CLIMATE SIMULATIONS OF STORM SURGES AND WIND WAVES IN THE MEDITERRANEAN SEA Piero Lionello DiSTeBA (Dipartimento Scienze e Tecnologie Biologiche e Ambientali, University of Salento, Lecce, Italy, and CMCC (EuroMediterranean Center on Climate Change), Lecce, Italy e-mail: [email protected] Luigi Marzo DiSTeBA (Dipartimento Scienze e Tecnologie Biologiche e Ambientali, University of Salento, Lecce, Italy, Dario Conte CMCC ( EuroMediterranean Center on Climate Change), Lecce, Italy 1 INTRODUCTION of wind waves using the WAM model. HYPSE, which is a two-dimensional model The severity of future hazards along the based on depth averaged currents (Lionello et coastlines depends on sea level rise, vertical al. 2005), has been implemented on regular land motion and intensity of marine lon-lat grid, which covers the whole storminess. This study describes the effect of Mediterranean sea with a 0.2 degree climate change on this last factor at the coast resolution. WAM (WAMDI, 1988) covers the of the Mediterranean Sea. Specifically, we whole Mediterranean Sea at a 0.25 resolution. have computed the distribution of large surges Simulations cover the period 1951-2050 and wave heights along the Mediterranean under the A1B emission scenario Nakićenović Sea coastline in the present condition and in a et al. (2000). future climate scenario. This analysis is obviously important for evaluation of coastal HYPSE and WAM are driven by the risks and management of coastal defences meteorological fields produced by a 7- (e.g. Nichols & Hoozemans, 1996). member model ensemble which has been produced within the CIRCE project (Gualdi et al., 2012). These climate models have the peculiarity of including an ocean circulation component describing the marine circulation in the Mediterranean Sea at high resolution. Therefore, air-sea interaction at sub-regional scale is expected to be better reproduced in these than in previous simulations. The ensemble is composed of the following simulations: Figure 1: the Mediterranean basin and the coastal • CMCC-LR (Euro Mediterranean Centre points analysed in this study. for Climate Change Low Resolution), which has used the global climate model CMCC- 2. MODELS AND DATA Med with a horizontal resolution of about 0.75 x 0.75 degrees; This study performs an ensemble of • CMCC-HR (Euro Mediterranean Centre simulations of sea level using a hydro- for Climate Change High Resolution), which dynamical shallow water model (HYPSE, has used the CMCC-CLM Regional Climate Hydrostatic Padua Sea Elevation model) and model (a climate version of the regional COSMO model) with an horizontal storm surge and the significant wave height in resolution of 0.12 x 0.12 degrees independent events. They are denoted as high • MPI (Max Plank Institute-Germany), SSI (storm surge index) and WSI (wave storm which has used REMO (REgional Model) index) in this paper. Only events separated by with a horizontal resolution of 0.22 x 0.22 at least 120 hours, which represent an degrees, coupled to the Max-Planck-Institute estimate of the maximum duration of a storm for Meteorology ocean model (MPI-OM) in this area, have been considered, in order to • ENEA (Italian National agency for new ensure that only independent events are technologies, Energy and sustainable included in the statistics. These two indicators economic development) which has used the are meant to describe intense meteorological PROTHEOUS system (consisting of events that occur regularly every year (and REGCM3 with a lat/lon resolutions of 0.27 x not extreme values which would be 0.35 degrees coupled to MITGCM characterized with longer return times). implemented in the Mediterranean Sea at 1/8° resolution) 3. RESULTS • CNRM (Centre National de Recherches Météorologiques - MeteoFrance), which has Figure 2, top panel shows the SSI distribution used the ARPEGE atmospheric circulation along the Mediterranean coast for the model (Déqué and Piedelievre, 1995), whose individual climate simulations. The SSI is stretched grid reaches a minimum 50 km largest along two stretches of the coast, which resolution over Europe-Mediterranean-North are located in the Northern Adriatic Sea and Africa) and it is coupled to NEMO-MED8 in the Gulf of Gabes, where high SSI values (1/8° resolution) for the Mediterranean Sea are explained by the presence of a relatively circulation; long wind fetch over shallow water (the effect • IPSL3 (Institute Pierre Simon Laplace) of the wind is proportional to the inverse of dataset, which has used LMDZ RCM (30km the water depth). Other four local maxima are resolution) coupled to MEMO-MED at 1/8° present in figure 2. Two of them in the Gulf deg resolution in the Mediterranean Sea. of Lion (France) and at the Tuscany coast • The IPSL2, which has used the same (Italy), while the other two correspond to the models as IPSL3, but adopted a two away Aegean sea (at the Greece-Turkey boundary) coupling for the nest, that is four models -- and the Gulf of Alexandretta (near the two atmospheric (global and regional) and Turkey-Syria boundary. These areas are two oceanic (global and regional) -- have characterized by shallow water too, even been run together allowing the results at though fetch is much shorter than in the North regional scale to feedback on the global Adriatic Sea and in the Gulf of Gabes. Figure models. 2 bottom panel shows the percent change of the SSI between the 2021-2050 and 1971- This contribution considers the climate 2000 periods. The thick colored parts of the change along the coast, which in represented lines denotes the stretches of the coastline by the subset coastal grid points of the model where the climate change percent index is grid (figure 1 shows them for the HYPSE larger than its standard deviation. The thick model grid). In the following figures 2 and 3, gray line denotes the climate change the Mediterranean Sea coastal points have according to the ensemble mean of all been ordered clockwise around the whole simulation and the black parts where it is basin, i.e. eastwards along its European significantly different from zero. In general northern coast and westwards along its changes are small (maxima changes are lower African southern coast. than 5%), but the ensemble model mean shows a spatially coherent and significant The indicators used for describing the attenuation of large storm surges. intensity of severe marine storms are the yearly mean of the 3-largest values of the Figure 3 shows the same information, except 111:159-173, ISSN 0921-8181, is consider the SWI and it does not report the http://dx.doi.org/10.1016/j.gloplacha.2013 analysis of the ARPEGE, IPSL2 and IPSL3 .09.006. simulations, which has not been completed, yet. The spatial distribution of the WSI is Gualdi, S., Somot, S., Li , L., Artale , V., obviously different with respect to that of the Adani, M., Bellucci, A., Braun, A., SSI and it presents the largest value at the Calmanti , S., Carillo, A., Dell’Aquila, A., north African coast, where the combination of Déqué, M., Dubois, C., Elizalde, A., long fetch and intense winds favors the Harzallah, A., Jacob, D., L’Hévéder, B., occurrence of large significant wave height May, W., Oddo, P., Ruti, P., Sanna, A., conditions. However, also for wind waves, the Sannino, G., Scoccimarro, E., Sevault, F., ensemble mean (to be extended in future to & Navarra, A. (2012). The CIRCE include the three missing simulations) shows simulations: a new set of regional climate a widespread decrease of high values with change projections performed with a climate change. realistic representation of the Mediterranean Sea, 10.1175/BAMS-D-11- 4. CONCLUSIONS 00136. In general results suggest a future attenuation Lionello P, Mufato R, Tomasin A. 2005. of marine storminess along the coastline of Effect of sea level rise on the dynamics of the Mediterranean Sea. In spite of large free and forced oscillations of the Adriatic differences among the results of the 7 model Sea. Climate Res. 29: 23–39. simulations (the inter-model spread is a large source of uncertainty), their ensemble mean Lionello P., U.Boldrin, F.Giorgi, 2008. Future shows a significant decrease of intensity of changes in cyclone climatology over large surge and high waves. Such decrease of Europe as inferred from a regional climate the intensity of marine storms is consistent simulation Clim.Dyn. 30:657-671 DOI with the reduction of cyclones, which some 10.1007/s00382-007-0315-0 simulations suggest for future climate scenarios in the Mediterranean region (e.g. Nakićenović , R., Alcamo, N.J., Davis, G., de Lionello et al., 2008). The readers are Vries, B., Fenhann, J., Gaffin, S., addressed to Conte and Lionello (2013) for Gregory, K., Grübler, A., Jung, T.Y., more details on the storm surge analysis. Kram, T., La Rovere, E.L., Michaelis, L., Mori, S., Morita, T., Pepper, W., Pitcher, ACKNOWLEDGEMENTS H., Price, L., Raihi, K., Roehrl, A., We are very grateful to Dr. Gabriel Jordà of Rogner, H.-H., Sankovski, A., University of Balearic Islands for the hourly Schlesinger, M., Shukla, P., Smith, S., data of the tide gauges used in this study, to Swart, R., van Rooijen, S., Victor, N., & Dr. Laurent Li, Alberto Elizalde, Clotilde Dadi, Z., 2000. IPCC Special Report on Dubois, Enrico Scoccimarro for the Emissions Scenarios. Cambridge meteorological forcings of the climate University Press, Cambridge, United simulations that they have made available for Kingdom, New York, NY, USA. p. 599. this study. Nicholls, R.J., & Hoozemans, F. M. J. ,1996. REFERENCES The Mediterranean: vulnerability to coastal implications of climate. Ocean Conte D. and P. Lionello, 2013. Coast. Manage. - Ocean & Coastal Characteristics of large positive and Management, 31:105-132 DOI: negative surges in the Mediterranean Sea 10.1016/S0964-5691(96)00037-3. and their attenuation in future climate scenarios, Global and Planetary Change WAMDI group (S.