Impact of city size on precipitation-modifying potential

This study investigates how increasing city size affects local weather modification potential using an innovative new method: the real atmosphere, idealized land-surface (RAIL) method. The RAIL method simplifies the land surface by making a flat, homogeneous land surface for a control simulation. Using the Regional Atmospheric Modeling System, an instance of weak linear convection was simulated over three nested grids with a minimum grid spacing of 0.75km. Using the RAIL method, cities of radius 5 to 40km were placed in the path of the simulated precipitation to study the impact. For the weak-convection case, the urban area effects showed urban heat island and urban moisture depression effects and produced regions of both precipitation suppression and invigoration downwind of the city. Modification increased up to a radius of 20km and more slowly after indicating a threshold city size for urban modification on thunderstorms.