Examples of spatial digital information on soil for urban planning

Soil provides many ecosystem services like the regulation of climate and water cycle. It supports biodiversity but also human activities. In urban areas, soils are often sealed, thus affecting their health. In order to preserve natural, agricultural, and forest soils, the Europe's 'No Net Land Take' (NNLT) policy aims to limit artificialisation. The transcription of this target in the French regulation is based on soil functioning, promoting its integration in planning documents. The poor knowledge on urban soils is however a gap. The following examples on soil infiltration, multifunctionality and pollution from western France illustrate the possibility to build spatial knowledge on the basis of existing data.

Soil infiltration capacity may be assessed in different ways (Lucassou et al., 2025). The Phoebus method considers various parameters such as the relative permeability of pedogeological units, clay content, hydromorphism and the depth of the groundwater table. Its application on Nantes Metropolis and Rennes Metropolis provided maps used to build some urban planning rules regarding rainwater management to reduce flooding linked to runoff. It is also used to elaborate desealing or renaturation strategies, or as an input to soil multifunctionality.

Adaptation of the French MUSE method (Branchu et al., 2021) carried out within the DESIVILLE and QUASOZAN projects allow the assessment of urban soil multifunctionality. The biodiversity and carbon storage capacities are based on correlations with land uses available at a national and pedoclimatic scale, respectively. The soil infiltration capacity is based on the Phoebus method. The agronomic potential of soils is based on the regional soil map and associated soil characteristics stored in a national database. In urban areas with no soil maps, this function s assessed in a qualitative way. The assessed soil multifunctionality map, obtained by crossing the four soil function indices, helped Nantes Métropole to update the areas identified in the urban planning zoning as open to urbanisation. Soil multifunctionality improvement is also considered as a benefit of desealing (DESIVILLE, PERMEPOLIS). Rennes Metropolis is testing its integration in a tool helping to build urban planning strategies achieving No Net Land Take and Land Degradation Neutrality (LDN) together.   

Mapping soil pollution hazards carried (DESIVILLE, QUASOZAN) considers various potential sources of pollution like former industrial activities, anthropogenic deposits, and agricultural activities. Further methodological developments on anthropogenic deposits mapping are in progress (PERMEPOLIS). Soil pollution hazard map is used as an informative layer to alert on pollution pressure, for desealing scenarios by Nantes Métropole or for NNLT and LDN urban planning scenarios by Rennes Métropole. The pedogeochemical background, in progress on Nantes Métropole territory (NEO-SOLOCAL) based on soil analyses, is going to give information on diffuse contamination.

Even if the knowledge on urban soils is limited, some GIS layers may be produced to raise awareness on soils and identify problem areas where more precise knowledge is needed. The banking of soil data is necessary to build a common and shared knowledge on soils. Better urban subsurface knowledge is also essential to build a more precise knowledge on urban soils.