Paris region (Île-de-France County) accounts for 20% of French population on 2% of the French territory. Climate change in Paris region is a reality: the metropolitan area has faced several flood events in the past years (2016) and strong heat waves (2018). At the same time, biodiversity is facing a strong decline in urban areas: common birds populations have dropped by 33% in abundance whereas butterflies species have declined by 22%. As a consequence, there is a growing interest for nature-based solutions that could address both either climate change and biodiversity issues. However, there is still lack knowledge about how to design and manage these new ecosystems. The effectiveness of nature-based solutions has rarely been evaluated and stakeholders needs to understand clearly the real quantitative and qualitative benefits provided by these ecosystems in terms of ecosystem services (water regulation, carbon storage, habitats for biodiversity). For instance, is planting effective in reducing air pollution, storing rainwater or carbon? How this would differ between different tree species or spatial patterns? In order to answer that question, the regional Agency for biodiversity in Paris region (ARB îdF) has carried out a research on green roofs: 36 green roofs have been selected throughout Paris region.
Results/Conclusions
The methodology developed by ARB îdF is based on the evaluation of different ecological aspects such as biodiversity and three different ecosystem services (cooling effect, water storage and carbon capture). We used existing citizen sciences protocols (a participatory science program called Vigie-nature) for plants and pollinators and designed new protocols for ecosystem services. After 2 years of research, we found that all green roofs are attractive for biodiversity, but the composition of species strongly differs from extensive to intensive ones. Intensives green roofs are more attractive to pollinators than others. We also found that semi-intensive and intensive green roofs are more efficient to store water and cool local atmosphere by evapotranspiration than extensive ones. These results help us to understand the real functioning of green roofs and show that the “multifunctionality model” of green infrastructure has its limits: each green roof have specific patterns in terms of ecosystem services. This methodology can be easily adapted to other kinds of green infrastructure. This study will help stakeholders to better design and manage green roofs with respect to the expected ecosystem services.