Analytic Hierarchy Processes (AHP) evaluation of green roof- and green wall- based UHI mitigation strategies via ENVI-met simulations

The present study investigates by Analytic Hierarchy Processes (AHP) approach—a structured technique for organizing and analyzing complex decisions—the effect, at pedestrian level, of urban heat island (UHI) mitigation scenarios in Mediterranean climate densely urbanized areas. AHP has been developed using the temperature outputs of 18 ENVI-met-baseline and 99 ENVI-met-mitigation scenarios applied to one urban area in Rome, one in Bari, and one in Florence. The mitigation scenarios are based on extensive green roof, living wall and green façade deployment varying building heights, coverage percentage, and leaf area index (LAI). AHP results showcase that augmenting coverage percentage linearly increases UHI mitigation potential for all the green envelope technologies and augmenting LAI from 3 to 5 increases the UHI mitigation potential by 10%, 20% and 30% for green roofs, living walls, and green façades, respectively. Besides, the UHI mitigation increases by 70% and 90% augmenting LAI from 1.5 to 3 for green roofs and living walls, respectively. Extensive green roof UHI mitigation decreases increasing building height, reaches an inflection point at 20 m becoming negligible at 40 m. Conversely, living wall and green façade cooling performances increase augmenting the building height until 20 m is reached.