Urban ascent with sustainable human development: Extensive cultivated land conservation and urban population capacity growth supported by hillside urban expansion

The phenomenon of hillside urban expansion (HUE) has emerged in numerous countries as a strategic response to topographical constraints and the relentless encroachment upon cultivated land due to urban expansion. Despite its prevalence, the literature has often undervalued the constructive impact of HUE on the sustainable advancement of human societies. To address this gap, an integrated methodology leveraging remote sensing data and statistical analysis was developed to thoroughly examine the global implications of HUE on sustainable human development, with a focus on the conservation of cultivated land and the enhancement of population capacity from 2000 to 2020. Over these 20 years, HUE accounted for 43.29% of total urban expansion (23.19 million km²), with low HUE dominating (74.54%), followed by moderate HUE (15.85%) and heavy HUE (9.61%). Theoretically, HUE preserved an extensive area of 11.57 million km² of cultivated land, thereby mitigating the pressure on such lands by 21.63%, and augmenting grain production by 24.61 × 10⁶ t/year. In addition, HUE provided shelter for an urbanized population of 78.81 million people, contributing significantly to urban population capacity by 38.22%, which is especially vital in low income (LI) countries. A human sustainable development index (SDI) was formulated by integrating the contributions of HUE to both cultivated land conservation and population capacity. Globally, the average SDI stood at 1.04, with the highest values observed in LI countries. This study presents a novel perspective on the role of HUE in bolstering global sustainability initiatives and furnishes a theoretical framework for cultivating a harmonious human-land relationship at a global scale.