A Commentary on: Probable Impact of Deforestation on Hydrological Processes

Abstract

The thrust of this paper is to examine the observational basis for relating reductions in forest cover to changes in rainfall. It does not take up the simpler issue of relationships to changes in runoff, which are well known in small basins, independent of atmospheric effects. While there is considerable literature pointing to rainfall reduction with deforestation, it is fair to say that very little meets the standards of rigorous controlled experimentation. As the author discusses, at least some of these results can be interpreted in terms of changes in the exposure of the rain gauges independent of the actual rainfall. Little effort has been made to exclude natural variability of rainfall as an explanation, although such is recognized as a major factor in interpreting rainfall patterns in regions dominated by convective rainfall. How many of the results arise from authors finding data to match their prior conception of the answer? In spite of these difficulties, the large amount of supporting evidence certainly lends credence to the hypothesis that conversion of large areas in the tropics from forest to shorter cover can significantly reduce the overall amount of rainfall and perhaps extend the length of the dry season. This possibility is further supported by recent climate model experiments (Lean and Warrilow, 1989), (Shukla et al., 1990).