Summary of Key Points
The occurrence of waterlogging in Shanghai, a megacity with advanced infrastructure, despite the impact of Typhoon “Baihaidun,” was not caused by a single factor. It was the result of a combination of extreme weather conditions (prolonged duration and intense local rainfall exceeding expectations) and the city's own hydrological characteristics (low-lying terrain, ground subsidence, hardened surfaces, limitations in the drainage system, and elevated water levels in the river network). Shanghai’s approach to dealing with this issue is not to completely eliminate waterlogging but to balance engineering solutions with natural factors in order to reduce the risk and impact of such events, thus achieving a long-term coexistence with water.
Detailed Analysis
1. Shanghai's Geographical “Weaknesses”: Relying on Man-made Drainage Systems
Shanghai is an estuarine alluvial plain formed by the accumulation of Yangtze River silt, resulting in a particularly flat terrain (with almost no natural elevation differences in the central urban area). Unlike mountainous or hilly regions, rainwater cannot flow naturally into rivers; instead, it must be removed through man-made systems such as drainage networks and pumping stations. Additionally, historical ground subsidence has further compromised drainage efficiency. This is similar to a flat floor where water can only be cleared with a mop (pumping stations), and if the floor has uneven surfaces, it becomes even more difficult to drain.
2. The “Special Pattern” of Typhoon Rainfall: Peripheral Circulation + Prolonged Duration + Intense Local Precipitation
Many people assume that heavy rainfall only occurs in the center of a typhoon, but this is not the case. The typhoon’s peripheral circulation can carry warm and humid air over large areas, leading to intense rainfall even when the center is far from the city. Typhoon “Baihaidun” was particularly severe, lasting for four days. The initial rainfall had already saturated the river network and soil, leaving little space for additional water. The intense local downpours (e.g., 93 millimeters of rain in one hour on Xutu Road in Xuhui) overwhelmed the drainage system.
3. Urban Hardening Increases Rainwater Flow Rate
The city’s extensive use of concrete roads and building roofs creates impermeable surfaces that prevent water from infiltrating into the ground, forcing it to flow directly into drainage systems. In natural areas like grasslands and farmland, more rainwater is absorbed, but in Shanghai’s central urban area, most of the rainfall becomes surface runoff, quickly overwhelming the drainage network.
4. A Strong Drainage System, But with Limits
Shanghai’s drainage system is impressive, featuring extensive networks and pumping stations, as well as regular maintenance to maintain its capacity. However, it is designed to handle rainfall occurring once every 3–5 years. The intense downpours exceeded the capacity of some local facilities. This is like trying to drain water from a bucket through a narrow pipe; even if the pipes are large enough, excessive flow will still cause overflow.
5. Elevated River Water Levels: An Additional Barrier to Drainage
Rainwater in cities ultimately needs to be discharged into rivers, but if river levels are also high, they can impede drainage. During Typhoon “Baihaidun,” the water level in the Suzhou River rose significantly, forcing Shanghai to use large pumps to divert excess water into the Huangpu River to prevent flooding. This is similar to trying to pour water into a nearly full bucket; the increased water pressure prevents proper drainage.
Conclusion
The waterlogging in Shanghai was not due to inadequate infrastructure but is a common challenge for megacities during extreme weather events. The city’s strategy focuses on improving drainage systems, creating “sponge cities” (which can retain water), and optimizing river network management to minimize the duration and impact of waterlogging. After all, Shanghai is built on an estuarine plain, and dealing with water is part of its daily reality. Instead of trying to completely eliminate it, the city aims to learn how to coexist with it effectively.