The need to prepare cities for climate change adaptation requests the urban modeller community to implement sustainable adaptation strategies within their models to be tested against specific city morphologies and scenarios. Greening city roofs is part of these strategies. In this context, the GREENROOF module for TEB (town energy balance) has been developed to model the interactions between buildings and green roof systems at the scale of the city. This module, which combines the ISBA model (Interaction between Soil Biosphere and Atmosphere) and TEB, allows for one to describe an extensive green roof composed of four functional layers (vegetation – grasses or sedums; substrate; retention/drainage layers; and artificial roof layers) and to model vegetation-atmosphere fluxes of heat, water and momentum, as well as the hydrological fluxes throughout the substrate and the drainage layers, and the thermal fluxes throughout the natural and artificial layers of the green roof. TEB-GREENROOF (SURFEX v7.3) should therefore be able to represent the impact of climate forcings on the functioning of green roof vegetation and, conversely, the influence of the green roof on the local climate. An evaluation of GREENROOF is performed for a case study located in Nancy (France) which consists of an instrumented extensive green roof with sedums and substrate and drainage layers that are typical of this kind of construction. After calibration of the drainage layer hydrological characteristics, model results show good dynamics for the substrate water content and the drainage at the green roof base, with nevertheless a tendency to underestimate the water content and overestimate the drainage. This does not impact too much the green roof temperatures, which present a good agreement with observations. Nonetheless GREENROOF tends to overestimate the soil temperatures and their amplitudes, but this effect is less important in the drainage layer. These results are encouraging with regard to modelling the impact of green roofs on thermal indoor comfort and energy consumption at the scale of cities, for which GREENROOF will be running with the building energy version of TEB – TEB-BEM. Moreover, with the green roof studied for GREENROOF evaluation being a type of extensive green roof widespread in cities, the type of hydrological characteristics highlighted for the case study will be used as the standard configuration to model extensive green roof impacts at the scale of cities.

Green infrastructure has a role to play in climate change adaptation strategies in cities. Alternative urban spaces should be designed considering new requirements in terms of urban microclimate and thermal comfort. Pervious pavements such as green parking lots can contribute to this goal through solar evaporative cooling. However, the cooling benefits of such systems remain under debate during dry and warm periods. The aim of this study was to compare experimentally the thermal behavior of different parking lot types (PLTs) with vegetated urban soil. Four parking lots were instrumented, with temperature probes buried at different depths. Underground temperatures were measured during summer 2019, and the hottest days of the period were analyzed. Results show that the less mineral used in the surface coating, the less it warms up. The temperature difference at the upper layer can reach 10 °C between mineral and non-mineral PLTs. PLTs can be grouped into three types: (i) high surface temperature during daytime and nighttime, important heat transfer toward the sublayers, and low time shift (asphalt system); (ii) high (resp. low) surface temperature during daytime (resp. nighttime), weak heat transfer toward the sublayers, and important time shift (paved stone system); and (iii) low surface temperature during daytime and nighttime, weak heat transfer toward the sublayers, and important time shift (vegetation and substrate system, wood chips system, vegetated urban soil). The results of this study underline that pervious pavements demonstrate thermal benefits under warm and dry summer conditions compared to conventional parking lot solutions. The results also indicate that the hygrothermal properties of urban materials are crucial for urban heat island mitigation.

Purpose: In urban areas, soil functions are deeply impacted by all human activities, e.g., water infiltration, carbon storage, and chemical substances degradation potential. In this context, nature-based solutions (NBS) are assumed to deliver multiple environmental benefits for soil quality improvement. The H2020 Nature4Cities project (N4C) offers the framework to develop physical, chemical, and microbiological indicators to the performance assessment for addressing NBS soil quality (performance assessment of soil quality) to be included in a tool-box designed for architects or municipalities. Materials and methods: A simplified performance assessment methodology was developed for addressing NBS soil quality. It is based on the comparison of physical, chemical, and biological characteristics to soil reference baseline. In this setting, we present here the results obtained from case studies selected in three European cities (Nantes (F), Nancy (F), Bustehrad (CR)) to test the methodology. The case studies correspond to three different NBSs: former market turned into gardening areas (FMG), green roofs (GR), and urban allotment gardens (UAG). The performance assessment was based on two criteria: (1) soil fertility and (2) soil contamination. Results and discussion: The basic soil properties (e.g., pH, bulk density) and soil fertility (e.g., soil organic matter (SOM)) for the two open soil NBS (FMG and UAGs) are equivalent to cultivated soils. Those of GR are highly controlled by the type of natural materials used in the substrate. Concerning contamination, the soil quality of FMG was shown to be significantly impacted by former agricultural practices (pesticide residues, trace metals (TE)). Measured molecular biomass of FMG was compared with predictive molecular biomass (determined according to the soil physicochemical properties). Data showed that 12 of the 14 measured plots are classified as altered or very altered soils with regard to this parameter. TE in UAGs soils exhibit various concentrations, depending on former land use, cultural practices, and geological contexts. Conclusions: In conclusion, the study showed that soil fertility is a rather interesting tool in the evaluation of urban soil quality. Nevertheless, basic soil properties seem to be influenced by the effects of trace element and pesticide contamination. The presence of NBSs seems to have a favorable impact (e.g., filtration of pollutants). Inappropriate management of urban soils can lead to a decrease in soil quality and thus influence the current major issues (e.g., carbon sequestration, contamination of urban spaces by organic, and inorganic pollutants).