The goal, at least on paper, is that by 2030, 70 percent of the rain that falls on China’s sponge cities during extreme weather events should be absorbed locally rather than accumulate in the streets.

Whether enough land can be converted is a key question.

Mr. Yu, who studied landscape architecture in China and at Harvard, with hand-drawn landscape designs. Credit…Mark Schiefelbein/Associated Press

Edmund Penning-Rowsell, a research associate at the University of Oxford who focuses on water security, said the scale of the sponge city projects would have to be huge to cope with flooding on their own. “Take New York City,” he said. “How many Central Parks would you need to absorb this kind of problem? You’d probably need half of Manhattan.”

Zhengzhou, in northeastern China on the banks of the Yellow River, was an enthusiastic early adopter of the sponge city concept, spending hundreds of millions of dollars building related projects from 2016 to 2021. But torrential rains inundated much of the city in July 2021, creating scenes of destruction and killing hundreds, including at least 14 in a subway tunnel.

Why were the floods so disastrous in Zhengzhou? Mr. Yu said some of the money earmarked for sponge projects was diverted to other programs and that the land set aside for them was insufficient. If permeable surfaces or green spaces make up 20 to 40 percent of a city’s area, he said, “you can virtually solve the problem of urban inundation.”

Niall Kirkwood, a professor of landscape architecture at Harvard who has known Mr. Yu for years, acknowledged that it can be difficult, and sometimes impossible, to convert land in city centers that have already been densely built. Still, he said, Mr. Yu’s impact as a innovator has been incalculable.

“He’s created a clear and elegant idea of enhancing nature, of partnership with nature that everyone, the man on the street, the mayor of a city, an engineer, even a child, can understand,” Professor Kirkwood said.

Where large tracts of land are not available, sponge city projects are replacing concrete and asphalt with permeable pavement, installing green roofs and creating trenches called bioswales that channel storm-water runoff and use vegetation to filter out debris and pollution.

The sponge city concept is not unique to China. One of Mr. Yu’s projects abroad is the Benjakitti Forest Park, a maze of ponds, trees and miniature islands in Bangkok that was opened to the public in 2022 and occupies more than hundred acres on the site of a former tobacco factory.

Separately, in 2007 the Dutch government began a program called Room for the River that consists of more than 30 projects around four rivers, including the Rhine. The idea is to restore natural floodplains in key areas around sites that need protection. The Danish capital, Copenhagen, is using “floodable parks” that turn into temporary ponds during heavy rains. Philadelphia and Malmo, Sweden, also have projects.

The site of Benjakitti Forest Park in Bangkok in 2020.Credit…Courtesy The Cultural Landscape Foundation

The park, which was rehabilitated by Mr. Yu’s firm, in 2022.Credit…Lauren DeCicca for The New York Times

In addition to flood control, these projects have the advantage of being an inexpensive way to recharge local aquifers and a low-tech adaptation to help overheated city neighborhoods, because evaporating water has a cooling effect.

John Beardsley, the curator of the Oberlander International Landscape Architecture Prize, which was awarded to Mr. Yu last year, echoed Professor Kirkwood, saying Mr. Yu’s impact on policy in China, a country that has been more likely to imprison environmental activists than take their messages to heart, has been astonishing.

Mr. Beardsley attributes this to Mr. Yu’s adroit political skills and infectious enthusiasm, as well as the Chinese government’s powerful incentive to appear to be addressing the problem of urban flooding, which has grown alarmingly in recent years.

“Kongjian has managed to be very critical of the government’s environmental policies while still maintaining his practice and his academic appointments,” he said. “He’s both brave and deft in this regard, threading a very narrow needle.”

“Sponge cities isn’t a total solution, but it makes a significant impact,” Mr. Beardsley said. “I mean, we need to start doing something.”

Courtesy The Cultural Landscape Foundation