Question: how is utnapishtim warned of the upcoming flood?
Answer: Enlil, god of the air, decided to send a rainstorm that would flood the earth and destroy the unruly people. ... So that he would not break his promise to Enlil, Ea whispered a warning to the reeds that grew by the banks of the River Euphrates. Then the reeds whispered the secret to Utnapishtim while he slept.