IMPLIT - Impact of extreme events (storms and surges) on the Mediterranean coast hydrosystems

IMPLIT – Impacts of extreme events (storms and positive surges) linked to climate change on French Mediterranean coastal hydrological systems - AO 2003 of the Climate Change Impacts and Management Program (GICC-2) of the MEDD.


Project Summary

This project's aim is to analyse changes in the features of extreme events (storms = strong swell and surges) at the regional scale of the Gulf of Lions, their geomorphological and hydrological impacts on coastal hydrological systems, and the application of public policy to the problem. This research combines several fields of natural sciences (climatology, geomorphology, hydrology).


Effects of eustasy in the Gulf of Lion

While eustatic rise in sea level is a major issue associated with climate change, over the last few decades it has accounted for only around 10% of shoreline retreat in the Gulf of Lions (Sabatier and Provansal, 2000). At the local scale, sudden severe events (storms) represent a more significant risk, as they lead to erosion of beaches, breach of the dune ridge and flooding of low-lying coastal areas, thus threatening lagoon hydrological systems. Due to increasing populations in coastal areas and their role in economic development, it is important to obtain a clearer picture of coastal risks and to provide a scientific basis on which to establish "Coastal Risk Protection Plans".


Questions and answers expected in the context of this ANR

Increased frequency and intensity of storms?

It is generally acknowledged that climate change is likely to increase the frequency and severity of storms, but there are still various uncertainties at regional scale in the middle latitudes, due to variability between different climate models (Houghton et al., 1995). Although a trend towards increasing extreme events in the North Atlantic and North Sea has been demonstrated over the last few decades (Lamb, 1991, Warrick et al., 1993, Costa, 1997, Héquette and Vasseur, 1998), changes in the Mediterranean are not as clear-cut (Bruzzi, 1998). These changes will be studied in detail in this project, on the basis of investigations into contemporaneous relationships (in the 20th Century) between meteorological conditions (wind and pressure in particular) and swell/surge data at several different timescales (interannual to multidecadal). A comparison between different records (Port-Vendres, Marseille, Grau de la Dent and Sète) will help isolate the "regional" signal and provide an idea of the specific local situation. The relationships that are demonstrated will enable us to propose surge/swell change scenarios based on pressure field and wind data produced by integrated general circulation models (GCM) forced by greenhouse gas increases. Different GCM versions will be used (Météo-France, Hadley Centre) in order to gain the most robust picture of swell/surge response to the climate change predicted for the period 2050-2100.


What about coastal morphological response?

The situation regarding coastal morphological response (speed of retreat, frequency of flooding) is not clearly defined at present: is it possible to define a threshold for morphogenetic intensity, or frequency of occurrence of different flood levels? At what point are the impacts of an event so severe as to be irreversible? Which has the greatest impact: the frequency of events or their severity? Using the body of data for the Mediterranean shoreline (Suanez, 1997, Bruzzi, 1998, Sabatier, 2001, Certain, 2002), we are now able to investigate a correlation between regional/local weather forcing and the geomorphological risk at different timescales (from the event to the long term), so as to identify patterns and stabilising or even replenishing effects and to determine the coastal hydrological systems' fragility thresholds. From the hydraulic point of view, sea level represents a hydraulic load which determines whether or not there will be surface runoff from or into the lagoons; it also determines underground salt water intrusion via the salt wedge, when the water level in the lagoons is lower than that of the sea. The research will analyse the limiting conditions for hydrological management of the environment in an extreme hydroclimate context, in order to facilitate discussion on the hydraulic management planning and/or regulations that need to be envisaged in response to predictable climate change effects.


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Last updated: 12/12/2012

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