We have a fine tradition of helping each other and jointly coping with major natural disasters," the Chinese ambassador said. "China and Pakistan are true friends and good brothers by sharing weal and woe. In Zhengzhou, the government estimates, the July floods wiped $10 billion off the local economy-almost as much as completing the sponge city project would cost.Workers unload relief supplies donated by China for Pakistan's flood victims at an airport in southern Pakistani port city of Karachi on Aug. Flood toleranceīenefits aside, cities increasingly have no other choice but to invest in water management, as untamed floods are more costly than preemptive renovations. study in 2019 found that homes with simply a view of water sold for 2% more than their landlocked counterparts. “If you design a better environment, using green infrastructure, it actually increases the land value and increases people’s willingness to live in the city,” Xu says. But creating green space produces an indirect return on investment. With an urban area of some 762 square kilometers, Zhengzhou would have to spend $11.4 billion to completely renovate itself-much more than the $80 million it has spent so far. In May, researchers at the University of Nottingham estimated the cost of turning city to sponge at $15 million per square kilometer. But to achieve Beijing’s dream of renovating 80% of Chinese city space, analysts say the cost will run into the trillions. The central government has spent $14 billion on sponge city concepts to date, designating 30 cities as pilot schemes since 2014. But “hundreds” of acres aren’t many in a city that sprawls across nearly 200,000 of them.īilling urban development as part of sponge city planning is a way for municipal administrators to unlock extra government funding, too. Since adopting the sponge city mindset in 2016, Zhengzhou has built more than 3,000 miles of new drainage, eliminated 125 flood-prone areas, and created hundreds of acres of new green spaces, the New York Timesreports. Yet the issue might just be that Zhengzhou hadn’t created the right sponge-to-city ratio. Hu Caihong, a hydrologist at Zhengzhou University, told Science that the city’s water management systems were designed to withstand a “100-year flood,” but that the rainfall in July had a likely recurrence of once in a millennium-10 times what the city was built for. The guiding principle of slowing the flow and drainage of water means water will accumulate if rain falls too quickly-as it did in Zhengzhou. In the U.S., the same idea is often called “low-impact development.” In an ideal system, green and gray infrastructure are integrated, creating opportunities to store and reuse rainwater for flushing systems or for irrigation.īut sponge cities have limits. The rushing water turns designated drainage points into bottlenecks. That need for speed becomes an issue when rainfall is too heavy. It seeks to drain the water away as quickly as possible and not accommodate it at all,” says Yu. “Gray infrastructure is built to fight against water. Yu Kongjian, a professor of landscape architecture at Peking University, calls this type of management system “gray infrastructure.” Concrete sidewalks and asphalt roads channel rainwater into gutters cut beneath the side of the streets, where the runoff flows into sewer pipes and is, eventually, disposed of at sea. Green over grayĬlassic cityscapes rely on cement sewer systems to keep the streets dry. But advocates say the city simply hadn’t spent enough-and that the effects of climate change mean Zhengzhou, like all cities, will have to spend a lot more. In the wake of Zhengzhou’s floods, critics say the concept has been a waste of money.
The central government has spent $14 billion on sponge city concepts across China since 2014 and plans to convert 80% of urban areas to sponge by 2030. Since 2016, Zhengzhou has invested over $80 million to redesign itself as a so-called sponge city-an urban planning concept promoted by Chinese President Xi Jinping that advocates for creating green space to absorb and mitigate floodwater. This in a city of 10 million that is supposed to be a model for floodwater management.
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