Impacts of greenhouse warming on water temperature and water quality in the southern United States

The implications of possible increases in carbon dioxide and other greenhouse gases on water resources have attracted increasing attention. Well-established techniques have been used to relate air temperature scenarios produced by GISS, GFDL and OSU global climate models to surface water temperatures and, subsequently, to water quality through a waste load allocation model for streams across the southern United States. There is a consensus among the 3 GCM scenarios studied that surface water temperature increases of up to 7 °C can be expected. Results of the application of a Streeter-Phelps waste load allocation model indicate that even though existing advanced treatment technology would be sufficient to maintain desirable levels of instream dissolved oxygen under elevated water temperature conditions, the use of such technology would be necessary on a much wider scale than at present. The use of extensive riparian vegetative shading was considered as a supplement to advanced water treatment technology. Results show that under 2 of the 3 climate change scenarios and projected patterns of forest migration, shading could appreciably offset the greenhouse-induced water temperature increases east of longitude 97 °W. If present maximum levels of natural riparian assemblages were maintained but no species migration were to take place, water temperatures could still rise in some areas as much as 7 °C. If other environmental or anthropogenic stresses were to result in a major decrease in vegetative cover, such water temperature increases could easily be exceeded.