Abstract
The configuration of urban land-covers is essential for improving dwellers’ environments and ecosystem services. A city-level comparison of land-cover changes along the Belt and Road is still unavailable due to the lack of intra-urban land products. A synergistic classification methodology of sub-pixel un-mixing, multiple indices, decision tree classifier, unsupervised (SMDU) classification was established in the study to examine urban land covers across 65 capital cities along the Belt and Road during 2000–2015. The overall accuracies of the 15 m resolution urban products (i.e., the impervious surface area, vegetation, bare soil, and water bodies) derived from Landsat Enhanced Thematic Mapper Plus (ETM+)/Operational Land Imager (OLI) images were 92.88% and 93.19%, with kappa coefficients of 0.84 and 0.85 in 2000 and 2015, respectively. The built-up areas of 65 capital cities increased from 23,696.25 km2 to 29,257.51 km2, with an average growth rate of 370.75 km2/y during 2000–2015. Moreover, urban impervious surface area (ISA) expanded with an average rate of 401.92 km2/y, while the total area of urban green space (UGS) decreased with an average rate of 17.59 km2/y. In different regions, UGS changes declined by 7.37% in humid cities but increased by 14.61% in arid cities. According to the landscape ecology indicators, urban land-cover configurations became more integrated (△Shannon’s Diversity Index (SHDI) = −0.063; △Patch Density (PD) = 0.054) and presented better connectivity (△Connectance Index (CON) = +0.594). The proposed method in this study improved the separation between ISA and bare soil in mixed pixels, and the 15 m intra-urban land-cover product provided essential details of complex urban landscapes and urban ecological needs compared with contemporary global products. These findings provide valuable information for urban planners dealing with human comfort and ecosystem service needs in urban areas.
Highlights
The urbanization process has a profound effect on human comfort and ecosystem service needs
Monitoring land-covers and associated changes across all the capital cities provides a potential avenue for research on urbanization processes and intra-urban land structure changes over the Global Belt and Road, and a total of 65 capital cities were selected in the study
The misclassification information was reasonable because complicated man-made coverage materials and divergent urban land surface colors resulted in widespread spectral signatures in the impervious surface area (ISA); the high-albedo impervious surface had similar spectral signatures with that of bare soil
Summary
The urbanization process has a profound effect on human comfort and ecosystem service needs. The majority of the additional urban dwellers will be in developing countries, especially along the Belt and Road initiative [6]. Continuous urbanization is one of the major global land-use changes in 21st century [7,8] and global urban areas will triple by 2030 with respect to urban areas in 2000 [9]. The sustainability of an increasingly urbanized world is tightly associated with intra-urban changes according to spatial configurations of varied land-surface types in built-up areas [10,11,12]. Monitoring urban land-cover and structure along the Belt and Road can provide an intra-urban land assessment for the increasingly urbanized world, and urban land-cover products can provide basic data for this assessment
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