The impact of future sea-level rise on the global tides

Tides are a key component in coastal extreme water levels. Possible changes in the tides caused by mean sea-level rise (SLR) are therefore of importance in the analysis of coastal flooding, as well as many other applications. We investigate the effect of future SLR on the tides globally using a fully global forward tidal model: OTISmpi. Statistical comparisons of the modelled and observed tidal solutions demonstrate the skill of the refined model setup with no reliance on data assimilation. We simulate the response of the four primary tidal constituents to various SLR scenarios. Particular attention is paid to future changes at the largest 136 coastal cities, where changes in water level would have the greatest impact. Spatially uniform SLR scenarios ranging from 0.5 to 10 m with fixed coastlines show that the tidal amplitudes in shelf seas globally respond strongly to SLR with spatially coherent areas of increase and decrease. Changes in the M2 and S2 constituents occur globally in most shelf seas, whereas changes in K1 and O1 are confined to Asian shelves. With higher SLR tidal changes are often not proportional to the SLR imposed and larger portions of mean high water (MHW) changes are above proportional. Changes in MHW exceed ±10% of the SLR at ~10% of coastal cities. SLR scenarios allowing for coastal recession tend increasingly to result in a reduction in tidal range. The fact that the fixed and recession shoreline scenarios result mainly in changes of opposing sign is explained by the effect of the perturbations on the natural period of oscillation of the basin. Our results suggest that coastal management strategies could influence the sign of the tidal amplitude change. The effect of a spatially varying SLR, in this case fingerprints of the initial elastic response to ice mass loss, modestly alters the tidal response with the largest differences at high latitudes

Evaluation and comparison of the operational Bristol Channel Model storm surge suite

Due to its exceptional tidal range, complex geometry, and exposure to flood risk the operational storm surge modelling system for the Bristol Channel (running four times each day as part of the UK Coastal Monitoring and Forecasting service) comprises a number of nested hydrodynamic models. Forecasts for the region are available from the shelf-wide storm surge model, CS3X, as well as from two finer-scale models of the Bristol Channel itself (the Bristol Channel model, BCM, and the Severn River Model, SRM). This report provides for the first time a systematic comparison of the accuracy of the three models when compared against tide gauge observations, for five significant storm surge events in the model archive. We find that overall the most accurate model predictions for these events (and it should be borne in mind that it is not a large sample size) are from the high-resolution models (BCM and SRM). There is however a large spread of variability and there are instances where the coarser resolution CS3X model has the most skill at particular locations. It is recommended that forecasting methods for the Bristol Channel area should adopt some combination of model outputs in a weighted multi-model ensemble. The good performance of the finer resolution models suggests that they are an important part of the current operational storm surge suite. Any future developments of the UKCMF forecasting system (e.g. based on coupled wave-surge models) should ensure that model performance in the Bristol Channel maintains or improves upon the accuracy described in this report

Application of rule based methods to predicting storm surge

The accurate forecast of storm surge, the long wavelength sea level response to meteorological forcing, is imperative for flood warning purposes. There remain regions of the world where operational forecast systems have not been developed and in these locations it is worthwhile considering numerically simpler, data-driven techniques to provide operational services. In this paper, we investigate the applicability of a class of data driven methods referred to as rule based models to the problem of forecasting storm surge. The accuracy of the rule based model is found to be comparable to several alternative data-driven techniques, all of which result in marginally worse but acceptable forecasts compared with the UK's operational hydrodynamic forecast model, given the reduction in computational effort. Promisingly, the rule based model is considered to be skillful in forecasting total water levels above a given flood warning threshold, with a Brier Skill Score of 0.58 against a climatological forecast (the operational storm surge system has a Brier Skill Score of up to 0.75 for the same data set). The structure of the model can be interrogated as IF–THEN rules and we find that the model structure in this case is consistent with our understanding of the physical system. Furthermore, the rule based approach provides probabilistic forecasts of storm surge, which is much more informative to flood warning managers than alternative approaches. Therefore, the rule based model provides reasonably skillful forecasts in comparison with the operational forecast model, for a significant reduction in development and run time, and is therefore considered to be an appropriate data driven approach that could be employed to forecast storm surge in regions of the world where a fully fledged hydrodynamic forecast system does not exist, provided a good observational and meteorological forecast can be made

The impact of future sea-level rise on the European Shelf tides

This paper investigates the effect of future sea-level rise (SLR) on the tides of the northwest European Continental Shelf. The European shelf tide is dominated by semidiurnal constituents. This study therefore focuses primarily on the changes in the M2 tidal constituent and the spring and neap tidal conditions. The validated operational Dutch Continental Shelf Model is run for the present day sea-level as well as 2 and 10 m SLR scenarios. The M2 tidal amplitude responds to SLR in a spatially non-uniform manner, with substantial amplitude increases and decreases in both scenarios. The M2 tidal response is non-linear between 2 and 10 m with respect to SLR, particularly in the North Sea. Under the 2 m SLR scenario the M2 constituent is particularly responsive in the resonant areas of the Bristol Channel and Gulf of St. Malo (with large amplitude decreases) and in the southeastern German Bight and Dutch Wadden Sea (with large amplitude increases). Changes in the spring tide are generally greater still than those in the M2 or neap tides. With 2 m SLR the spring tidal range increases up to 35 cm at Cuxhaven and decreases up to −49 cm at St. Malo. Additionally the changes in the shallow water tides are larger than expected. With SLR the depth, wave speed and wave length (tidal resonance characteristics) are increased causing changes in near resonant areas. In expansive shallow areas SLR causes reduced energy dissipation by bottom friction. Combined these mechanisms result in the migration of the amphidromes and complex patterns of non-linear change in the tide with SLR. Despite the significant uncertainty associated with the rate of SLR over the next century, substantial alterations to tidal characteristics can be expected under a high end SLR scenario. Contrary to existing studies this paper highlights the importance of considering the modification of the tides by future SLR. These substantial future changes in the tides could have wide reaching implications; including for example, correctly calculating design level requirements for flood defences, the availability of tidal renewable energy and dredging requirements

Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea

During July–September 1998 a comprehensive survey was undertaken of the Celtic Sea and St. George's Channel of the Irish Sea in order to resolve the three-dimensional density field and circulation. Towed undulating CTD data revealed that isolated below the seasonal thermocline was a dense (cold and saline) pool flanked by strong near-bed density gradients. The trajectories of 23 satellite-tracked Argos drifters demonstrated the existence of a cyclonic (anti-clockwise) circulation pattern. This was in accord with persistent and narrow (ca. 20 km) cores of cyclonic flow (dense water to the left) as revealed by geostrophic current estimates and moored acoustic Doppler current profiler data, with velocities >0.1 m s?1 and exceeding 0.3 m s?1 in St. George's Channel.The results are consistent with a seasonal baroclinic circulation that advects saline Atlantic water through the south and west of the region to St. George's Channel. Westward flow across St. George's Channel is directed south into the Celtic Sea and west along the Irish coast. The southward flow, an artefact of the baroclinic circulation, often appears in infrared satellite imagery as a meander in the Celtic Sea front. At the southward extension a secondary clockwise circulation is formed (diameter40 km) before water joins westward flow. Fresher water of coastal origin, present in the northern Celtic Sea in late spring, is advected westward by the summer circulation. The advent of summer thermal stratification and associated flow fields reduces exchange between the Celtic and Irish Seas.The understanding provided by such datasets such as those described here provides the necessary basis for environmental management and knowledge of the pathways for contaminants, the dynamics of nutrients and an understanding of the movement of larvae and juvenile fish. It also provides a template against which to test the prognostic capabilities of present and emerging baroclinic numerical models

Neuroprotection by a selective oestrogen receptor {beta} agonist in a mouse model of global ischaemia

The present study employs selective estrogen receptor (ER) agonists to determine whether 17-estradiol-induced neuroprotection in global ischemia is receptor mediated and, if so, which subtype of receptor (ERα or ER) is predominantly responsible. Halothane-anesthetized female C57Bl/6J mice were ovariectomized, and osmotic minipumps containing ER agonist diarylpropiolnitrile (DPN) (8 mg·kg–1·day–1, n = 12) or vehicle (50% DMSO in 0.9% saline) (n = 9) or ERα agonist propyl pyrazole triol (PPT) (2 mg·kg–1·day–1, n = 13) or vehicle (50% DMSO in 0.9% saline) (n = 10) were implanted subcutaneously. One week later transient global ischemia was induced by bilateral carotid artery occlusion under halothane anesthesia, and the mice were perfusion fixed 72 h later. ER agonist DPN significantly reduced ischemic damage by 70% in the caudate nucleus and 55% in the CA1 region compared with vehicle controls (P < 0.05, Mann-Whitney U-statistic). In contrast, pretreatment with the ERα agonist PPT had no effect on the extent of neuronal damage compared with controls. The data indicate a significant estrogen receptor-mediated neuroprotection in a global cerebral ischemia model involving ER

Interpolation of Tidal Levels in the Coastal Zone for the Creation of a Hydrographic Datum

As part of the U. K. Hydrographic Office (UKHO)-sponsored Vertical Offshore Reference Frames (VORF) project, a high-resolution model of lowest astronomical tide (LAT) with respect to mean sea level has been developed for U.K.-Irish waters. In offshore areas the model relies on data from satellite altimetry, while in coastal areas data from a 3.5-km-resolution hydrodynamic tide-surge model and tide gauges have been included. To provide for a smooth surface and predict tidal levels in unobserved areas, the data have been merged and interpolated using the thin plate spline method, which has been appropriately tuned by an empirical prediction test whereby observed values at tide gauges were removed from the solution space and surrounding data used to predict its behavior. To allow for the complex coastal morphology, a sea distance function has been implemented within the data weighting, which is shown to significantly enhance the solution. The tuning process allows for independent validation giving a standard error of the resulting surface of 0.2 m for areas with no tidal observation

Data assimilation for morphodynamic prediction and predictability

This paper gives an overview of the project Changing Coastlines: data assimilation for morphodynamic prediction and predictability. This project is investigating whether data assimilation could be used to improve coastal morphodynamic modeling. The concept of data assimilation is described, and the benefits that data assimilation could bring to coastal morphodynamic modeling are discussed. Application of data assimilation in a simple 1D morphodynamic model is presented. This shows that data assimilation can be used to improve the current state of the model bathymetry, and to tune the model parameter. We now intend to implement these ideas in a 2D morphodynamic model, for two study sites. The logistics of this are considered, including model design and implementation, and data requirement issues. We envisage that this work could provide a means for maintaining up-to-date information on coastal bathymetry, without the need for costly survey campaigns. This would be useful for a range of coastal management issues, including coastal flood forecasting