Understanding Three-dimensional Global Urban Growth

Kurzfassung

Urban structural growth has significant local to global environmental impacts resulting from associated changes in local climate, urban materials stock, and greenhouse gas emissions. As part of contemporary urbanization, urban areas are expanding at unprecedented scales and rates. However, much of our understanding of urban expansion is predicated on examining outward spread. Urban expansion in vertical dimensions resulting from the increase in building heights remains relatively less studied and more so from the perspective of a decadal to multi-decadal time horizon and global urban scale. Our research examines urban structural growth across urban areas globally from the 1990s through the 2010s, using multisource space-borne scatterometer-derived backscatter and urban built fraction datasets. In 478 large cities (population size > 1 million) and during the 2000s, we identify five characteristic urban structural growth typologies: stabilized, outward, mature upward, budding outward, upward and outward. Examining a longer time horizon, i.e., 1990s-2010s and over 1550 urban areas globally, however, we find a significant shift in urban structural growth characteristics of large urban areas from increasing built fractions and increasing building volume (measured as a proxy with microwave backscatter) to decreasing growth in built fractions but increasing building volume. Additionally, we find increasing microwave backscatter in all urban areas, with more significant increases concentrated in Asian cities. Our findings advance our understanding of how urban areas are evolving under contemporary urbanization and have implications for changes in urban living, associated materials and energy needs, and local climate.