Hong Kong has a colour-coded warning system for rainstorms, from amber to black, part of the city shuts down when black rain warning is in effect.  Hong Kong is undoubtedly paved with asphalt and concrete and there was a time when the city easily floods during a rainstorm.  Older parts of the city is particularly vulnerable, since drainage system was built prior to the increase of population, which now stands at 8 million.  

Since the late 90s, Hong Kong’s existing drainage system has been retrofitted and expanded.  Additionally, four stormwater storage tanks were built and 11 more are being constructed.  It is worth noting that stormwater management in Hong Kong is tailor to the district: dykes and channels protects rural villages and towns, while the city and urban areas are assigned with far more intensive engineering work.  

These solutions, which now direct rainwater away from vulnerable areas and into the ocean, have significantly reduced flooding – from 126 floods in 1995 to five in 2020.  

I have recently read about the construction of Racecourse water storage tanks, which lie beneath the famous landmark, The Happy Valley Racecourse.  These water tanks look like empty parking lots which, at its fullest, hold up to 60,000 sq. m. of water.

In addition to storing water (instead of discharging as it has before 1995), Hong Kong has also adopted design solutions such as porous pavements, wetlands, rain gardens and green rooftops, many of which I can attest to seeing more of during my annual visits to Hong Kong since the late 90s.  

Reference: 

Griffiths, James.  “Hong Kong’s vast $3.8 billion rain-tunnel network” Cnn.com