A FLOODED CITY: Drivers struggle to pass through downtown areas of Kunming, Yunnan Province, after a torrential rain on July 21 (LIN YIGUANG)

A crumbling system

Cheng said that the most direct cause for worsening urban flooding in China is its relatively poor drainage infrastructure.

Experts with the MOHURD identified more specific problems such as the low coverage rate of drainage networks and inadequate drainage capacity. According to the ministry, although Beijing's built-up urban area has doubled over the past decade, the construction of an underground network has not kept pace.

The revised Code for Design of Outdoor Wastewater Engineering, issued by the MOHURD in 2011, stipulates that a drainage system for general areas in cities should withstand high-intensity rainfall once every one to three years, while design for important areas should withstand rainfall once every three to five years.

Cheng said that most cities have taken advantage of the flexible description of precipitation in the regulation and built the weakest drainage systems possible.

Along with his team, Cheng has spent the last three years conducting field surveys in cities across the country, compiling a report entitled Flood Control in Chinese Cities: Current situations, Problems and Solutions. According to their findings, more than 70 percent of cities in China, including Beijing and Wuhan in central China's Hubei Province, have designed their drainage systems based on handling high-intensity rainfall occurring once a year, while old areas in 90 percent of cities have poor drainage facilities.

The report also identified the less-than-satisfactory coverage of drainage networks across cities, even in Shanghai.

Cheng attributes this handicap in drainage development to rapid urbanization. "Suburban areas have been turned into urban areas on an unprecedented scale over the past two decades," he said.

Cheng said that in other countries, where urbanization progressed at a much slower pace, the government had enough time to finish constructing infrastructure before selling land to real estate developers. But this is not the case in China, and the situation is worsened by the fact that the country is yet to establish a sound legal framework to avoid such infrastructure loopholes.

Another important reason is that during the development of large cities in China, open soil, wetland and lakes, which could store water during rapid precipitation, have shrunk enormously. Take Beijing for example. Cheng's research team discovered that the number of lakes across the capital had plummeted from more than 200 to around 50 over the past six decades.

Many experts have suggested that cities must fully tap storage potential among existing water bodies to alleviate urban flooding. However, widening rivers has become almost impossible in Beijing because of high-density construction on their banks.

Another typical city suffering from the consequences of land reclamation from lakes and ponds is Wuhan.

Wuhan has been hit by severe urban flooding at least once every summer since 2008. After torrential rains on June 18, 2011, 82 stretches of roads were severely flooded and traffic paralyzed, forcing the highest level of response to deal with the problem.

Nicknamed "city of 100 lakes," Wuhan used to have more than 100 lakes in its city center during the 1950s and was famed for its lakeside scenery. By 2012, the total number of lakes had dropped to 40 following waves of land reclamation over the past three decades.

Although the local legislature adopted a regulation on protecting lakes and ponds from random land fill and pollution, shrinkage has not be effectively checked until recently. According to official statistics, Wuhan's built-up urban area grew from 455.06 square km in 2006 to 507.54 square km in 2011, up 11.53 percent during five years.

"To prevent 'urban flooding' from devastating Wuhan as a manmade disaster, related laws and regulations must be perfected and more strictly enforced," Liao Hua, an associate professor at the Law School of South-Central University for Nationalities in Wuhan, told newspaper Legal Weekly.

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