Built vs. Green cover: an unequal struggle for urban space in Medellín (Colombia)

Urban green cover provides ecosystem services for human well-being and better conditions for biological conservation. Structural analysis and monitoring across space and time at landscape scale can aid better design and management of urban green cover. In this study, we used Sentinel-2 satellite imagery and semiautomatic reclassification methods (i.e., supervised classification) in Google Earth Engine (GEE), to analyze changes in built and urban green cover of Medellín and adjacent municipalities (Colombia) between 2016 and 17 and 2022-23. We used total area, patch number, mean patch area, and patch cohesion index as proxies of landscape structural changes, differentiating grass from trees. Built cover increased its total area from 77.1 to 80.5%, whereas grass and trees decreased it from 6.4 to 5.8%, and 16.6–13.8%, respectively. Built cover decreased in patch number by 1.4% and increased in mean patch area from 7.08 to 7.72 ha, whereas trees decreased in patch number by 7.8% and grass increased by 9.2%. Both green cover categories decreased in mean patch area (trees: 0.27 to 0.23 ha; grass: 0.24 to 0.15 ha). Otherwise, the patch cohesion index decreased in grass and trees, while in built cover it remained constant over time. Urban green cover in Medellín urban area and adjacent municipalities is increasingly reduced and isolated, whereas urbanization sprawls and densifies, suggesting that local development policies need improvement to prevent urban green cover degradation.