1. Storm Surge Network ForumVenice, 18-20 November 2013 Storm Surge modelling in Venice and the Mediterranean Sea: Improving the forecast tuning ECMWF wind fields Marco Bajo (1), Stefano Zecchetto (2), Georg Umgiesser (1), Francesco De Biasio (2) (1) - ISMAR-CNR, Venezia (2) - ISAC-CNR, Padova

2. Storm Surge Network ForumVenice, 18-20 November 2013 Operational SHYFEM-based systems Storm surge + total sea level inside the Venice lagoon: - ICPSM model (since 2003) : neural network post- processing - ISPRA model (since 2011): data assimilation (4D-PSAS) with data from 9 stations Total sea level + waves on Mediterranean and Black Sea: - Kassandra (since 2010)

3. Storm Surge Network ForumVenice, 18-20 November 2013 Storm Surge Forecast System for the Mediterranean Sea The models is operational from May 2010. Information, results and forecasts can be found under: http://www.ismar.cnr.it/kassandra

4. Storm Surge Network ForumVenice, 18-20 November 2013 80002 nodes 143286 elements Resolution: open sea 15-20 km coast 5 km Italian coast 1 km

5. Storm Surge Network ForumVenice, 18-20 November 2013 eSurge Venice eSurge-Venice (ESA Storm Surge for Venice) is a project funded by the European Space Agency, part of its Data User Element (DUE) programme. It aims to increase the usage of Earth Observation (EO) satellite data, from both ESA and other spacecraft, within the storm surge community. www.esurge-venice.eu Introduction

6. Storm Surge Network ForumVenice, 18-20 November 2013 Storm surges in Venice Introduction Sea levelFlooded pavement ratio 190 cm88% 140 cm59% 130 cm46% 120 cm28% 110 cm12% 100 cm5%

7. Storm Surge Network ForumVenice, 18-20 November 2013 Satellite data ALTIMETER DATA: to improve the initial state of the storm surge model, using data assimilation techniques or other methods. SCATTEROMETER DATA: to improve the wind forcing of the storm surge model, looking for a tuning of the modelled wind. Introduction

8. Storm Surge Network ForumVenice, 18-20 November 2013 Correction of the wind fields w c = w e + ( Δ w/w s ) w e θ c = θ e + Δθ ECMWF wind speed (w e ) was tuned using scatterometer data (w s ): (w s -w e )/w s, averaged over a specific time window around each SEV. A similar method was used to obtain a field Δθ, for the directions: Methods

9. Storm Surge Network ForumVenice, 18-20 November 2013 SEV list 12 SEVs recorded in Venice from 2010 to 2012 were considered. Methods SEV 2010-02-28 SEV 2010-11-10 SEV 2010-11-19 SEV 2010-11-21 SEV 2010-11-26 SEV 2010-12-23 SEV 2011-02-16 SEV 2012-10-27 SEV 2012-10-31 SEV 2012-11-02 SEV 2012-11-11 SEV 2012-11-28 Venice Acqua Alta Platform

10. Storm Surge Network ForumVenice, 18-20 November 2013 Methods Wind forcing From the 0.125 degree wind and pressure fields, 0.25 and 0.5 degree fields were sub-sampled, in order to investigate the importance of the resolution. For each SEV the original and the tuned fields were tested. A total of 6 simulations were carried on for each SEV. First 10 days are considered spin-up time.

11. Storm Surge Network ForumVenice, 18-20 November 2013 The model uses the wind stress (Liu et al., 1979), which was computed using the ECMWF air density fields, the wind fields and the drag coefficient C d fields. These depend also on the wind correction. Hydrodynamic model A finite element model, solving the shallow water equations (SHYFEM) was used to run the hydrodynamic simulations. This model runs operationally every day at the storm surge forecasting and warning Centre in Venice (ICPSM). Methods

12. Storm Surge Network ForumVenice, 18-20 November 2013 Methods Computational grid used by the model: - open boundary in the Gibraltar Strait; - only wind and pressure forcings; - sea level in the Acqua Alta Platform are used to run a second simulation inside the Venice Lagoon. Acqua Alta Platform Mediterranean Sea

13. Storm Surge Network ForumVenice, 18-20 November 2013 CASE 1: SEV 2010-11-26 Results

14. Storm Surge Network ForumVenice, 18-20 November 2013 Normalised bias Δ w/w scat between ASCAT and ECMWF related to a selected SEV for the Mediterranean Sea. Quickscat vs ECMWF Results SEV 2010-11-26

15. Storm Surge Network ForumVenice, 18-20 November 2013 Statistics of the tuned data shows more directionality and higher wind speeds. SpeedDirection Results SEV 2010-11-26 Quickscat vs ECMWF

16. Storm Surge Network ForumVenice, 18-20 November 2013 Results SEV 2010-11-26 Original Tuned

17. Storm Surge Network ForumVenice, 18-20 November 2013 Results CASE 2: SEV 2012-11-11

18. Storm Surge Network ForumVenice, 18-20 November 2013 Results SEV 2012-11-11 Original Tuned

19. Storm Surge Network ForumVenice, 18-20 November 2013 Results Statistics Original Tuned Errors on maximum peaks

20. Storm Surge Network ForumVenice, 18-20 November 2013 Skew surge Observed Original Tuned

21. Storm Surge Network ForumVenice, 18-20 November 2013 Results Average statistics Resolution RMSE [m]CorrelationPeak error [m] Original data 0.1250.0720.908-0.102 0.250.0720.906-0.102 0.50.0730.904-0.104 Tuned data 0.1250.0660.918-0.062 0.250.0660.917-0.063 0.50.0670.915-0.067

22. Storm Surge Network ForumVenice, 18-20 November 2013 Conclusions Spatial wind resolution seems to have a low importance in the storm surge forecast in the Adriatic Sea. Until 0.5 degree grid size the performances are similar. Tuned wind fields improve statistics What about temporal resolution? Better reproduction of the storm surge peaks. The improvement is higher with storm conditions.

23. Storm Surge Network ForumVenice, 18-20 November 2013 Thank you for your attention!