Since the mid fifties, when Frank Law published the results of his studies from Stocks Reservoir, a controversy has raged concerning the effects of upland afforestation on evaporation and water resources of the UK. Originally the concern centred on the effects of spruce afforestation of upland moorland water catchments which were being used for supply purposes; then, by the late seventies, the deleterious effects of afforestation on hydroelectric power generation were recognised. More recently, experimental studies were carried out in the relatively warm climate of Wales and England, primarily on grass and forest vegetation, but the results could not necessarily be applied in Scotland, where the climate is cooler and snow can form a significant component of the annual precipitation and heather rather than grass moorland predominates. Further studies, involving both process and catchment experiments were executed to quantify the effects. The research was funded by a consortium which included the British Waterways Board, Department of Energy, North of Scotland Hydro-Electric Board, Scottish Development Department, Forestry Commission, Department of the Environment and the Water Research Centre. The results of these process studies are presented and the implications for water resources are discussed.
Part 1 Introduction: Frank Law and the Stocks Reservoir controversy; Frank Law's studies; the plynlimon catchment results; the Plynlimon forest lysimeter; the Thetford micrometeorological and soil physical studies. Part 2 Physics and physiology of evaporation: the Dalton equation; the "del" approximation and the combination equation; the Penman equation; physiological resistance - the Penman-Monteith equation. Part 3 The interception process: the rutter interception model; the stochastic interception model. Part 4 Further transpiration studies in the uplands. Part 5 Rainfall interception from short vegetation - the "wet surface" lysimeter experiment. Part 6 Gamma - Ray Attenuation studies of rainfall interception from forests. Part 7 Plastic-sheet net-rainfall gauge measurements of forest interception. Part 8 Evaporation from snow covered vegetation. Part 9 Predicting the effects of land use change - evaporation models. Part 10 Implications of upland afforestation - a case study, Crinan canal.