Contrasting effects of lake breeze and urbanization on different types of precipitation in Chicago metropolitan area

Impacts of urbanization on precipitation has been an active yet challenging research area. There were studies showing the urbanization may intensify precipitation, while others show some inhibition from the urbanization due to aerosol effects. In addition, the impacts of urbanization on precipitation is not only about the magnitude but also about the spatial patterns. For example, large urban building clusters may split a rainfall system or change the path of a rainstorm. Chicago Metropolitan area is unique given its geolocation, with rural area on the west, and Lake Michigan on the east. The temperature gradients between these different land use/land type can cause local circulations such as lake breeze (wind blowing from lake to urban), and land breeze (wind blowing from rural to urban). When the synoptic-scale circulations are relatively weak, these local circulations may trigger convections. In this study, we choose three different precipitation events: (1) with strong moisture transport from the Gulf of Mexico (GoM) and persistent low pressure system sitting over the Great Chicago region; (2) with moisture transport from the south but no clear synoptic-scale low pressure system near the Chicago region; (3) no moisture transport from GoM, and no low pressure system at large scale, but still have some heavy rainfall and a flooding warning over the Chicago area. Such event may be driven by the local scale conditions such as lake breeze and moisture from the lake. We will use the latest version Weather Research and Forecast model coupled with urban canopy model to simulate these events. Model validation will be conducted using state-of-the-art in-situ observations. Sensitivity experiments will be carried out to isolate the impacts of urbanization and the lake on these different types of precipitation events.

Impacts of urbanization on precipitation has been an active yet challenging research area. There were studies showing the urbanization may increase or intensify precipitation, while others show some inhibition from the urbanization due to aerosol effects. In addition, the impacts of urbanization on precipitation is not only about the magnitude but also about the spatial patterns. For example, large urban building clusters may split a rainfall system or change the path of a rainstorm. Chicago Metropolitan area is unique given its geolocation, with rural on the west, and Lake Michigan on the east. The temperature gradient between these different land use/land type can cause local circulations such as lake breeze (wind blowing from lake to urban), and land breeze (wind blowing from rural to urban). When the synoptic-scale circulations are relatively weak, these local circulations may trigger convections. In this study, we choose three different precipitation events: (1) with strong moisture transport from the Gulf of Mexico (GoM) and persistent low pressure system sitting over Chicago and the greater region; (2) with moisture transport from the south but no clear synoptic-scale low pressure system near the Chicago region; (3) no moisture transport from GoM, and no low pressure system at large scale, but still have some strong precipitation and there were even flood warning. Such event may be driven by the local scale conditions such as lake breeze and moisture from the lake. We will use the latest version Weather Research and Forecast model coupled with urban canopy model to simulate these events. Model validation will be conducted using state-of-the-art in-situ observations. Sensitivity experiments will be carried out with the optimal model setup to isolate the impacts of urbanization and the lake on the different types of precipitation events.