Acqua alta is an exceptional tide peak that occurs periodically in the northern Adriatic Sea. The term is used specifically in the Italian region of Veneto, where the peaks reach their maximum in the Venetian Lagoon, causing partial flooding of Venice and Chioggia. The first documented description of acqua alta in Venice dates back to 782, with other events recorded in 840, 885, and 1102. In 1110, a violent sea storm completely destroyed Metamauco, Venice’s political center at the time.
The phenomenon occurs when certain conditions coincide, such as a very high tide during a full or new moon, low atmospheric pressure, and a scirocco wind blowing up the narrow Adriatic Sea. Acqua alta is characterized as a tide exceeding 80 to 110 centimeters above zero on the Punta della Salute scale. When the tide exceeds 110 centimeters, only 12% of the city is flooded. An exceptional tide is when the water level measures over 140 centimeters.
Acqua alta mainly occurs between autumn and spring when astronomical tides are reinforced by seasonal winds that hamper the usual reflux. The main winds involved are the sirocco, which blows northbound along the Adriatic Sea, and the bora, which has a specific local effect due to the shape and location of the Venetian Lagoon.
The last major acqua alta occurred on November 13, 2019, when strong winds and rainstorms pushed water levels in Venice to the second-highest levels ever recorded at 74 inches (187 centimeters). The worst acqua alta occurred on November 4, 1966, when the sea level rose to a record height of 76.4 inches (194 cm), earning it the nickname “acqua granda.” This historic event caused significant damage to Venetian buildings and left many people homeless.