Abstract
Accelerations in population growth and urban expansion are transforming landscapes worldwide and represent a major sustainability challenge. In the United States, land conversion to impervious surfaces has outpaced population increases, yet there are few spatial metrics of urbanization and per capita land change available nationwide for assessing local to regional trends in human footprint. We quantified changes (2000–2010) in housing density, imperviousness, per capita land consumption, and land-use efficiency for block groups of the contiguous U.S. and examined national patterns and variation in these metrics along the urban–rural gradient and by megaregion. Growth in housing (+13.6%) and impervious development (+10.7%) resulted in losses of rural lands, primarily due to exurbanization and suburbanization. Mean per capita consumption increased in all density classes but was over 8.5 times greater in rural lands than in exurban, suburban, and urban areas. Urban and suburban areas had significantly lower mean consumption, yet change was unsustainable in 60% of these areas. Megaregions across the sprawling Sun Belt, spanning from Arizona to North Carolina, grew most unsustainably, especially compared to regions in the Pacific Northwest and Front Range. This work establishes 21st-century benchmarks that decision-makers can use to track local and regional per capita land change and sustainable growth in the U.S.; however, these metrics of the form, extent, rate, and efficiency of urbanization can be applied anywhere concurrent built-up area and population data are available over time. Our web mapping application allows anyone to explore spatial and temporal trends in human footprint and download metrics, and it is designed to be easily updatable with future releases of validated developed land cover, protected areas, and decennial Census data.
Highlights
Accelerations in population growth and urban expansion are transforming regional landscapes worldwide and represent a major global sustainability challenge
We developed fine-scale metrics of human footprint using three foundational, public datasets (Figure 1a): (1) population and housing unit counts for 215,836 block groups from two decennial Censuses (2000, 2010) [62], (2) locations of public parks and protected open spaces from the Protected Areas Database of the United States (PAD-US) [61], and
We found that two the of megaregions examined had a majority of their urban and suburban areas considered land-use efficient, where rates of new impervious development are below the population growth rates: Cascadia (63% efficient lands) and Southern California (56% efficient lands) (Figures 6a and 7)
Summary
Accelerations in population growth and urban expansion are transforming regional landscapes worldwide and represent a major global sustainability challenge. Land changes due to rapid urban expansion impact local and regional biodiversity [4,5,6,7], hydrology and water quality [8,9], biogeochemistry [10], and climate [11,12,13,14] through increased landscape fragmentation [15] and wholesale replacement of natural and working lands with impervious surfaces. Historical growth in the global urban footprint and its impacts are well documented [19,20,21,22], and urbanization is increasingly recognized as a driver of environmental and socioeconomic changes beyond the urban fringe, including rural and exurban lands, through urban land teleconnections [23,24].
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