A rescuer helps a woman with a child disembark from a rubber boat as trapped residents evacuate through floodwaters in Zhuozhou in northern China’s Hebei province, south of Beijing, Wednesday, Aug. 2, 2023. China’s capital has recorded its heaviest rainfall in at least 140 years over the past few days. Among the hardest hit areas is Zhuozhou, a small city that borders Beijing’s southwest.Credit: AP/Alamy
The floods that swept through China’s capital this week were exacerbated by urban development and insufficient drainage systems, researchers say.
Typhoon Doksuri hit southern China’s coast in Fujian province on 28 July. It then rolled north to Beijing, dissipating to a lower grade of storm, but in the process dumping up to 745 millimetres of rain on the capital over 5 days — 4 times the city’s average August rainfall. The tail end of the storm also soaked the nearby city of Tianjin and the nearby Hebei province. The deluge of rain was the heaviest to hit Beijing in 140 years, leading to floods killing more than 20 people, destroying roads, cutting off power and forcing thousands of residents to evacuate. “We didn’t expect that the typhoon could impact such a large, vast area,” says Junqing Tang, who focuses on urban resilience and disaster risk reduction at Peking University Shenzhen Graduate School in Shenzhen, China.
But as tragic as this week’s events have been, Beijing is no stranger to flooding and disaster. Floods that have resulted in injuries and casualties have hit the capital at least seven times over the past two decades. The deadliest of these occurred in July 2012, when 190 millimetres of rain drenched the city in a day, leading to flash floods that killed 79 people.
One factor behind Beijing’s recent vulnerability to floods is its rapid development, says Shao Sun, a climatologist at the University of California, Irvine. Over the past three decades, the city’s population has almost tripled. The result is a concrete sprawl of buildings, roads and other infrastructure.
“China’s rapid urbanization has led to a proliferation of impermeable surfaces,” he says. “Green spaces such as parks and gardens play a vital role in water retention. Their dwindling presence due to urbanization diminishes their capacity to effectively manage excessive rainfall.”
Duafang Lu, who specializes in urban development in China at the University of Sydney in Australia, says that urbanization has also wiped out many of Beijing’s wetlands, which reduce flood risk by capturing and absorbing excess rainwater.
The drainage systems in Beijing have also not kept pace with its rapid development, says Tang. Many of these systems were not designed to handle such huge volumes of water and are not maintained or upgraded on a regular basis. “This can lead to waterlogging and exacerbate the impact of floods,” he says.
A vehicle was left on a bridge, which collapsed by torrential rain in the suburbs of Beijing on August 1st, 2023. Flooding and fierce rain have killed at least 11 people.Credit: AP/Alamy
Sponge cities
The Chinese government has taken steps to reduce the risk of urban floods. In 2015, it introduced a plan to construct ‘sponge cities’ that can retain and reuse 70% of rainfall. The aim is to ensure that 80% of urban built-up areas in these cities meet this target by 2030. Since then, some 30 cities — including Beijing — have been testing various approaches to mitigate floods, such as using permeable materials for roads and pavements, restoring wetlands and natural waterways, and creating more green spaces.
Although the sponge-cities strategy is “very ambitious”, the approach was not designed to handle extreme weather events like the Doksuri storm, says Hongzhang Xu, who specializes in urban planning and infrastructure development at the Australian National University in Canberra. “Its design is based on average annual rainfall,” says Xu. And given Beijing’s low-lying location, drainage systems need to ferry excess rainwater quickly, he says. “The most important thing is to divert the water away as soon as possible.”
Urban drainage in Beijing and other cities in China will need to be improved to withstand more frequent extreme weather as climate change intensifies, says Sun. Although this will be challenging, he says it would “significantly reduce the risk of urban waterlogging during the rainy season”. He adds that cities across China will need tailored flood-management strategies. “A one-size-fits-all approach is not the most optimal choice,” says Sun.
Tang adds that Beijing and other Chinese cities will also need to create infrastructure that facilitates evacuations and provides information to help people respond to extreme weather. “At the end of the day, it’s people who react to those kinds of disasters,” he says.
Source: Resources - nature.com
