Noah was sent to his people: the people of Nineveh (near Mosil city in Iraq.)

In that region, his city might be near Nineveh; now there is a small city called Ain Siphney, which means the "water fountain and the ship."

So like the rest of apostles of God: when their people deny and insist on the disbelief --> then God Almighty will destroy them in many ways: like the hurricanes, the earthquake, the plagues or epidemics ..etc.

Therefore, when his people denied Noah and refused to accept his mission of the exclusive devotion to God alone and to abandon their idols --> then God destroyed them by the deluge or flood which involved their region: Mesopotamia ( or Iraq).

So the flood of Noah was restricted to Iraq, not to the entire world.
There are many indictions in the Quran which confirm this notion: that the deluge or flood of Noah was restricted to Iraq (or Mesopotamia as was it called in the ancient times: i.e. the land between the two rivers: Tigris and Euphrates.