Extremes and marine storms in the Mediterranean Sea

Extremes and marine storms in the Mediterranean Sea P. Lionello, Univ. of Lecce, Italy 1 Intro: GEV and generalities examples from RON and sea level in Venice 2 some insight I): Storm surge trends for Venice 3 generalities on waves and wave modeling 4 some insight II): futures scenarios for storminess and implications for waves and surges. . .

EXTREME VALUE ANALYSIS is well established common paradigm return values for relatively long periods But many of other aspects are in practice mostly specific to the problem, and only general guidelines are available Event definition: a set of independent event, the set should contain many items, but few of them are used Data gathering: long homogeneous series of data from observations or models

Cyclones (winds) , waves and surges 4 NOV. 1966 event SLP and U 10 Surge and waves

alghero crotone =0. 30± 0. 14 =7. 42 0. 21 mazara =0. 43± 0. 15 =4. 66 0. 14 monopoli =0. 07± 0. 28 =4. 76 0. 16 =-0. 10± 0. 22 =3. 70 0. 11 pescara ponza la spezia =0. 17± 0. 16 =4. 29 0. 14 =0. 02± 0. 17 =4. 82 0. 18 =-0. 10± 0. 19 =4. 74 0. 15

alghero crotone monopoli pescara mazara ponza la spezia

Venice surge: Extreme values distribution 1940 to 1969 GEV distribution 1940 to 1969 1970 to 2000

EXTREMES WAVES, SURGES IN THE ADRIATIC SEA IN A 2 x. CO 2 SCENARIO P. Lionello, F. Dalan, E. Elvini, A. Nizzero

The common element of wave and surges is WIND More intense cyclones Higher wind speeds Higher waves and storm surges Loss of lives, loss of properties, loss of economic resources, cultural and environmental heritages, increased costs of coastal defences

CONSEQUENCES ON WAVE FIELDS AND STORM SURGE A DOWNSCALING PROCEDURE APPLIED TO THE ADRIATIC SEA

The downscaling procedure consists of two steps. 1) A regional wind field is derived from the sea level pressure field (available every 6 hours) by CCA of the PCA prefiltered fields PREDICTOR: SLP SIMULATED PREDICTOR 2) The surge level and the wave field are computed from the wind field using a barotropic (single layer) circulation model and a spectral wave model (WAM) SIMULATED WAVES AND SURGES STATISTICAL MODEL DYNAMICAL MODELS OF OCEAN WAVES AND STORM SURGES PREDICTAND: U 10 SIMULATED PREDICTAND: U 10

downscaling Observations downscaling T 106 The downscaling procedure has been tested applying it to the ERA-15 SLP data. The same period has also been simulated using directly the T 106 winds. The downscaling produces a large improvement in the simulated Significant Wave Height and surge levels. However, levels during peak events remain underpredicted. T 106

RESULTS: SIGNIFICANT WAVE HEIGHT scenario max 100 years depth OBS 5. 1 6. 75 0. 6 CTR 5. 6 6. 1 0. 4 CO 2 4. 5 5. 6 0. 3

CTR MAX CTR FREQUENCY CO 2 CTR 100 -YEAR RETURN VALUES CO 2

STORM SURGE

Are the surges in Venice a result of recent climate changes? Venice: Frequency of surges 800 2000 Is their frequency related to global processes? East coast of England: Frequency of surges Figs from D. Camuffo, (1993)Theor. Appl. Climatol. 47, 1 -14

Source: Report by P. Canestrelli Surges above 110 cm level (reference: fixed reference level) Trend in frequency/intensity of storm surges? Sea level rise 1865 Surges above 110 cm level (reference: annual mean sea level) 2000

Trend in frequency/intensity of storm surges? The observed trend is mostly produced by loss of ground level. This has no relation with more intense storms in a changed climate… however, a smaller trend could be present. Is this small trend an indication of what could be expected in a 2 XCO 2 CLIMATE?

RESULTS: SURGE scenario max 100 years depth OBS 129 CTR 109 128 8 CO 2 119 125 8 184 150 8

CTR MAX CTR FREQUENCY CO 2 CTR 100 -YEAR RETURN VALUES CO 2

The doubled CO 2 simulation is characterized with more extreme weather events, but the (significant) difference between the two scenarios is small, and not fully significant for Mediterranean region The CO 2 scenario presents a marginally diminished wave activity in the southern Adriatic. The two scenarios present substantially equivalent extreme surge levels. There is a minor increase in the CO 2 scenario.

THE END Clim. Res. (2002), 22, 147 -159, Clim. Res. (2003) 23, 217 -231