How does the comparison to Noah's flood show that the coming judgment is worldwide?
The comparison rests on Noah's flood being universal, not local. Jesus said the days before His coming would mirror Noah's day, so the same worldwide scope applies to end-time judgment. Though centered on Jerusalem and the Middle East, the whole planet comes under it.
Les explains that the end-time judgments are primarily the time of God dealing with Israel, but they are not confined to that region. Because Noah's flood was universal, and Jesus likened His coming to the days of Noah, the same worldwide application follows: even though He comes to the Middle East and Jerusalem, the whole planet will come under the judgment. The context also describes Him smiting the nations and ruling with a rod of iron, meaning absolute, righteous rule.