An Integrated Urban Weather Modeling System for Heterogeneous Urban Processes in Summer Chicago

Current numerical models for urban weather and climate simulations still have significant research gaps at the city scale, where heterogeneity in land-use types influences atmospheric processes. The Greater Chicago Area, positioned between rural areas, Lake Michigan, and a dense metropolitan region, presents a complex urban environment with diverse building heights and vegetation distributions that are not accurately represented in existing models. Under the Community Research on Climate and Urban Science (CROCUS) project, advancements have been made to the Weather Research and Forecasting (WRF) model, specifically improving the Building Effect Parameterization (BEP) to better account for urban street trees, low-rise building effects on atmospheric circulations, and detailed representations of urban structures. To evaluate these potential improvements, we utilize data from two Intensive Observational Periods (IOPs, 48 hours each) in July in Chicago. The IOP data include high-spectral-resolution and Doppler lidar profiles, 2- and 10-meter meteorological observations, and radiosondes (balloon launches) across the Chicago area, including the city and southwestern Lake Michigan. These periods feature distinct meteorological conditions, including a lake breeze, a cold front, and a convective system passing through the region, allowing for comprehensive validation of the updated WRF-Urban model and a better physical understanding of city-scale urban heterogeneity. The study highlights urban processes that were previously underrepresented in coarser-resolution models and demonstrates the benefits of high-resolution, realistic simulations, as well as comprehensive urban observations, for improving urban weather and climate modeling.