How to assess ecodistrict resilience to urban heat stress under future heatwaves? A case study for the city of Paris

It is now well-known that the frequency, intensity and duration of heatwaves will strongly increase along the XXIth century, which introduces the urban built environment resilience as a new paradigm. In Paris, the intense 2003 heatwave demonstrated that warm urban temperatures could result in serious adverse health issues. Temperatures were particularly elevated during nighttime, due to the urban heat island effect. Since air-conditioning has not penetrated yet in residential French buildings, studying the potential of combined mitigation strategies at the district and building scale to increase the neighbourhood and buildings resilience in strong urbanized areas under future heatwaves is a key subject matter. The climate change aspect is integrated through a future heatwave weather file, re-assembled from dynamically downscaled multi-year regional climate change projections from the EURO-CORDEX project. The new ecodistrict Clichy-Batignolles in central Paris is chosen as a case study, recognized as innovative for low-energy and environmental solutions. It is composed of high-rise residential and commercial buildings, large green areas, cool surfaces, and reduced anthropogenic sources. We used an Urban Canyon Model (Urban Weather Generator) to model the neighbourhood and different design configurations (building height and density, green and cool surfaces). The designs and measures were evaluated through a sensitivity analysis to analyse their potential to mitigate the urban local microclimate air temperature during the heatwaves. We quantified the neighbourhood resilience and found that the ecodistrict is exposed to a strong urban heat stress under the future intense heatwave. These results highlight how outdoor overheating assessment can be used to evaluate the district mitigation and adaptation strategies. This approach can be used for urban planning, while the modelled future urban heatwaves can be used as an input for building simulations and evaluate the resilience of the buildings to urban heat stress.