The Potential of Small-Scale Urban Greening Interventions for Heat Mitigation and Biodiversity Conservation. A Neighbourhood-Scale Case Study in Cologne, Germany

Urban green infrastructure (UGI) is gaining popularity for disaster risk reduction and climate change adaptation in urban contexts, but dense development obstructs the realisation of large-scale greening measures. This thesis investigates the potential of small-scale, site-specific urban greening in a residential area in Cologne, Germany, to improve ecosystem service supply. The objective is to assess how much the capacity for heat mitigation and biodiversity conservation can be increased through small-scale solutions, such as grass, shrubs, trees, green roofs and green facades. A spatial analysis is conducted to inventory the current UGI and map opportunities for functional upgrading, i.e. increasing, enriching, and connecting the existing UGI, resulting in a maximal greening scenario. Heat mitigation and biodiversity conservation are quantified based on the spatial dimensions of the UGI, using published supply rates and indicators. The urban surface exhibits enormous potential for UGI implementation, which is currently underutilised, particularly regarding roofs, facades and streets. Through small-scale interventions, about 1.2 million square meters of UGI can be added, increasing the green cover of the urban surface from 8 to 23%. The cooling capacity can be more than doubled, largely due to building-based solutions. The increase in tree canopy also contributes significantly, but a deficit remains regarding the provision of shadow. The biodiversity conservation can be improved through greater habitat, larger patches, and a significant increase in connectivity (proximity index increases by five times). Public and private efforts are required to utilise this potential and participatory processes are recommended to ensure environmental justice.
Transforming roofs, facades and streets into green spaces can significantly cool cities and enhance biodiversity. Discover how small-scale greening interventions can improve urban life and create resilient cities. GREEN SUPERPOWERS TO TACKLE URBAN CHALLENGES As cities grow and the planet warms, urban areas are increasingly at risk from disasters like heatwaves, while global and local biodiversity is shrinking due to habitat loss. This makes new urban planning strategies essential for sustainable and safe living conditions. One promising approach is to improve the urban green infrastructure (UGI), which can offer multiple benefits: cooling through evapotranspiration and shading, air filtration, noise reduction, carbon storage, flood mitigation, and enhanced recreational and aesthetic value. These "superpowers" make urban greening a powerful tool in urban resilience strategies. However, implementing these solutions often faces challenges, such as limited space and insufficient data on their benefits. The city of Cologne, Germany, aims to increase greenery to combat heat, conserve biodiversity, and provide other ecosystem services. Considering the dense development, this thesis explores how small-scale greening interventions—like greening roofs and facades, and planting street trees—can enhance heat mitigation and biodiversity conservation. ENORMOUS UNTAPPED POTENTIAL By conducting a case-study in two of the least-greened neighbourhoods in Cologne, this study finds enormous potential for small-scale greening. In the study area, around 90% of the roof area and at least 7% of the facade space can be greened, amounting to ca. 1.1 million square meters of additional green surface, and around 1,900 street trees can be planted. By applying these measures, the overall green area can be tripled, leading to double the current cooling capacity, and a five-fold increase in the green space connectivity, which improves biodiversity. Additionally, some great co-benefits can be expec