Rapid Response Flux Site – Where Eddy Covariance Meets Chicago’s Urban Landscape

Understanding urban climate through measurements of surface-atmosphere exchanges

US-CU1 at University of Illinois at Chicago (UIC) Plant Research Laboratory (Photo: Martin Hernandez/UIC)

Science

Eddy covariance has become the standard method for measuring exchanges of biogeochemicals, water, and energy between ecosystems and the atmosphere. However, many of the assumptions that underpin the technique, including homogeneous land cover, unobstructed fetch, and well-developed turbulence, rarely hold in cities. Buildings, roads, parks, and other urban features create a complex landscape that challenges traditional flux measurements, while offering unique opportunities to better understand urban processes.

To address this challenge, DOE’s CROCUS Urban Integrated Field Laboratory established Chicago’s first long-term urban AmeriFlux site (Site ID: US-CU1) at the University of Illinois (UIC) Plant Research Laboratory. The site continuously measures exchanges of biogeochemicals, water vapor, heat and energy between the city and the atmosphere, helping researchers understand how urban vegetation, infrastructure, and weather interact to shape Chicago’s environment.

Since this initial deployment in July 2024, the effort has expanded into the Chicago Urban Flux Network (Raut et al. 2025). A second site at Chicago State University extends observations to the city’s South Side from a rooftop at a small campus setting situated within a dense residential area (Site ID: US-CU2), while a third site at the Argonne Testbed for Multiscale Observational Science (ATMOS) facility provides measurements from a suburban prairie on the outskirts of the metropolitan area (Site ID: US-CU4). Together, these sites capture a gradient of urbanization, from the urban core to suburban natural landscapes.

The network is a key component of the broader CROCUS Micronet (Muradyan et al. 2026), which combines atmospheric, ecological, and remote-sensing measurements to improve our understanding of urban systems. Comparison of fluxes across these contrasting environments provides an opportunity to investigate how urban landscape, vegetation, and land use influence atmospheric processes, evapotranspiration, and surface energy balance.

Chicago’s location along Lake Michigan adds another dimension to the critical science questions. Phenomena such as lake-breeze circulations, heat waves, and extreme weather events strongly influence the movement of biogeochemicals, water, and energy through the urban environment. Long-term observations will help reveal how these processes affect different parts of the city and provide critical information for improving urban earth system models.

US-CU4 at Argonne Testbed for Multiscale Observational Science (ATMOS)

Impact

Urban areas remain underrepresented within flux observational networks despite housing the majority of the U.S. population and generating a substantial fraction of emissions. The Chicago Urban Flux Network provides one of the few coordinated efforts to measure long-term ecosystem-atmosphere exchanges across a major metropolitan area. By integrating flux measurements within the broader CROCUS observational network, local ecosystem processes can be connected with neighborhood and city-scale atmospheric phenomena. The observations will support studies of urban processes, biogeochemical cycling, vegetation function, heat mitigation, etc. while providing a foundation for evaluating and improving urban land-surface and Earth system models.

US-CU2 on the rooftop of the Williams Science Center at Chicago State University, Chicago, Illinois.

Summary

The Chicago Urban Flux Network extends AmerFlux measurements into one of the nation’s largest metropolitan regions. Spanning environments from the urban core to a suburban prairie, the network provides new observations of biogeochemicals, water, and energy exchanges across the Chicago metropolitan region. As the observational records grow, these measurements will help researchers better understand how cities function as ecosystems and how urban environments respond to weather variability and Earth system processes.

Raut, B.A., Muradyan, P., Pal, S., Ivans, S., Tuftedal, M., Sherman, Z., Grover, M., O’Brien, J., Jackson, R., Wawrzyniak, E. and Cho, A., 2025. The Chicago Urban Flux Network with Perspectives from an Eddy Covariance Workshop. Bulletin of the American Meteorological Society, 106(8), pp.E1724-E1730.

Muradyan, P., S. Collis, J.R. O’Brien, M. Tuftedal, R. Jackson, B. Raut, M. Grover, S. Pal, and Coauthors, 2026: CROCUS Micronet: A Distributed Urban Observation System in Chicago. Bulletin of the American Meteorological Society, manuscript under revision.