This article accompanies the fable
Water is the key destructive force in these drawings, cloudbursts and floods rather than fire and lightning. At times the curls resemble Salai's locks of hair... Whether these are the anxieties of an aging Leonardo mixing memory and desire, or a scientific fascination with extreme weather and the forces of nature, or reflections of Italy's constant political upheavals is an open question. All of them perhaps. His journal writings of the time are highly detailed and descriptive, even overly so. He was a better artist. The drawings are in the Windsor Royal Collection.
Or it could have been the Biblical Deluge, except that Leonardo was skeptical of it from his lifelong research into geology and fossils. Michelangelo too would confront the theme in The Last Judgment in the Sistine Chapel more than 20 years later. Surprisingly few other Italian painters tackled the theme.
Below, the final deluge: Château d'Amboise, France. Leonardo's tomb is in the chapel of Saint-Hubert on the right. This is the Château website. Leonardo's house, known now the Château du Clos Lucé, is a short walk from here, outside the castle walls. This is the house website.
Lower photo: Tango7174/Wikipedia.