Global change and relative sea level rise at Venice:
what impact in term of flooding
L. Carbognin, L. Tosi
Institute of Marine Sciences, CNR, Venezia, Italy
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
A. Tomasin
University Ca' Foscari in Venice, Venice, Italy
ABSTRACT
Relative sea level rise (RSLR) due to climate change and geodynamics
represents the main threat for the survival of Venice, emerging today
only 90 cm above the Northern Adriatic mean sea level (msl). The 25 cm
RSLR occurred over the 20th century, consisting of about 12 cm of land
subsidence and 13 cm of sea level rise, has increased the flood frequency
by more than seven times with severe damages to the urban heritage.
Reasonable forecasts of the RSLR expected to the century end must be
investigated to assess the suitability of the Mo.S.E. project planned
for the city safeguarding, i.e., the closure of the lagoon inlets by
mobile barriers. Here we consider three RSLR scenarios as resulting
from the past sea level rise recorded in the Northern Adriatic Sea,
the IPCC mid-range A1B scenario, and the expected land subsidence.
Available sea level measurements show that more than 5 decades are
required to compute a meaningful eustatic trend, due to pseudo-cyclic
7-8 year long fluctuations. The period from 1890 to 2007 is
characterized by an average rate of 0.12±0.01 cm/year. We demonstrate
that linear regression is the most suitable model to represent the
eustatic process over these 117 year. Concerning subsidence, at present
Venice is sinking due to natural causes at 0.05 cm/year. The RSLR is
expected to range between 17 and 53 cm by 2100, and its repercussions
in terms of flooding frequency are associated here to each scenario.
In particular, the frequency of tides higher than 110 cm, i.e., the
value above which the gates would close the lagoon to the sea, will
increase from the nowadays 4 times per year to a range between 20 and
250. These projections provide a large spread of possible conditions
concerning the survival of Venice, from a moderate nuisance to an
intolerable aggression. Hence, complementary solutions to Mo.S.E. may
well be investigated.
