ABOVE: During acqua alta, necessity is the mother of improvisation.

No, the title of this post isn't a misspelled homage to Simon and Garfunkel--it refers to the alert sirens and warning tones that tell Venetians and visitors when acqua alta flooding is on the way and what level of inundation to expect.

Several hours before a flood tide, you'll hear one blast on a World War II-style air-raid siren followed by a series of warning tones that forecast the expected water level at high tide:

• One prolonged single-frequency tone means the water will peak at 110 cm above the benchmark of zero.


• Two tones, each ending in a rising note, indicate an expected level of 120 cm or more.


• Three tones, each ending in a rising note, indicate an expected level of 130 cm or more.


• Four tones, each ending in a rising note, indicate an expected level of 140 cm or more.

Note: The tones may be repeated two or more times, so don't assume the worst if you hear two or three sets of tones with gaps between them.

What to do when you hear the sirens:

1. Don't panic. Alta acqua can be annoying, but it won't hurt you unless you slip on wet pavement or are foolish enough to step off a flooded fondamenta into a canal.


2. The area around the Piazza San Marco is the most flood-prone tourist area of the city, so avoid it unless you're willing to get your feet wet.


3. Put on rubber boots or, if you're in a flooded tourist area, consider buying a set of overpriced temporary plastic boots from a street vendor.


4. Stay close to buildings if you're walking along a fondamenta without a wall or railing. Canal edges are usually indicated by a border of white--and possibly slippery--Istrian marble, but why risk falling into a canal when it's just as easy to be sensible?


5. Try not to splash when you're walking around--you'll just get yourself and other people wet, and you'll annoy Venetians who take little pleasure in the flooding of their streets, shops, and ground-floor apartments.

To hear samples of the initial acqua alta warning siren and the tones that indicate what tide level to expect, click here and scroll down to "Scarica i Segnale" for links to sound files in MP3 format.