The picture above is not quite as clear as I’d hoped. I was returning from a site visit in Brooklyn yesterday just before an extremely heavy downpour started. I took that shot from Brooklyn Bridge Park, near the ferry landing, looking west. I was standing in bright sun, lower Manhattan is already under a dark cloud, and the color of the clouds in the far background suggests it was already pouring in New Jersey.
The warning earlier was fairly dramatic, and we ended up getting about 1.1 inches (2.8 cm) of rain in less than an hour.
One point regarding engineering: an inch of rain in a day is not a big deal. But sewers have a maximum flow capacity, which can be exceeded during a heavy downpour, and then the water isn’t moved away as fast as it comes down. Streets, and rooftops, and open plazas have drains that may also be flooded because the rain coming down exceeds their capacity. Walking home, I had to go around a number of areas where pavement and gutters were temporarily flooded because of this difference between the flow in (from rain) and the flow out (from drains).
It’s a mistake to focus on totals when rates, and particularly maximum rates, may be what causes trouble. Of course, it can also be a mistake to focus on rates if the totals cause trouble, with an example being a long-term drought. People’s water usage rates go down in a drought, but if the total supply is inadequate, that doesn’t help enough. This whole post is, perhaps, a roundabout way of pointing out something that people should already know: much of our environment is designed, and the quality of the design matters.