The physical expansion of urban areas lead to lasting impacts on landscapes and livelihoods. Here, we conduct a global synthesis of trends in urban land expansion, in urban population densities, and lands converted into urban from 1970 to 2010. We find that small-medium urban areas lead their larger counterparts in both rates of urban land expansion and decreases in urban population densities. Urban population densities have consistently declined only in India, China, North America, and Europe with significant exceptions across city sizes. Over 60% of the reported urban expansion was formerly agricultural land with China, Southeast Asia, and Europe in the lead. Counterfactual analysis suggests that, due to the decrease in urban population densities, an estimated 125 000 km 2 land was converted to urban land uses that could have otherwise remained in cultivation or as natural vegetation. In particular, in India and Nigeria, with much of their populations dependent on agriculture, 85% and 30% more land, respectively, was converted to urban land due to decreasing urban population densities. With increasing urbanization, proactive management of urban land expansion, especially in small and medium cities, will be critical for saving agricultural lands in periurban regions while creating equitable and affordable urban landscapes.
Lowland rivers regularly flood and create complex inundation patterns where energy and matter are exchanged between landscape patches over a dynamic network of surface‐water connections. Scale‐freeness of networks for phenomena in many disciplines have been studied with mixed results. Here we present the first documented example of a (roughly) scale‐free network of surface‐water connections within a river‐floodplain landscape. We accomplish this by simulating 23 inundation maps across the historical range of flows for the Mission River in Texas. We then analyze the topology of the surface‐water connections between the river and two habitat patch types. Results show that surface‐water connectivity is scale‐free for ≥64% of simulated flows (≥70% for flows with floodplain inundation). Moreover, the dynamic surface‐water connections meet five of the six conceptual criteria of scale‐free networks. Our findings indicate that river‐floodplain landscapes are self‐organizing toward scale‐free surface‐water connections among patches that optimizes energy and matter exchange.
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