Fig. 1: Changes in rain cell speed between urban areas and surrounding regions derived from weather radar data.

a Change in median object speed from the control to the three urban bins, plotted against city size. The color of the points refers to the urban bin, and the error bars represent the 95% confidence intervals of the median differences. Square (round) symbols refer to (not) significant change (p < 0.05). Purple crosses mark the median change in object mean rainfall intensity from the control to the central urban bin. Opaque crosses indicate statistically significant changes, while transparent crosses indicate non-significant changes. Cities are labeled by their two-letter acronyms: Mi (Milan), Bi (Birmingham), Be (Berlin), Lo (London), In (Indianapolis), Ch (Charlotte), Ph (Phoenix), and At (Atlanta). b Composite of mean rainfall object speed over Indianapolis, expressed as the deviation from the mean. Each rainfall object is rotated around a fixed center located at Indianapolis’s city center, based on the corresponding track’s mean direction of motion. For all tracks, the downwind direction is to the east, and the upwind direction is to the west. The black circle indicates the average radius of the city, and the city center is marked with a cross. The black, blue, green, and red dashed lines indicate the edges of the urban, upwind, downwind, and control bins, respectively.