Short-term energy and carbon balance calculation and footprint-based land cover classification at an urban site

The research takes place within the EU Horizon 2020 program, and the ICOS Cities project, that aims to support cities in formulating climate action plans, through the delivery of data on fossil fuel emissions from urban areas. The EC station is located on the roof of a building in Sassari (Sardinia, Italy N 40° 43' 0.4836 E 8° 34' 32.88, 254 m asl). Measurement height is fixed at 23 m from ground. Instruments include a Gill HS-50 sonic anemometer and a closed-path LI-7200 gas analyzer, for H₂O and CO₂ fluxes. The Eddy Covariance approach for environmental studies is a powerful technique that is used in many applications in the study of urban ecosystems and fluxes. The post-processing phase of data consisted in energy and carbon budgets calculations, together with the flux footprint land mapping, at the ICOS urban EC site ‘ITSas’, which were realized using the software ‘Tovi’ (from LI-COR®). The daily variation of the energy components revealed that the heat storage reaches high values in the morning, while drops out later in the evening. The correction of the regression model revealed the action of GHGs in delaying the daily heat flux peak. The seasonal variations of energy terms revealed that the latent heat flux, the evapotranspiration and the water vapor flux varied at the same rate and correlated positively with high air temperatures and strong radiation values. The energy balance residuals seemed to correlate well with energy availability and heat storage, while they kept a fairly constant variation, with only little deviations falling along the main wind directions (NW and SW winds). The daily C cycle was made up of two main daily maximum peaks, associated with traffic peaks and urban emissions. The footprint-based land mapping of flux contributions demonstrated the urban typology of the flux data since most of the contributions (about 60%) to footprint climatology came from urban areas, while a minor input was delegated to vegetated surfaces.