It will be global, but I do not see that in focus in those passages. The
parallel with Sodom particularly suggests that geography is not the focus
here.
Mt. 24:26-31 and Lk. 17:22-24 speak of its universal obviousness, but Mt.
24:32-25:46 and Lk. 17:26-33 focus on "Be ready!". Nothing about the
extent seems to be stated.
If you haven't, I would recommend that you read Glenn Morton's scenario for
the Flood and see how well it meets your objections. The whole land is
destroyed by flooding.
David C.