Green or grey? Integration of nature-based solutions for climate change adaptation in densifying cities

Urban green and blue spaces such as water bodies, parks and street trees reduce outdoor temperatures and energy consumption of buildings through evaporative cooling and shading and are thus promoted as nature based solutions to enhance climate resilience. However, in growing cities, supply of urban green space often conflicts with increasing housing demand, resulting in dense neighbourhoods with lack of green. Therefore, the transdisciplinary project “Future green city” seeks to identify possibilities for balancing population growth and increasing living space demand with the development of nature-based solutions for climate change adaptation. In a transdisciplinary approach with the City of Munich, living labs are used to investigate how nature-based solutions can be integrated into spatial planning processes.

For the case of an urban redevelopment site with row buildings and a vast amount of greenery, eight densification scenarios were elaborated with city planners to derive planning guidelines for the further development of the area. The scenarios consider the effects of densification with additional floors and new buildings, the use of new building materials and energy efficiency standards, the construction of underground car parks and consequently a loss of green space to varying degrees. We are particularly interested in the interplay of densification and availability of green and its impact on indoor and outdoor thermal comfort, energy efficiency of buildings and their life cycle based emission balance. Microclimate modelling is employed to quantify and evaluate the impacts of densification on outdoor thermal conditions during heat days and the benefits of urban green in reducing heat stress.

First modelling results show that additional floors have less impact on human thermal comfort than loss of green space caused by the provision of required parking space. Though underground car parking avoids surface soil sealing, it leads to the removal of existing urban green and excludes the planting of large trees. Informal instruments such as mobility concepts can reduce space consumption by car parking. Moreover, urban redevelopment also bears the potential to increase climate resilience of the stock by targeted greening strategies. The potential is greater, the earlier climate change adaptation is considered as a topic in planning processes. Modelling helps to explore strength and weaknesses of different alternatives in early design stages.