VENICE — On Wednesday night, Venice suffered the worst flooding in half a century. Most of the time, “acqua alta” comes across as local folklore: the piazza filled with water, the gleefully splashing kids and the amused tourists. You put on your rubber boots and go about your life. But recently there have been more and more soaring floods. At dinnertime, we received the text messages and heard the sirens with the four distinct tones announcing the highest-possible water levels.

And then the sirens sounded again — the last tone eerily prolonged — and we knew that something terrible was about to happen. Two violent winds — the warm southern sirocco and the cold northern bora — started howling together, and with the full moon, the rising tide and the torrential rain, the perfect storm was engulfing Venice.

The sirens start when the water rises to 110 centimeters (3 feet 6 inches) above sea level. Up to 140 centimeters (4 feet 5 inches) is considered manageable; shopkeepers know they have to elevate their merchandise and electrical appliances.

Our social media was bursting with alarming reports: Water had risen to a calamitous 160 centimeters (5 feet 2 inches) above sea level. Then it rose to 170 centimeters (5 feet 5 inches) and then to 180 centimeters (5 feet 9 inches). Safe on a high second floor, we saw the plants in our inner courtyard floating on water. From our windows, hit hard by the wind, we observed the boundary between street and canal dissolve. Our anxiety was tempered only by the fact that our small son had already fallen asleep.