Forests and water resources: problems of prediction on a regional scale

Abstract

Forests have profound effects on water resources and it is essential that water resources be jointly considered with forests wherever in the world these assets are valuable for national development or for environmental balance. However, despite a strong and often urgent need for prediction in forest hydrology, universality of scientific guidance is seldom possible across climatic boundaries, between soil types, between land management practices and, occasionally, between species of tree. This paper reviews the current state of predictability of water use by forests, of hydrological extremes and of water quality factors, all of which affect the utilization of water resources. Contrasts between climatic zones are stressed in relation to evaporation processes. In reviewing hydrological extremes and water quality, the influence of local soil- and land management is drawn out. There seems some justification for a continuation of lengthy and expensive hydrological experimentation, despite the urgency of the need for guidance in land use and land management. It is essential, however, to make maximum use of new spatial techniques that aid extrapolation from the detail provided by studies of process.