Abstract
Earth’s surface is rapidly urbanizing, resulting in dramatic changes in the abundance, distribution and character of surface water features in urban landscapes. However, the scope and consequences of surface water redistribution at broad spatial scales are not well understood. We hypothesized that urbanization would lead to convergent surface water abundance and distribution: in other words, cities will gain or lose water such that they become more similar to each other than are their surrounding natural landscapes. Using a database of more than 1 million water bodies and 1 million km of streams, we compared the surface water of 100 US cities with their surrounding undeveloped land. We evaluated differences in areal (A WB) and numeric densities (N WB) of water bodies (lakes, wetlands, and so on), the morphological characteristics of water bodies (size), and the density (D C) of surface flow channels (that is, streams and rivers). The variance of urban A WB, N WB, and D C across the 100 MSAs decreased, by 89, 25, and 71%, respectively, compared to undeveloped land. These data show that many cities are surface water poor relative to undeveloped land; however, in drier landscapes urbanization increases the occurrence of surface water. This convergence pattern strengthened with development intensity, such that high intensity urban development had an areal water body density 98% less than undeveloped lands. Urbanization appears to drive the convergence of hydrological features across the US, such that surface water distributions of cities are more similar to each other than to their surrounding landscapes.
Highlights
Surface water plays contrasting roles in cities, both supporting and hindering development of urban landscapes
We evaluated two predictions of the urban convergence hypothesis as it applies to hydrography: first, the variance of hydrographic parameters (X = any hydrographic parameter) in the urban land cover is less than the variance of these parameters in the undeveloped land cover (Figure 1, Panel 1)
Based on patterns in US cities, we conclude that urbanization causes the convergence of surface water abundance at broad scales
Summary
Surface water plays contrasting roles in cities, both supporting and hindering development of urban landscapes. To increase the area of urban land and control water supply and drainage, humans drain, fill, and bury surface water features. This practice has resulted in substantial loss of stream channels in cities in mesic regions (Elmore and Kaushal 2008; Roy and others 2009; Pataki and others 2011). A broader assessment of how urbanization changes the channel and water body abundance, distribution, and form (hydrography) in cities is essential to understanding both the environmental constraints on land-use change (Dunne and Leopold 1978) and the environmental and societal consequences of rapid and ongoing urbanization of human populations and landscapes (Paul and Meyer 2001; Cohen 2003; Foley and others 2005; Kareiva 2007; Grimm and others 2008a)
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