Implications of feedback processes in plant water usage and resulting climate change

Increased carbon dioxide in the atmosphere has the secondary effect on plan ts of reducing transpiration. The degree of reduction in transpiration has been studied mostly at the leaf scale and as such, has not taken feedbacks into account that come into play when the plant canopy or the atmosphere as a whole is considered. The objective of this paper is to examine the role of negative feedback processes that act through the dynamics of the canopy and the atmosphere. This is done through the application of two canopy mode ls, one of which is later coupled to a full Atmospheric General Circulation Model (AGCM) called GENESIS. The results suggest that the reduction in tra nspiration in a double CO2 environment compared to present day will not be as considerable as the leaf scale experiments suggest - a 7 percent reducti on compared to 15 to 57 percent when feedbacks are considered. At the regio nal scale, precipitation patterns appear to be the primary factor in determ ining evapotranspiration. The implications for agriculture, in terms of wat er usage, would therefore not seem to be as acute as the leaf scale experim ents depict. Regarding climate change, there is a suggestion that regional water usage may vary from present day values in certain areas.