Green roof effects on daytime heat in a prefabricated residential neighbourhood in Berlin, Germany

Berlin currently experiences increasing environmental challenges especially through the combined effect of urbanization and climate change. The intensification of summer temperature extremes has become increasingly evident in recent years, urging the city to promote mitigation and adaptation measures for local heat load reduction. Green roofs have been widely recognized as an effective urban greening strategy to reduce heat stress in cities. This study thus analyses the effect of rooftop greening on outdoor thermal conditions in an inner-city prefabricated residential area in Berlin. The studied neighbourhood is one of the inner-city hot-spot areas of environmental loads, highlighting the need for green solutions. We quantified thermal effects of intensive green roof implementation using the ENVI-met model which, for the first time, has been applied at the city's official planning scale. The study thereby aims at overcoming the mismatch between research scales and planning scales, facilitating the knowledge transfer between the science community and urban practitioners, particularly in land use planning. Results indicate that on a hot summer day, green roofs can significantly improve daytime thermal comfort at the roof level with an estimated decrease in physiological equivalent temperature (PET) by 9 K. Green roofs can thus provide spaces of qualitatively increased thermal comfort compared to street-level areas. Overall, our results highlight the effectiveness of rooftop greening in terms of heat adaptation at the neighbourhood level. Therefore, this study suggests that these greening systems should be emphasized in future effect-oriented and sustainable urban planning assessments, especially of inner-city prefabricated housing estates.