Sustainability performance of blue-green infrastructure across seasons and with various designs

Sammanfattning: Global sustainability requirements affect societal development and have an impact on how cities are planned and built today, both strategically and at street level. For example, the overall strategy for urban stormwater management has evolved from being pipe-based, including only control of runoff volumes, to a more multi-functional nature-based blue-green infrastructure, where "blue" areas are characterized by open water and "green" areas by vegetative systems. Nowadays, blue-green infrastructure (BGI) is associated with nature-based features, which enable ecosystem services, which is considered to be the sustainable approach to stormwater management. BGI has mainly been developed in countries with temperate climates.An example of BGI at street level is urban bioretention systems. The design options for bioretentions are vast, including different building and filter materials, and plants. So far, research into these design options of urban bioretention has mainly included technical evaluations, i.e. the impact on pollution treatment and hydraulic control of stormwater. Knowledge of how the different designs of bioretention affect other sustainability criteria, such as economic, social and environmental aspects, needs to be developed. For BGI in general, aspects other than the blue and green parts need to be contextualized since BGI is now globally implemented, also outside the temperate climate zones, for example by also including white aspects from snow-covered urban environments. The purpose of this licentiate thesis was to evaluate and compare different bioretention designs to gain a better understanding of the relative sustainability of different bioretention systems. In addition, the aim was to lay the theoretical foundation for an extended BGI concept by also including white urban environments in the concept of blue-green-white infrastructure (BGWI). The overall goal was to contribute with new and relevant knowledge about design aspects for bioretention systems in particular and regarding BGI in general.By identifying social, economic and technical-environmental indicators in a life cycle and multi-criteria analysis, 12 different designs of bioretentions could be evaluated. The results showed that although design features had a large impact on the performance of bioretentions, no single design configuration excelled in all sustainability aspects among the bioretention options. High performance in the social criteria was associated with the use of trees and smaller volumes of pumice in the filter material mixture. In the economic criteria, costs increased when using concrete and a complex mixture of filter materials. Bioretentions with a saturated water zone and a variety of plant species outperformed the other systems in the technical-environmental criterion.Laying the foundation for the BGWI concept was done in a perspective essay. That work showed that the theoretical framework developed to expand BGI to BGWI is a promising concept. The approach shows that several ecosystem services can be delivered via BGWI. However, while the technical functionality of BGI is well known, its performance in cold climates (like BGWI) presents additional challenges and problems. However, the extension of the BGI concept to BGWI allows for functional urban environments over seasons and over a temperature range of -30°C to 30°C.The conclusion and recommendation are that the results from the licentiate thesis can be used in both strategic and practical planning of urban stormwater management, which aims to accomplish requirements regarding the sustainable development of cities.