In a near future where super-cell storms drop massive amounts of water (300 l/m²) in the blink of an eye, cities- built upon the cities of old- have adapted to these tsunami like flash floods. But how? How do buildings and cellars look? What happens to subways, cars, and canal systems? What prevents buildings (containing air) from becoming pontoon boats when the floor of valleys turn into temporary lakes? What does the warning system look like? Please use a typical concrete city as a example wherever possible.

Addition: As stated in the comments, there are examples of industrialized nations in asia (India, China, Bangladesh) that have this problem. However, due to the rainfall significantly increasing, even this industrialized nations are not properly prepared. Brand new cities in the tropical regions get regular flooding and all that keeps them up, is continous rebuilding and repairing. Something that might not be viable in a more constricting economic environment. So to mak the question more precise - how to adapt a existing city, located in the danger zones, to these new ocassional floods?

In a near future where super-cell storms drop massive amounts of water (300 l/m²) in the blink of an eye, cities  - built upon the cities of old  - have adapted to these tsunami-like flash floods. But how? How do buildings and cellars look? What happens to subways, cars, and canal systems? What prevents buildings (containing air) from becoming pontoon boats when the floors of valleys turn into temporary lakes? What does the warning system look like? Please use a typical concrete city as a example wherever possible.

Addition: As stated in the comments, there are examples of industrialized nations in Asia (India, China, Bangladesh) that have this problem. However, due to the rainfall significantly increasing, even this industrialized nations are not properly prepared. Brand new cities in the tropical regions get regular flooding and all that keeps them up, is continuous rebuilding and repairing. Something that might not be viable in a more constricting economic environment. So to make the question more precise - how to adapt a existing city, located in the danger zones, to these new occasional floods?

In a near future where super-cell storms drop massive amounts of water (300 l/m²) in the blink of an eye, cities- built upon the cities of old- have adapted to these flash floods. But how? How do buildings and cellars look? What happens to subways, cars, and canal systems? What prevents buildings (containing air) from becoming pontoon boats when the floor of valleys turn into temporary lakes? What does the warning system look like? Please use a typical concrete city as a example wherever possible.

In a near future where super-cell storms drop massive amounts of water (300 l/m²) in the blink of an eye, cities- built upon the cities of old- have adapted to these tsunami like flash floods. But how? How do buildings and cellars look? What happens to subways, cars, and canal systems? What prevents buildings (containing air) from becoming pontoon boats when the floor of valleys turn into temporary lakes? What does the warning system look like? Please use a typical concrete city as a example wherever possible.

Addition: As stated in the comments, there are examples of industrialized nations in asia (India, China, Bangladesh) that have this problem. However, due to the rainfall significantly increasing, even this industrialized nations are not properly prepared. Brand new cities in the tropical regions get regular flooding and all that keeps them up, is continous rebuilding and repairing. Something that might not be viable in a more constricting economic environment. So to mak the question more precise - how to adapt a existing city, located in the danger zones, to these new ocassional floods?