[Xylakant]

No, he means "schwammstadt" (sponge city), the concept idea that you need to create the capacity to soak up excess rainfall and store it like a sponge instead of relying on drainage entirely.

https://en.wikipedia.org/wiki/Sponge_city

[jajko]

Which isn't a bad idea generally, but for cities like Zurich (and its sister city Geneva which is the same also in this regard) there isn't much need - it sits at the end of a massive lake, most of the city center isn't much higher than lake itself.

Effect of the lake subsides somewhat with distance form it, but it definitely creates its own micro-climate thats always colder and more humid than further away from it. To have more high trees that prevent all that tarmac, concrete and stone from heating up during day is definitely a plus, but these cities are not some scorched Phoenix, AZ equivalent.

[Xylakant]

Berlin, one of the leading cities in Germany on those concepts is located on two rivers, plenty of canals and between a few lakes. Hamburg is another very active place and it's close to the seaside, with a huge river and plenty of water in the city. A lot of concepts refer back to city planning that Kopenhagen started after a massive rainfall event in 2011 - a city which is fairly flat, has a large river front and plenty of canals.

Still, there's need to evaluate such city planning concepts because the lakes and rivers do not solve all of the problems associated with heavy rainfalls and drought cycles. They do nothing to handle the runoff if you get massive rainfalls in a short period of time because the water management gets overwhelmed. Also, city trees do not benefit substantially from the high ground water level and still suffer in drought.

So while not all of the concepts ideas may be applicable to Berlin, Hamburg, Kopenhagen, Zurich or Geneva, concepts like green roofs, local water storage etc. are still required to respond to the incread frequency of high rainfall events and increasing summer temperatures.

[BSDobelix]

I'm so old I can still remember when Sechseleuten Square was green grass, now replaced with searing heat assemblers of stone....so even the city is working against that sponge thing, but yeah it sounds good from a politician's mouth.

[Xylakant]

It's a relatively novel concept, though the problems of replacing open surfaces with stone slabs and asphalt could have been obvious decades ago :(

[danaris]

Ah, but you see, stone slabs and asphalt cost nothing to maintain. /s

(...Even this is, of course, untrue, but it seems true when you're only paying attention to the next year or so.)

[BSDobelix]

Just 17 milion swiss franks made out of "Valser Quarzit" and a "fountain" that needs constant maintenance because it has to be drinking quality instead of lake-water, just look at that sh*t:

https://aquatransform.ch/projects/sechselaeutenplatz-opernha...

EDIT: But please don't waste energy otherwise (your politician)