Tree-like evolution pathways of global urban land expansion

Abstract

Urban expansion has become a global trend and has a significant impact on global sustainable development. However, previous studies usually explored the spatiotemporal pattern of global urban expansion while ignoring the evolutionary pathways of urban expansion among different industrial structures. To explore the evolution of global urban expansion, we applied a geographic evolution tree model (Geotree) to organize 162 countries' urban expansion into a tree-like hierarchical structure, which consists of branches, twigs, and leaves. Branches represent evolution pathways identified by industrial structures (initial, accelerated, mature, and post-industrialization); twigs describe development stages (low, lower-middle, upper-middle, and high); and leaves are composed of countries’ urban expansion. Four industrial structures were found in the tree-like structure, depicting the stratified heterogeneity of the evolutionary system. Countries in post-industrialization developed into the high stage and experienced decreased urban expansion rates; countries in initial industrialization stayed in the low- or lower-middle development stage and experienced severe urban expansion. For land conversions, approximately 50% of the new urban land occurs on cropland regardless of industrial structures and economic development. Based on the Geotree structure, countries can learn experience from other countries with similar industrial structures (the same branches).