I would argue that hyper dense urban centers, ala Manhattan, are flood protection by preventing the building on of floodplains with impermeable surfaces upstream by sprawl. But that's a lot to get into in a dev thread lol.
The 'hardening' of a lot of core areas is a concern but I think a policy of greening the streets and making them more porous can do a lot of the water retention that backyards used too.
Charles Street here is wide enough at the moment to facilitate a car parked on either side of the street and one active travel lane in the center, which works seeing as it's one way. With the surplus of off street parking being created in the area by recent devs, getting rid of on street parking is a real possibility.
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Placing bio swells like this great one on Robert Street where parking used to be accommodated along the length of Charles would reverse the trend of permeable surfaces disappearing. Combine that with the one travel lane no longer being laid down with asphalt, but instead pavers, that allow water to filter through.
Intensification is inevitable and defiantly poses new challenges but really I think it may finally force us to see streets as anything other than strips of pavement which will make the city better in the long run.