatian (east) Adriatic coast. Analyses were done on time series of 3 to 15 years length, with the latest data coming from 2020, and with longer data series available for the Croatian coast. Sea level data were thoroughly checked, and spurious data were removed. 

For each station, extreme sea levels were defined as events during which sea level surpasses its 99.9 percentile value. The contribution of short-period oscillations to extremes was then estimated from corresponding high-frequency (T < 2 h) series. Additionally, for four Croatian tide gauge stations (Rovinj, Bakar, Split, and Dubrovnik), for period of 1956-2004, extreme sea levels were also determined from the hourly sea level time series, with the contribution of short-period oscillations visually estimated from the original tide gauge charts.  

Spatial and temporal distribution of contribution of short-period sea-level oscillations to the extreme sea level in the Adriatic were estimated. It was shown that short-period sea-level oscillation can significantly contribute to the overall extremes and should be considered when estimating flooding levels. 

How to cite: Ruić, K., Šepić, J., Karlović, M., and Međugorac, I.: Estimating contribution of high-frequency sea-level oscillations to the extreme sea levels in the Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4602, https://doi.org/10.5194/egusphere-egu21-4602, 2021.

Extreme sea level, coastal innundation and risk
15:47–15:49
|
EGU21-14257
|
ECS
Spatial and Temporal Variations in Sea Level Extremes along the Bay of Bengal Coast
(withdrawn)
Mathilde Romanteau, Mélanie Becker, and Mikhail Karpytchev
15:49–15:51
|
EGU21-12284
|
ECS
Elin Andrée, Jian Su, Martin Drews, Morten Andreas Dahl Larsen, Asger Bendix Hansen, and Kristine Skovgaard Madsen

The potential impacts of extreme sea level events are becoming more apparent to the public and policy makers alike. As the magnitude of these events are expected to increase due to climate change, and increased coastal urbanization results in ever increasing stakes in the coastal zones, the need for risk assessments is growing too.

The physical conditions that generate extreme sea levels are highly dependent on site specific conditions, such as bathymetry, tidal regime, wind fetch and the shape of the coastline. For a low-lying country like Denmark, which consists of a peninsula and islands that partition off the semi-enclosed Baltic Sea from the North Sea, a better understanding of how the local sea level responds to wind forcing is urgently called for.

We here present a map for Denmark that shows the most efficient wind directions for generating extreme sea levels, for a total of 70 locations distributed all over the country’s coastlines. The maps are produced by conducting simulations with a high resolution, 3D-ocean model, which is used for operational storm surge modelling at the Danish Meteorological Institute. We force the model with idealized wind fields that maintain a fixed wind speed and wind direction over the entire model domain. Simulations are conducted for one wind speed and one wind direction at a time, generating ensembles of a set of wind directions for a fixed wind speed, as well as a set of wind speeds for a fixed wind direction, respectively.

For each wind direction, we find that the maximum water level at a given location increases linearly with the wind speed, and the slope values show clear spatial patterns, for example distinguishing the Danish southern North Sea coast from the central or northern North Sea Coast. The slope values are highest along the southwestern North Sea coast, where the passage of North Atlantic low pressure systems over the shallow North Sea, as well as the large tidal range, result in a much larger range of variability than in the more sheltered Inner Danish Waters. However, in our simulations the large fetch of the Baltic Sea, in combination with the funneling effect of the Danish Straits, result in almost as high water levels as along the North Sea coast.

Although the wind forcing is completely synthetic with no spatial and temporal structure of a real storm, this idealized approach allows us to systematically investigate the sea level response at the boundaries of what is physically plausible. We evaluate the results from these simulations by comparison to peak water levels from a 58 year long, high resolution ocean hindcast, with promising agreement.

How to cite: Andrée, E., Su, J., Drews, M., Dahl Larsen, M. A., Bendix Hansen, A., and Skovgaard Madsen, K.: What can idealized storm surge simulations tell us about worst case scenarios?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12284, https://doi.org/10.5194/egusphere-egu21-12284, 2021.

15:51–15:53
|
EGU21-5418
|
ECS
Vesna Bertoncelj, Tim Leijnse, Floortje Roelvink, Stuart Pearson, Jeremy Bricker, Marion Tissier, and Ap van Dongeren

Many coral reef islands are low-lying, which in combination with population growth, sea level rise and possibly more frequent extreme weather events is likely to result in increased coastal risk (e.g. Storlazzi et al., 2015). On smaller scales of O(10 km) wave-driven coastal inundation can be accurately predicted with advanced models such as XBeach (Roelvink et al., 2009), at already high computational costs. For larger scales, larger number of islands, for scenario modelling, and for implementation in early warning systems, computationally faster methods are needed. Reduced physics models, which neglect some of the processes (e.g. non-hydrostatic pressure gradient term and viscosity), are a potential solution. However, their accuracy and the best method to force them has not been established.

In this research we propose a new methodology to model wave-driven flooding on coral reef-lined coasts. A look-up-table (LUT), composed of XBeach model runs, is combined with a reduced-physics model, SFINCS (Leijnse et al., 2021), to achieve high accuracy predictions at limited computational expense. The LUT consists of pre-run 1D XBeach simulations for several reef profiles from Scott et al. (2020), forced with different offshore wave and water level conditions. Wave conditions close to the shore as predicted by the LUT are used to force SFINCS which then simulates the wave runup, overtopping and flooding. These are forced in SFINCS using random wave timeseries from an interpolated parameterized wave spectrum following Athif (2020).

The accuracy of the method is investigated for 6 distinctive cross-shore profiles from Scott et al. (2020), for two wave scenarios (gentle swell and stormy conditions). Results of complete XBeach simulations are compared to LUT-SFINCS simulations with different boundary forcing locations. The sensitivity analysis shows that the preferred boundary location to initialize the SFINCS model is at a water depth between 0.5 m and 2.5 m, preferably shoreward of the reef edge. Errors introduced by the generated parameterized spectra lead to runup estimation errors of up to around 40% depending on reef geometry. The developed methodology will be applied to a case study of Majuro Island, the Republic of Marshall Islands, as proof of concept.

 

References

Athif, A. A. (2020). Computationally efficient modelling of wave driven flooding in Atoll Islands: Investigation on the use of a reduced-physics model solver SFINCS. Master’s thesis, IHE, the Netherlands.

Leijnse, T., van Ormondt, M., Nederhoff, K., and van Dongeren, A. (2021). Modeling compound flooding in coastal systems using a computationally efficient reduced-physics solver: Including fluvial, pluvial, tidal, wind-and wave- driven processes. Coastal Engineering, 163:103796.

Roelvink, D., Reniers, A., Van Dongeren, A. P., De Vries, J. V. T., McCall, R., and Lescinski, J. (2009). Modelling storm impacts on beaches, dunes and barrier islands. Coastal engineering, 56(11-12), 1133-1152.

Scott, F., Antolinez, J. A. A., Mccall, R., Storlazzi, C., Reniers, A., and Pearson, S. (2020). Hydro-Morphological Characterization of Coral Reefs for Wave Runup Prediction. Frontiers in Marine Science, 7(May):1–20.

Storlazzi, C. D., Elias, E. P., and Berkowitz, P. (2015). Many atolls may be uninhabitable within decades due to climate change. Scientific reports, 5:14546.

How to cite: Bertoncelj, V., Leijnse, T., Roelvink, F., Pearson, S., Bricker, J., Tissier, M., and van Dongeren, A.: Efficient and accurate modeling of wave-driven flooding on coral reef-lined coasts: Case Study of Majuro Atoll, Republic of the Marshall Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5418, https://doi.org/10.5194/egusphere-egu21-5418, 2021.

15:53–15:55
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EGU21-9476
|
ECS
Hector Lobeto, Melisa Menendez, Iñigo J. Losada, and Ottavio Mazzaretto

The assessment of the projected changes in wave climate due to climate change has been subject of study during the last two decades (Morim et al., 2018), largely due to the severe impacts these changes may have on coastal processes such as flooding and erosion. The wind wave climate is fully described by the sea surface elevation spectrum, which represents the distribution of energy resulting from the contributions of several superimposed waves with different periods and directions. Nevertheless, to this day the standard approach to address the future behavior of wind waves is based on the use of integrated wave parameters (e.g. significant wave height, mean wave period, mean wave direction) as a representation of the full spectrum. In this study, we analyze the changes in wave energy from directional spectra discretized in 24 directions and 32 frequencies in a number of locations distributed across all ocean basins, shedding light on the added value that an assessment based on the full spectrum offers with respect to the standard approach. In addition, the ESTELA method (Pérez et al., 2014) is applied to ease the understanding of the changes obtained in wave energy at the locations of study.

The spectral approach helps to assess the projected change in the energy of each wave system that reach a specific location. Results demonstrate that the use of integrated wave parameters can mask important information about the sign, magnitude and uncertainty of the actual projected changes in mean wave climate due to the offset of the expected variations in the different wave systems that integrate the spectrum. It is especially relevant at locations where an increase in the wave period or wave energy is hidden by the application of the standard approach, as these parameters are proven to play a key role in coastal processes. In addition, we reach relevant conclusions about the future behavior of swell systems. For instance, a robust increase in the energy carried by swells generated below 40°S can be observed in every ocean basin and both hemispheres, even beyond 30°N. Similarly, a decrease in the energy carried by northern swells can be observed close to the equator.

How to cite: Lobeto, H., Menendez, M., Losada, I. J., and Mazzaretto, O.: Projected changes in wind wave directional spectra and their impact on coastal processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9476, https://doi.org/10.5194/egusphere-egu21-9476, 2021.

15:55–15:57
|
EGU21-1174
Agnieszka Indiana Olbert and Jennifer IM Kirkpatrick

In coastal floodplains, high river flows and high coastal water levels can result in extensive flooding. Mechanisms of flooding play a crucial role in flood characteristics with distinctive differences in flood wave propagation pattern and geographical extent of inundation. Climate change is expected to alter these flood mechanisms. This paper presents an assessment of urban inundation due to a combined effect of multiple source flooding. Cork City, a coastal city in the south of Ireland, frequently subject to complex coastal-fluvial flooding is used as a case study to investigate changes in flood mechanisms, dynamics and extents due to climate change. The MSN_Flood was used to compute potential future inundation patterns for a range of climate scenarios under various hydrological conditions. Scenarios were based on estimates of current, medium-range and high-end projections of extreme river flows and sea levels. 

How to cite: Olbert, A. I. and Kirkpatrick, J. I.: Probability, mechanisms and impact of future coastal urban flooding., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1174, https://doi.org/10.5194/egusphere-egu21-1174, 2021.

15:57–15:59
|
EGU21-12752
|
ECS
Shubhankar Sengupta, Jürgen Scheffran, and Dmitry Kovalevsky

We develop a single-agent-based model in Netlogo of a coastal city facing climate change, using the VIABLE framework. The coastal city is threatened by damages from sea level rise and subsequent extreme sea level events. The agent, representing an urban planner, uses capital generated by the city to mitigate these damages by investing into one of two adaptation options available to it- developing coastal defenses or relocating the vulnerable coastal territories of the city inland. As the simulation progresses, gradually rising sea levels and randomly occurring extreme sea level events incur damages, and the agent alters its investments to optimize its value, resulting in dynamic reactive behavior. We track the response of this agent to the changing system through its investment patterns.

How to cite: Sengupta, S., Scheffran, J., and Kovalevsky, D.: A Single-Agent Urban Coastal Adaptation Model: Adaptive decision-making within the VIABLE modeling framework, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12752, https://doi.org/10.5194/egusphere-egu21-12752, 2021.

15:59–16:01
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EGU21-11999
|
ECS
Tim Toomey, Angel Amores, Marta Marcos, Alejandro Orfila, and Romualdo Romero

Medicanes, for Mediterranean hurricanes, are mesoscale cyclones with morphological and physical characteristics similar to tropical cyclones. Although less intense, smaller and rarer than their Atlantic counterparts, Medicanes remain very hazardous events threatening islands and continental coasts within the Mediterranean Sea. The latest strong episode Medicane Ianos (September 2020), resulted in severe damages in Greece and several casualties. This work investigates the oceanic response to these extreme events along the Mediterranean coasts under present-day and future (21 st century) conditions. To this end, a coupled hydrodynamic-wave model is used to simulate both storm surges and wind-waves generation and propagation in the Mediterranean Sea at high resolution (~2 km) along the coastlines. A dataset of thousands of Medicanes synthetically generated from twenty global climate models and two reanalyses is used to derive the atmospheric forcing fields. Regional coastal risks assessment is performed for the present and future climate. We found increased coastal extreme sea levels in line to the reported changes in Medicane activity, with fewer events but of larger intensity projected by late 21 st century.

How to cite: Toomey, T., Amores, A., Marcos, M., Orfila, A., and Romero, R.: Coastal risks induced by Mediterranean hurricanes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11999, https://doi.org/10.5194/egusphere-egu21-11999, 2021.

16:01–16:03
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EGU21-8201
|
ECS
Tihana Dević, Jadranka Šepić, and Darko Koračin

An objective method for tracking pathways of cyclone centres over Europe was developed and applied to the ERA-Interim reanalysis atmospheric data (1979-2014). The method was used to determine trajectories of those Mediterranean cyclones which generated extreme sea levels along the northern and the eastern Adriatic coast during the period from 1979 to 2014. Extreme events were defined as periods during which sea level was above 99.95 percentile value of time series of hourly sea-level data measured at the Venice (northern Adriatic), Split (middle eastern Adriatic) and Dubrovnik (south-eastern Adriatic) tide-gauge stations. The cyclone pathways were tracked backwards from the moment closest to the moment of maximum sea level up to the cyclone origin time, or at most, up to 72 hours prior the occurrence of the sea-level maximum.

Our results point out that extreme sea levels in Venice normally appear during synoptic situations in which a cyclone centre is located to the south-west and north-west of Venice, i.e., when it can be found over the Gulf of Genoa, or the Alps. On the contrary, extreme sea levels in Dubrovnik are usually associates with cyclone centres above the middle Adriatic, whereas floods in Split seem to appear during both above-described types of situations.

Occurrence times and intensity of cyclones and extreme sea-levels was further associated with the NAO index. It has been shown that the deepest cyclones and corresponding extreme floods tend to occur during the negative NAO phase.   

How to cite: Dević, T., Šepić, J., and Koračin, D.: The northern and the eastern Adriatic Sea floods: connecting the extreme sea-levels to cyclone pathways , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8201, https://doi.org/10.5194/egusphere-egu21-8201, 2021.

16:03–16:05
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EGU21-4090
|
ECS
Jadranka Sepic, Mira Pasaric, Iva Medugorac, Ivica Vilibic, Maja Karlovic, and Marko Mlinar

The northern and the eastern coast of the Adriatic Sea are occasionally affected by extreme sea-levels known to cause substantial material damage. These extremes appear due to the superposition of several ocean processes that occur at different periods, have different spatial extents, and are caused by distinct forcing mechanisms.

To better understand the extremes, hourly sea-level time series from six tide-gauge stations located along the northern and the eastern Adriatic coast (Venice, Trieste, Rovinj, Bakar, Split, Dubrovnik) were collected for the period of 1956 to 2015 (1984 to 2015 for Venice) and analysed. The time series have been checked for spurious data, and then decomposed using tidal analysis and filtering procedures. The following time series were thus obtained for each station: (1) trend; (2) seasonal signal; (3) tides; (4-7) sea-level oscillations at periods: (4) longer than 100 days, (5) from 10 to 100 days, (6) from 6 hours to 10 days, and (7) shorter than 6 hours. These bands correspond, respectively, to sea-level fluctuations dominantly forced by (but not restricted to): (1) climate change and land uplift and sinking; (2) seasonal changes; (3) tidal forcing; (4); quasi-stationary atmospheric and ocean circulation and climate variability patterns; (5) planetary atmospheric waves; (6) synoptic atmospheric processes; and (7) mesoscale atmospheric processes.

Positive sea-level extremes surpassing 99.95 and 99.99 percentile values, and negative sea-level extremes lower than 0.05 and 0.01 percentile values were extracted from the original time series for each station. It was shown that positive (negative) extremes are up to 50-100% higher (lower) in the northern than in the south-eastern Adriatic. Then, station-based distributions, return periods, seasonal distributions, event durations, and trends were estimated and assessed. It was shown that the northern Adriatic positive sea-level extremes are dominantly caused by synoptic atmospheric processes superimposed to positive tide (contributing jointly to ~70% of total extreme height), whereas more to the south-east, positive extremes are caused by planetary atmospheric waves, synoptic atmospheric processes, and tides (each contributing with an average of ~25%). As for the negative sea-level extremes, these are due to a combination of planetary atmospheric waves and tides: in the northern Adriatic tide provides the largest contribution (~60%) while in the south-eastern Adriatic the two processes are of similar impact (each contributing with an average of ~30%). The simultaneity of the events along the entire northern and eastern Adriatic coast was studied as well, revealing that positive extremes are strongly regional dependant, i.e. that they usually appear simultaneously only along one part of the coast, whereas negative extremes are more likely to appear along the entire coast at the same time.

Finally, it is suggested that the distribution of sea-level extremes along the south-eastern Adriatic coast can be explained as a superposition of tidal forcing and prevailing atmospheric processes, whereas for the northern Adriatic, strong topographic enhancement of sea-level extremes is also important.

How to cite: Sepic, J., Pasaric, M., Medugorac, I., Vilibic, I., Karlovic, M., and Mlinar, M.: Climatology and process-oriented analysis of the Adriatic sea-level extremes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4090, https://doi.org/10.5194/egusphere-egu21-4090, 2021.

16:05–16:07
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EGU21-8727
Christian Ferrarin, Piero Lionello, Mirko Orlic, Fabio Raicich, and Gianfausto Salvadori

Extreme sea levels at the coast result from the combination of astronomical tides with atmospherically forced fluctuations at multiple time scales. Seiches, river floods, waves, inter-annual and inter-decadal dynamics and relative sea-level rise can also contribute to the total sea level. While tides are usually well described and predicted, the effect of the different atmospheric contributions to the sea level and their trends are still not well understood. Meso-scale atmospheric disturbances, synoptic-scale phenomena and planetary atmospheric waves (PAW) act at different temporal and spatial scales and thus generate sea-level disturbances at different frequencies. In this study, we analyze the 1872-2019 sea-level time series in Venice (northern Adriatic Sea, Italy) to investigate the relative role of the different driving factors in the extreme sea levels distribution. The adopted approach consists in 1) isolating the different contributions to the sea level by applying least-squares fitting and Fourier decomposition; 2) performing a multivariate statistical analysis which enables the dependencies among driving factors and their joint probability of occurrence to be described; 3) analyzing temporal changes in extreme sea levels and extrapolating possible future tendencies. The results highlight the fact that the most extreme sea levels are mainly dominated by the non-tidal residual, while the tide plays a secondary role. The non-tidal residual of the extreme sea levels is attributed mostly to PAW surge and storm surge, with the latter component becoming dominant for the most extreme events. The results of temporal evolution analysis confirm previous studies according to which the relative sea-level rise is the major driver of the increase in the frequency of floods in Venice over the last century. However, also long term variability in the storm activity impacted the frequency and intensity of extreme sea levels and have contributed to an increase of floods in Venice during the fall and winter months of the last three decades.

How to cite: Ferrarin, C., Lionello, P., Orlic, M., Raicich, F., and Salvadori, G.: Multiple drivers of extreme sea levels in the northern Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8727, https://doi.org/10.5194/egusphere-egu21-8727, 2021.

Climate change impacts on coasts
16:07–16:09
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EGU21-1282
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ECS
Maurizio D'Anna, Bruno Castelle, Déborah Idier, Jeremy Rohmer, Gonéri Le Cozannet, Rémi Thieblemont, and Lucy Bricheno

Most sandy coasts worldwide are under chronic erosion, which increasingly put at risk coastal communities. In the context of adaptation to climate change and sea-level rise (SLR), predictions of shoreline evolution patterns are critical for decision-making. Sandy shorelines are highly dynamic environments, which respond to multiple complex processes interacting at different spatial and temporal scales, making shoreline predictions challenging, especially on long time scales (decades and centuries). However, modelling shoreline predictions inherit uncertainties in the primary driver boundary conditions (e.g. sea-level rise and wave forcing) as well as uncertainties related to model assumptions and/or misspecifications of the physics. In this work, we analyze the uncertainties associated with shoreline evolution by 2100 of the high-energy, cross-shore transport dominated, sandy beach of Truc Vert (France).  Using  two equilibrium shoreline models based on different disequilibrium principles, and the Bruun Rule, we explicitly resolved wave-driven shoreline change produced continuous probabilistic predictions of the Truc Vert shoreline evolution to 2100 for two carbon emission scenarios (RCP 8.5 and 4.5), incorporating uncertainties related to SLR, depth of closure, and model free parameters. The shoreline models were forced with continuous wave projection time series, issued by the National Oceanography Center (UK) for the RCP 4.5 and 8.5 scenarios, based on a single global climate model.  We assigned a probability distribution to each uncertain input variable. For both shoreline models, an optimization algorithm was used to identify all the realistic combinations of model free parameters leading to a skillful hindcast against 8 years of in situ shoreline data. A Gaussian distribution was assigned to the yearly probabilistic SLR estimates based on SROCC to 2100, and depth of closure. We further addressed the relative impact of each source of uncertainty on the model results performing a Global Sensitivity Analysis (GSA). The results show that, for both RCP scenarios, shoreline response position during the first half of the century is mainly sensitive to the equilibrium model parameters, with the influence of SLR emerging in the second half of the century. The results also reflect the strong relation between the model parameters uncertainties and the interdecadal variability of wave conditions. Using a single wave time series, such variability and related chronology has a much stronger impact on shoreline change with the Splinter model than the Yates model, highlighting that the choice of the modelling approach is critical to future shoreline change estimates in changing wave climates. We also emphasize the need for more continuous wave projections in order to generate ensemble wave time series and include uncertainty in future wave conditions.

How to cite: D'Anna, M., Castelle, B., Idier, D., Rohmer, J., Le Cozannet, G., Thieblemont, R., and Bricheno, L.: Uncertainties in shoreline projections to 2100 at Truc Vert beach (France): Unravelling the role of sea-level rise and equilibrium model assumptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1282, https://doi.org/10.5194/egusphere-egu21-1282, 2021.

16:09–16:11
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EGU21-2142
Rémi Thiéblemont, Gonéri Le Cozannet, Jérémy Rohmer, Alexandra Toimil, Moisés Alvarez, and Iñigo J. Losada

Global mean sea-level rise and its acceleration are projected to aggravate coastal erosion over the 21st century, which constitutes a major challenge for coastal adaptation. Projections of shoreline retreat are highly uncertain, however, namely due to deeply uncertain mean sea-level projections and the absence of consensus on a coastal impact model. An improved understanding and a better quantification of these sources of deep uncertainty are hence required to improve coastal risk management and inform adaptation decisions. In this work we present and apply a new extra-probabilistic framework to develop shoreline change projections of sandy coasts that allows considering intrinsic (or aleatory) and knowledge-based (or epistemic) uncertainties exhaustively and transparently. This framework builds upon an empirical shoreline change model to which we ascribe possibility functions to represent deeply uncertain variables. The model is applied to two local sites in Aquitaine (France) and Castellón (Spain). First, we validate the framework against historical shoreline observations and then develop shoreline change projections that account for possible (although unlikely) low-end and high-end mean sea-level scenarios. Our high-end projections show for instance that shoreline retreats of up to 200m in Aquitaine and 130m in Castellón are plausible by 2100, while low-end projections revealed that 58m and 37m modest shoreline retreats, respectively, are also plausible. Such extended intervals of possible future shoreline changes reflect an ambiguity in the probabilistic description of shoreline change projections, which could be substantially reduced by better constraining SLR projections and improving coastal impact models. We found for instance that if mean sea-level by 2100 does not exceed 1m, the ambiguity can be reduced by more than 50 %. This could be achieved through an ambitious climate mitigation policy and improved knowledge on ice-sheets. 

How to cite: Thiéblemont, R., Le Cozannet, G., Rohmer, J., Toimil, A., Alvarez, M., and Losada, I. J.: Deep uncertainties in shoreline change projections: an extra-probabilistic approach applied to sandy beaches, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2142, https://doi.org/10.5194/egusphere-egu21-2142, 2021.

16:11–16:13
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EGU21-10849
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ECS
Moisés Álvarez-Cuesta, Alexandra Toimil, and Iñigo J. Losada

A new numerical model for addressing long-term coastline evolution on a local to regional scale on highly anthropized coasts is presented. The model, named IH-LANS (Long-term ANthropized coastlines Simulation tool), is validated over the period 1990-2020 and applied to obtain an ensemble of end-of-century shoreline evolutions. IH-LANS combines a hybrid (statistical-numerical) deep-water propagation module and a shoreline evolution model. Longshore and cross-shore processes are integrated together with the effects of man-made interventions. For the ease of calibration, an automated technique is implemented to assimilate observations. The model is applied to a highly anthropized 40 km stretch located along the Spanish Mediterranean coast. High space-time resolution climate data and satellite-derived shorelines are used to drive IH-LANS. Observed shoreline evolution (<10 meters of root mean square error, RMSE) is successfully represented while accounting for the effects of nourishments and the construction and removal of groynes, seawalls and breakwaters over time. Then, in order to drive the ensemble of end-of-century shoreline evolutions, wave and water level projections downscaled from different climate models for various emissions scenarios are employed to force the calibrated model. From the forecasted shoreline time-series, information from multiple time-scales is unraveled yielding valuable information for coastal planners. The efficiency and accuracy of the model make IH-LANS a powerful tool for management and climate change adaptation in coastal zones.

How to cite: Álvarez-Cuesta, M., Toimil, A., and Losada, I. J.: Forecasting long-term shoreline evolution in highly antrhopized coastal areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10849, https://doi.org/10.5194/egusphere-egu21-10849, 2021.

16:13–16:15
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EGU21-1294
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ECS
Natascia Pannozzo, Nicoletta Leonardi, Iacopo Carnacina, and Rachel Smedley

Salt marshes are widely recognised as ecosystems with high economic and environmental value. However, it is still unclear how salt marshes will respond to the combined impact of future sea-level rise and possible increases in storm intensity (Schuerch et al. 2013). This study investigates marsh resilience under the combined impact of various storm surge and sea-level scenarios by using a sediment budget approach. The current paradigm is that a positive sediment budget supports the accretion of salt marshes and, therefore, its survival, while a negative sediment budget causes marsh degradation (Ganju et al. 2015). The Ribble Estuary, North-West England, was used as test case, and the hydrodynamic model Delft3D was used to simulate the response of the salt marsh system to the above scenarios. We conclude that the resilience of salt marshes and estuarine systems is enhanced under the effect of storm surges, as they promote flood dominance and trigger a net import of sediment.  Conversely, sea-level rise threatens marsh stability, by promoting ebb dominance and triggering a net export of sediment. Ultimately, when storm surge and sea-level scenarios are combined, results show that storms with the highest intensities have the potential to counteract the negative impact of sea-level rise by masking its effects on the sediment budget.

Acknowledgements

We acknowledge the support of the School of Environmental Sciences, University of Liverpool.

References

Ganju, N.K., Kirwan, M.L., Dickhudt, P.J., Guntenspergen, G.R., Cahoon, D.R. and Kroeger, K.D. 2015. “Sediment transport-based metrics of wetland stability”. Geophysical Research Letters, 42(19), 7992-8000.

Schuerch, M., Vafeidis, A., Slawig, T. and Temmerman, S. 2013. “Modeling the influence of changing storm patterns on the ability of a salt marsh to keep pace with sea level rise”. Journal of Geophysical Research-Earth Surface, 118(1), 84-96.

How to cite: Pannozzo, N., Leonardi, N., Carnacina, I., and Smedley, R.: Salt marsh resilience to sea-level rise and increased storm intensity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1294, https://doi.org/10.5194/egusphere-egu21-1294, 2021.

16:15–16:17
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EGU21-548
Md Salauddin, Zhong Peng, and Jonathan Pearson

Recent studies by the Intergovernmental Panel on Climate Change indicate that sea level will continue to rise in many low-lying areas due to the global climate change that would potentially cause the occurrence of more frequent extreme meteorological events and storm surges in future years. Concurrently, the damage to the critical infrastructures and surrounding properties from extreme climatic events such as wave overtopping, and scouring are expected to be exacerbated in future. Reliable prediction tools for wave overtopping and toe scouring characteristics at sea defences are therefore significantly important for climate resilience of coastal infrastructures. To date, however, most parametric studies regarding these aspects have tended to focus either only overtopping or scouring at sea defences, with investigations on the effects of wave impacts on both overtopping and scouring characteristics simultaneously, particularly for permeable shingle beaches in front of the structure being less well-studied. This limitation and research gap have driven the need to carry out a comprehensive suite of experimental investigations on the influence of wave impacts on toe scour and overtopping concurrently at sea defences with shingle foreshores.

Here we investigate the effects of wave impacts on overtopping and scouring characteristics on a seawall as well as on a smooth sloping (1V:2H) structure in a suite of laboratory tests performed in a 2D wave flume (22 m in length, 0.6 m in width, and 1.0 m in depth) at the University of Warwick, UK. Permeable shingle sloping (1V:20H) foreshores were constructed in front of the tested structures using the crushed filtered anthracite with a quoted specific gravity of 1.40 T/m3. At a 1 in 50 scale, tested anthracite d50 values of 2.10 mm and 4.20 mm represented prototype shingles with d50 values of 13 mm and 24 mm, respectively. Overtopping volumes and scour depths were measured for each test comprised of around 1000 JONSWAP (gamma = 3.3) pseudo-random waves. Two nominal deep-water wave steepness values of 0.02 and 0.05 were tested to simulate both long and short wave conditions.

Results of this laboratory investigation showed that toe scouring and overtopping is principally caused by plunging or near plunging wave breakers for the tested both vertical and sloping structures on permeable slopes, which are in consistent with results that were previously reported for coastal structures on sandy beaches. The analysis of measured scour depths for vertical walls showed that overall greater scour depths were observed for the experiments under impulsive (violent wave impacting) conditions, when compared to those reported for the non-impulsive conditions. For both vertical and smooth sloping structures, it was found that there is no apparent relationship between toe scour depths and shape parameter of Weibull distribution function of wave-by-wave overtopping volumes in a test sequence. Measurements of this experimental study could be employed as a reference to further investigate the impacts of toe scouring on overtopping characteristics at coastal infrastructures.

Keywords: Coastal Resilience, Overtopping,  Scouring, Wave impacts.

References

EurOtop, 2018. www.overtopping-manual.com 

Salauddin and Pearson, 2019a. https://doi.org/10.1016/j.oceaneng.2018.11.011

Salauddin and Pearson, 2019b. https://doi.org/10.3390/jmse7070198

Salauddin and Pearson, 2020. https://doi.org/10.1016/j.oceaneng.2019.106866

How to cite: Salauddin, M., Peng, Z., and Pearson, J.: The effects of wave impacts on toe scouring and overtopping concurrently for permeable shingle foreshores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-548, https://doi.org/10.5194/egusphere-egu21-548, 2021.

16:17–16:19
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EGU21-14453
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ECS
Hannes Nevermann, Amir AghaKouchak, and Nima Shokri

Sea level rise (SLR) is a well-documented aspect of anthropogenic climate change which is primary due to the thermal expansion of seawater and melting of ice caps and glaciers (1). Climate change is expected to exacerbate sea-level rise within the next century, much larger than the observations since the beginning of the recordings. Next to various natural hazards and extreme environmental events such as flooding, the sea level rise poses serious long-standing and possibly irreversible consequences on human timescales in coastal regions. For example, soil salinity is expected to increase near shorelines due to sea level rise. Soil salinization, referring to excess accumulation of salt in soil, is a global problem (2) adversely affecting many environmental and hydrologic processes such as terrestrial ecosystem functioning, water cycle and biodiversity. SLRs shift the saltwater-freshwater boundary in coastal regions which will increase the risk of soil salinization further inland. Considering the growing population living in coastal regions, SLR-driven soil salinization has a severe socio-economic impact posing significant threat to farmlands, wetlands, coastal marshes, forests and other ecosystems. Motivated by the importance of the interaction between SLR, climate change and soil salinization, this study aims to determine how the saltwater-freshwater interface moves under different Representative Concentration Pathways (RCP) scenarios in coastal regions. Groundwater data of coastal wells, Digital Elevation Model’s and satellite images will be used to highlight areas under high risk of soil salinization. The results will enable us to quantify the possible extent of the soil salinization as a result of SLR under different climate scenarios with the associated socio-economic consequences. Such information could support decision making and sustainable resource management under different RCPs.

1. Moftakhari H.M., Salvadori G., AghaKouchak A., Sanders, B.F., Matthew, R.A. (2017). Compounding Effects of Sea Level Rise and Fluvial Flooding. Proc. Nat. Acad. Sci., 114 (37), 9785-9790.

2. Hassani, A., Azapagic, A., Shokri, N. (2020). Predicting Long-term Dynamics of Soil Salinity and Sodicity on a Global Scale. Proc. Nat. Acad. Sci., 117 (52) 33017-33027.

How to cite: Nevermann, H., AghaKouchak, A., and Shokri, N.: Sea-level rise driven soil salinization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14453, https://doi.org/10.5194/egusphere-egu21-14453, 2021.

16:19–17:00