Evaluating the Impact of Nature-Based Solutions: A Handbook for Practitioners

The Handbook aims to provide decision-makers with a comprehensive NBS impact assessment framework, and a robust set of indicators and methodologies to assess impacts of nature-based solutions across 12 societal challenge areas: Climate Resilience; Water Management; Natural and Climate Hazards; Green Space Management; Biodiversity; Air Quality; Place Regeneration; Knowledge and Social Capacity Building for Sustainable Urban Transformation; Participatory Planning and Governance; Social Justice and Social Cohesion; Health and Well-being; New Economic Opportunities and Green Jobs. Indicators have been developed collaboratively by representatives of 17 individual EU-funded NBS projects and collaborating institutions such as the EEA and JRC, as part of the European Taskforce for NBS Impact Assessment, with the four-fold objective of: serving as a reference for relevant EU policies and activities; orient urban practitioners in developing robust impact evaluation frameworks for nature-based solutions at different scales; expand upon the pioneering work of the EKLIPSE framework by providing a comprehensive set of indicators and methodologies; and build the European evidence base regarding NBS impacts. They reflect the state of the art in current scientific research on impacts of nature-based solutions and valid and standardized methods of assessment, as well as the state of play in urban implementation of evaluation frameworks

The GREENROOF module (v7.3) for modelling green roof hydrological and energetic performances within TEB

International audienceThe 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 (Inter-action 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 roof aging: Quantifying the impact of substrate evolution on hydraulic performances at the lab-scale

International audienceGreen roofs are valuable solutions for rain management improvements in urban areas as they can partly store and delay rainfall water. Here, we point out that green roofs cannot be considered as static systems, which performances remain constant over time. This work is based on the cross-use of a lab-scale experiment and a modelling approach to evaluate the hydraulic performances of a green roof substrate over time. Experiments were conducted on new and aged materials, after 30 months of in situ aging. The experimental device was designed and implemented to simulate irrigation or rainfall and accurately monitor hydraulic fluxes. An estimation of hydraulic parameters was obtained by using inverse modelling of experimental data with HYDRUS-1D software. Comparisons between measured and modelled data demonstrated the reliability of the model for simulating the hydraulic behavior of the green roofs. Considering an incoming water event – which mimics a heavy rainfall – of 43 mm h−1 and similar water content initial conditions, our simulations indicate that the retention capacity and the delay effect were always higher for the new substrate than for the aged one. Both of these performance indicators strongly vary with the initial water content of the substrates. Whereas the relation is linear for the retention capacity ranging from 100% of retention for the drier conditions to 0% for the saturated substrates, it is more complex for the delay effect. Such performances were comparable to analogous data from the existing literature. Furthermore, this comparison confirmed that green roofs are submitted to an early aging in terms of structure, i.e. porosity. In our study, the aged substrate presented less favorable performances thus highlighting the key role of the composition of green roof substrate not only on the initial performances but also on their sustainability

How lysimetric monitoring of Technosols can contribute to understand the temporal dynamics of the soil porosity

International audienceHighlights • Lysimetric monitoring of the water budget of a range of soils, including Technosols • Different hydrodynamics were visible as a function of both soils and time. • Temporal dynamics of water budget followed the seasonal climatic variations. • The most anthropised soils exhibited a decrease of their total water storage capacity. Soil poral architecture controls soil functioning and is submitted to temporal changes. The monitoring of soil structure dynamics is complicated by inherent technical constraints in its measurement that are either punctual or complex. In this study, four soils, from a natural one to incrementally anthropized (including three Technosols: Spolic Toxic, Terric Transportic, Spolic Garbic Hydric), have been studied. Seven 2-m3 lysimetric columns have been setup to compare planted and non-planted treatments over 3 to 6 years. Data on the water balance and the hydrodynamics were continuously acquired. Differences were observed between the various soils as a function of their texture. The presence of vegetation also led to significant differences, especially in hot periods, between the vegetated and the bare soils treatments: the amount of water stored into the soil was up to 210 L m− 2 higher for bare soil. Furthermore, the analysis of the “critical water storage capacity” highlighted differences in the hydrodynamics at two time scales. For vegetated soils, similar seasonal variations depending on the climatic conditions were observed for all soils, with higher SCRIT values in cold periods compared to hot periods (differences were up to 190 L m− 2). These results were attributed to roots development over the climatic year that decreases water storage capacity and increases preferential flows. Besides, significant trend evolution was also observed but only for the youngest i.e. the most anthropized soils. Their total water storage capacity decreased down to 52%. It is possibly due to soil compaction, the increase of pore connectivity related to root development and the formation of organo-mineral associations. Our work promotes the association of monitored lysimeters as tool and the study of soils within a gradient of anthropization in order to describe a pedogenetic process like the dynamics of soil porosity

Individual contributions of anthropogenic physical processes associated to urban traffic in improving the road surface temperature forecast using TEB model

International audienceFor years, some work has been undertaken on the traffic heat issue input in the Town Energy Balance (TEB). It has been the subject of many studies related to the summer period and urban heat islands topic. However, during winter conditions, the traffic energy input was marginally integrated into the modeling of the road surface parameters. This deficiency, may explain the differences between forecast and observations for road surface status (RSS) during winter season. Over the past decade, identification and quantification of traffic effects were undertaken. However, they have been studied independently, and non-numerical model integrates the energy contribution of traffic into the RSS. Based on the (TEB) model (v7.2), recent research provided a detailed integration of the traffic thermal contribution in the TEB. This study showed traffic increases the road surface temperature (R S T) by 2-3°C, and its heat inputs improve significantly the R S T modeling. This study consists in evaluating the thermal contribution of each traffic process to improve the R S T modeling based on field experiments. Secondly, the most significant physical processes of traffic responsible for R S T changes have been identified and their contributions discussed. Finally, we analyzed the effects of weather conditions onto the thermal contribution of traffic processes