Kelly Hayes, a co-owner of Gowanus Gardens, a bar in Brooklyn, said that at least once a year, her business floods.

She has equipped herself with a metal stop to keep water from streaming in under the front door and has a sump pump in the basement. And when rainfall is heavy, Ms. Hayes keeps an eye on the data streaming online from a sensor placed a few blocks away as part of a city-backed initiative to track flooding virtually in real-time.

“We are just in the zone,” Ms. Hayes said, “so if we’re getting a lot of rain in a short amount of time, there is going to be flooding here.”

City officials brought together researchers at New York University and the City University of New York in 2020 to begin an initiative called FloodNet, which now has more than 250 flood sensors at street corners across the city, all beaming information to a data set available online at floodnet.nyc. The sensors emit ultrasonic pulses toward the ground and calculate the height of a flood by measuring the time they take to hit water. That data is delivered to an interactive map.

The project is unique among major cities because of the granular, street-level data it captures, researchers for the project said. It is funded by the New York City Department of Environmental Protection, and there are efforts underway to double the number of sensors to 500 by 2027. The city’s roughly $7 million investment in the project was spurred by the flood damage after Hurricane Ida four years ago.