The Washington PostDemocracy Dies in Darkness

Satellite maps shows explosion in paved surfaces in D.C. region since 1984

K Street in D.C. during a rainy rush hour  Feb. 23, 2016. ( <a href="">Andrew Pasko-Reader via Flickr</a> )

It’s no secret the D.C. area has witnessed a development boom since 1984. But to see it from the vantage point of space is eye-opening.

University of Maryland researchers recently published satellite-based maps showing the extent of impervious surfaces in both 1984 and 2010.  Impervious surfaces are those that water cannot penetrate, like roofs and roads.

In the animation below, the changes in the extent of these man-imposed surfaces are glaring.

The amount of dark blue, representing areas with the densest concentration of paved surfaces, increases dramatically.

NASA summarizes some of the most noticeable transformations in the landscape:

In addition to the widening of the Beltway, notice how pavement has proliferated in Fairfax and Loudoun counties in Virginia and Prince George’s and Montgomery counties in Maryland. The District of Columbia was already densely developed in 1984, so the changes there are less noticeable.
The spread of impervious surfaces was widespread across the region, but development was particularly intense along key lines of transportation. Much of the development occurred along the Beltway in communities such as Tysons Corner, Springfield, College Park, and New Carrollton. Inside the Beltway, building followed the Metro rail lines.

The maps were published and analyzed in a study published in the journal Remote Sensing of Environment.

“The pace of development — 9 to 11 square kilometers per year — was striking,” Joseph Sexton, one of the researchers, told NASA.

Lead author Xiao-Peng Song noted the rate of expansion in the region doubled between 1984 and 2010. “One might assume that a region such as the D.C. metropolitan area is ‘built out,’ but this is not true,” Song said.

The increase in impervious surfaces has important implications for the region’s climate. They are generally dark and absorb more heat than the surfaces they replace like grass and forest cover.

The proliferation of such surfaces since D.C. was established has resulted in a large and expanding “heat island,” the zone of warmer temperatures in D.C.’s urban core compared to surrounding rural areas.

Climate Central, the noprofit science communication group based in Princeton, N.J., determined that D.C. had the nation’s sixth most intense heat island. Its nighttime temperatures have averaged more than seven degrees above surrounding areas since 2004, it found.

D.C. has one of the most intense urban heat islands in the U.S.

But the growing built environment not only impacts weather in the city. As outlying areas into Loudoun County get paved over, the darker land surfaces there exert a warming influence as well.

Sure enough, during the study period from 1984 to 2010, temperatures at Dulles Airport in eastern Loudoun County trended upwards.

Inside Washington, D.C.’s urban heat island effect