Urban Eddy Covariance - The INFLUX Network

The eddy covariance method is a useful tool used by various disciplines to measure surface-atmosphere fluxes. Urban environments are still underrepresented in the global flux network. One reason for the lack of urban flux measurements is the complexity and heterogeneity of these urban environments, mixing anthropogenic and biogenic greenhouse gasses (GHG), and making traditional micrometeorological measurements difficult. But in the era of anthropogenically exacerbated climate change, cities pledge lofty goals in reducing GHG emissions. Given this, the eddy covariance method can be a useful tool to quantify urban GHG fluxes within the tower’s footprint. One project that has successfully deployed multiple eddy covariance towers measuring GHG (e.g., CO2, H2O), energy, and momentum fluxes in an urban environment is the Indianapolis flux experiment (INFLUX). This experiment is an ongoing urban GHG flux quantification testbed. The network, in total, has deployed and collected data from thirteen eddy covariance flux towers comprising over two decades of flux years. These tower locations range from agricultural sites on the outskirts of Indianapolis to towers in the cities’ interior over turfgrass, suburban forests, residential areas, and heavily developed urban regions. The data collected from this network of towers have been used to address several uncertainties around the urban environment. For example, using measurements from multiple turfgrass flux towers, we quantified the impact of turfgrass, both spatially and seasonally, integrated across the city, on total urban CO2 fluxes. Before the turfgrass project, biogenic fluxes during the winter were often assumed negligible. However, after measuring photosynthetic drawdown at our turfgrass towers during the winter season, the validity of this assumption was questioned. This project illustrated the importance of representing turfgrass when quantifying urban GHG fluxes, especially in the winter. Other research questions like this have and continue to be addressed using urban flux measurements from the INFLUX network, but many still need addressing. As the INFLUX data become publicly available on flux tower databases like Ameriflux, we would like to share our experiences collecting urban flux measurements, the data available, and questions we have tried to address, supporting cross-collaboration with other projects, labs, and institutions.