Life-cycle-thinking in the assessment of urban green infrastructure: systematic scoping review

Abstract

Abstract Urban green infrastructure (UGI) delivers multiple social, environmental and economic benefits. A life cycle thinking (LCT) approach is proposed as a viable methodological basis for the holistic valuation of UGI. The purpose of this scoping review is to provide a thorough overview of the emerging literature on LCT application for UGI evaluation. The scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol. A search was conducted in three databases to identify studies which employ LCT for UGI assessments. Eligibility screening and data extraction were performed by three reviewers. The review identified 164 relevant studies, published from 1992 to 2019 across 83 journals. There is a clear prevalence of theoretical UGI cases (54%) over real-life UGI assessments (20%). We also observed a large (84%) and increasing share of comparative studies, mostly comparing UGI with ‘grey’ infrastructure. Although cost-benefit-assessment methods initially dominated, recent studies apply LCT methods more and 7% combine both. The focus has primarily been on UGI types of smaller scale, lower biological complexity, and those integrated with built infrastructure. Green roofs are the most assessed type (40% of all cases), with urban farms second (15%). The assessments of more complex UGI objects lag behind. Most of the reviewed studies include one to three life cycle stages out of seven based on the life cycle assessment (LCA) standards, therefore very few identified studies can be considered comprehensive LCAs. Most studies assess fewer than five UGI benefits (out of 65 identified) and half assess fewer than three UGI disbenefits (out of 36 identified). The two most assessed benefits are energy savings and greenhouse gas (GHG) emissions reductions. The most assessed disbenefits are the monetary cost of implementation and maintenance and GHG emissions. Social aspects are the least assessed.