China struggles with urban drainage.

Floods have affected at least 30 million people in China since the beginning of 2023, including 20 deaths in the recent heavy rains.

According to Bloomberg , following the 2012 floods in Beijing that killed 79 people, China invested billions of dollars to cope with extreme rainfall and accelerated the construction of "sponge cities."

Simply put, these types of cities increase their rainwater absorption capacity by using rooftop gardens, absorbent sidewalks, underground water tanks, etc., and then gradually releasing the water into the river and reservoir systems.

For over a decade, dozens of cities from Beijing in the north to Chongqing in the south have followed this approach. But what has happened seems to be shaking this strategy, as rising global temperatures have fueled massive urban rainfall.

Take Daxing International Airport on the outskirts of Beijing as an example. Its network of landscaped lakes, reservoirs, and drainage systems is large enough to absorb the amount of rainwater equivalent to approximately 1,300 Olympic-sized swimming pools. Yet, the airport's runways were still deeply flooded during Beijing's recent record rainfall – over 744.8 mm from July 29th to August 2nd, the highest in 140 years.

Floodwaters caused by Typhoon Doksuri in Zhuozhou City, Hebei Province, China, on August 3. (Photo: REUTERS)

In neighboring Hebei province, Xingtai city, despite participating in the "sponge rain" movement since 2016, could not withstand the rainfall of two years (approximately 100 cm) in just two days recently, according to Caixin .

According to Dr. Hongzhang Xu of the Australian National University, the problem with the "sponge city" strategy is that it doesn't take extreme weather events into account.

"This plan was initially quite good because it took a comprehensive approach to urban water management issues, including pollution control, storm response, and flood mitigation. However, it did not take into account extreme events and disasters such as flash floods," commented Dr. Hongzhang Xu.

Dr. Li Zhao, a researcher at Greenpeace , points out that the water treatment designs of the "sponge city" strategy are based on rainfall data from the 30 years prior to 2014. Therefore, they are not adaptable to the current climate change situation.

For example, by 2020, Zhengzhou City in Henan Province had invested 53.5 billion yuan in "sponge-based" drainage, even leaving some areas vacant to be used for floodwater drainage. But just one year later, a devastating flood claimed the lives of 380 people in Zhengzhou and caused property damage totaling 41 billion yuan.

"Even sponges can't absorb indefinitely," Ma Jun, director of the Institute for Public and Environmental Affairs in Beijing, told Bloomberg , adding that this strategy needs to be combined with other solutions to cope with heavier rainfall.

Urban development in this populous country is increasingly taking storm response into account. With cities situated on areas that were once natural drainage systems such as lakes, swamps, and forests, China has to build new stormwater drainage infrastructure.

Another secret lies in expanding green infrastructure, such as parks and rooftop gardens, within urban areas. It is thanks to this natural storm response system that 800,000 residents of Chizhou, one of the early "sponge cities," avoided flash floods in 2016 despite rainfall that year being at least 30% higher than normal – according to a Chinese government assessment.

To enhance the effectiveness of "sponge cities" in China, Dr. Xu proposed reusing traditionally constructed waterways for flood discharge and diversion. Simultaneously, he suggested strengthening the warning system to minimize damage.

Source: https://nld.com.vn/thoi-su-quoc-te/trung-quoc-chat-vat-thoat-nuoc-do-thi-20230803205716435.htm