The study looked at how rainwater flows in cities and found that it's important to separate runoff from paved and unpaved areas. Small storms mostly cause runoff from paved surfaces, while bigger storms cause runoff from both paved and unpaved areas. The time it takes for runoff from paved surfaces to start decreasing can be predicted by looking at how the water level in rivers goes down after a storm. A model with two reservoirs is suggested as a good way to predict how water levels change in cities during storms.