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Watch the acqua alta in Venice today! December 1, 2008

Posted by dorigo in news, personal, science, travel.
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Oh, I love the feeling.

I was woken up this morning at 6.30AM by the sirens, but then forgot about it and tried to concentrate on a last half hour of sleep. Then I got up, showered, checked my mailbox, had a quick coffee, and got ready to go to work. Then, upon getting down the stairs into the flooded atrium, I remembered. Acqua alta!

Venice is constantly under siege, particularly between September and December. Low barometric pressure, heavy rainfalls, a south-eastern wind, or the phenomenon of “Sesse” -a coherent oscillation of the waters of the Adriatic Sea basin- these are all possible sources of the phenomenon called “acqua alta”, a sea tide which surpasses +80cm above average sea level. That is enough to flood part of the streets, in their lowest points. When the tide is predicted to get above 110cm over average sea level, Venice inhabitants get an early warning with high-pitch sirens which they cannot ignore -and which usually wake them up, since the highest tides usually occur in the morning hours. And when the water is predicted to get to 130cm above sea level, as this morning, or above that level, well -things get ugly.

130cm above sea level, as will happen in about three hours in the Venice lagoon (see graph above), is enough to flood 80% of the town, and make unusable some of the highways created for pedestrians with wooden gangways (see picture below). A few commercial business will get in trouble because water will soar above their protective bulkheads. Some places will be basically unreachable unless you wear thigh-high protections -or swim.

It should be fun for an outsider to visit Venice today. The city will appear under siege. People wandering around, trying to figure out how to go from A to B; public transportation making detours to avoid low bridges; water a bit everywhere; and a general feeling of disconcert. If you want to have a peek, there are webcams around. Try this one, looking down to Piazza San Marco (a place which is only 75cm above sea level, so it is already flooded right now):

S.Marco square in real time

UPDATE:Another webcam showing a canal in Cannaregio, with the water almost closing in on the passage under a bridge.

You can find many others around… Have fun.

UPDATE: the water is now predicted to get to 140cm above sea level, which configures itself as a real flood, one of the twenty or thirty highest in Venice’s history. For a comparison, the highest ever measured was 194cm on November 4th, 1966 -but that was a real catastrophe. Check the updated graph below:

UPDATE: the tide should be peaking right now (at noon, so a bit later than expected), and the level it has reached is the fourth highest, ever: 156 centimeters above average sea level. That means about two feet of water over most of the streets of the city.



1. Lauren Vianello - December 1, 2008

I can’t believe that someone could think that Venice being ‘under siege’ while experiencing acqua alta could or should be ‘fun’.
This is a phenomenon which greatly affects the everyday lifestyle of Venetians, as you well described, many businesses will suffer costly and inconvenient consequences and many residents who happen to be unlucky enough to reside on the ground floor will see themselves in dire straits to simply have a normal day. But this should be ‘fun’ to watch…
Have a little sensitivity and respect.

2. dorigo - December 1, 2008

Lauren, get real. People enjoy watching disasters, or have you never stood on a car jam provoked by nosy drivers looking at the scene of a car accident ?

I live in Venice and I do not like tourists, let alone those who will have fun today, but I am just reporting facts.


3. beyondthebridge - December 1, 2008

It’s normal that tourists enjoy it, we can’t avoid it, but I believe that most of them understand that it is a big problem.
I think that very few people live on a ground floor now, no Venetians would buy a ground floor.

4. Alejandro Rivero - December 1, 2008

T, please upload some pictures to facebook 🙂

5. Lauren Vianello - December 1, 2008

You hate tourists.. tell me, what should a 4th generation Venetian feel?
I do not reside in Venice permanently but upkeep an inherited family home – which happens to have a floor on the ground floor- and in which I spend long, nostalgic months in the spring and summer.
To the person that said no ‘venetian’ would buy a ground floor.. I happen to count among my friends some that live on a piano nobile on the Canale Grande and some of my dearest friends who live on the ground flor in a small flat in Castello. I suppose I should offer to come to laugh at his misfortune today.
It is called Venice – so many young people nowadays leave the city in search of a place where life, including housing, it’s more affordable. And the ones that choose to stay sometimes are forced to buy a ground floor apartment. Is it not like that everywhere? or do people in the US live in basement apartments because they find it excentric?
No more to share here as I’m afraid we simply don’t see eye to eye.
Have a pleasant day.

6. dorigo - December 1, 2008

Dear Lauren,

I “hate” tourists because tourism is what is making Venice an attraction park arther than a city. Precisely the same reason that is driving away young people unable to shell out 500,000 euros for a barely decent house.

So we are on the same page about that. And I agree, many still live in
ground floor apartments. I did from 1992 to 2000 myself, and now the
place is rented to students.

Thank you for your visit,


7. beyondthebridge - December 1, 2008

I grow up in Venice and have there many friends, many of them bought an apartment in the last years, some had to go in the mainland because of the house cost, but no one ever thought to buy a flat in a ground floor.
I’m sorry there is still some people in the ground floor, I guess that many are students. But I still think that no Venetians would buy for his family a ground floor. It’s not like in the other town, here you know that acqua alta happens.

8. Tony Smith - December 1, 2008

The BBC web site today (1 Dec 2008) has an article that says:
“… Venice has been hit by the biggest flood in more than 20 years, with waters rising 1.56m above normal. …
An underwater dam to protect the city is planned for 2011. …”.

How will a dam that is under water stop a flood ?

Tony Smith

9. Iphigenia - December 2, 2008

Regarding “Venice as a theme park”: The second-most depressing thing in Venice is the presence of MacDonald’s, an institution which, I’m delighted to say, has never really taken root in Italy. *The* most depressing thing about Venice is that most of the people in the MacDonald’s there were young Italians…..my greatest fear is that young Italians will start drinking Starbucks coffee….please tell me that this will never happen!

10. dorigo - December 2, 2008

Beyondthebridge, the situation is not as clear-cut as you picture it. Ground floors have levels above sea water ranging from +80 to +180cm. It is clear that the (relatively few) ground floor apartments still inhabited live in the upper end of that range. However, there are citizens who prefer to live in a ground floor in Venice than move inland. Among them, many students, but also elderly people. As I said above, I myself lived in a ground floor apartment (+170) for 8 years. Never had water in, but it can be quite damp at times.

Tony, the project is called “Mose”, and it consists in strings of large submerged blocks filled with water, which normally lie on the lagoon floor, lined up at the sea entrance canals. As a high tide is coming, air is pumped inside, and these “tiles” rotate as they rise up, forming a barrier that blocks the water influx.

Iphigenia, that is so not the second-most depressing thing… There are worse ones: the rising price of housing, the continuous fall in the number of residents, the disappearance of groceries and appearance of Murano glass shops and carnival mask boutiques…


11. Tony Smith - December 2, 2008

Thanks for the information about Mose, which I see by web searching means either Modulo Sperimentale Elettromeccanico
or Moses (parting the sea).
There was some web commentary about missing money (about $550 million Euros maybe transferred to Rome for a subway)
and objections from various groups (some Venetian),
I was particularly interested in a 7 January 2008 NPR web article by Sylvia Poggioli that said in part:
“… Starting in the 16th century, the Venetians diverted major rivers outside of the lagoon to prevent silt from filling it up. Left alone, lagoons like the one in Venice either tend to dry up and become land or they are overwhelmed by the sea and turn into bays. …
In the last century, the city sank 11 inches, mostly due to the pumping of groundwater and methane gas for local industries.

the mobile gates are designed to last at least a century and to protect Venice from a difference in water level between the sea and lagoon of up to six and half feet.
The latest prediction of the United Nations Intergovernmental Panel on Climate Change is for a one- or two-foot increase by the end of this century. …”.

If “six and half feet” is taken to be about 200 cm
if an Acqua Alta like the present one is about 160 cm
that looks like MOSE, if in place now, should protect Venice from Acqua Alta like the present one with 40 cm to spare.

However, looking ahead 100 years,
if methane and ground water pumping continue at the present rate maybe there would be another 11 inches = about 30 cm of subsidence
maybe there would be a sea level rise of one or two feet = about 30 or 60 cm,
that 100 years from now MOSE would be too short by
either 30 + 30 = 60 – 40 = 20 cm
or 30 + 60 = 90 – 40 = 50 cm
(depending on how much sea level rise).

If the sea level rise is on the high side and subsidence remains the same, then after only 50 years MOSE would be too short by about
15 + 30 = 45 – 40 = 5 cm.

An engineering thing that bothers me is whether the subsidence would be uniform. If not, would diffferential subsidence beneath MOSE itself distort the MOSE system, possibly affecting its raising mechanism and/or its being a good water-tight dam.

Tony Smith

12. dorigo - December 2, 2008

Hi Tony,

the piece was accurate in some of the points, not in others. It is true that subsidence was caused by ground water pumping, but that process was stopped thirty years ago (I might be mistaken though). My father wrote a full book on this issue, “Una legge contro Venezia” (A law against Venice) in the early seventies.

I believe that the MOSE will not be able to withstand high tides of 2 meters. I think it will stop high tides of +120:+140 cm, and only alleviate the stronger ones.

In any case, there is no choice, because the rise in sea water levels is a fact.


13. dorigo - December 2, 2008

About differential subsidence: this cannot be an effect on the range of a few hundred meters, which is the clearance of the sea entrances.


14. Ian - December 4, 2008

Hello Dorigo, can you tell me what the conditions are like at the moment in the city?

I can see the San Marco webcam, and in it the water seems to have cleared, is that correct? I read on some websites that the water can clear quickly, but it looks to be all gone from that webcam.

I can understand the dislike of tourists by the local population living in any place that is so popular. Hate is a strong word to use though. Living and housing costs inevitably rise, and some local people can longer afford to live there. A side effect of a more mobile population, though I think a place like Venice has always been popular, though not in the numbers visiting now.

With regards to McDonalds, I was quite surprised to see so many in Rome recently. It was my 1st visit to Italy, and I’d read/and seen shows on TV, that Italians liked there own food, and maybe even mostly the style of food from their own region. Maybe that was a blinkered view though.

15. dorigo - December 4, 2008

The current tide conditions can be obtained from the site linked above, http://www.comune.venezia.it/maree

Water rises and goes in the matter of few hours. 80 hours have passed, so it’s no surprise…

McDonalds live because of tourists at least as much as they do with italian citizens. You don’t find them where there is no tourism in Italy…


16. Martin Gutowski - December 5, 2008

Venice under water still

17. Fred - December 5, 2008

I fell upon these photos while reading an unrelated article at this site:



Are these photos typical of the city when the tides rise too high?

18. Exceptional acqua alta foreseen in Venice again « A Quantum Diaries Survivor - December 10, 2008

[…] Exceptional acqua alta foreseen in Venice again December 10, 2008 Posted by dorigo in astronomy, news, science. Tags: acqua alta, venice, weather, weather forecasts trackback Nine days ago Venice withstood the assault of an exceptional surge of sea water, the fourth highest in recent history. Water reached the level of +1.56 meters above average sea level at 11.15AM, flooding most of Venice’s streets with two feet of water. I reported about the event in real time here. […]

19. RNDr. Pavel Smutny - December 14, 2008

There was conjunction of new Moon, Jupiter, Venus,..Sun was close too,… during acqua alta in Venice. I live in central Europe-Slovakia and there is usually problem to see such conjunction. Why? There is typically rainy weather, when there is new moon and when there is conjunction with Venus and Jupiter, so it is even worse. But it has scientific reason. There are spring tides and those are even stronger,higher in such time, because gravitational force from Venus and from Jupiter is added to gravitational tidal force of Moon and of Sun. Spring tides, sucked underearth water-stronger evaporation, flooded rivers, cummulation of clouds,..There are also more stronger earthquakes, vulcanoes explosion, stronger hurricanes in such time. For example not far from us is Venetia and that area is again quite often extremly flooded during last time, but also there are more closures of Thames barrier -against spring tidal surges,…similar it is on Java-in Jackarta. Earth axis is oriented direction Orion,…in circa these some thousends years (due to precession motion) and so those tidal effects are strongest in november and especially in december, but also in jun,…It is probable that during last december week there would be stronger earthquakes, floods, tsunami, how it was on 26th, december 2004.
Venezia bee aware during last week of this december -2008.

dorigo - December 14, 2008

Pavel, please understand that posting more than one, or maybe a couple, of comments in a row can be considered spamming.

In any case, the gravitational effect of Venus and Jupiter is ridiculously small, not even worth mentioning.


dorigo - December 14, 2008

To be clear, the gravitational pull of your body at one meter from the water is roughly same as that of jupiter. Is that clear enough ?


20. RNDr. Pavel Smutny - December 14, 2008

These days, of new Moon,..there is also danger of acqua alta because Moon is circa in place where planet X is arriving to perihelia,..from places above constellation Orion,…

21. RNDr. Pavel Smutny - December 14, 2008

mistake there was, not new, but full moon in last 20. amendment.

22. RNDr. Pavel Smutny - December 14, 2008

dorigo, you are not right. For example gravitation pull of Venus during transit, or down conjunction is till one thirth of that of Moon, because at Moon, or at Sun there is only gravit. tidal influence what is proportional d/(L.L.L), where d is diameter of Earth and L is distance of Earth to Moon,…or to other body, but at Venus, Jupiter,,,, its proportional to d/LL, because Venus is not circling around Earth or vice versa,…grav. tidal force of Moon is circa only 1/60 of Moons gravity on Earth. That fact about tides enforces by Venus was prooved also by chineese scientiests on Chinas lakes,…many years long research,….

dorigo - December 14, 2008

No, it is you who is not right. One, I discussed Jupiter, and you counter with Venus. Second, you discuss December 1st and on December 1st Venus was very far from conjunction.


23. Brian - December 15, 2008

I will sail from Corfu tomorrow morning and arrive in Venice about 8am Wednesday.
I will need to go from the port to Treviso Airport.
Is this going to be possible?

Thanks if you may help.

24. dorigo - December 15, 2008

Hi Brian,

if you arrive at the Venice passenger port, you will find transportation to Piazzale Roma, from which you can take an ATVO bus to Treviso-Istrana airport. Not a problem. Try visiting http://www.atvo.it .


25. beyondthebridge - December 16, 2008

Le ultime parole famose…
mio cugino ha appena comperato un piano terra (ralzato) :-).

26. RNDr. Pavel Smutny - December 17, 2008

Influence of Jupiter on tides (on Earth) is circa 1/3 of that of Venus,..because Jupiter can be partly considered for body circling around Earth, because Earth is quite close to Sun, when compared with Jupiter’s distance from Sun,…During conjunctions, or when celestial bodies are circa,+-10,…degrees in line so, to tidal force of Moon and of Sun (approx. 1/2 of tidal force of Moon), we can add gravit. force of Venus (less than 1/2 of Moon), what espec. at transits, inferior conjunctions when Venus is from us only 40million km. Jupiters gravity makes approx. till 15percent of Moons tidal force,…

dorigo - December 19, 2008

Hi Pavel,

Ok, you convinced me that if one wants to be really accurate, one might consider taking the effect of planets into account in the astronomical tide. However, when it comes to Venetian floods, the effects of barometric pressure, wind over the Adriatic sea basin, and coherent oscillations of the Adriatic waters, plus local effects such as rain, all have a much, much stronger effect.


27. RNDr. Pavel Smutny - December 20, 2008

Hi dorigo,…yes, influence of barometric pressure, wind of Adrtiatic sea basin, coherent oscillations of barometric pressure,…plus local effects are powerfull, but those effects are secondary effect mainly due to primary stronger tidal effects. I think that due to stronger tidal forces evaporation is much intensive mainly on continents. Underground water level is due to stronger tidal forces 30cm and more higher and so trees,…all plants can suck more water, can more evaporate,…
Higher underground water presses also rivers, brooks, lakes to have much higher level to flood surrounding countryside. I have devoted time to scope those phenomena in Slovakia, …and it is typical that intensive rains, snowfalls are usually in days during and after New, Full Moon,..

28. Luboš Motl - December 20, 2008

Too bad I missed the event – it could have been fun. Was it warm and sunny enough for tourists?

I am kind of amazed by the “sensitive” people. The fact that similar things do occur in Venice is one of the main reasons why the city is so attractive and special. It’s both about tourism as well as the very feeling of being special. If a local citizen is really unhappy about these events, maybe she should move out of the city.

Being constantly “sensitive” about a regular event that is a part of laws of Nature – and a part of someone’s environment – is just utterly ludicrous.

Dr Paul Sad of Slovakia is generating a lot of nonsense here, too. Tidal forces (or accelerations) go like mass (of the other celestial body) divided by distance cubed. The minimum Earth-Venus distance is 40 million kilometers, or 100 times the distance from our Moon. When you cube it, you get a factor of million. So even though Venus is about 60 times heavier than the Moon, the ratio is 60/1,000,000 or close to 1/10,000 – Venus is negligible.

Similarly Jupiter is about 800 million km from us, which is 2,000 times the distance from the Moon. Take the third power to obtain 8 billion. So even the ratio of Jupiter/Moon masses, around 30,000 in favor of the Jupiter, won’t be able to make things better: Jupiter’s tidal forces are about 1/30,000 of the Moon’s ones – or 1/3 of the Venus’ tidal forces. All these things are unmeasurable in practice.

It’s not shocking to agree with the local Tommaso here. Except that he thinks that he has discovered a dragon created at gigantic 200 picobars, for no good reasons, he surely has many things to teach Dr Paul Sad of Slovakia, despite the RNDr degree of the latter. 🙂

29. RNDr. Pavel Smutny - December 21, 2008

Motl, you are absolutely wrong. Earth is circling around Sun, Moon is circling around Earth so gravitational force is compensated by centrifugal force!!! There is only circa 1/60 of gravity of Moon what is causing tidal effects on Earth. But Venus is not circling around Earth or vice versa !!! There is whole gravity working, or much biger than at MOON. Jupiter is little other case, because Earth is much closer to Sun than Jupiter and so only circa 1/3 of gravity in compare with Venus case is working. Motl go back to school,….!!!

30. RNDr. Pavel Smutny - December 21, 2008

Venus (during inferior conjunction) is 40mil. km from us, Moon is about 400000km from us, so gravity of Moon is 100×100=100000 stronger, when we compare bodies with the same mass. but Venus is 80x heavier than Moon and tidal force of Moon is only 1/60 of its gravity. so how much is 100000: (80×60)=2,1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

31. Luboš Motl - December 21, 2008

Dear Mr Smutný, I am not convinced that because of certain limitations, an additional explanation will be useful for you but it might be useful for children from kindergartens who read Tommaso’s blog.

The overall gravitational force and acceleration from the Moon – going like “mass over distance squared” – is indeed “compensated”. But the same thing holds for the force from Venus or Jupiter. It is “compensated”, too. It is completely irrelevant whether a body orbits around another body.

In fact, the Earth doesn’t follow an orbit around exact ellipses around the Sun. It follows a trajectory given by the forces from all celestial bodies including the Sun, the Moon, Jupiter, and Venus. All of them contribute, just with different coefficients.

While the overall force, “othermass / distance squared”, has no observable effect on Earth, because it is “compensated” by the centrifugal force of a freely falling Earth (for all celestial sources of the force), the gradient of the force, i.e. the tidal force, is not compensated.

This gradient goes like “othermass / distance cubed”, as one can figure out by differentiating the force with respect to the radius. And this gradient from any celestial body, like Jupiter, Venus, but also more importantly, the Moon and the Sun, matters and remains “uncancelled”. See


The Moon and the Sun are the most important sources of these tidal forces on Earth. The Moon matters because it is very close and the Sun matters because it is very heavy. But it turns out that the Moon is the absolute winner among the sources of the tidal forces. Jupiter and Venus are by factors of 30,000 or 10,000 suppressed relatively to the Moon, respectively. If there is a 30% error in these numbers, it is deliberate because this is an order of magnitude estimate meant to prove that Jupiter’s and Venus’ effect on the tides on Earth are unnoticeable.

You have heard the holy word and please ask the schools to remove the RNDr (and also your high school diploma) from you so that Slovakia doesn’t look like a third-world country. I kindly ask Tommaso Dorigo to confirm my words again, close this ludicrous discussion, and moderate further silly comments about this topic away.

32. RNDr. Pavel Smutny - December 21, 2008

Motl, it was long amendment but only inline with mainstream dogmas. Expres yourself on board of ISS or of Discovery,…on orbit arround Earth. What part of Earths gravity is over there? You are flying inside of space capsule, because gravity is compensated by centripetal (centrifugal) force. There is, tidal force of moon on Earth is only fraction, circa 1/60 of gravity force commonly proportional 1/(L.L). That fraction is proportional d/(L.L.L) , where d is Earths diameter, and L is distance of Moon to Earth.
Express yourself but on cosmic capsule what suddenly stopped in its orbit aroun Earth. You fall to Earth with full gravitational acceleration.
Tidal force from Moon has two maximas and two minimas per 24 hours within circa 25 hours. So that 1/60 of gravity of Moon changes direction 90 degrees 4x per 25 hours.
Gravity of Venus also changes because Earth rotation arround its axis 4x per day, but it is full gravity, not only tidal part!!!!!!!!! Express yourself so you look at Venus during transit. it is 12hours/midday,…so you are falling with Earth toward Venus with small acceleration proportional full gravity of Venus on Earth. After 6 hours you but have gravity of Venus in angle 90 degrees toward state before 6hours. After next 6 hours gravity of Venus is working from opposite direction on you-compare with state before 12hours. In this case whole gravity from venus is changing direction!!!!
It is not only 1/60 of gravity, how it is in case in system Moon/Earth or 1/200000 in system Earth/Sun!!!!!!

33. Luboš Motl - December 22, 2008

Dear crackpot Smutný, the equivalence principle guarantees that a freely falling Earth feels no overall gravitational field, and this is true for the gravitational fields created by the Sun, the Moon, but also Venus, Jupiter, or anything else. Only the tidal forces, i.e. the gradients of the acceleration, have a measurable effect on the oceans, and Venus and Jupiter are 10,000-30,000 times less important than the Moon.

dorigo - December 22, 2008

Motl, Smutny, sorry if I do not contribute to your discussion. I think scientific truth does not need more than one or two iterations in a comments thread. If it grows longer, it is not science anymore.


34. Mary Johnson - December 22, 2008

I find it very sad that you hate tourists. My sister and I have been to Venice in December two years running (the year before I went with my boyfriend and the year before that with my cousin – also in December).

We love your city and consider it an honour and pleasure to visit. While we’re there we do our best not to get under the Venetians’ feet while we’re enjoying our holiday.

This year my sister and I were there from 12-15 December. The acqua alta sirens sounded at 07.10 every morning and the main square and surrounding areas were flooded every day – Monday 15 December it was also raining all day and the floods were the highest since we’d been there.

Whilst we did find this “exciting” because it threw a whole different light on the city, we felt nothing but sympathy for the residents and businesses which were affected by their premises being inundated with dirty water day after day (and indeed year after year). What made us particularly sad was when we went into the Duomo on Monday morning, to find the whole of the entrance area under around a foot of water.

We’re very sorry that tourists can be a nuisance but please don’t tar us all with the same brush.

35. dorigo - December 22, 2008

Mary, I do not hate tourists, ok ? I hate what tourism is doing to Venice.


36. Luboš Motl - December 23, 2008

Well, your countrymate and the founder of the field you mention, science, namely Galileo Galilei, needed about 587 iterations and most of your typical, more zealous countrymates didn’t get it, anyway.

I am afraid that whether something is science or not – or correct science or not – has nothing to do with the number of iterations. 😉

37. Mihaela - December 29, 2008

I will go to Venice on december 30th, that means tomorrow, and I want to know if there is any danger of “acqua alta” durong this period. I don`t know where to search for up-date information, as the site of comune.venetia has some connection problems.

dorigo - December 29, 2008

hi Mihaela,

the site seems ok to me, only it is venezia, not venetia. Anyway there is no “danger”, and the event of last December 1st was really exceptional, while not being threatening to tourists in any way. Only some damage to businesses and ground floors.

The graph of water level for tomorrow is here: http://www.comune.venezia.it/flex/cm/pages/ServeBLOB.php/L/IT/IDPagina/1748

As you see, no peak above 60-70 cm, which is way below the ground level.

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