The Noahic flood covered the entire world. Anyone who rejects this has rejected the history which the Bible plainly presents. The Bible presents a global flood, not a local flood. If the flood was local, how could the water have risen 15 cubits above the highest local mountains?
The only way in which water can ever rise above the highest peak of an entire mountain range is if the water reaches the same height on both sides of the range. How then could the flood have been local? How could a flood which reaches a water level equal to the highest peak of the highest mountain range in the area be only local in its impact?
To even attempt to argue that the mountains referred to in Genesis 7:19-20 are merely mountains located in Noah's local area is absurd. Indeed, such an interpretation goes against the very reason for which the flood was sent. The flood was not merely a natural disaster; it was not a random act of nature. Rather, the flood was a planned act of God. It was the judgment of God poured out upon wicked men.
The clear emphasis of Genesis has been that God, because of man's wickedness, would blot out all men— that everything with the breath of life would be destroyed. And so, as the last mountain plunged into the depths of that watery abyss, Noah was certainly aware that God had indeed been faithful to His word— and so He had sent a flood— a destructive global flood which towered above every mountain in the world.
Evidence for a Global Flood: Every Living Thing Dies - Genesis 7:21-22
The Destruction of The City of Enoch (Part 1) - Genesis 7:17-18
The Pre-Flood World Soon To Be Blotted Out - Genesis 6:7
State Of The World (2469 BC): 120 Years Before The Flood - Genesis 6:3
State of the World (2349 BC): The Flood - Genesis 7:11