The storm surge, recent rain and high tide all combined to make the flooding more severe but the trend of flooding has increased in frequency and severity. Half of this caused by sea level rise which has been accelerated by human activity and the other half from Venice sinking which is also partly due to human activity.
See the following article and Figure 2. The frequency of tidal flooding in Venice of at least 110 cm (43.3″)—enough to inundate over 14% of Venice—has ramped up from about once every three years in the early 20th century to about nine times per year in the 2010s.
Here is what the climate change deniers have trouble comprehending: Yes! Venice is built on a series of low laying marshy islands. Yes! Over the centuries there has been damage by high water. Yes! Yes!
But….here’s the Thing: never before has the FREQUENCY of the dangerously high water been this devastating.
Anthropomorphic climate change is about the RATE of change, and about the severity. No thinking intelligent person would claim that Venice has never before had water damage…. but no thinking intelligent person should ever deny the impacts of releasing millions of tons of carbon ( that had been sequestered deep beneath the Earth’s crust for Millenia) back into the biosphere . Greenhouse effect: it’s a Thing.