The Changing Geography of the U.S. Water Budget

Changes in temperature and precipitation patterns have a dramatic effect on the availability of surface water for natural vegetation, streamflow, agricultural production, and human consumption. Through a combination of historical observational climate data and water budget equations, C. Mark Howell and Michael A. Urban have created time-series and maps of twentieth-century water variables within the contiguous United States and compared these with the anticipated twenty-first-century patterns projected by global climate models. The results graphically demonstrate regional variation in hydroclimatic trends. 

Changes in the water budget reflect the interaction between varying temperature and precipitation. During the twentieth-century, most of the United States experienced an upward trend in the temperatures of the southwestern and northern sections (increase of 1°C), while the southeast ended slightly cooler (0.5°C). At the same time, precipitation stayed generally the same, except for an average increase of 100mm throughout much of the Gulf South and the Great Lakes region.

In the future, both of these trends will continue their paths, with the average temperatures increasing as much as 4.5°C, while the precipitation increases little throughout much of the West and South while the Northeast and Northwest may see an increase of more than 100mm. 

In summary, the hydroclimatic conditions we are most likely to see in the twenty-first-century are those that were the most extreme during the twentieth-century, with a noticeable decrease in moisture levels in the South and West, and with the Great Lakes region remaining the most unchanged from the twentieth-century. 

"The Changing Geography of the U.S. Water Budget: Twentieth-Century Patterns and Twenty-First-Century Projections"

C. Mark Howell and Michael A. Urban

Department of Geography, University of Missouri, Columbia

 Annals of the Association of American Geographers, 100(4) 2010, pp. 740-754