Quantifying urban land expansion using remote sensing data and multi-evaluation indices in the Lower Yellow River, China

Monitoring and assessing the dynamic trajectory, spatial patterns, and sustainability of urban construction land expansion is crucial for achieving the Sustainable Development Goals (SDGs) and has become a key issue in current urban research. This study proposes an urban expansion assessment framework that leverages the "trend-pattern-efficiency-coordination" research path to monitor the spatiotemporal dynamics and sustainability of urban expansion in China's Lower Yellow River urban agglomeration (LYR) from 1990 to 2020 at 10-year intervals with multi-source remote sensing images and socioeconomic census data. The research findings indicated a significant acceleration in LYR's urban land growth over the past three decades, albeit with pronounced regional disparities in the magnitude and trend of urban land expansion across different prefectural cities. This study further integrated radar map and equal fan analysis to identify three dominant urban expansion patterns, explicitly showing the dominant direction and spatial shape features. Additionally, the EGRLCR and EGRPGR revealed a consistent downward trend from 1990 to 2020, with the LCRPGR ratio experiencing an initial decline followed by an increase over time. The investigation into the coupling coordination degree showed that most cities were in the high-level coupling stage accompanied by the continuously strengthening degree of coupling coordination. This paper also puts forward targeted countermeasures for cities experiencing uncoordinated urbanization to boost land use efficiency and sustainability. • A quantitative framework of "trend-pattern-efficiency-coordination" was developed to monitor urban expansion. • Urban land expansion in the LYR presented an ever-accelerating trajectory from 1990 to 2020. • Urban expansion trends and patterns exhibited significant regional differences. • It is imperative to strengthening urban planning is to improve the coordination of population-economy-land urbanization.