For my thesis, I model flash floods in urban areas. A book with recommended practices says to use events with a recurrence interval of 30 and 50 years. Regarding the duration of the precipitation event, it says to use a "relevant duration".
Now I'm wondering what "relevant" means, and can't find information so far. What rainfall duration should be used in urban areas, and why? In papers many use 1h events, but there is no explanation for the chosen duration. Sometimes I read 15min, sometimes 6h.
Perhaps someone can give me ideas in what situations what rainfall duration is "relevant".