Strategies for desealing soils in urban areas: stakeholder co-construction method – PERMEPOLIS

GIS coupled with multi-criteria analysis

Serious game design

Thematic maps of the pilot study area (Nantes Metropolitan Area) to improve knowledge of the urban system

The project's primary goal is to develop a method that can be used in collaboration with the various stakeholders to co-construct optimised unsealing strategies and the associated tools.

Drawing on input from a GIS, the resulting multi-criteria analysis tool will improve the reliability of the map of areas that could potentially be unsealed (based on the analysis of benefits and risks, the uses, stakeholders' points of view and any uncertainties) and thus help in the co-construction of unsealing scenarios.

A serious game designed for the various stakeholders will facilitate the co-construction process by helping them to understand the complexity of urban areas and the issues involved in unsealing.

The project will also produce thematic maps of the pilot study area (Nantes Metropolitan Area) to improve knowledge of the urban system, while incorporating a presentation of any related uncertainties. Artificial intelligence and geostatistics will be used to address the uncertainties, which will be categorised in a concerted manner in order to facilitate their integration in the GIS and ensure they are taken into account in the decision-making process.

The results are intended to be used by local and regional planning bodies

The disadvantages of soil sealing in the city (flooding linked to rainwater runoff, wellbeing of people living in urban heat islands) are exacerbated by climate change. Desealing is therefore a necessity. However, it must take into account its own disadvantages such as the release of pollutants. Desealing, as a step of the renaturation process, is one answer to the European ‘no net land take’ objective by 2050, adopted by the French Climate and Resilience Act in 2021. Estimated currently around 100 M€/year, the French desealing market is expected to grow over the short to medium terms. However, local authorities, lack tools and methodologies, eg. for defining territorial and local desealing strategies.

In this frame, the Permépolis project ambitions to develop a methodology to build territorial co-constructed desealing strategies. The current desealing operations aim to restore the water cycle, improve the resilience of cities to climate change and/or limit the artificialization of soils. Considering the different regulations (e.g. urban planning and environment), the various benefits and risks associated to desealing, and the different points of view of the stakeholders, the PerméPolis project identifies the following issue: How to combine, in a framework co-constructed with stakeholders, the relevant technical, legal and social information, in order to converge towards an efficient strategy for the desealing of soils in urbanized areas?

The project associates, in an interdisciplinary approach, public research institutes (University G. Eiffel, Nantes University, MinesParis-PSL, UTC, ESGT, ONERA, BRGM, Cerema), a private partner (OTEIS) and a local authority (Nantes Metropolis). The consortium will address more particularly the following research questions:
i) How to better characterize sealed soil properties at territorial scale? The consortium aims at improving hyperspectral data acquisition and treatment to map the nature and properties of sealed surfaces (materials, albedo, use frequency…) and to map the land and legal constraints affecting soils;
ii) How to better characterize the benefits and risks associated with soil desealing? The project aims at assessing the effects of desealing on water runoff flooding and thermal comfort as well as on potential pollutant release ;
iii) How to co-construct a territorial and local desealing strategy? The consortium aims to develop a method and to demonstrate its replicability on several territories, taking into account their specificities, the divergence factors (stakeholder points of view, regulations, legal constraints) as well as uncertainties.

The main expected result is a method to co-construct optimized desealing strategies with stakeholders. It will include: i) a multi-criteria analysis tool coupled with GIS to improve the robustness of the potential of desealing map (with regard to the benefit/risk analysis, to the uses, to the points of view of the stakeholders, and to uncertainties) and help building desealing scenarios, and ii) a serious game dedicated to the stakeholders to facilitate the understanding of the city complexity, the issues of desealing and the co-construction process. Taking into account local specificities (mainland and overseas) will ensure the replicability of the work in different territories. Legal discrepancies will also be addressed. The project will also produce thematic maps on the pilot study area (Nantes Métropole territory) that improve knowledge of the urban system. To help building scenarios, the benefits of desealing watersheds on water runoff and of desealing in urban heat islands on thermal comfort will be assessed by numerical modelling. Artificial intelligence and geostatistics are used to address uncertainties, which will be qualified in a concerted way to facilitate their combination under GIS and their consideration in the decision-process.