A Change in the Weather?


If the biophysical parameters influencing the interactions between the atmosphere and the land changed so dramatically over the entire eastern half of the United States, how has the weather changed? This is the sort of question that can’t be answered without plotting the changes in a model, says NASA Earth system scientist Jim Collatz. “You could have more extreme climate events. You may have longer droughts or more thunderstorms or localized thunderstorms. You don’t know until you run a climate model.”

  Photograph of a storm approaching over the suburbs.

You need a model, says climate researcher Roger Pielke, Sr., a senior research scientist at the University of Colorado in Boulder, because the changes in the biophysical parameters have competing effects on the weather. “If you cut down a forest, you might make a surface that has a low albedo go to a higher albedo,” says Pielke. Since higher-albedo surfaces reflect more and absorb less of the Sun’s energy than low albedo surfaces, they tend to be cooler. “But then, you might have less water to transpire,” Pielke continues. Plants breathe out water, which cools the air. If the trees are gone, less water will enter the atmosphere, leading to warmer temperatures. Between the competing effects of a higher albedo and lower water content, “you still might have a higher temperature,” says Pielke.

“I think the bottom line is that our study area represents roughly half of the conterminous United States, and we can see that a lot of major changes have taken place since 1650,” says Steyaert. “The fundamental question is, given these historical land cover and land use changes and their effects on the biophysical parameters, what will the modeling experiments reveal about the consequences for land and atmosphere interactions?”

Pielke and his colleagues have already started to run Steyaert and Knox’s land cover and biophysical parameters data in a regional climate model. Preliminary results show temperature changes that vary by region. As experiments go forward, the weather-related consequences of past land use decisions will become clearer. In addition, we may learn something about how the land use decisions we make today will affect the weather tomorrow. Perhaps leaving or planting a swath of native forest such as Old Belt Woods within our cities or suburbs will be a part of moderating local weather and adapting to global warming.

  • References
  • Braun, E.L. (1950). Deciduous Forests of Eastern North America, Philadelphia: Blakiston Company.
  • DeBow, J.D.B. (1853). The Seventh Census of the United States: 1850. Washington, D.C.: Robert Armstrong: Public Printer. Reprinted in Historical Census Publications. United States Department of Agriculture. Accessed December 3, 2007.
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  • Küchler, A.W. (1964). Potential Natural Vegetation of the Conterminous United States. New York: American Geographical Society.
  • Steyaert, L. T., and Knox, R.G. (2008, January 16). Reconstructed historical land cover and biophysical parameters for studies of land-atmosphere interactions within the eastern United States. Journal of Geophysical Research. 113, D02101, doi:10.1029/2006JD008277
  • Williams, M. (1989). Americans and their Forests: A Historical Geography. Cambridge, New York, Melbourne, Madrid: Cambridge University Press.

With few trees to slow the rush of the wind over the land, these suburban residents might find themselves more prone to windstorms than early settlers who were surrounded by forest might have been. However, the overall effect of land cover change on the weather can't be determined without climate models. As we come to understand how land cover affects the weather, land-use planning may play a role in moderating local weather and adapting to global warming. (Photograph © 2005 Angelrays.)