Investigating urban land-atmosphere exchanges of heat, moisture, and carbon via eddy covariance measurements

The concentration of humans in cities has led to various environmental issues such as the urban heat island effect, urban rain island effect, and substantial emissions of greenhouse gases. Flux observations can provide valuable insights into urban surface-atmosphere interactions, which would help mitigate these environmental problems. In this study, we choose a typical middle-rise campus in a hot and humid city, i.e., Wuhan in central China, an international wetland city, as our test bed. To the best of our knowledge, there is a lack of relevant research in Wuhan. Therefore, we deployed the first EC tower with a height of 10m on the top of a 22.1-meter-high building. This study systematically investigates urban land-atmosphere exchanges using datasets from the EC tower, including air temperature, humidity, wind velocity, carbon dioxide flux, net radiation(Q*), sensible(Q_H) and latent(Q_E) heat fluxes, etc., as well as anthropogenic activity data, such as traffic scheme and building energy consumption. First, we used typical analytical footprint models proposed by Kljun et al. and Kormann & Meixner to analyze the diurnal and seasonal changes in the flux source area. Second, anthropogenic heat flux(Q_F) was simulated using a large-scale urban energy model(i.e., LUCY), while storage heat flux(Q_S) was estimated through an objective hysteresis model (OHM). Then, we conducted an energy balance closure analysis.  Finally, we analyzed the spatiotemporal evolution patterns of urban heat, moisture, and carbon fluxes to further our understanding of two fundamental questions: (1) how will anthropogenic and biospheric contributors influence urban heat, moisture, and carbon fluxes? (2) how will meteorological factors affect urban heat, moisture, and carbon fluxes? The objective of this study is to provide a scientific basis and decision-making insights for promoting sustainable urban development.