APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE SURGE STATISTICS R APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE SURGE STATISTICS R. Mel, P. Lionello, A. Sterl Palma de Mallorca, November 13th 2012

= + Introduction Topic of this work APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Introduction The target is to investigate the influence of climate change in Venice climate statistics The study analyzes changes in frequency of storm surges (APPENDIX 1) ,that can be threat Venice in addition to subsidence and sea-level rise (NOT considered here) Topic of this work Future storm surge scenario Future storm surge scenario Storm surge scenario Future storm surge scenario Future storm surge scenario Future storm surge scenario Sea Level mean Sea Level rise Sea Level rise Sea Level rise Future flood statistic Surge statistic = +

APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Introduction Meteo fields are supplied by EC-Earth climate model (based on ECMWF forecast system) 30 ensemble 5-year statistics of present-time (2004-2008) are compared with 30 ensemble future statistics (2094-2098) Surge statistics are computed by a hydrodynamic model “HYPSE” that solves the shallow water equations (APPENDIX 2) PRESENT Meteo fields Surge output PRESENT Hydrodinamical model t test FUTURE FUTURE

Method ECMWF Tide model HYPSE ECMWF APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Method EC Earth can provide the statistic evolution of the climate, using the same model but with gasses concentration parameters of the future obtained with rcp45 scenario 30 tipical 5-year PRESENT FIELDS PRESENT 150 years of tide statistic ECMWF PRESENT REANALYSIS PARAMETERS 30 Random initial conditions Tide model HYPSE 30 tipical 5-year FUTURE FIELDS ECMWF FUTURE TIME PARAMETERS FUTURE 150 years of tide statistic

Work area Model domain Tide output gauges Meteo output gauges APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Work area Model domain Tide output gauges Meteo output gauges

SURGE Which resolution can be used? APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Which resolution can be used? EC Earth ran with two different resolutions: HRV and LRV More ensemble data with LRV resolution but… LRV CAN NOT represent wind (and tide) in the Adriatic sea WIND SURGE PRESSURE

APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Rcp future scenarios EC Earth ran with two different scenarios: rcp45 and rcp85 In this work rcp45 scenario is used

Surge results Results show no change in tide statistics APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Surge results Results show no change in tide statistics

Wind results No significant changes in South-East wind statistics APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Wind results No significant changes in South-East wind statistics A significant decrease on number of hours of weak wind No significant change in strong winds

APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Pressure changes A significant increase of medium and high pressure statistics No changes in low pressure statistics

Conclusions No change in surge statistics More high pressure periods APPLICATION OF NEW CLIMATE CHANGE RESULTS TO VENICE TIDE STATISTICS Conclusions No change in surge statistics More high pressure periods Less windy day No change in strong wind and low pressure statistics LRV is developed for rcp85 extreme scenario: for pressure is possible to use LRV scenario: the difference between present time and rcp45 future time statistics is the same of that between rcp45 and rcp85

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1 Tide in Venice APPENDIX The tide has two components: astronomical tide and storm surge, produced by wind and pressure gradient These components could be treat as indipendent factors to get the measured tide The astronomical tide is caused by the gravitational attraction that the heavenly bodies, mainly the Moon and Sun, have on the body of water. It can be calculated with high precision and in advance of even many years According to the method of the harmonic analysis, the astronomical tide at a given location can be calculated as a superposition of sinusoidal oscillations, each characterized by its amplitude and phase In Venice eight harmonics are sufficient to describe accurately the astronomical tide in order of 1 cm

1 Tide in Venice APPENDIX To alter the regularity of the astronomical tide by a way sometimes substantial, meteorological factors intervening and among them especially the wind and pressure In the case of the Adriatic Sea, long and narrow basin, closed in the upper part and open in the lower one, a strong wind blowing from the southeast along the longitudinal axis, produces an accumulation of water to the closed end. The phenomenon is favored by a big fetch and is further amplified because of the shallow waters of the northern Adriatic The atmospheric pressure alters the level of the sea with "inverse barometer effect": a decrease of pressure corresponds to an increase in the level and vice versa; with a variation which can lead to 20 cm

2 Hydrostatic Padua Surface Elevation Model APPENDIX 2 Hydrostatic Padua Surface Elevation Model HYPSE is a standard single layer nonlinear shallow water model, whose equations are derived from the vertical average of the momentum equation, assuming a constant velocity profile It adopts an orthogonal C-grid and uses the leap-frog time integration scheme with the Asselin filter It includes astronomical tide, meteorological forcing (mean sea level pressure and wind stress), a quadratic bottom stress …and a Smagorinsky horizontal diffusivity with coefficient:

APPENDIX 3 t Test The basic statistics for the test are the sample means Y and Z, and the sample standard deviations S1 and S2 with degrees of freedom v estimated using the Welch-Satterthwaite approximation (Harvey J. Motulsky 1995) Because it cannot be assumed that the standard deviations from the two processes are equivalent, the test statistic has the following form: The strategy for testing the hypothesis is to calculate the appropriate t statistic from the formulas above (Harvey J. Motulsky 1995), and then perform a test at significance level α, where α is chosen 0.05. The hypothesis associated is rejected if: