Maps

D.C. Is Packing on Huge Amounts of Impervious Surfaces

The city has added “1 million cubic meters of pavement, buildings, and the like every year for nearly three decades,” researchers say.

The only way to have not noticed a development boom in Washington, D.C., is if you were living at the bottom of the Potomac River. Now we can actually see the huge spread of pavement and eruptions of edifices, thanks to these maps of impervious surfaces from 1984 and 2010.

NASA based the images on a recent study of Landsat data by researchers at the University of Maryland. Blue areas depict dense accumulations of mostly humanmade surfaces like asphalt and rooftops; white ones have low concentrations of such things. Here’s 1984:

NASA/Joshua Stevens

Now fast-forward to 2010. Things to note include the widening of the Capital Beltway and explosions of impervious material in suburbs like Tysons Corner, College Park, and Springfield, as well as along corridors served by the Metro:

NASA/Joshua Stevens

The impervious incursion is a matter of significance because it can contribute to environmental woes—worsening the heat-island effect, for instance—and alter the natural flow of stormwater to trigger flooding. The district has taken some inventive steps to encourage more green spaces that can absorb stormwater, but the issue will no doubt continue to be a concern to urban planners in D.C. as the city’s rapid pace of development rolls on. Writes NASA:

“The percentage of impervious cover inside the Beltway went from 22 percent in 1984 to 26 percent in 2010,” explained Xiao-Peng Song, the University of Maryland scientist who led the team that conducted the research. “The pace of development—9 to 11 square kilometers per year—was striking. If we assume, conservatively, that the depth of impervious cover is about one-tenth of a meter, then that equals one million cubic meters of pavement, buildings, and the like every year for nearly three decades,” added Joseph Sexton, one of the University of Maryland scientists who conducted the research.

Also striking, Song said, is that the pace of development increased over the period of the study. “The annual rate of expansion has doubled since the 1980s, from 6 to 12 square kilometers,” said Song. “One might assume that a region such as the DC metropolitan area is ‘built out,’ but this is not true.”

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