Equity-oriented GIS-MCDA mapping of urban rooftops for green roofs and photovoltaic systems: competition and synergies in Padua

Climate change and urbanization intensify environmental risks and deepen social inequalities, calling for equitable adaptation and mitigation strategies. Urban rooftops provide untapped multifunctional spaces for integrated climate actions. Yet, their assessment is often limited to single-technology approaches, neglecting integrated perspectives. This study presents the Rooftops for Equity and Sustainability (RT4ES) model, a GIS-based multi-criteria decision analysis combining rooftop suitability with vulnerability-informed prioritization. Using open-access spatial data, RT4ES evaluates the feasibility of extensive and intensive green roofs, rooftop gardens, and photovoltaic systems, integrating socio-economic and environmental vulnerability indices. Applied to Padua (Italy), the model identifies 11.67 km2 of net suitable rooftops across 29,493 buildings, emphasizing eastern, northeastern, and central areas where feasibility and vulnerability converge. Overall rooftop greening opportunity yields around 10.94 km2 of additional vegetated surfaces, which corresponds to 20.95% of the inventoried on the ground green- space stock. Concerning rooftop PVs potential, this yields around 302% of municipal household electricity consumption. Results suggest that individual and co-locating green roofs and photovoltaics enhances both energy efficiency and ecosystem services. By incorporating social and environmental vulnerability, RT4ES reorients priorities toward compact, underserved neighborhoods, fostering inclusivity and resilience. This open-source, replicable tool supports equitable multifunctional rooftop planning aligned with local and international frameworks.