China has invested billions of dollars in recent years to protect against extreme rainfall after a 2012 flood in Beijing killed 79 people and prompted President Xi Jinping to call for building “cities like sponges.” The idea is simple: Using rooftop gardens, permeable pavements, underground storage tanks and other sponge-like features to soak up heavy precipitation and then slowly release it into rivers or reservoirs. Since then, dozens of Chinese cities from Beijing in the north to Chongqing in the south have pledged to make the transformation.
But the climbing death toll in northern China since Saturday has sounded the alarm of whether these tactics are fit for purpose as rising global temperatures supercharge more intense rainfall events. Worldwide it’s becoming increasingly difficult for communities, from Vermont villages to London neighborhoods, to keep up with the fast changes in precipitation.
Take Daxing airport, a major aviation hub on the outskirts of Beijing. Its scenic lakes, water storage tanks and drainage systems are designed to absorb as much rainwater as roughly 1,300 Olympic-size swimming pools. Despite being the first in the country to be deemed a “sponge airport,” part of its runways were still swamped as the Chinese capital battled record rain.
In neighboring Hebei province, the city of Xingtai has also fallen victim to intense rainfall, even though it has joined the national campaign since 2016 to add more “sponges.” As two years worth of rain — 39.5 inches — fell on Xingtai in two days, the resulting floods have killed five people there as of Tuesday, with four still missing, according to Chinese media outlet Caixin.
Daxing airport and Xingtai are not the only examples where sponge-related infrastructure has struggled to withstand the forces of nature. Towards the end of the last decade, Zhengzhou invested 53.5 billion yuan ($7.4 billion) to retrofit existing infrastructure and turn itself into a “sponge.” Yet in 2021 a devastating flood in the city caused 380 deaths and washed away about 41 billion yuan worth of assets.
In some locations, the “sponge” infrastructure covers only a fraction of a city and in other areas, regions have been inundated because they’ve been specifically designated for floodwater discharge.
A wider problem with China’s “sponge city” strategy is that it doesn’t take into account extreme events, according to Hongzhang Xu, a researcher who studies climate change adaptation at the Australian National University.
“It was a fairly good plan when it was initiated, because it wants to have some kind of comprehensive and holistic approach to deal with urban water management issues, including pollution control, storm water management, and flood mitigation,” he said. “But it ignores the extreme events and disasters like the flash flood.”
Water management designs under the strategy were based on rainfall levels in the 30 years prior to 2014, and extreme weather events are now far in excess of what the systems were designed to cope with, according to Li Zhao, a Beijing-based researcher at Greenpeace.
The “sponge” strategy is useful and should be more widely adopted, though the tactics aren’t sufficient alone in extreme cases and need to be combined with other measures, said Ma Jun, director of the Institute of Public & Environmental Affairs, a nonprofit environmental research organization in Beijing.
Future developments should consider how to deal with heavier rains and take lessons from recent high-profile flooding events, he said. “Even the real sponge has a problem of capacity,” Ma said.
Flooding isn’t a new problem in China, as urban development has increasingly put a strain on storm management. Cities have encroached upon areas that were once natural drainage systems such as lakes, wetlands and forests, forcing China to build new infrastructure to handle rainwater runoff. This is now being pushed to extreme limits with global warming driving more frequent and intense precipitation worldwide.
Expanding green infrastructure such as urban parks and rooftop gardens could lessen weather perils to a certain extent. For instance, in Chizhou, one of the country’s first “sponge cities,” the use of natural stormwater management helped its 800,000 dwellers avoid flash floods in 2016, even though it received at least 30% more precipitation that year than the normal level, according to an assessment by the central government.
To up the ante on the capability of “sponge cities,” Xu suggested reviving abandoned waterways that were built as early as the Qing Dynasty for flood release and diverting water. Chinese authorities should also improve warning systems to minimize damages, he said.
“Urban design is still an ad hoc problem,” Xu said, “so it means homogenous or one-size-fits-all for urban design may not work for all cities.”