1. 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

2. = + 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 = +

3. 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 ( ) are compared with 30 ensemble future statistics ( )
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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Thanks for your attention

13. 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

14. 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

15. 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:

16. 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 The hypothesis associated is rejected if: