Urban vertical profiles of three most urbanized Chinese cities and the spatial coupling with horizontal urban expansion

Earth has entered the century of city. Horizontal urban expansion has long been studied and is relatively well understood, but the knowledge of the vertical profiles of built structures remains limited. Here we propose a spatially explicit ensemble model and map the wall-to-wall building height of the three most urbanized Chinese cities in 2017 based on open-access Sentinel-1 SAR data, biophysical indices derived from Sentinel-2 multispectral imageries, and nighttime light (NTL) intensity. We further conduct a chronosequence analysis of the building height for these cities along with their horizontal urban expansion between 1985 and 2017. We show that our proposed method performs well in generating 1 km × 1 km building height maps in Beijing (R2 = 0.87, RMSE = 3.53 m), Shanghai (R2 = 0.82, RMSE = 4.21 m), and Shenzhen (R2 = 0.78, RMSE = 6.92 m). Shenzhen has the tallest (mean building height (MBH) = 37.63 m) and most diverse (coefficient of variation (CV) = 63.84%) vertical landscapes, followed by Shanghai (MBH = 29.86 m, CV= 51.14%). And the vertical profile is the lowest (MBH = 19.21 m) and relatively homogeneous (CV = 44.93%) in Beijing. We also find that vertical urban profiles are coupled with horizontal urban expansion, evidenced by an increase in building height along with the decreasing proximity to urban centers and the increasing urbanization intensity, and a clear imprint of urbanization age in all three cities. The specific characteristics vary among cities due primarily to local urbanization strategies. The knowledge of the vertical profiles of the three most urbanized Chinese cities complements the horizontal insights into urbanization and can assist sustainable land use and urban planning.