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Urban carbon dioxide Flux Monitoring using Eddy Covariance and Earth Observation

Periodic Reporting for period 1 - diFUME (Urban carbon dioxide Flux Monitoring using Eddy Covariance and Earth Observation)

Reporting period: 2019-09-01 to 2021-08-31

Monitoring carbon dioxide emissions of urban areas is increasingly important to assess the progress towards the Paris Agreement goals for climate neutrality. The current urban emission inventories are based on bottom-up approaches that use activity data (e.g. fuel and electricity consumption statistics) and emission factors for determining carbon dioxide emissions. So far, such approaches are not systematically assessed, present consistency issues and have restricted spatial and temporal resolution. Moreover, these approaches focus on the fossil fuel emissions and neglect the biogenic components of the urban carbon cycle (i.e. plant photosynthesis/respiration, soil respiration, human respiration) which can significantly affect the urban carbon balance. The main goal of diFUME project is to provide a robust and independent methodology for mapping and monitoring the actual urban carbon dioxide flux (i.e. emissions by buildings, traffic, human-soil-plant respiration versus photosynthetic uptake) at optimum spatial and temporal scales, meaningful for urban design and planning decisions.
diFUME developed a novel observation-based approach to monitor urban carbon dioxide flux in high temporal and spatial resolution. The approach combines urban in-situ Eddy Covariance measurements, Earth Observation (EO) monitoring and bottom-up modelling. The method is developed and applied in the city of Basel, Switzerland, where two urban Eddy Covariance measurement systems are available within the city centre. It is demonstrated that Eddy Covariance, combined with high resolution EO-based bottom-up modelling, can effectively resolve the spatial and temporal variability of urban carbon dioxide fluxes and quantify the relative contribution of the different emission sources (i.e. buildings, vehicles, humans, plants/soil). The approach is based on in-situ observations of the carbon dioxide fluxes, therefore can be used as an independent reference to urban inventories but also as a tool for sustainable urban planning.
The work during diFUME project focused on and made significant progress in i) advancing and optimising the methodologies for urban Eddy Covariance data processing and quality control based on the long time series available for Basel case study, ii) Eddy Covariance source area modelling according to different roughness parameterisations derived by EO datasets, iii) developing high-resolution geospatial datasets to describe key urban variables relevant for carbon dioxide fluxes, iv) developing bottom-up modelling approaches for all the urban flux components according to activity and EO datasets, v) developing the final methodology to combine Eddy Covariance observations with the bottom-up model estimations in an integrated high resolution monitoring system. Special focus during the project was on the investigation of the biogenic component (i.e. plants and soils) contribution to the urban carbon dioxide balance. Field in-situ measurement campaigns across the city of Basel were performed for the characterisation of the photosynthetic activity across the urban trees and the respiration of the urban soils. The measurements were also used to develop and calibrate a biogenic flux model which considers the complexities of the urban environment.
In summary, the main achievements of the project concern:
• the development of a methodology to successfully combine Eddy Covariance flux measurements with high resolution geospatial information;
• the development of new algorithms that exploit EO datasets and products for urban applications;
• the use of activity information for modelling spatially resolved anthropogenic emissions in hourly time step;
• the advancement of the current knowledge and modelling tools regarding the dynamics of the biogenic flux components (i.e. photosynthesis, respiration) within the urban environment;
• the introduction of a new observation-based approach to monitor urban carbon dioxide fluxes which can be useful for designing and evaluating local climate change mitigation actions.
The diFUME project methodology and achievements are disseminated across the scientific community, urban planners, climate policy makers and the public. The dissemination and exploitation actions specifically towards the scientific community included conference presentations, seminar/workshop lectures and scientific article publications. Local urban planning and policy maker communities were reached during a Demonstration Event organised by the end of the project. Dissemination to the public was performed by operating a project website, social media accounts, producing video and flyer material and through articles in local newspapers.
The observation-based approach for monitoring carbon dioxide emissions in urban areas, developed in diFUME project, is the first attempt to apply an inversion methodology (i.e. combination between bottom-up and top-down methods) at such high spatial and temporal resolution across an urban landscape. Furthermore, it is the first time to successfully use urban Eddy Covariance flux measurements in a data assimilation scheme. The developed approach demonstrates the usefulness of the Eddy Covariance application in urban areas, which has been largely criticized in the past. Furthermore, the biogenic components within the urban carbon dioxide fluxes had not received enough focus until recently. Characterizing the dynamics of urban biogenic components is a key research gap, relevant to the scientific communities that model surface-atmosphere gas exchanges at high or medium resolution. diFUME introduces a new method for modelling biogenic carbon dioxide fluxes in the urban environment which captures the extreme variability of photosynthesis and respiration across the urban landscape.
The feasibility of climate change mitigation policies to achieve the Paris Agreement target of limiting global warming to 1.5 °C depends on effective monitoring of major greenhouse gas emission hotspots such as the cities. The research implemented in diFUME contributes towards the EU’s ambition of becoming the world’s first climate-neutral continent with the European Green Deal strategy and the related UN’s 2030 Agenda of Sustainable Development Goals (SDGs). The carbon dioxide emission monitoring approach developed in diFUME can be used as a tool for designing effective climate actions at the local scale, quantifying the efficiency of the implemented climate actions and monitoring the progress of cities towards net-zero emissions.
Map of the annual (left) and time-series of the daily (right) modelled carbon dioxide flux (Basel).