Blue space accessibility, quality, and equity in the Global South: the renaturalization of urban stream corridors in Medellín

ABSTRACT Blue urban spaces foster mental health and well-being, yet they remain understudied compared to green spaces. Latin American cities are adopting green infrastructure, sponge cities, and nature-based solutions to improve ecological connectivity, multifunctionality, and climate adaptation. This study examines urban nature in Colombia's second-largest city, which is implementing a network of blue and green corridors. Using publicly available satellite, municipal, and Google Street View data, we assessed ecosystem services of nearly 300 streams, evidencing widespread degradation. Nearly 40% of reaches are buried; 70% of those remaining are inaccessible, 39% channelized, and many exhibit poor water quality. Our spatial analysis reveals a correlation between socioeconomic inequality and environmental injustice: low-income neighborhoods have less blue-green space, tree canopy cover, and multi-layered vegetation, with narrower riparian buffers and more solid waste. However, recreational facilities and vegetation diversity show no correlation, suggesting partial policy success. River corridors provide key ecosystem services associated to habitat, biodiversity, air pollution and heat mitigation, and cultural/non-material benefits. There are 27 km of walkable streams, 70% featuring riparian vegetation (580 species, 50% native, Shannon's Index 0.8–4.0). Additionally, we identify opportunities for improved accessibility and stream daylighting and discuss the role of the Main Ecological Structure concept in operationalizing blue-green infrastructure.