[questhimay]

In case for China, there are numerous reasons, from rapid urbanisation which meant the spread of impermeable concrete surfaces and reduced natural wetlands and marshes that had in the past absorbed rain. To Soviet-era urban drainage systems of shallow buried pipes leaves cities vulnerable to waterlogging during heavy rain.

here's a video of how crazy flooding gets in China https://www.youtube.com/watch?v=Cfhd7bVEnh0.

[verisimi]

Interesting video, thanks.

Fwiw, the 2 factors you mention - urbanisation and reduced wetlands - would fall into bad town planning, in my book, ie a local cause.