Understanding urban expansion at the watershed scale is important because watersheds are important carriers of ecological and environmental impacts. However, current analyses are mainly restricted to administrative units only. Here, we used a long-term multitemporal data set of urban land to quantify the spatiotemporal trends in the extent and form of urban expansion from 1992 to 2016 in endorheic and exoreic watersheds, globally. Overall, urban expansion in 70% of watersheds (154/220) showed a decelerating trend. The average urban expansion speed of these watersheds in the last 6 years was approximately half of that in the last 24 years. Urban expansion speed in endorheic watersheds lagged behind the counterparts in exoreic watersheds, with the former approximately 1/4 of the latter. More importantly, the pattern of urban expansion in endorheic watersheds was following the low-density and sprawling trend in exoreic watersheds, which could exert far-reaching impacts on the sustainability of endorheic watersheds located in arid lands. These findings suggest the need to look beyond administrative city boundaries for land use planning and policies in the context of watershed management.

中文翻译：

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全球流域城市扩张模式与分布

了解流域尺度的城市扩张很重要，因为流域是生态和环境影响的重要载体。然而，目前的分析主要仅限于行政单位。在这里，我们使用城市土地的长期多时相数据集来量化 1992 年至 2016 年全球内流和外流流域城市扩张程度和形式的时空趋势。总体而言，70%的流域（154/220）的城市扩张呈减速趋势。这些流域近 6 年的平均城市扩张速度约为过去 24 年的一半。内流流域城市扩张速度落后于外流流域，前者约为后者的1/4。更重要的是，内流流域的城市扩张模式遵循外流流域的低密度和蔓延趋势，这可能对位于干旱地区的内流流域的可持续性产生深远的影响。这些发现表明，在流域管理的背景下，土地利用规划和政策需要超越行政城市边界。