The challenges of the 21st century, namely, climate change and loss of biodiversity, especially present in heavily populated areas, should be addressed. Nature-based Solutions (NBS) seem to offer a suitable answer to these challenges. However, this new concept is not always easy to implement in a sustainable manner. In an effort to identify the barriers and levers for the implementation in cities of these sustainable NBS, several professionals working on them in France were interviewed. The first analysis with the most quoted words shows that the constraints would be mainly related to technique, management, biodiversity and people. The levers would be related to projects, roofs, people, legislation and services. Further analysis shows that most of the interviewees feel that the main barriers are the lack of knowledge, political will, financial resources and regulations. There are also cultural limitations, such as the use of exotic horticultural plants rather than wild local species. According to them, the technical problems should be easy to solve. To address these issues, the interviewees propose the development of transdisciplinary research disciplines, as well as on-field collaboration between all NBS actors in cities. They also recommend specific funds for NBS and their implication in related regulations. Demonstrative examples of urban NBS highlighting their multiple benefits are also needed to encourage their replication or upscaling. Education and communication are essential to shift the traditional points of view on nature in the city.

Climate change may have significant consequences for water resources availability and management at the basin scale. This is particularly true for areas already suffering from water stress, such as the Mediterranean area. This work focused on studying these impacts in the Llobregat basin supplying the Barcelona region. Several climate projections, adapted to the spatiotemporal resolution of the study, were combined with a daily hydrological model to estimate future water availability. Depending on the scenario and the time period, different assessment indicators such as reliability and resilience showed a future decrease in water resources (up to 40%), with drought periods becoming more frequent. An additional uncertainty analysis showed the high variability of the results (annual water availability ranging from 147 hm³/year to 274 hm³/year), thus making accurate projections difficult. Finally, the study illustrates how climate change could be taken into account to provide adaptive measures for the future.

The Blue Green Wave of Champs-sur-Marne (France) represents the largest green roof (1 ha) of the greater Paris area. The Hydrology, Meteorology and Complexity lab of École des Ponts ParisTech has chosen to convert this architectural building into a full-scale monitoring site devoted to studying the performance of green infrastructures in storm-water management. For this purpose, the relevant components of the water balance during a rainfall event have been monitored: rainfall, water content in the substrate, and the discharge flowing out of the infrastructure. Data provided by adapted measurement sensors were collected during 78 d between February and May 2018. The related raw data and a Python program transforming them into hydrological quantities and providing some preliminary elements of analysis have been made available. These measurements are useful to better understand the hydrological processes (infiltration and retention) conducting green roof performance and their spatial variability due to substrate heterogeneity. The data set is available here: https://doi.org/10.5281/zenodo.3687775 (Versini et al., 2019b).

Worldwide, a large set of initiatives have been carried out aiming to understand the benefits offered by Nature-Based Solutions (NBS) in urban areas. The European Commission (EC) has founded different projects that have performed scientific literature reviews regarding this topic. To objectively compare their results and consolidate the consensus about the impacts and benefits of NBS, we performed a text mining analysis. This methodology coupled with a visual representation of the data allowed to convert the EC funding projects reports (corpus) into a meaningful structured analysis. This method demonstrated that despite the different literature review methodologies of each report, there are common trends exhibited by the results, e.g., the NBS installation as a strategy of urban resilience, the recognition of ecosystem services (ESS) delivered by nature in urban spaces, or the importance of the EC’s supporting role in the promotion of NBS. In addition, some network specific trends have also emerged and complemented the analysis: the assessment of the NBS performance with indicators, the participatory planning approach to NBS (involving citizen and local communities) and the economic value of their services.

The Green Wave (GW) site is located in the heart of the Paris-East Cluster for Science and Technology (Champs-sur-Marne, France). Initially designed on aesthetic criteria, this large wavy-form vegetated roof (1 ha) is a particularly interesting case study regarding hydrological and thermic issues. Since 2013, several measurement campaigns have been conducted during the Blue Green Dream project to investigate and better understand its hydrological behaviour. Rainfall, humidity, wind velocity, water content and temperature have been particularly studied. The data collected have been used to study the spatio-temporal variability of these variables. Results have shown they are all characterized by a non-gaussian distribution and a scaling behaviour.These results have justified the implementation of a continuous monitoring of the GW. It will serve to develop a specific model simulating its hydrological behaviour and able to assess green roof performances. La Vague Verte (GW) se situe au cœur du cluster de Sciences et Technologies Paris-Est (Champs-sur-Marne, France). Initialement conçue sur des critères esthétiques, cette vaste structure ondulée et végétalisée (1ha) représente un cas d'étude particulièrement intéressant pour aborder des questions liées à l'évaluation des bilans hydriques et énergétiques. Depuis 2013, plusieurs campagnes de mesures ont été conduites dans le cadre du projet Blue Green Dream pour mieux comprendre son fonctionnement hydrologique. Précipitations, humidité, vitesse du vent, teneur en eau, température ont ainsi été particulièrement étudiées. Les données collectées ont été utilisées pour appréhender les variabilités spatio-temporelles de ces variables. Les analyses menées ont permis de démontrer que celles-ci sont caractérisées par des distributions non gaussiennes et des comportements scalants. Ces résultats ont justifié la mise en œuvre d'un suivi expérimental continu de la Vague Verte. Celui-ci permettra de développer un modèle spécifique capable de simuler son comportement hydrologique et d'évaluer les performances de structures végétalisées.