| Forests, Climate, and Hydrology: Regional Impacts (1988) |
|3. Effects of tropical forest on water yield|
The tropical zone and the transition to the subtropical forests experience a range of humid climates. This together with the varied vegetation results in a variety of distinct hydrological regimes. The rapid exploitation of tropical forests makes it imperative that the effects on the hydrology of a region are understood. For this, the individual hydrological processes in the forest must be studied. The components of tropical forest evapotranspiration approach the meteorological potential value and this contribution to regional rainfall suggests that deforestation might reduce rainfall. The differences in organic matter decomposition on the forest floor are poorly understood and result in a variety of surface runoff conditions.
Many parameters of water yield from a catchment may be studied by stream flow measurements, but scientific criteria for calibration and treatment must be met. Generalizations on the effects of forest on water yield are drawn from all the successful catchment experiments in six tropical regions. In the first year after clearing forest, stream flow increased by a maximum of 6 mm for each of of the area cleared. The average was about 5 mm; variations are due to regrowth or different land uses. More experiments are needed in tropical areas to elucidate the causes of the observed effects of forest clearance.