1. Introduction

 

The city of Venice is situated inside the Venice lagoon at the northwestern end of the Adriatic Sea, a marginal sea in the Mediterranean. Here some of the highest tides in the Mediterranean help in flushing out brackish waters and replacing it with marine waters from the coastal shelf in front of the lagoon. The city has been nomi-nated a UNESCO world heritage site due to the beauty of its buildings and churches and its unique setting with its canals and its gondolas.

However, climate change is threatening this delicate system. If IPCC projections are right we could have a sea level rise between 30 cm and 1 m, depending on the RCP scenarios considered (IPCC, 2001, 2007, 2014). Other semi-empirical models predict up to 175 cm of sea level rise (Vermeer & Rahmstorf, 2009). It is clear that for a city that is on average situated only 80 cm above mean sea level, such an increase in water level would be lethal. It is therefore of utmost importance to see how the city can be safeguarded against this global threat.

In the past Venice was subjected to high water events intermittently. The highest event has happened in 1966 with a water level of 194 cm (Trincardi et al., 2016). Recently, on 12th of November 2019, the second highest high water has struck Venice with a water level of 187 cm. What was important in this event was the fact that for one week, water levels were very high and on 4 days they exceeded 140 cm,


a water level that classifies the high water events as exceptional. In the last 150 years there were only 23 of these exceptional events, 9 before year 2000, 14 in this millennium, and 5 in the last 2 years (Cavaleri et al., 2019). A clear sign that Venice will have to prepare for these high water events.

In the last years, construction of the mobile barriers (MOSE) has started in order to be able to defend the city of Venice against high tides and storm surges (Magistrato Alle Acque, 1997). Other (alternative and soft) solutions (Comune di Venezia, 2005) have been proposed that would either decrease the section of the inlets to make it more difficult for the water to enter the lagoon or open the fishing valleys inside the lagoon to create a larger basin for the tide to expand. However, it seems that with a sea level rise above a certain level the only viable way of defending the city against high tides is blocking the water fluxes at the inlets of the lagoon. One of the possible ways to do so is the MOSE project. The starting date of these works was 2003, however, even if now over 90 % of the works have been completed, it is still not yet clear when the whole works will be finished and operational. A possible date of completion is now (at the end of 2019) the year 2021. However, 10 years ago the completion date was 2014 (Water Technology, 2019), so nothing sure can be said about when the MOSE will be finally finished.

In any case, it would be interesting to see how the MOSE will be able to defend the city against high water taking into account sea level rise

 

 

⁎ Corresponding author at: CNR – National Research Council of Italy, ISMAR – Institute of Marine Sciences, Castello 2737/f, 30122, Venice, Italy.

E-mail address: georg.umgiesser@ismar.cnr.it.

 

https://doi.org/10.1016/j.jnc.2019.125783

Received 7 June 2019; Received in revised form 19 November 2019; Accepted 18 December 2019

1617-1381/©2019PublishedbyElsevierGmbH.

 

 

 

due to climate change. Other studies have looked into the climate change impact on the city. A study (Umgiesser & Matticchio, 2006) has explored two possible values of sea level (30 and 50 cm) to see how often the barriers had to be closed and its implication on ship traffic. Based on a static analysis of the tides, another study (Carbognin, Teatini, Tomasin, & Tosi, 2010) estimates the number of closures with a SLR of 50 cm to be around 250. Other studies looked at the economic implications of the closures (Vergano, Umgiesser, & Nunes, 2010).

Here we present a study where we systematically look at a range of sea level rises (from 0 to 200 cm) in order to cover the complete range between best and worst case scenarios. We do on purpose not indicate in what year these scenarios will be reached. This approach makes our study independent from the climate scenarios chosen and therefore more general. This study is also based on simulating the storm surge and the barrier closures with a hydrodynamic model, and not on a static analysis of the tidal peaks.

In the following, we present in Section 2 the study site, the nu-merical model, the closing mechanism and describe the simulations that have been carried out. In Section 3 the results are presented and in Section 4 they are discussed. Finally, conclusions are drawn in Section 5.