[verisimi]

Deforestation would cause water too run off more quickly, overwhelming local services, drains, ditches. Building on flood plains also puts people at risk - rivers might not flood every year. These factors could play a role in this situation. These are the factors I would like to know more about for the Brazil and China flooding... Is it just bad governmental town planning?

[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.

[jalbertoni]

> These are the factors I would like to know more about for the Brazil and China flooding... Is it just bad governmental town planning?

The systems Porto Alegre and Canoas had in place used to work. When the river there goes over 3 meters it starts to flood some places, okay? Once every few years there was a flood of like, 3.5 meters, 3.7 sometimes. Those were floods that rose slowly, giving ample time to answer to situations as they arose.

In this case, on the 2nd of May, the river reached 3 meters. By midnight, the river was at 3.60 meters already. 24 hours later, the river was at 4.9 meters, and it still rose, slowly now, to 5.3 meters.

The system that was in place was completely overwhelmed. Pumping stations failed and the water started coming through the pumping stations, for example.

That said, yes, the writing was on the wall. If a place regularly floods a bit to the point you need to have dykes and pumping stations in place, eventually it will flood a lot.