Recent evolution of surge-related events and assessment of coastal flooding risk on the eastern coasts of the English Channel |
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| Authors: | Paolo Antonio Pirazzoli Stéphane Costa Uwe Dornbusch Alberto Tomasin |
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| Institution: | (1) CNRS-UMR 8591, Laboratoire de Géographie Physique, 1, place Aristide Briand, 92195 Meudon, France;(2) Geophen UMR-CNRS LETG 6554, Université de Caen Basse-Normandie, Caen Cedex, France;(3) University of Sussex, Falmer, Brighton, BN1 9QJ, UK;(4) CNR-ISMAR & Università di Venezia, Venice, Italy |
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| Abstract: | This paper is based on statistical analysis of hourly tide measurements for some 285 equivalent full years from the stations
of Weymouth, Bournemouth, Portsmouth, Newhaven, Dover and Sheerness in the UK, and of Cherbourg, Le Havre, Dieppe, Boulogne,
Calais and Dunkirk in France. For each tidal value, surge heights have been determined and correlated with hourly or three-hourly
wind and air pressure data from nearby meteorological stations. Major surges in the area are generally produced by storms
associated with wind from north-west or south-west that tend to push oceanic water into the Channel. Recent medium-term climate
evolution does not seem to increase the flooding risk at French stations, where surge-related winds tend to decrease in frequency
and speed (Cherbourg, Dieppe and Boulogne) or show little change (Le Havre). However, the long-term risk of flooding will
increase through the loss in land elevation due to a continuation of the local relative sea-level rise, especially if this
effect will be enhanced by an acceleration in the global sea-level rise predicted by climatic models. The northern side of
the Channel (Weymouth, Bournemouth and Portsmouth) is mainly exposed to southerly winds that show variable trends. It is also
apparently affected by strong subsidence trends during the last two decades. If lasting, such trends can only increase long-term
flooding risk. The flooding risk has not increased near the eastern end of the Channel. The duration of significant cyclonic
events tends to decrease near Cherbourg but tends to increase near Weymouth, with no conclusive trends in other stations (Portsmouth,
Calais and Dunkirk), where extreme surges may occur also in relatively high-air-pressure situations. In conclusion, medium-term
coastal flooding risk seems to increase especially at Weymouth, Bournemouth and Portsmouth, and also, but less so, at Le Havre
and Sheerness. In addition, few extreme surges occurred during the last decades at the time of spring high tide, which would
seem to be a fortunate coincidence or, in some cases, an effect of tide–surge interaction. The risk of occurrence of less
favourable random events in the near future is therefore of concern, and flood potential would greatly increase if the global
sea-level rise expected in the near future is also considered. |
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| Keywords: | Tide Surge Meteorology Coastal flooding risk Climate change English channel |
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