در نظر گرفتن خاک در اسناد برنامه ریزی شهری – مطالعه موردی فرانسه Consideration of soil in urban planning documents—a French case study

1 Introduction The world population is continually on the rise, as 9 billion human beings are expected in 2050 with the number of people living in urban areas rising from 54% today to 66% in 2050 (United Nations 2014). Consequently, cities are continually growing. In 2010, urban areas covered close to 3% of the total land areas and 0.45% of the total surface area of soils in the world were sealed, excluding only Antarctica and Greenland (Liu et al. 2014). If current trends continue, urban land cover will increase by 1.2 million square kilometers in 2030, according to Seto et al. (2012). This urban growth constitutes a major challenge, as it entails major environmental issues (Vanoudheusden and Blanc 2014). For example, researchers have long identified environmental impacts of urban sprawl (Johnson 2001), such as a loss of fragile environmental lands, higher energy consumption, an increase in storm-water runoff, and an increasing risk of flooding (Adelmann 1998), as well as a reduced species diversity and ecosystem fragmentation (Margules 1992). In recent years, in addition to this phenomenon of urban growth (centrifugal phenomenon), cities are facing a phenomenon of densification (centripetal phenomenon). Cities are being renovated and public policies encourage the population to come and live there. In this context, cities need multifunctional soils. Soil is an ecosystem at the interface between the atmosphere, the biosphere, the hydrosphere, and the lithosphere. Soil is the place where humans develop most of their economic, social, and cultural activities. From an initial vision of soil as exclusively a physical support of human activities, urban soil management has progressively come to focus on the constraints associated with soils, in particular via health approaches. This has been done in response to major health crises induced by soil degradation due to industrial activities in a context of land use pressure. This approach is still conducted in order to detect and to limit the risks of pollutant dissemination, with a view to preserving human health and ecosystems. More recently, a change of outlook on soils has been accompanied by an increased consideration of their multifunctionality in urban projects. Indeed, soils are able to provide some ecosystem services that ensure the development of human societies (e.g., support of infrastructures, food sufficiency) and that participate in the mitigation of the environmental urban issues (e.g., flood mitigation, climate regulation, food sufficiency) (Craul 1992; MEA 2005; Escobedo et al. 2011; Jenerette et al. 2011; TEEB 2011; Gómez-Baggethun and Barton 2013; Adhikari and Hartemink 2016). For example, soils, by storing carbon, are able to regulate climate change. They are also the place where town dwellers can cultivate fruit and vegetables for their food consumption. Furthermore, unsealed urban soils are able to mitigate flooding which is a major environmental issue. For spatial planning, the challenge is then to extend this logic in order to take soil characteristics into account (e.g., level of contamination, geotechnical properties). This would generate a more integrated approach, which includes the agronomic quality of urban soils, by translating soil properties into their ability to provide services (Blanchart et al. 2018).