The sensitivity of the water balance of a wet multilayer model pine canopy to variations in meteorological input

Abstract

A multilayer canopy model of a pine forest is used to investigate the sensitivity of the water balance of the wet canopy to variations in meteorological input. The multilayer model does not take into account large-scale eddies, which are now considered to be of importance to canopy transport. It does, however, provide realistic simulations of wet canopy water balance and often predicts interception loss rates higher than those predicted by a unilayer model for the same meteorological input. Stable layers both within and above the canopy are often simulated during rainfall events, and these may help to spontaneously generate large-scale eddies or waves within forest canopies. The sensitivity study for a wet canopy suggests that low vapour pressure deficits and low wind speeds are associated with unstable surface conditions, and increasing values of both variables are associated with decreasing canopy drainage values and increasing evaporative losses. Low short- or long-wave radiation inputs are associated with stable surface conditions, and increasing values of both variables are associated with decreasing canopy drainage values and increasing evaporative losses. Increasing temperature is associated with increasing surface stability and increasing canopy drainage and decreasing evaporative losses. In real situations the tendency for increasing temperature to cause surface stability and decreased evaporative loss is probably compensated by the opposite effects of increasing short- or long-wave radiation. The model simulations suggest that wet forest canopies may be better ventilated at low temperatures, if other meteorological conditions are constant.