The rule 3-30-300 for a healthier and greener compact Mediterranean city

Urban trees and vegetation provide a wide range of ecosystem services, including mitigation of urban heat islands, reduction of air pollution, and substantial contributions to the physical and mental health and well-being of urban residents. To support cities in developing evidence-based urban greening strategies, the 3-30-300 rule has been proposed as a practical framework. Each residence, school or workplace should: (i) have at least three trees visible from its window, (ii) locate in neighbourhood with more than 30% of tree canopy cover, and (iii) within 300 m of a high-quality green space. We evaluated this rule in Valencia, a compact and dense Mediterranean city, using tree inventory data and very-high-resolution satellite imagery. Results showed that 70.7% of buildings met the 3-trees visibility requirement, 44.41% were compliant with the 300 m proximity to green spaces, but only 0.03% met the requirement of 30% tree canopy cover within its egocentric neighbourhood (500 m). Mapping the percentage of tree canopy cover is preferable, as it reveals spatial patterns that remain hidden by a simple compliant/non-compliant classification. The analysis reveals that districts with the lowest mean gross income show significantly lower compliance. These results are expected to support urban planners in prioritising areas for re-naturing, setting realistic 3-30-300 targets, and designing greening strategies that enhance the city's resilience to environmental and climatic challenges while providing a healthier environment for its residents, and promoting more equitable access to urban nature in compact Mediterranean contexts.