Because nobody expected such a high tide in Venice


venice marea record causes

Marco Bertorello / AFP

High water in Venice, 13 November 2019

"Nobody expected it. When the municipality decided to set the tide forecast at 145 cents yesterday at noon we were all convinced that it was a precautionary measure and that it would not even reach that altitude, but instead it reached 187 centimeters, so it was absolutely not predictable ". He explained it to the Agi Georg Umgiesser, researcher at the Institute of marine sciences of the National Research Council (Cnr-Ismar) which follows the tide in the Venice lagoon.

Just yesterday he had argued that the expected tide could be lower than the one announced. "The persistence of a very strong flow of winds from the north, of Bora, had led us to think that this constituted a factor of attenuation of the tide, a real block that clashed with the sirocco winds. But this created a a very complicated situation in the Northern Adriatic, a situation that has produced this exceptional and unpredictable event, even by the Centro Maree itself which has been forecasting for 40 years ", the researcher reiterated.

Yesterday was indeed quite complicated in terms of meteorological evolution. The presence of a minimum of pressure to the south of Sicily in the ascent towards the coasts of the Tyrrhenian triggered dynamics on a national scale that had repercussions from Gela to Venice, just as last year occurred during the storm Vaia, which discharged its energy in the Dolomites. The theme is therefore that of the reliability of forecasts in front of events that seem to be quite exceptional.

"The forecasts – added Umgiesser – all have an uncertainty and the more unstable the situation of meteorology the greater the uncertainty becomes. If we have a relatively stable weather situation we are also able to predict a tide with a fork of 5 centimeters of error, so quite accurately. When instead – he continued – we are faced with a meteorological instability the uncertainty is amplified. For example, the gusts of sirocco at 100 kilometers per hour did not foresee anyone, even if you looked at the models better, like those of the European Center for Forecasts (European Center for Medium-Range Weather Forecasts, ECMWF) .The same happened a year ago at the Vaia storm with 230 km hour gusts which was also something absolutely unpredictable Unfortunately – he said – we must increasingly expect these situations because these extreme events will become more and more frequent i and will also become increasingly unpredictable ".

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