Geography Reference
In-Depth Information
Box 7.1 Increased coastal flood hazard in Venice, Italy
The historic city of Venice in northern Italy is one of the
most famous cases of increasing flood threat. A
combination of subsidence in the city and rising sea
levels means that the frequency of flooding in St Marks
Square in the city centre has risen from seven per year
in 1900 to about fifty per year today. A major flood
occurred in 1966, causing widespread damage (see
below). Projections of sea level rise indicate that this
frequency could rise to over 300 per year by the year
2050. Many solutions have been suggested, including a
system of gates between the lagoon in which Venice is
located and the Adriatic Sea (Bandarin 1994). However,
these proposals are controversial in that they
appear to tackle only the symptoms of Venice's many
problems rather than their causes (Penning-Rowsell et
al. 1998). They therefore may not solve the flooding
problem in the long term—i.e. 50+years—and do not
tackle the associated problems of pollution in the city and
the Lagoon, the city's declining population, and the decay
of the ancient Venetian buildings. Even the local
government Comune in Venice has voted against the
proposals, which remained mired within the labyrinthine
and corrupting Italian political system for years, until
vetoed by the Italian Environment Minister in 1998: the
problem remains unsolved.
Figure 7.1 Increasing flooding in Venice, 1926-93
pressure meteorological conditions. Changes in
the relative height of land and seas caused by land
subsidence or climate change-induced sea level
rise also contribute to coastal flooding (Nicholls
1995). Tropical cyclones such as in Southeast Asia
also contribute to flooding of coastal regions, as
they bring onshore both extreme waves and
intense rainfall.
Flooding in urban areas away from the coast or
major rivers occurs when summer thunderstorm
conditions (or intense cyclonic rain) occur on
urban catchments, where infiltration rates are
reduced by paved surfaces. The result is rapid and
almost complete runoff far exceeding the capacity
of drainage and sewer systems. Without
deliberately designed storage ponds or other
control systems for this runoff, it is liable to cause
damage, especially in the basements of buildings
or where underground railways or telecoms
systems are at risk.
More locally important flood-causing agents
are ice-dammed rivers, dam and dike breaks, and
tsunamis. In many of these instances, damage is
extreme, caused by high water velocities and
associated intense storm conditions.
Flood extremes
Table 7.1 gives this data for the twenty-four most
extreme floods as measured by their discharge
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