This is an important question to address as we examine the possibility of a local flood. Why save Noah if others could survive? Why not have Noah leave the area? Why build a boat? Why save the animals? Noah could have just left the region with his family, cattle, and belongings. Doesn't this prove that the flood must have been global?
This is something that is very controversial among Christians in particular. Scientifically, it is generally accepted that there has never been a global flood. Does this mean that there was no global flood? Of course not, it simply means that the existing physical evidence, as interpreted by the majority of scientists, indicates that there has not been one. This is something that could easily change with time. Some new evidence may be discovered which changes everything, but until then Christians will need to be able to defend the idea of a Genesis flood without scientific confirmation.