How does the relative spatial pattern of green within cities impact carbon uptake? A European scale analysis

Cities constitute the main source of CO2 emissions into the atmosphere. Urban areas exhibit a variety of land use profiles and carbon metabolisms. Yet it is important to assess to what extent they can cope with their own emissions. We address this issue by examining how the internal spatial organization of cities can impact the flow of anthropogenic CO2 between their major sources - human activities - ; and their main storage infrastructures, with a focus here on urban green spaces and forests. Is it better to have a dense core with a peripheric green belt? Large green patches within the core centre? Or small and fragmented green spaces?

The objective of the present work is to tests whether the internal spatial organization of urban areas - in terms of green infrastructure characteristics and land use types - matters for evaluating carbon sequestration potentials within urban areas. Or whether they can simply be considered as single objects with a quantity of carbon emissions and a carbon sink capacity derived directly from aggregated land use data.

We present a spatially explicit urban carbon flow model. Using land use data, an emission inventory and sequestration potentials from the vegetation we allocate a carbon budget to each spatial unit within the urban systems. Anthropogenic CO2 emissions are accounted from different land use categories using the TNO CAMS dataset. The potential of carbon sequestration by the urban forest is set using estimates from the literature. Urban carbon flows are then simulated for all Functional Urban Areas (FUAs) of European cities using the Urban Atlas 2012 database.
Most studies on carbon dioxide uptake into vegetation at city or metropolitan scales estimate carbon stocks or aggregated carbon flows, while spatially explicit urban carbon flow analyses are made on spatially limited areas - i.e. neighbourhood level. Also, the homogenous land use data and emissions inventory at the continental level allows for a comparison of the different urban areas. We then compare the aggregated budget of the areas of study – commonly done in budget approaches from micro to global scale – to the spatially explicit budget. It allows us to estimate the real contribution of the urban forest to the uptake of anthropogenic emissions within the same urban ecosystem. The analysis then investigates the level of efficiency of CO2 uptake for different typology of urban areas for different carbon profiles. The efficiency is defined as the share of local emissions captured within the urban boundaries.

In the future, the model will be validated using eddy covariance empirical data.