Outlook on the knowledge gaps to reduce soil sealing and increase the reuse of urban soil

The third specific objective of the Soil Mission is to achieve "no net soil sealing and increase the reuse of urban soil" (European Commission: Directorate-General for Research and Innovation 2022 p. 16). Soil sealing is considered as the main process that causes land degradation in urban areas (European Environment Agency et al. 2022). When soil is sealed, an impermeable layer interrupts the connection between the soil and the atmosphere, leading to the loss of soil resources, biodiversity, and ecosystem services. The process of soil sealing is strictly linked to land take, i.e. the conversion of natural and semi-natural land into artificial land (see definitions in Table 1). The Soil Mission implementation plan estimates that the area with poor soil health due to soil sealing is probably <1% of EU land, but can be as high as 2.5%. These figures are based on the assumption that sealed areas represent around 50% of artificial areas, which cover 4.2% of the EU. Locally, sealed surfaces can reach very high levels, with some areas exhibiting rates as high as 70% (Decoville and Feltgen 2023). Both soil sealing and land take have been steadily growing during the last decades (European Environment Agency et al. 2022). Between 2000 and 2018, artificial areas expanded by 7.1%, with net land take averaging 440 km²/year between 2012 and 2018, primarily at the expense of arable lands, pastures, and grasslands. Concerning the second part of the objective, soil reuse refers to the use of excavated soil from construction sites for other purposes (Reicosky and Wilts 2005). In many European countries, excavated soils are still classified as waste, contributing over 520 million tonnes to the total waste generated in the EU in 2018 (Scialpi and Perrotti 2022). The European Commission proposal for a Directive on Soil Monitoring and Resilience drafted in 2023 and currently under trilogue negotiations, aims to specify the conditions for healthy soils and to lay out regulations to promote sustainable soil use and restoration. The proposal includes mandatory monitoring of land take and soil sealing by Member States, to be conducted according to a common framework of indicators and methodological criteria (European Commission: Directorate-General for Environment 2023). The proposed indicators include total artificial land; land take, including reverse land take (i.e., the renaturalization of previously developed land); net land take (i.e., total minus reverse land take); and soil sealing. Member States may also measure optional indicators such as land fragmentation, land take for specific uses, and impacts on ecosystem services. According to the Commission's proposal, the monitoring of soil sealing and land take indicators should be conducted at least annually. The "no net soil sealing and increase the reuse of urban soils" objective is linked to several other strategies, goals, and targets of the EU, including those of the Roadmap to a Resource Efficient Europe (European Commission 2011) (which included especially the no net land take by 2050 target), the EU Biodiversity Strategy to 2030 (European Commission: Directorate-General for Environment 2020), the Nature Restoration Regulations (European Parliament and Council 2024), and the EU Action Plan “Towards Zero Pollution for Air, Water and Soil” (European Commission 2021). Achieving "no net soil sealing and increase the reuse of urban soil" would also contribute to other EU Missions and related policy areas, such as Oceans, Seas and Waters (management of water quality and quantity in urban areas), Adaptation to Climate Change (flood mitigation), and Climate Neutral and Smart Cities (climate mitigation and resource efficiency). In addition, the objective is directly linked to several targets of SDG 11 - Make cities and human settlements inclusive, safe, resilient and sustainable and SDG 15.3 – End Desertification and Restore Degraded Land.This document provides an overview of the state of knowledge related to this objective, by identifying specific knowledge gaps, actions to address them and potential bottlenecks. This document was prepared by the members of the “Soil sealing and urban soils” Think Tank within the SOLO project.