Urban sprawl in a topographically constrained region of Western China: Patterns, drivers, and differentiated governance strategies for the Lanzhou urban agglomeration

Understanding the spatiotemporal dynamics and drivers of urban sprawl in underdeveloped, topographically constrained urban agglomerations is critical for sustainable regional planning, yet such contexts remain underexplored in China’s western interior. This study investigates the Lanzhou urban agglomeration (2012–2023)—a valley-bounded, medium-small city cluster in Northwestern China—by constructing a composite sprawl index that integrates VIIRS nighttime lights and LandScan population data to capture population–land decoupling. Applying linear trend analysis, exploratory spatiotemporal data analysis (ESTDA), and geographical detector modeling, we reveal a medium-to-high sprawl level with a distinct trajectory from initial sprawl through intensification to fluctuating expansion. Spatially, sprawl intensity exhibits a center-low/periphery-high gradient, with local stability declining outward from central leading areas to peripheral areas. Approximately 60% of counties show low temporal volatility, and spatiotemporal transitions are predominantly Type I by low mobility, and high stability. Critically, we identify a dual-driver regime in which economic factors including tertiary GDP, regional GDP, and public budget together with policy interventions jointly propel sprawl in the central leading areas, whereas peripheral development is primarily shaped by agro-pastoral activities. This pattern contrasts sharply with the diffusion patterns of eastern Chinese agglomerations. These findings underscore the need for differentiated governance: intensifying compact, quality-oriented development in the core while steering peripheral areas toward clustered growth, reinforced by ecological redline enforcement. By elucidating a valley-urbanization pathway for the upper Yellow River region, this work offers actionable insights for balancing socio-economic development with ecological constraints in analogous underdeveloped settings.