Understanding the Influence of Urban Form on the Spatial Pattern of Precipitation

Urban areas are known to modify the spatial pattern of precipitation climatology. Existing observational evidence suggests that precipitation can be enhanced downwind of a city. Among the proposed mechanisms, the thermodynamic and aerodynamic processes in the urban lower atmosphere interact with the meteorological conditions and can play a key role in determining the resulting precipitation patterns. In addition, these processes are influenced by urban form, such as the impervious surface extent. This study aims to unravel how different urban forms impact the spatial patterns of precipitation climatology under different meteorological conditions. We use the Multi-Radar Multi-Sensor quantitative precipitation estimation data products and analyze the hourly precipitation maps for 27 selected cities across the continental United States from the years 2015-2021 summer months. Results show that about 80% of the studied cities exhibit a statistically significant downwind enhancement of precipitation. Additionally, we find that the precipitation pattern tends to be more spatially clustered in intensity under higher wind speed; the location of radial precipitation maxima is located closer to the city center under low background winds but shifts downwind under high wind conditions. The magnitude of downwind precipitation enhancement is highly dependent on wind directions and is positively correlated with the city size for the south, southwest, and west directions. This study presents observational evidence through a cross-city analysis that the urban precipitation pattern can be influenced by the urban modification of atmospheric processes, providing insight into the mechanistic link between future urban land-use change and hydroclimates. Previous studies have shown that cities can influence the spatial rainfall patterns, and one of the strongest influences is that the precipitation tends to increase over downwind of city areas. The goal of this study is to understand how different urban forms impact rainfall spatial patterns under different weather conditions. We analyze the hourly precipitation accumulation data from Multi-Radar Multi-Sensor for a selected set of 25 cities across the continental United States from the years 2015-2021 summer months. The results indicate that more than 80% of the studied cities have a significant increase of rainfall in downwind regions. In addition, the rainfall spatial patterns have different characteristics with varying meteorological conditions such as precipitation intensities, wind speeds, and wind directions in terms of the location of rainfall maxima, the magnitude of downwind enhancement. 22 out of 27 cities show statistically significant downwind enhancement of climatological precipitationThe precipitation patterns exhibit different spatial characteristics with varying meteorological conditionsDownwind enhancement factor is positively correlated with city size under dominant wind direction