After a devastating typhoon killed more than 1,200 people in the late 1950s, Japan embarked on a series of public works projects aimed at taming its many rivers. Levees and dams sprang up on nearly every river, and civil engineers sheathed long stretches of riverbeds in concrete .

While the projects have saved countless lives , they are insufficient to meet the challenge of increasingly extreme weather patterns, said Shiro Maeno, a professor of hydraulic engineering at Okayama University.

“In the current state, it wouldn’t be strange for a flood to happen anytime, anywhere,” Mr. Maeno said. “Things we never could have considered have started happening in the last few years.”

The heavy investment in infrastructure has not come without a cost. The spending has helped send Japan’s national debt to record highs, as the country has approved many projects that turned out to be minimally effective or, at worst, damaging to the environment.

The Japanese government has also used infrastructure spending to stimulate an economy that was stagnant for decades. Critics note that some of the projects are little more than a tool for enriching construction companies, with part of the proceeds being returned to local politicians in the form of campaign donations.

Whatever the motivation for the spending, engineers are warning that as storms grow in intensity, the government faces diminishing returns as it contemplates raising levees or digging new drainage tunnels. But in the wake of the typhoon, the burning question among Japanese politicians is whether the country should be investing even more.