Objectives

So far we have considered simply the broad question of whether there is an effect of vegetation change and if so to what degree and to what extent. However, there are several points about the dependence of climate on the management of the surface vegetation that need to be understood to assist in the rational development of both national and international land use policies. This entails examination of two rather distinct phenomena. The first is the direct effect of vegetation change on the evaporation input to the general atmospheric circulation (see chaps. 7 and 8). The second is the less direct effect of deforestation increasing the carbon dioxide concentration of the atmosphere and so changing the radiation balance and, in turn, the air temperature, evaporation, and rainfall.

Although we have previously questioned the objectivity of the observational evidence attempting to relate regional climatic changes with deforestation or reforestation, which has been accumulating for the best part of a century, one of the tasks set for the workshop was to review and assess this evidence. In chapter 3 observations from tropical countries have been reviewed. Specific empirical investigations from India are reported by Meher-Homji in chapter 4, while Shiklomanov and Krestovsky give details of Russian studies in chapter 5. The reviewers were further asked to postulate what mechanisms could account for the observed climatic effects. Without an explanation that includes feasible hypothesized processes, it is difficult to pursue the matter further.

The evidence thus reviewed may not be definitive but is certainly indicative that there could be significant effects of forests on rainfall if not on the volume of runoff.

At the very least it indicates that we are right in looking for a different approach to resolve the arguments.