KASUKABE, Japan — The cavernous underground cisterns here north of Tokyo could hold the Statue of Liberty, a scale that underscores the site’s immense task: protecting the world’s most populous metropolis from flooding.

Linked by tunnels that divert water away from the region’s most vulnerable floodplains, the $2 billion underground anti-flood system, completed in 2006, is an extraordinary example of the defenses that global cities are readying as they face an era of extreme weather brought on by climate change.

In the United States, towns and cities battered by a string of devastating hurricanes are just starting to come to terms with what it could take to bolster their storm protections. Houston city officials have pleaded for state and federal funds to help build a new $400 million reservoir that could keep storm water from inundating downstream neighborhoods.