Dr. Jeff Masters' WunderBlog

Venice suffers its fourth-worst flood since 1872

Posted by: Dr. Jeff Masters, 07:59 PM GMT am 03. Dezämber 2008

Venice, Italy, suffered ocean flooding 1.56 meters (5.1 feet) above mean sea level on Monday, December 1, its fourth-worst flood since modern record keeping began in 1872. The flooding was triggered by a strong low pressure system that passed through Europe, dumping rains of 1-2 inches that helped fill the salt-water lagoon surrounding Venice with high levels of river run-off. The counter-clockwise flow of air around the low brought warm, southerly winds up the length of the Adriatic Sea, which piled up high levels of ocean water into the lagoon. Sustained winds reached 30 mph on the morning of December 1 in Venice. High tides submerged the city again yesterday, but only to a depth of 1.02 meters. As the low pulls away from Italy and river run-off gradually subsides, no further flooding of Venice should occur this week.

Figure 1.Flooding in Venice from the December 1, 2008 flood. Image credit: Venice Water Authority.

Sinking land, rising seas
When Venice was founded sixteen hundred years ago, sea level was about six feet lower than today. Sea level has risen over the centuries as a natural response to our continued emergence from the last Ice Age, thanks to melting of glaciers and ice caps. Global sea level rose eight inches during the 20th century (2 mm/year). The sea level rose by only about 4-5 inches in the Adriatic Sea near Venice during that time, though. However, the rate of global sea level rise has increased by 50% to 3 mm/year in recent decades and was 5 mm/year near Venice during the period 1993-2008. As the seas have risen, Venice has sunk. Since 1897, natural compression of the sediments Venice sit on has resulted in the city sinking about 1.5 inches. Additional sinking of three inches due to pumping of fresh water from an aquifer beneath the lagoon between the 1920s and early 1970s has left the city 4.5 inches lower than at the beginning of the century. In 1900, famed St. Marks Square flooded at high tide six times per year, on average. By 1999, that number had increased to 99 times per year, thanks to the combined effects of higher sea levels and the sinking of the city.

Figure 2. Satellite image of Venice. The city is on an island in a lagoon that opens to the ocean in three places. Image credit: NASA Earth Observatory.

Jetties
Jetties built at the three entrances to Venice's lagoon help to hold back the sea, but have also acted as barriers to the natural inflow of fresh sand to replenish beaches within the lagoon. This sand now accumulates along the jetties. The jetties also act as barriers that disrupt ocean currents and contribute to coastal erosion.

Barrier island erosion
Venice's lagoon is protected by a number of barrier islands. These islands are steadily eroding, due to construction projects, summer beach crowds, and beach-going vehicles. Sea walls were built along many of these barrier islands in the 14th century, but high tides now regularly overtop these sea walls.

Salt marsh erosion
Additional flooding in Venice occurs because the protective salt marshes in the lagoon surrounding the city are steadily eroding. This is largely due to the fact that 600 years ago Venice diverted the courses of the four major rivers that flowed into the lagoon, forcing them to empty into the ocean directly. This was done so that sediments would not build up and allow attackers to approach the city via land. Without new sediments to replenish them, the marshes in the lagoon have been steadily eroding away. Water pollution has also contributed to erosion problems. The pollution kills eelgrass, the chief building block of the salt marshes.

Protecting Venice
The "official" word on climate, the 2007 report of the U.N.'s Intergovernmental Panel on Climate Change (IPCC), predicts a 0.6 - 1.9 foot sea level rise by 2100. However, they cautioned in their report that due to the lack of knowledge about how melting glaciers behave, the actual sea level rise might be higher. A paper published by Pfeffer et al. in Science this September concluded that when considering these unknown glacier melting processes, the "most likely" range of sea level rise by 2100 is 2.6 - 6.6 feet (0.8 - 2.0 meters). These sea level rise possibilities make it imperative that Venice construct barriers to keep the sea out. In 2003, construction began on the MOSE Project, a $5.5 billion system of inflatable gates that will rise up out of the ocean bed to block incoming storm surges from the Adriatic Sea during storm situations. The barriers will block all three entrances to Venice's lagoon, but allow ship traffic to pass through using a lock system. The gates are scheduled to be completed in 2012. In theory, the gates will protect Venice up to a maximum sea level rise of two meters (6.6 feet), which should be adequate for the remainder of the century. However, some scientists have argued that the gates will only protect Venice up to a sea level rise of one foot, and will allow high levels of toxic pollution to build up in the lagoon without the cleansing action of the tides to disperse the pollutants. A 2005 paper warned that if sea level rises 0.5 meters (1.6 feet), the gates would still allow considerable flooding of Venice, and block or delay 2/3 of all shipping traffic trying to pass through the gates.

Figure 3. Schematic drawing of the MOSE gate in the inflated (closed) position. Normally, the gate lies flat on the ocean bottom. When a storm surge threatens, the hollow top of the gate will be filled with air, and the hinged gate will rise to the surface, blocking any incoming storm surges. Image credit: Venice Water Authority.

Resources
The Venice Water Authority has complete info on the MOSE construction project.
NOVA aired a 1-hour show in 2002 on the sinking of Venice, and has some nice interactive web features to look at.

Jeff Masters

St Marks Cathedral Venice (ARG)

St Marks Cathedral Venice

sunrise Venice (donjuan)

Grand Canal elegence

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201. Orcasystems 01:12 PM GMT am 05. Dezämber 2008
Cancun, where I will be on Tuesday :) 60 °F Partly cloudy * Feels Like: - * Wind: NW 4m/h * Relative Humidity: 94% * Pressure: 1,019.10 mb * Visibility: 6.8 miles * Ceiling: 30000 ft Complete Blog Refresh Mirror Site Member Since: Oktober 1, 2007 Posts: 77 Comments: 26110

202. Orcasystems 01:13 PM GMT am 05. Dezämber 2008
Quoting MissNadia: Good Morning all from Coastal N.C. 50F Calm wind cloudy skies with good vis. NO ORCAS HERE...yet! Everyone should have ORCA's. we make great pets, and we can be house trained :) Member Since: Oktober 1, 2007 Posts: 77 Comments: 26110

203. zoomiami 01:42 PM GMT am 05. Dezämber 2008
Quoting Orcasystems: Everyone should have ORCA's. we make great pets, and we can be house trained :) Hmm - about the house trained part, would have to have your significant other weigh in on that one. Member Since: August 13, 2007 Posts: 10 Comments: 4071

205. Orcasystems 01:55 PM GMT am 05. Dezämber 2008
Quoting zoomiami: Hmm - about the house trained part, would have to have your significant other weigh in on that one. No way.. she fibs :) Member Since: Oktober 1, 2007 Posts: 77 Comments: 26110

206. sporteguy03 02:18 PM GMT am 05. Dezämber 2008
Dr.Masters, Thank you for that tragic update, I hope you have a great day! Member Since: Juli 7, 2005 Posts: 0 Comments: 4840

208. Orcasystems 03:02 PM GMT am 05. Dezämber 2008
Latest message from surfmom, comment 333 in my blog. Keep the prayers and good thoughts flowing :) Member Since: Oktober 1, 2007 Posts: 77 Comments: 26110

209. zoomiami 03:19 PM GMT am 05. Dezämber 2008
Quoting Orcasystems: No way.. she fibs :) lol Member Since: August 13, 2007 Posts: 10 Comments: 4071

210. TampaSpin 03:58 PM GMT am 05. Dezämber 2008
Quoting 15hurricanes: 1851 to 1994 Atlantic hurricane seasons! "WE JUST CAME OUT OF AN INACTIVE PERIOD (that ended in the mid-1990's)." he said. Why aren't you in school....Isn't grade school in session today......ROFLMAO Member Since: Septämber 2, 2007 Posts: 176 Comments: 19767

211. TampaSpin 04:40 PM GMT am 05. Dezämber 2008
The Jobless claims was almost Double what was expected in November.....get ready for a rough ride on Wall Street....no bottom yet! Member Since: Septämber 2, 2007 Posts: 176 Comments: 19767

212. TampaSpin 04:41 PM GMT am 05. Dezämber 2008
Everyone have a good day......IM out till late evening. Member Since: Septämber 2, 2007 Posts: 176 Comments: 19767

213. TampaSpin 04:45 PM GMT am 05. Dezämber 2008
One thing of note! The storm that is predicted next week seems to be looking stronger on models on the last runs......Go to my blog to look at the models....Next week looks like a major extreme weather week with a very strong NorEaster developing and severe weather in the South. Member Since: Septämber 2, 2007 Posts: 176 Comments: 19767

214. BtnTx 05:33 PM GMT am 05. Dezämber 2008
"The price of Brent crude oil slumped to 39.77 dollars a barrel in trading here on Friday -- the lowest point in almost four years -- on prospects of a severe drop in energy demand, traders said. " From Breitbart.com. I am not sure whether this is good or bad news. Maybe it is not news at all... Member Since: Oktober 12, 2001 Posts: 20 Comments: 876

215. futuremet 05:45 PM GMT am 05. Dezämber 2008
Back from School It looks like tropical cyclone seven in the Indian Ocean remain relatively the same. Some strengthening is possible tomorrow, as shear decreases. I JUST HOPE THE GFS MODEL IS WRONG ABOUT THIS FORECAST. It Has been forecasting a tropical cyclone to hit Bangladesh for the past 48 hours now. GFS MODEL SELECT THE FOLLOWING Level: 925 MB and MSL Domain: Southern Asia Member Since: Juli 19, 2008 Posts: 43 Comments: 4049

216. WxLogic 05:49 PM GMT am 05. Dezämber 2008
Good afternoon... Member Since: August 14, 2008 Posts: 4 Comments: 4720

217. Hurricane4Lex 06:14 PM GMT am 05. Dezämber 2008
Here's an article (link) to read concerning Our (US) economy not good at all Link Member Since: August 14, 2008 Posts: 0 Comments: 657

218. Bonedog 06:55 PM GMT am 05. Dezämber 2008
hey folks Member Since: Juli 14, 2005 Posts: 14 Comments: 7418

219. Bonedog 07:14 PM GMT am 05. Dezämber 2008
MORE IMPORTANTLY...STRONG WINDS USHERING IN ARCTIC AIRMASS IN WAKE OF LOW PRESSURE EXPECTED LATE SUN/SUN NIGHT. POSSIBLE WIND ADVISORY WINDS (25 TO 35 MPH WITH GUSTS INTO THE MID 40S MPH) LATE SUNDAY/SUN NIGHT WITH A TIGHT GRADIENT...STRONG CAA AND STRONG PRESSURE RISES BETWEEN BOMBING LOW OVER GEORGES BANK AND HIGH PRESSURE BUILDING EAST FROM OHIO VALLEY. TEMPS WILL LIKELY FALL INTO TEENS/LOWER 20S AREAWIDE...WITH WIND CHILLS IN SINGLE DIGITS CITY/COAST AND SINGLE DIGITS BELOW ZERO INTERIOR. going to be a cold weekend folks!! Member Since: Juli 14, 2005 Posts: 14 Comments: 7418

220. NEwxguy 07:21 PM GMT am 05. Dezämber 2008
Hey,Bone,looks like the Tuesday storm is going to be mostly wet for us,but a late week storm may be different Member Since: Septämber 6, 2007 Posts: 820 Comments: 13275

221. Bonedog 07:27 PM GMT am 05. Dezämber 2008
NE I noticed that. The tuesday storm on these runs seems to be a ridge runner the late week system has the biggest potential right now. I am still keeping my eye on the tuesday system for my area if it runs more offshore then the models (which just happened today actually) show then its a winter wonderland here. By you though would maybe see a changeover late at night to snow but mostly a rain event for you. The late week storm has the distict possiblity of being the biggie for the I-95 though. Still wishcasting for the tuesday one though =) LET IT SNOW LET IT SNOW LET IT SNOW Member Since: Juli 14, 2005 Posts: 14 Comments: 7418

222. NEwxguy 07:56 PM GMT am 05. Dezämber 2008
Quoting Bonedog: NE I noticed that. The tuesday storm on these runs seems to be a ridge runner the late week system has the biggest potential right now. I am still keeping my eye on the tuesday system for my area if it runs more offshore then the models (which just happened today actually) show then its a winter wonderland here. By you though would maybe see a changeover late at night to snow but mostly a rain event for you. The late week storm has the distict possiblity of being the biggie for the I-95 though. Still wishcasting for the tuesday one though =) LET IT SNOW LET IT SNOW LET IT SNOW LOL,neighbors must be getting tired of seeing you out there doing your snow dance,but in a very active pattern,so one of these is going to hit us,talking maybe upper 50's at some point for us Tuesday. Member Since: Septämber 6, 2007 Posts: 820 Comments: 13275

223. pottery 08:17 PM GMT am 05. Dezämber 2008
Good afternoon. Temp 79F Wind, Calm. It is raining. Nice, gentle, constant rain. AAAAAAHHHHHHHHH!!! Member Since: Oktober 24, 2005 Posts: 0 Comments: 20866

224. DDR 08:22 PM GMT am 05. Dezämber 2008
Quoting pottery: Good afternoon. Temp 79F Wind, Calm. It is raining. Nice, gentle, constant rain. AAAAAAHHHHHHHHH!!! typical december rains my friend. Member Since: April 27, 2007 Posts: 13 Comments: 1501

225. pottery 08:25 PM GMT am 05. Dezämber 2008
True, DDR. How are you doing ? Member Since: Oktober 24, 2005 Posts: 0 Comments: 20866

226. Drakoen 08:40 PM GMT am 05. Dezämber 2008
The last two GFS runs look interesting conducting baroclinic cyclogenesis along the tail end of a cold front in the Gulf of Mexico. If the forecast hold true that would be some beneficial rains for the deep south. The ECMWF looks likes this solution but shows the development occurring a little later as some shortwave energy ejects around the base of a longwave trough over the ECONUS. The CMC has a more aggressive solution with the vertically titled low evolving deeply in the mid and upper levels lower the 500mb heights behind the surface low. Will be interesting to see which solution pans out. Member Since: Oktober 28, 2006 Posts: 57 Comments: 29012

229. NEwxguy 09:01 PM GMT am 05. Dezämber 2008
Drak, Either solution,sounds like it spells trouble for the northeast Member Since: Septämber 6, 2007 Posts: 820 Comments: 13275

230. HadesGodWyvern 09:09 PM GMT am 05. Dezämber 2008
Subject: Deep depression over southeast Bay of Bengal At 23:30 PM IST, The Deep Depression over southeast Bay of Bengal moved westwards and lay centered near 8.5N 87.0E, about 900 km southeast of Chennai, India, 800 km east-southeast of Nagapattinam, India, and 600 km east of Trincomalee, Sri Lanka. The system is likely to intensify further and move in a west-northwesterly direction towards Tamil Nadu & Puducherry coasts skirting north Sri Lanka coast during next 72 hours. Based on the latest analysis with Numerical Weather Prediction (NWP) models and other conventional techniques, the estimated future track and intensity of the system are given in the Table below: Current (23:30 PM IST) 8.5N 87.0E - 30 knots 24 HRS: 9.5N 84.0E - 35 knots 48 HRS: 10.0N 81.0E - 35 knots 72 HRS: 10.5N 78.0E - 25 knots Member Since: Mai 24, 2006 Posts: 43 Comments: 36925

232. Drakoen 09:14 PM GMT am 05. Dezämber 2008
Quoting NEwxguy: Drak, Either solution,sounds like it spells trouble for the northeast The jet stream will steer it up the eastern seaboard as coastal system. It will be a problem on the backside of the low behind the 0C line at the surface and the negatives at 850mb the 540dm looks well inland perhaps not until the low moves up north into the Gulf of Maine will the residual moisture allow snowfall closer to the coast. The prospects look good for the inland areas as for a snowfall is concerned the ECMWF has a more degenerative process with the low moving out farther east, the CMC and GFS looks to have more aggressive solutions with the development of the frontogenesis and cyclogenesis when the low tracks up the eastern seaboard. Member Since: Oktober 28, 2006 Posts: 57 Comments: 29012

233. IKE 09:57 PM GMT am 05. Dezämber 2008
New blog folks...... Member Since: Juni 9, 2005 Posts: 23 Comments: 37070

234. jride 10:14 PM GMT am 05. Dezämber 2008
TO WHOM IT MAY CONCERN: NO TIME TO STAY ON THE BLOG... ALTHOUGH: THANKS TO THOSE OF YOU WHOM HAVE EDUCATED ME OVER THE PAST SEVERAL YEARS. I AM A CATASTROPHE (WIND) ADJUSTER LOOKING FOR INFORMATION ON SURVIVORS OF HURRICANE IKE. IF YOU HAVE ANY INFORMATION, PLEASE SEND AN EMAIL TO JASONCZERWINSKI@YAHOO.COM I AM ATTEMPTING TO CLOSE FILES FOR THOSE CLAIMS DOWN ON THE SHORELINE AND AM MAKING A FINAL ATTEMPT WITH DIFFERENT AVENUES TO COLLECT AS MUCH INFORMATION I CAN TO HELP BOTH INSURED AND TWIA. THANKS. JASON

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