Slope climbing of urban expansion worldwide: Spatiotemporal characteristics, driving factors and implications for food security.

The tendency of global urban expansion to be slope climbing has partly become possible with scarce cropland resources in plains. However, the scientific understanding of the quantity, intensity, pattern, and effect of the slope climbing of urban expansion (SCE) is minimal globally. In this study, we have attempted to quantify and evaluate global SCE from Suomi National Polar-orbiting Partnership (SNPP)-Visible Infrared Imaging Radiometer Suite (VIIRS)-like data and other auxiliary data. Results revealed that global SCE areas unevenly increased from 22,760 km to 90,720 km from 2000 to 2020, with an annual growth rate of 21.72%, in which low-environment cost type areas increased from 21,550 km to 84,010 km while high-environment cost type (HEC) areas increased from 1210 km to 6710 km. One remarkable phenomenon is that China's SCE areas in 2020 were more than 11 times those in 2000. In addition, global SCE intensity increased by about 3.4-fold from 2000 to 2020 and the rapid growth of HEC intensity is concentrated in Asia and North America. SCE is mostly affected by urban population growth and terrain. Economic development also promotes its development to a certain extent. We also noted that global SCE potentially made a considerable contribution to saved cropland, saving about 46,747 km with a theoretical increased grain yield of 25,020 × 10 t. Our study provides timely and transparent monitoring of global SCE and offers new insights into sustainable urban development.