Impact of Urbanization on Precipitating Systems and Rain Microphysics Across the Hyderabad Urban Sprawl, India

Understanding the impact of urbanization on precipitating systems’ characteristics, the present study is first of its kind, focused on rain microphysics during the Indian summer monsoon (ISM) season in the upwind, downtown, and downwind sites of Hyderabad urban sprawl and a surrounding reference (rural) station. During the ISM, precipitating systems are deeper over the upwind and downtown locations of Hyderabad than over the downwind and rural sites. Convergence, high water vapor, and moderate low-level vertical wind shear favor convective initiation across the city. Enhanced mid-tropospheric moisture, weak upper-level divergence, and relatively weak shear further support the growth of deeper convective systems over the upwind and downtown areas. In contrast, stronger mid-tropospheric wind shear over the rural and downwind regions suppresses vertical cloud development and lowers storm-top heights. The upwind and rural regions contain abundant small raindrops; however, the upwind region also shows a higher concentration of large raindrops, whereas the rural region has fewer large drops than the downtown and downwind areas. Despite this, convective rain mass-weighted-mean-diameter (Dm) differs little between the upwind and rural sites because the reduced number of medium-sized drops in the upwind region shifts Dm toward smaller values. In stratiform rain, the downwind region exhibits larger Dm values than other locations, while downtown and rural regions show similar Dm. The ISM low-level jet transports continental air into Hyderabad, giving the urban raindrop size distribution a continental character. Urban-induced collisions among small droplets enhance the formation of medium and large raindrops over downtown areas.