Towards an Integrated Framework for Understanding the Landscape Pattern of Coupled Urban Green and Blue Spaces

Urban green and blue spaces (UGBS) provide key ecosystem services, and growing research has sought to examine their synergistic effects using landscape metrics. However, inconsistent choices of indicators for characterizing the coupled UGBS patterns hinder comparability across studies. To address this, we developed a systematic framework that integrates key spatial relationships between green and blue spaces—such as blue-green distances and waterfront green areas—into UGBS landscape characterization. Using Nanjing as a case study, we quantified the integrated UGBS patterns at 500 m and 1 km scales and assessed their distributive equity. At the 500 m scale, the average distance from green space to the nearest blue space was 334 ± 292 m, and mixed blue–green areas accounted for 43% of the total UGBS landscape. Composition metrics of UGBS showed weak positive associations with the proportion of elderly residents and negative associations with socioeconomic indicators. Newly developed urban areas contained larger, less fragmented green spaces, shorter blue–green distances, and more extensive waterfront green zones. Our findings highlight the frequent co-occurrence of green and blue spaces in subtropical cities. The proposed framework offers methodological support for advancing the understanding of UGBS synergies.