Summary of the project URBA-SOIL

Half of the world’s population is currently living in cities. Ecosystem services (ESS) play a critical role in human wellbeing in urban environments. Soils are an essential but yet underestimated factor in providing ESS. This project focuses on two crucial ESS, namely water and heat regulation provided by urban soils. The potential to improve these services through targeted management is mainly untapped because essential aspects of urban soils are not sufficiently understood. The critical knowledge gaps concern the physical properties of urban soils, their heterogeneity, the feedback mechanisms between heat and water transport and the role of earthworms in the formation and evolution of such soils.

The first step is to investigate the diversity and the current status of the properties of the urban soils. The main aim is to obtain data on pedogenesis focusing on soil functions in terms of water and heat regulation. A prospecting campaign will permit to discriminate, classify the soil types, and select the study plots at the city scale. As a complement, several experiments will quantify the links between infiltration and temperature dynamics to understand urban soils' water and temperature dynamics. The role of earthworms in the genesis of soil structure and porosity will be investigated using mesocosm and in-situ experiments. The state-of-the-art tomography technology will characterize the porous network of the soil, the spatial distribution of its components and the soil compaction at different scales in a non-destructive way.

Moreover, we assess the potential for using green covers (mulch straw and green waste compost) to improve the regulation of water and temperature dynamics in soils. The field and tomography data will provide the basis for a numerical modelling approach, in which the feedback mechanisms between water and heat transport are systematically explored with the latest generation of numerical models. The models will also be employed to identify an “optimal soil configuration” for soil optimization for different current and future climatic conditions. Furthermore, the dynamics of these virtual soils will be explored virtually for different climatic conditions (e.g. altitude, rainfall, temperature…) representative of two other cities in Switzerland following a climatic gradient (e.g. temperate versus Mediterranean climate).

Based on the above-mentioned steps, guidelines for stakeholders will be elaborated to guide the targeted and controlled development and implementation of urban soils. As this project is application-oriented, our results aim at being directly applicable in the field. Regular exchanges between researchers and practitioners will help develop the guidelines as close as possible to their concrete needs but with a broader impact on the better understanding of urban soils and their capacity to regulate water (i.e. floods) and its interlink with urban overheating.