The Southern Appalachian 'Ring of Asphalt' and climate change?

The built environment represents one mechanism by which anthropogenic (human-induced) activities alter the Earth. Over the past few decades, interest in the feedbacks between human activity and climate has been focused on global and hemispheric scales. Recently, researchers at the University of Georgia associated with the Coweeta LTER  have investigated how different climate change scenarios will affect counties in the southeastern United States.
An extension of this research is focused on better understanding what role urban land cover and land use and pollution have on climate change. Cities in themselves modify weather and climate at scales ranging from local to global. The most comprehensively studied effect of the built environment on climate is the urban heat island. Warmer surface and air temperatures generally characterize the urban heat island or UHI. Urban heat island-related temperature changes depend strongly on both land use and the structure and size of cities. UHIs are one of the most apparent forms of human-caused climate change as most people recognize that it is warmer in cities than the surrounding rural landscape.
While the urban heat island is relatively well understood, urban effects on cloud formation, precipitation patterns, and flooding (together called the hydroclimate) still require additional scientific research. There is interest in how urban development affects the unevenness of precipitation. For the past 12 years, Coweeta LTER researcher Marshall Shepherd and his colleagues have conducted research investigating the role of urban landscapes on the hydroclimate. Shepherd also recently served as co-author on a major urban meteorology report commissioned by NASA, National Science Foundation, and other federal agencies through the National Academy of Sciences.
Shepherd and his colleagues’ research methods are well situated to develop a better understanding of the complex interactions between regional exurbanization and climate change prevalent across southern Appalachia. This is even more important as Ted Gragson, another Coweeta LTER researcher, has shown the state of Georgia, which anchors the Piedmont Megapolitan Region socially and economically through the city of Atlanta, grew at an annualized rate of 3.6 percent between 1990 and 2003 making it the fastest growing state east of the Rockies. Atlanta sits on the doorstep of southern Appalachia and over the last decade its metropolitan area increased from 65 miles to 110 miles north to south while urban populations across the Southeast grew on average by 15.6 percent.
Shepherd, in collaboration with graduate student Chris Strother, analyzed several years of satellite data to reveal an apparent “Ring of Asphalt” in southern Appalachia, with extensive encroachment into the interior region. Urban land cover increased by 15 percent from 1992-2006. Analysis of rainfall trends finds upward trends with 1-2 percent more rain per year in summer rainfall in areas of rapid  urbanization from the early 1950s to 2006. A complementary analysis reveals that increases in summer rainfall amount and intensity are particularly apparent in the urban corridor from Atlanta to Charlotte.
While the linkage between impervious surfaces (asphalt, concrete, etc.) and precipitation may not be intuitive to the public, there is a very clear relationship between urbanization and flooding. Shepherd’s analysis of historic floods in Atlanta, Georgia in 2009 revealed that the flooding was related to meteorological factors as well as rapid runoff and reduced infiltration due to urban land cover. These studies underscore the potential vulnerabilities of southern Appalachia to increased flood activity, landslides and other hazards.
In summary, rainfall in the Southern Appalachians is a function of changes at many scales, ranging from the greenhouse-enhanced global scale to the urbanized regional scale. The region is characterized by the complexities of climate change, mountain-forced precipitation and urbanization. It also represents an important opportunity to study problems at intersections of the coupled human-natural system.
This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.
Original Citation: The Coweeta Listening Project. Franklin Press. Column on "Science, Public Policy, Community." Page B4. July 13, 2012.