Urbanization increases surface runoff, by creating more impervious surfaces, such as pavement and buildings do not allow percolation of the water down through the soil to the aquifer.
This is consistent with previous work indicating that segregation tends to concentrate racial/ethnic minority groups into densely populated neighborhoods, particularly in larger cities (Iceland et al. 2002; Lichter 1985; Massey and Denton 1989), which in turn are likely to have fewer trees and more impervious surfaces (Iverson and Cook 2000; Pozzi and Small 2001).
Sites with perennial flows had more vegetation and water compared to ephemeral sites and engineered sites had more impervious surface compared to natural sites.
Overall, the riparian bird community is shifting toward urban dwelling, resident species that are characteristic of riparian sites with less water and more impervious surface.
In particular, in parts of watersheds that remain rural or natural, we need to curb the spread of suburban sprawl, which inevitably brings with it more impervious surface in the form of roads, streets, parking lots, and rooftops.
In both the landscape and core areas of their home-range, birds positioned their home-range in areas with more trees, avoiding impervious surfaces and utilizing grassed areas.
In the United States alone, pavements and other impervious surfaces cover more than 43,000 square miles an area nearly the size of Ohio according to research published in the 15 June 2004 issue of Eos, the newsletter of the American Geophysical Union.
Globally, it is a little more difficult to judge the square mileage of impervious surfaces.
"The structure of the community changed along the urbanisation gradient, with more parasitic species in sites with [an] intermediate proportion of impervious surfaces," they observed.
[For more information on reducing runoff, see "Paving Paradise: The Peril of Impervious Surfaces," p. A456 this issue.] Even so, low-impact techniques alone will not be enough to fully control the CSO problem, according to the EPA's 2004 report.
More researches are also needed to better understand temporal resolution, change and evolution of impervious surfaces over time, and temporal requirements for urban mapping.
