Comparative analysis of the concepts of soil sealing and land take in major European cities

The objective of no net land take by 2050, first mentioned in 2011 in the document titled "Roadmap to a resource efficient Europe", is becoming one of the biggest challenges facing European planners. It aims to halt the dramatic expansion of the area covered by cities in Europe, an expansion that threatens biodiversity and food supply.

However, despite the apparent simplicity of the objective, the concept of land take can lead to misunderstandings and even potentially to counterproductive outcomes, as it introduces a dichotomous distinction between non-artificial areas, which benefit from a positive connotation, and urban areas, which appear, by contrast, to be problematic. In reality, the land use mosaic is much more complex.

For instance, the European Environment Agency's definition of artificial urban spaces includes intra-urban green spaces (parks, cemeteries, etc.) that can sometimes be more biodiverse than intensively farmed fields.

For instance, the European Environment Agency's definition of artificial urban spaces includes intra-urban green spaces (parks, cemeteries, etc.) that can sometimes be more biodiverse than intensively farmed fields.

This is why the proposal for a directive of the European Parliament and of the Council on soil monitoring and resilience suggests generalising the monitoring of soil sealing, a notion that complements that of land take. It has more objective attributes than the notion of land take, as it relates to a physical property of the soil: rainwater can no longer penetrate it deeply but instead runs off the surface.

In terms of land use planning, these seemingly small differences between the no net land take and no net soil sealing notions have tangible consequences. For instance, filling unbuilt land plots in the urban fabric may be compatible with a no net land take approach, whereas it will increase the degree of soil sealing. It is therefore important to take into account the degree of soil sealing in artificial areas to determine to what extent the internal horizontal densification of urban areas is desirable and compatible with other environmental concerns, such as the prevention of urban heat islands or the loss of intra-urban biodiversity.

In terms of land use planning, these seemingly small differences between the no net land take and no net soil sealing notions have tangible consequences.

The literature has already shown that, on average, the rate of sealing within built-up areas is close to 50 % (Prokop et al., 2011). However, this is an average value, and situations can vary considerably. An appropriate ratio of impervious surfaces in an artificial area could be considered a satisfactory compromise between, on the one hand, densifying the built-up substance to save land resources and, on the other hand, maintaining construction-free zones that provide more resilient and socially acceptable urban environments.

The map illustrates the importance of these variations, showing the proportions of sealed surfaces within the artificial areas of the most important European morphological agglomerations in terms of size and administrative power. To do this, data produced by the European Environment Agency were used, namely the Urban Atlas (for the artificial areas) and the Copernicus high-resolution layers of imperviousness density (for the sealed areas).

The rates of soil sealing within the artificial areas vary greatly, from 31.5 % in Stockholm to 72.6 % in Valetta.

Northern cities appear, in general, to be much less sealed than Mediterranean ones, with a few exceptions, such as Antwerp (where the proportion is largely linked to the sealing of its major port). This can be explained in various ways. In Scandinavia, low population densities have long favoured less compact urban forms thanks to the greater availability of land. In the United Kingdom, the urban planning tradition, which is favourable to the maintenance of vast urban parks, has allowed ratios of imperviousness that have remained quite moderated, despite substantial densities. In London, for instance which shows the highest rate of land take inside of the city limits of the whole sample (96.4 %) the proportion of surfaces that are sealed is 46.6 %, which is below the average of the sample.

The high rates of sealing in cities around the Mediterranean Sea may seem problematic, insofar as this region has been identified as one of the climate change hotspots in Europe, with a summer temperature that is expected to increase by 2 °Cover 2021-2050 compared with 1961-1990. This has the potential to result in severe drought episodes and water shortages that will become more and more critical.

The map also shows that cities located in eastern European countries, which were largely transformed by the post-World War II Soviet urban planning tradition, generally have lower imperviousness densities within their artificial spaces (Bratislava, Wrockaw, Iasi, etc.) than cities in western Europe.

This comparison shows that the potential for horizontal densification in urban areas, which is a priori the easiest way to allow new development within the urban fabric and without new land take, varies from one context to another. This underlines the need to adopt strategies tailored to the specificities of each context and to use the full range of potential tools to achieve the objective of no net land take, and not just horizontal densification. Renaturation, compensation and vertical densification are other avenues to consider.

To know more, please consult: Decoville, A. and Feltgen, V. (2023), "Clarifying the EU objective of no net land take: A necessity to avoid the cure being worse than the disease", Land Use Policy, 131: 106722.

Antoine Decoville and Valérie Feltgen are geographers working at the Luxembourg Institute of Socio-Economic Research (LISER). They run the Observatory for Spatial Development, which provides evidence-based recommendations to policymakers in Luxembourg