Impacts of Urbanization on the Occurrence and Spatial Distribution of Precipitation in Varying Kinematic and Thermodynamic Environments

Numerous studies have investigated the influence of urbanization on weather and climate. The effect of large metropolitan areas on temperature has been the thoroughly researched, and the urban heat island is a well-known and understood impact of such large scale urbanization. The role of urbanization on precipitation has also been studied, leading to the general consensus that urbanization can enhance precipitation amounts, particularly downwind of metropolitan areas. This study complements and builds upon previous investigations into the effects of urbanization on precipitation. Precipitation occurrence and spatial distribution with respect to large urban areas in the eastern United States was evaluated from 2002-2018 utilizing the 4 km National Centers for Environmental Prediction (NCEP) Stage IV gridded dataset. The potential influence of large metropolitan areas on precipitation was investigated throughout the calendar year across a spectrum of thermodynamic and kinematic conditions. Atmospheric conditions associated with observed precipitation events were extracted from the North American Regional Reanalysis (NARR) dataset. Wind direction- and stability-relative composites were produced to better understand the conditions under which the most significant impacts were observed. Results from this study for the Twin Cities metropolitan area will be presented to illustrate how a large urban area can influence the occurrence and spatial distribution of precipitation under various weather regimes. Atmospheric stability, wind direction, and wind speed throughout the lower- to mid-troposphere are shown to exert varying influences on precipitation production and relative location.