The world’s most vulnerable coastal communities are taking action against rising oceans and more severe floods. The Dutch are radically revising traditional flood-management thinking.

With his curly, salt-and-pepper hair and thoughtful demeanor, Chris West looks like just another mid-career professor as he crosses the streets of Oxford University. But West, trained as a zoologist, is more an activist than an academic these days. From his cramped office around the corner from Balliol College, he…