Abstract
Rapid urban expansion and structural changes are taking place in China’s capital city, Beijing, but without an update of urban land features in a timely manner our understanding of the new urban heterogeneity is restricted, as land-background data is indispensable for bio-geophysical and bio-geochemical processes. In this plain region, the investigations of multi-scale urban land mappings and physical medium environmental elements such as slope, aspect, and water resource services are still lacking, although Beijing can provide an exemplary case for urban development and natural environments in plains considering the strategic function of China’s capital city. To elucidate these issues, a remote-sensing methodology of hierarchical urban land mapping was established to obtain the urban land, covering structure and its sub-pixel component with an overall accuracy of over 90.60%. During 1981–2021, intense and sustained urban land expansion increased from 467.13 km2 to 2581.05 km2 in Beijing, along with a total growth rate of 452.53%. For intra-urban land structures, a sharp growth rate of over 650.00% (i.e., +1649.54 km2) occurred in terms of impervious surface area (ISA), but a greening city was still evidently observed, with a vegetation-coverage rate of 8.43% and 28.42% in old and newly expanded urban regions, respectively, with a more integrative urban ecological landscape (Shannon’s Diversity Index (SHDI) = −0.164, Patch Density (PD) = −8.305). We also observed a lower rate of ISA (0.637 vs. 0.659) and a higher rate of vegetation cover (0.284 vs. 0.211) in new compared to old urban regions, displaying a higher quality of life during urban expansion. Furthermore, the dominant aspect of low, medium, and high density ISA was captured with the north–south orientation, considering the sunlight conditions and traditional house construction customs in North China, Over 92.00% of the ISA was distributed in flat environment regions with a slope of less than 15°. When the water-resource service radius shifted from 0.5 km to 0.5–1 km and 1–2 km, high density vegetation displayed a dependence on water resources. Our results provide a new survey of the evolution of hierarchical urban land mapping during 1981–2021 and reveals the relationship with physical medium environments, providing an important reference for relevant research.
Highlights
Urbanization is one of the main forms of land change worldwide since the 21st century [1]
For the urban land boundary of 1981 (i.e., the old urban land region of 2021 (OULR2021)), we evaluated that the average component of impervious surface area (ISA) was 0.659, which was lower than that of 0.739 in the OULR2021, indicating a component increment of 0.080 in the old urban region
A multi-scale methodology was established to demonstrate the spatiotemporal heterogeneity and the evolution mappings of urban land, land use structure, and its component during the period of 1981–2021.We further investigated the relationship between hierarchical urban lands with using physical medium environments in the study area
Summary
Urbanization is one of the main forms of land change worldwide since the 21st century [1] It has a significant impact on salient environmental issues such as the hydrological cycle [2], natural dioxide emission [3], air pollution [4], soil degradation, and climate. An Asian country with the largest population in the world, is currently experiencing large-scale population migration from rural to urban regions, its urbanization rate has exceeded 60% in the year of 2020 This value in China will rise to. As China’s political, economic, cultural, traffic, and talent center, undertakes many functions of the state [15] It has an obvious siphon effect for people across whole country due to its advantages in infrastructure, society, the natural environment, education, medical care, and relatively high wages [15,16]. Continuous and up-to-date hierarchical urban-land descriptions, such as timely, synergetic land mappings of urban expansion, structural change at the pixel scale, and component change at the sub-pixel scale, are still lacking
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