Impact of Urbanization on Heavy Convective Precipitation under Strong Large-Scale Forcing: A Case Study over the Milwaukee–Lake Michigan Region

Abstract

In this study, observational and numerical modeling analyses based on the Weather Research and Forecasting Model (WRF) are used to investigate the impact of urbanization on heavy rainfall over the Milwaukee–Lake Michigan region. The authors examine urban modification of rainfall for a storm system with continental-scale moisture transport, strong large-scale forcing, and extreme rainfall over a large area of the upper Midwest of the United States. WRF simulations were carried out to examine the sensitivity of the rainfall distribution in and around the urban area to different urban land surface model representations and urban land-use scenarios. Simulation results suggest that urbanization plays an important role in precipitation distribution, even in settings characterized by strong large-scale forcing. For the Milwaukee–Lake Michigan region, the thermodynamic perturbations produced by urbanization on the temperature and surface pressure fields enhance the intrusion of the lake breeze and facilitate the formation of a convergence zone, which create favorable conditions for deep convection over the city. Analyses of model and observed vertical profiles of reflectivity using contoured frequency by altitude displays (CFADs) suggest that cloud dynamics over the city do not change significantly with urbanization. Simulation results also suggest that the large-scale rainfall pattern is not sensitive to different urban representations in the model. Both urban representations, the Noah land surface model with urban land categories and the single-layer urban canopy model, adequately capture the dominant features of this storm over the urban region.

Urban signatures in the spatial clustering of summer heavy rainfall events over the Beijing metropolitan region

“…Yang et al . [] examined the characteristics of storm cells during the entire lifecycle of a storm event in Milwaukee, WI, U.S. Maximum reflectivity, the height of maximum reflectivity, and number of simple tracks (simple storms that have no splits or mergers) increased while the storm passed through the urban region.…”

“…The radar data were obtained from the KMKX WSR‐88D (Weather Surveillance Radar, 1998 Doppler) (see Yang et al . [] for more details of this storm event). The verification statistics are summarized in Table .…”

“…Yang et al . [] also highlighted the role of urbanization in a heavy convective rainfall event with strong large‐scale synoptic forcing over the Milwaukee‐Lake Michigan region. At regional scale, Kishtawal et al .…”

Role and Impact of the Urban Environment in a Numerical Forecast of an Intense Summertime Precipitation Event over Tokyo

“…Interaction with local circulations: through their impact on turbulent exchanges of heat, moisture, and momentum with the atmosphere, many investigators have argued that cities could enhance local or mesoscale circulations such as breezes (for coastal cities) and cold fronts, resulting in increased low-level convergence and precipitation over urban areas (Yang et al 2014, Zhong and Yang 2015, Ryu et al 2016). …”

A need to revisit hydrologic responses to urbanization by incorporating the feedback on spatial rainfall patterns

“…Urban processes such as urban-rural heterogeneities, urban heat island, urban canopy, and urban aerosols can detectably modify rainfall patterns around urban areas (e.g., Bornstein and Lin, 2000;Collier, 2006;Lowry, 1998;Niyogi et al, 2006;Rosenfeld, 2000;Shepherd, 2005;Shepherd et al, 2010). Although some of the key mechanisms remain elusive, it is now understood that the presence of urban surfaces could noticeably change the physical properties of rainfall, including accumulated rainfall, intensity, frequency, dynamic properties of storm evolutions (e.g., structures, tracks, timings,) (Kusaka et al, 2013;National Research Council, 2012;Niyogi et al, 2011;Schmid and Niyogi, 2013;Yang et al, 2013aYang et al, , 2014.…”