The Greek word used throughout the Greek Bible text to describe the great flood of Noah’s Day is kataklusmos (it’s where we get the English word cataclysm). However, kataklusmos doesn’t mean flood. Kata means down, and klusmos means pour.
So this Bible translation uses Downpour, and not Flood.
Is this just unimportant nit-picking?
Well, a flood is a name given to a disaster, whereas a downpour is an action or method of destruction. When the Bible names the Great Flood the “Downpour,” it chooses to name the event after the destructive method (the falling of the rain) – not what resulted from it (the flood).
This distinction may be important. Imagine there is a speeding train that crashes. We choose to call it The Great Train Crash, but God decides to call the event The Speeding Train. Why would we reject God’s chosen name (that emphasizes the cause of the crash), in favor of our own name (that emphasizes the crash itself)?
Of course, it may not really matter; but we’re being cautious and assuming that it may be important, and therefore we translate the name as accurately as possible.