Multi-criteria assessment of vegetated walls: a scientific approach to nature-based solutions

The integration of nature-based solutions (NbS) into urban regeneration is increasingly recognized as a priority to address environmental, social, and economic challenges. However, the selection of vegetated wall systems remains complex due to the diversity of available technologies and their context-dependent performance. This study presents a methodological framework designed to support decision-making in this field, grounded in the MIVES multi-criteria approach. The framework integrates qualitative and quantitative indicators into a hierarchical requirements tree, structured across environmental, social, and economic dimensions. Indicator selection was informed by a literature review and stakeholder input, while weights were assigned using the Delphi method. The model was applied to a real-world pilot case at the University of Palermo, where five green wall alternatives were evaluated through a complete multi-criteria assessment. Among the 15 indicators analyzed, a new environmental performance criterion was experimentally tested on-site: the reduction of CO₂ concentration (I₈). Preliminary measurements showed a reduction of over 190 ppm in CO₂ levels near vegetated surfaces compared to control areas. The overall framework has also been tested through sensitivity analysis and multi-scenario simulations to evaluate the stability of rankings under varying stakeholder priorities. This research offers a replicable and adaptable methodology for evaluating NbS strategies, enabling transparent comparison across multiple sustainability objectives. By focusing on methodological development within a real context, it contributes to more informed, participatory, and context-sensitive planning in architectural and urban design.