notified of tsunamis and floods

How are people in dangerous regions notified of tsunamis and floods?

How are people in dangerous regions notified of tsunamis and floods?

Now in the industrial market it has become fashionable to install MASS Notification Systems https://www.atisystems.com/ they have a good sound and quickly work. Even in small settlements, people install such a system. People are warned of tsunami, floods and even about tornado or terrorist attacks.