Boston flash flood risk and urban drainage
Flash-flood risk is often a drainage problem before it is a river problem
The September 1 forecast for Southern New England included a marginal flash-flood risk, with widespread rain affecting Boston. My read is that the phrase can sound less relevant in a city than it really is.
In urban neighborhoods, the first trouble spots may be underpasses, low intersections, steep streets, and places where storm drains cannot keep up with intense rainfall. That is different from a stream overtopping its banks, but the consequences can still disrupt buses, cycling routes, and walking access.
I could be missing local context, but this is where neighborhood drainage maps and timely street reports become useful. A regional forecast tells us the conditions; local observations help identify the specific pinch points. See Boston.com’s report on the rain.