Temporal and spatial patterns of the Sealed-to-Artificial area Ratio in European urban areas

Land take is primarily driven by urbanisation and infrastructure development and is closely linked to soil sealing, which involves covering soil with impervious materials. Over recent decades, both processes have steadily increased in European urban areas, significantly impacting ecosystem services. To stop these processes, the European Commission has set two distinct targets: "no net land take" and ”no net soil sealing”. To examine the relationship between the two processes, we introduce the Sealed-to-Artificial area Ratio (SAR), a novel indicator defined as the ratio between sealed areas and artificial areas in a certain region. We computed SAR for 661 Functional Urban Areas (FUAs) in the 27 countries of the European Union plus the UK, and its change between 2012 and 2018. Two hypotheses were tested: (1) SAR tends to decrease in FUAs with predominant agricultural land cover, as opposed to artificial; and (2) SAR tends to increase as urban form becomes more compact, as opposed to sprawling. Results show a general decrease in SAR (median of –0.36), indicating a possible trend toward lower-intensity urban development. However, regional variations emerge, with the UK-Ireland showing a greater decrease and the Southern region a smaller reduction. As expected, SAR increased in FUAs with a high share of artificial land cover and a tendency towards a more compact urban form, while those with larger availability of agricultural land and a sprawling development showed the opposite trend. The proposed indicators can be used to support urban planning and local policies to achieve European targets.