La spada di damocle della piena impossibile

Extremely large floods are often considered virtually ‘impossible’ because they exceed our expectation based on historical experience. However, in reality, events often occur that are a priori considered impossible, causing enormous damage also as a result of their supposed improbability. Four reasons for the low importance attached to these floods are analysed here, including physical (e.g. climate change), psychological, socioeconomic and combined reasons. It is argued that the risk of an ‘impossible’ flood may be greater than one thinks, and potential solutions are proposed.