A standardized assessment framework for green roof decarbonization: A review of embodied carbon, carbon sequestration, bioenergy supply, and operational carbon scenarios

Decarbonization is essential for decelerating climate change and alleviating its associated impacts. Green roofs (GR) are expected to be a solution to the limited urban spaces for ground decarbonization strategies. To support this vision, this study develops a GR carbon assessment framework (GRCAF) in alignment with whole life cycle assessment, carbon capture and storage, renewable energy production, and local climate regulation. The GRCAF introduces four GR decarbonization (GRD) assessment pathways including embodied carbon, carbon sequestration, bioenergy supply, and operational carbon. The GRCAF also showcases standardized assessment scenarios for each pathway while devising a dual-indicator-based method (NV, C-PT) given diverse influencing factors and co-benefits analysis. Based on this framework, a systematic review was conducted to comprehend the research progress of each component in the GRCAF framework and to identify challenges toward GRCAF implementation. The results indicate that existing cognition of GR decarbonization benefits is comprehensive, but most studies only involve single-path assessment. Heterogeneity of assessment scenarios and boundaries under the assessment pathway results in large differences in normalized value indicators (NV), leading to cognitive deficiencies. Although comprehensive decarbonization assessment emerges, pathway completeness and spatiotemporal integrity of assessment scenarios are still defective. Toward the GRCAF implementation, the challenges in modelling and technical drawbacks, database and benchmarks, long-term maintenance pattern with dual-indicator (NV, C-PT) calculations, and synergies, trade-offs and future vision should be addressed. Overall, this study provides a consistent protocol for future GRD research and promote regulations and actions toward net-zero carbon cities.