Spatial Influence of Urban Areas on Surface Water Loss Across the Contiguous United States

Surface water sustains freshwater ecosystems by preserving the integrity of their habitats and supplies water to many anthropogenic sectors. However, human activities impact surface water bodies and determine a progressive reduction of their extent. In particular, the process of urbanization due to urban population growth is expected to produce an increase of the exploitation of surface water in the surroundings of cities.

Here, we examine the driving role of urban areas in the spatial distribution of surface water loss across river basins of the contiguous United States (CONUS) using remote sensing data. We define surface water loss as any conversion from surface water to land that occurred between 1984 and 2018 and we compute the frequency of these losses as a function of distance from urban areas. We find that in all the rivers basins of the CONUS surface water loss is more intense around cities and declines as the distance from human settlements increases. Therefore, we define a distance-decay model that follows a truncated exponential probability distribution which is able to reproduce the observed decreasing trend, proving that urban areas cause an increasing stress on surface water resources in the proximity of human settlements. Moreover, we observe that the decrease in surface water loss is faster in river basins with larger urban agglomerations, indicating that the influence of urban areas on the spatial distribution of surface water loss increases as the extent of urban areas increases as well.

Finally, we investigate the role played by climate in the spatial interaction between urban areas and surface water losses and we notice that different pattern of exponential decay of surface water loss are found across the main climatic regions of the CONUS. Specifically, in areas with temperate and continental climate the presence of urban areas determines local and concentrated surface water losses, while losses are more distributed and reach greater distances in arid regions.