Compounding Effects of Lake and Urbanization on Summer Precipitation in the Greater Chicago Area

This study uses observational data products and the Weather Research Forecasting (WRF) model to investigate the influences of Lake Michigan and urbanization on precipitation over the Greater Chicago Area. The observational analysis spans the past 20 years, while the modeling study focuses on an early summer rain event. Results show that, according to observational data analysis, urban areas consistently experience more precipitation than the adjacent lake area in south Lake Michigan, regardless of year or month. According to modeling experiments, both urbanization and the lake effect (including lake breezes) increase precipitation over urban areas mainly due to the convergence caused by the land breeze and lake breeze, promoted by the temperature gradient between urban and rural areas, and between urban and lake. However, both urbanization and the lake effect decrease precipitation over the adjacent lake area, mainly due to the lake providing a stable environment with a cold surface temperature and little evaporation in early summer, accompanied by the cool pool caused by urban precipitation.