Modelling green roof hydrologic performances for past and future climate in eight cities around the world

The Olympluie project investigates the modelled hydrological performance of green roofs under varying climatic conditions in eight cities in the world, through long-term simulations (13–29 years) for both historical and future climate data. It also examines performance metrics (e.g. evapotranspiration efficiency) for different green roof designs (varying substrate depths, underlying storage capacities, etc.). Simulations revealed that green roof performance varies significantly with geography, while the analysis of future climate scenarios (2071–2099) for the city of Lyon, France, projected a moderate drop in green roof performance. However, the variability across 12 future climate rainfall timeseries was substantial. These results highlight the necessity of site-specific designs to optimize green roof efficiency under both current and future conditions and confirms the potential of green roofs to mitigate urban runoff. However, in a context of climate change, uncertainty surrounding future rainfall patterns is high and must be accounted for in future design.