scholarly journals The long-term variability of extreme sea levels in the German Bight

2019 ◽  
Author(s):  
Andreas Lang ◽  
Uwe Mikolajewicz
Keyword(s):  
Sea Level ◽  
North Sea ◽  
German Bight ◽  
Large Scale ◽  
Climate System ◽  
Tide Gauge Record ◽  
Sea Levels ◽  
The North ◽  
The North Sea

Abstract. We investigate the long-term variability of extreme high sea levels (ESL) in the southern German Bight and associated large-scale forcing mechanisms in the climate system using simulations covering the last 1000 years. To this end, global MPI-ESM simulations from the PMIP3 past1000 project are dynamically scaled-down with a regionally coupled climate system model focusing on the North Sea. We find that the statistics of simulated ESL compare well with observations from the tide gauge record at Cuxhaven but show large variations on interannual to centennial timescales. ESL arise independent of preferred systematic oscillations and are to a large extent decoupled from variations of the background sea level (BSL). Large scale circulation regimes associated with periods of high ESL are regionally consistent and similar to those associated with elevated BSL, but the location of the respective centers of action of the governing sea level pressure (SLP) dipole differs. While BSL variations correlate well with the wintertime North Atlantic Oscillation (NAO), ESL variations are rather associated with a dipole between northeastern Scandinavia and the Gulf of Biscay, leading to a stronger local north-westerly wind component in the North Sea. Potential links with solar or volcanic forcing are masked due to the high ESL variability. The high internal variability stresses the irreducible uncertainties related to traditional extreme value estimates based on shorter subsets which fail to account for long-term variations. Existing estimates of future changes in ESL may be dominated by natural variability rather than climate change signals, thus requiring larger ensemble simulations to assess future flood risks.

scholarly journals The long-term variability of extreme sea levels in the German Bight

Ocean Science ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 651-668 ◽  
Author(s):  
Andreas Lang ◽  
Uwe Mikolajewicz
Keyword(s):  
Sea Level ◽  
German Bight ◽  
Large Scale ◽  
Internal Variability ◽  
Climate System ◽  
System Model ◽  
Tide Gauge Record ◽  
Sea Levels ◽  
The North

Abstract. Extreme high sea levels (ESLs) caused by storm floods constitute a major hazard for coastal regions. We here quantify their long-term variability in the southern German Bight using simulations covering the last 1000 years. To this end, global earth system model simulations from the PMIP3 past1000 project are dynamically scaled down with a regionally coupled climate system model focusing on the North Sea. This approach provides an unprecedented long high-resolution data record that can extend the knowledge of ESL variability based on observations, and allows for the identification of associated large-scale forcing mechanisms in the climate system. While the statistics of simulated ESLs compare well with observations from the tide gauge record at Cuxhaven, we find that simulated ESLs show large variations on interannual to centennial timescales without preferred oscillation periods. As a result of this high internal variability, ESL variations appear to a large extent decoupled from those of the background sea level, and mask any potential signals from solar or volcanic forcing. Comparison with large-scale climate variability shows that periods of high ESL are associated with a sea level pressure dipole between northeastern Scandinavia and the Gulf of Biscay. While this large-scale circulation regime applies to enhanced ESL in the wider region, it differs from the North Atlantic Oscillation pattern that has often been linked to periods of elevated background sea level. The high internal variability with large multidecadal to centennial variations emphasizes the inherent uncertainties related to traditional extreme value estimates based on short data subsets, which fail to account for such long-term variations. We conclude that ESL variations as well as existing estimates of future changes are likely to be dominated by internal variability rather than climate change signals. Thus, larger ensemble simulations will be required to assess future flood risks.

What can idealized storm surge simulations tell us about worst case scenarios?

2021 ◽  
Author(s):  
Elin Andrée ◽  
Jian Su ◽  
Martin Drews ◽  
Morten Andreas Dahl Larsen ◽  
Asger Bendix Hansen ◽  
...  
Keyword(s):  
Wind Speed ◽  
Sea Level ◽  
North Sea ◽  
Wind Direction ◽  
Water Levels ◽  
Sea Levels ◽  
The North ◽  
The North Sea ◽  
Sea Coast ◽  
North Sea Coast

<p>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.</p><p>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.</p><p>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.</p><p>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.</p><p>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.</p>

scholarly journals The significance of coastal bathymetry representation for modelling the tidal response to mean sea level rise in the German Bight

Ocean Science ◽  
2020 ◽  
Vol 16 (1) ◽  
pp. 31-44 ◽  
Author(s):  
Caroline Rasquin ◽  
Rita Seiffert ◽  
Benno Wachler ◽  
Norbert Winkel
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
North Sea ◽  
German Bight ◽  
Coastal Areas ◽  
Tidal Dynamics ◽  
Mean Sea Level ◽  
The North ◽  
The North Sea ◽  
The Impact

Abstract. Due to climate change an accelerated mean sea level rise is expected. One key question for the development of adaptation measures is how mean sea level rise affects tidal dynamics in shelf seas such as the North Sea. Owing to its low-lying coastal areas, the German Bight (located in the southeast of the North Sea) will be especially affected. Numerical hydrodynamic models help to understand how mean sea level rise changes tidal dynamics. Models cannot adequately represent all processes in overall detail. One limiting factor is the resolution of the model grid. In this study we investigate which role the representation of the coastal bathymetry plays when analysing the response of tidal dynamics to mean sea level rise. Using a shelf model including the whole North Sea and a high-resolution hydrodynamic model of the German Bight we investigate the changes in M2 amplitude due to a mean sea level rise of 0.8 and 10 m. The shelf model and the German Bight Model react in different ways. In the simulations with a mean sea level rise of 0.8 m the M2 amplitude in the shelf model generally increases in the region of the German Bight. In contrast, the M2 amplitude in the German Bight Model increases only in some coastal areas and decreases in the northern part of the German Bight. In the simulations with a mean sea level rise of 10 m the M2 amplitude increases in both models with largely similar spatial patterns. In two case studies we adjust the German Bight Model in order to more closely resemble the shelf model. We find that a different resolution of the bathymetry results in different energy dissipation changes in response to mean sea level rise. Our results show that the resolution of the bathymetry especially in flat intertidal areas plays a crucial role for modelling the impact of mean sea level rise.

scholarly journals Long-term Behavior of CO2 Stored on a Large Scale in the Utsira Formation, the North Sea, Norwegian Continental Shelf

2013 ◽  
Vol 37 ◽  
pp. 5240-5247
Author(s):  
V.T.H. Pham ◽  
E.K. Halland ◽  
I.M. Tappel ◽  
I.T. Gjeldvik ◽  
F. Riis ◽  
...  
Keyword(s):  
Continental Shelf ◽  
North Sea ◽  
Large Scale ◽  
The North ◽  
The North Sea ◽  
Long Term Behavior ◽  
Norwegian Continental Shelf

scholarly journals Assessment of tidal range changes in the North Sea from 1958 to 2014

2021 ◽  
Author(s):  
Leon Jänicke ◽  
Andra Ebener ◽  
Sönke Dangendorf ◽  
Arne Arns ◽  
Michael Schindelegger ◽  
...  
Keyword(s):  
North Sea ◽  
German Bight ◽  
Large Scale ◽  
Tide Gauge ◽  
Tidal Range ◽  
Tide Gauges ◽  
Tide Gauge Records ◽  
Large Spatial Scale ◽  
The North ◽  
The North Sea

<p>Tide gauges throughout the North Sea basin show significant changes in the local tidal regime since the mid-20th century, especially in the German Bight area. These changes were analyzed within the DFG-funded project TIDEDYN (Analyzing long term changes in the tidal dynamics of the North Sea, project number 290112166) and the final results were recently published in Jänicke et al. (2020, https://doi.org/10.1029/2020JC016456).</p><p>In this paper, we document an exceptional large-spatial scale case of changes in tidal range in the North Sea, featuring pronounced trends between -2.3 mm/yr at tide gauges in the UK and up to 7 mm/yr in the German Bight between 1958 and 2014. These changes are spatially heterogeneous and driven by a superposition of local and large-scale processes within the basin. We use principal component analysis to separate large-scale signals appearing coherently over multiple stations from rather localized changes. We identify two leading principal components (PCs) that explain about 69% of tidal range changes in the entire North Sea including the divergent trend pattern along UK and German coastlines that reflects movement of the region’s semidiurnal amphidromic areas. By applying numerical and statistical analyses, we can assign a baroclinic (PC1) and a barotropic large-scale signal (PC2), explaining a large part of the overall variance. A comparison between PC2 and tide gauge records along the European Atlantic coast, Iceland and Canada shows significant correlations on time scales of less than 2 years, which points to an external and basin-wide forcing mechanism. By contrast, PC1 dominates in the southern North Sea and originates, at least in part, from stratification changes in nearby shallow waters. In particular, from an analysis of observed density profiles, we suggest that an increased strength and duration of the summer pycnocline has stabilized the water column against turbulent dissipation and allowed for higher tidal elevations at the coast.</p><p>We would like to present these research results and the content of the paper (cf. Jänicke et al., 2020) at vEGU21, hoping to encourage subsequent questions and further discussions.</p>

Inter-annual and long-term mean sea level changes along the North Sea coastline

2013 ◽  
Vol 165 ◽  
pp. 1987-1992 ◽  
Author(s):  
Thomas Wahl ◽  
Ivan D. Haigh ◽  
Sönke Dangendorf ◽  
Jürgen Jensen
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
The North ◽  
The North Sea

scholarly journals EXTREME LEVELS ARISING FROM METEOROLOGICAL SURGES

1974 ◽  
Vol 1 (14) ◽  
pp. 1 ◽  
Author(s):  
P. Ackers ◽  
T.D. Ruxton
Keyword(s):  
Sea Level ◽  
North Sea ◽  
High Tide ◽  
Water Levels ◽  
Return Periods ◽  
The North ◽  
Extreme Water Levels ◽  
Independent Events ◽  
The North Sea

The design of coastal works depends on estimating the probabilities of extreme water levels, as well as of waves Previous studies of surge-affected levels have extrapolated observed annual maxima or the n highest levels in n years to predict rarer events In addition to using these well-established methods, m this study of tide levels on the Essex coast of Britain a long term record of extreme levels was synthesised by adding surge residuals at the time of predicted HW to predicted HW levels, treating them as statistically independent events Many more large surge residuals have been measured than extreme water levels as many surges are associated with small tides Events with return periods up to 1000 years may be estimated without extrapolating beyond the range of observed surge residuals and predicted tides This method is assessed in relation to previous methods and information relevant to the design of coastal works in the south western part of the North Sea was obtained In addition to forecasting the probabilities of high tide levels, the study included wave forecasts and the encounter probabilities of combinations of sea level and wave height for various aspects of coastal developments.

scholarly journals The significance of coastal bathymetry representation for modelling the tidal response to mean sea level rise in the German Bight

2019 ◽  
Author(s):  
Caroline Rasquin ◽  
Rita Seiffert ◽  
Benno Wachler ◽  
Norbert Winkel
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
North Sea ◽  
German Bight ◽  
Coastal Areas ◽  
Tidal Dynamics ◽  
Mean Sea Level ◽  
The North ◽  
The North Sea ◽  
The Impact

Abstract. Due to climate change an accelerated mean sea level rise is expected. One key question for the development of adaptation measures is how mean sea level rise affects tidal dynamics in shelf seas such as the North Sea. Owing to its flat coastal areas, especially the German Bight (located in the south-east of the North Sea) will be affected. Numerical hydrodynamic models help to understand how mean sea level rise changes tidal dynamics. By definition models cannot represent all processes in overall detail. One limiting factor is the resolution of the model grid. In this study we investigate which role the representation of the coastal bathymetry plays when analysing the response of tidal dynamics to mean sea level rise. Using a shelf model including the whole North Sea and a high-resolution hydrodynamic model of the German Bight we investigate the changes in M2 amplitude due to a mean sea level rise of 0.8 m and 10 m. To the mean sea level rise of 0.8 m the shelf model and the German Bight Model react in different ways. In the shelf model the M2 amplitude generally increases in the region of the German Bight. In contrast, the M2 amplitude in the German Bight Model increases only in some coastal areas and decreases in the northern part of the German Bight. In two case studies we adjust the German Bight Model in order to more closely resemble the shelf model. We find that a different resolution of the bathymetry results in different energy dissipation changes in response to mean sea level rise. Our results show that the resolution of the bathymetry especially in flat intertidal areas plays a crucial role for modelling the impact of mean sea level rise in the order of 1 m. For higher mean sea level rise scenarios (10 m) the resolution of the bathymetry is less important.

scholarly journals On analysing sea level rise in the German Bight since 1844

2010 ◽  
Vol 10 (2) ◽  
pp. 171-179 ◽  
Author(s):  
T. Wahl ◽  
J. Jensen ◽  
T. Frank
Keyword(s):  
Time Series ◽  
Sea Level Rise ◽  
Sea Level ◽  
North Sea ◽  
German Bight ◽  
Tide Gauge ◽  
South Eastern ◽  
The North ◽  
Positive Acceleration ◽  
The North Sea

Abstract. In this paper, a methodology to analyse observed sea level rise (SLR) in the German Bight, the shallow south-eastern part of the North Sea, is presented. The paper focuses on the description of the methods used to generate and analyse mean sea level (MSL) time series. Parametric fitting approaches as well as non-parametric data adaptive filters, such as Singular System Analysis (SSA) are applied. For padding non-stationary sea level time series, an advanced approach named Monte-Carlo autoregressive padding (MCAP) is introduced. This approach allows the specification of uncertainties of the behaviour of smoothed time series near the boundaries. As an example, the paper includes the results from analysing the sea level records of the Cuxhaven tide gauge and the Heligoland tide gauge, both located in the south-eastern North Sea. For comparison, the results from analysing a worldwide sea level reconstruction are also presented. The results for the North Sea point to a weak negative acceleration of SLR since 1844 with a strong positive acceleration at the end of the 19th century, to a period of almost no SLR around the 1970s with subsequent positive acceleration and to high recent rates.

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