Taipei Flooding: Expert Urges Urban Resilience, Cites Rainfall Exceeding Drainage Capacity

Rare flooding occurred in Taipei's Neihu district on June 25 due to intense rainfall, overwhelming the city's drainage capacity. While the Taipei city government stated the precipitation exceeded the sewer system's limits, city councilor Ho Meng-hua questioned whether human factors also contributed.

Ou Wen-sung, a professional with long-term experience in water conservancy and engineering planning, offered insights from a water resource engineering perspective. He noted that the actual rainfall intensity surpassed the current drainage system's design capacity, yet the system still retained some flood discharge capability. Ou suggested that the city should review its resilience in adapting to Neihu's development and leverage corporate ESG resources.

Ou outlined four key points. First, he analyzed the rainfall data, citing figures like 100.5 mm/hr in Dago Creek and 96 mm/hr at Bihu Elementary School between 9:30 and 10:30 a.m. He described this as a typical "short-duration, high-intensity rainfall" event, exceeding Taipei's stormwater drainage system design standard of approximately 78.8 mm/hr by 10-30%.

Second, Ou clarified that "ponding does not necessarily mean the drainage system has failed." He explained that engineering assessments consider factors like water depth, duration, speed of drainage, and systemic collapse. Based on available information, most of the accumulated water receded as the rain subsided, and water levels in flood control facilities returned to below alert thresholds. Ou categorized the Neihu flooding as a scenario where the system encountered rainfall exceeding its design standard but retained discharge capacity, rather than a complete system failure.

Third, Ou emphasized the need to review "resilience." Neihu's continuous development, including tech park expansion, increased commercial offices, residential construction, and land development, has theoretically increased impervious surfaces and runoff during heavy rain. Taipei's "stormwater runoff control" initiative, aimed at mitigating the impact of increased imperviousness, has been in place for over a decade. The core function is to retain rainwater within a site, reducing pressure on the city's drainage system during downpours. Therefore, the discussion should focus on whether the drainage system's upgrade speed matches the pace of extreme climate change, urban development, and population growth.

Finally, Ou called for a transparent review mechanism. He urged the city government to publicly disclose data on rainfall at various monitoring stations, drainage system design standards, pump station operational records, water accumulation depths, drainage times, and future improvement plans. Such transparency would help the public understand whether the flooding resulted from "extreme rainfall exceeding design standards" or if "the drainage system requires strengthening."

Ou concluded that while the city government needs to continuously review and enhance drainage capabilities, the maximum hourly rainfall of 100.5 mm/hr clearly exceeded the current design standard. He stressed that in an era of increasingly normalized extreme weather, Taipei needs more resilient actions and should integrate substantial corporate ESG resources. Resilience, he stated, is built through practical actions, not just words, and this forms the basis for constructive public discussion.