Investigate the urban growth and urban-rural gradients based on local climate zones (1999–2019) in the Greater Bay Area, China

Abstract

City development experiences scale expansion from urban to rural regions and built-up intensification across urban domains. This study adopts the local climate zone (LCZ) scheme to investigate urban-rural urbanization gradients from a three-dimensional perspective. A time series of LCZ maps were developed over the last two decades, i.e., 1999, 2009, and 2019, using Earth observation data and machine-learning classification based on Google Earth Engine. Spatiotemporal changes of urbanization gradients and urban forms were captured by measuring the Euclidean distance of built-up LCZ types from compact high-rise patterns of 2019. Results showed that cities in the study region experienced pronounced spatial coverage expansion and compact and high-rise intensification between 1999 and 2019. This phenomenon was especially noticeable in zones close to compact high-rise patterns and periods from 1999 to 2009. In 2019, the GBA region showed central and sprawl urban forms; however, urban forms differed among the eleven cities. A city with more build-up LCZ areas or closer to the Pearl River estuary tended to present central and compact urban forms. In contrast, a city with less build-up LCZ areas or far from the estuary trended to show decentralized and sprawl urban forms. Our findings indicate that the urbanization-gradient derived from LCZ in mega-urban and urban areas is an effective indicator for characterizing urbanization development given the unique role of LCZ presented to differentiate urban expansion and intensification, as well as urban forms. LCZ scheme shows the potentiality in identifying urban central zones and measuring the urbanization gradient in mega-urban urban areas. Besides, the LCZ scheme provides a unique perspective to investigate the urban form of cities which exhibited polycentric structures.