| Abstract/Description or Keywords |
Evaporation rates responded very quickly to surface desiccation, and the control by surface resistance (derived from the Penman-Monteith model) was very pronounced. The absence of an efficient means to transfer subsurface moisture to the surface resulted in an evaporation regime which was strongly moisture-limited only a few days after precipitation. However, the high frequency of precipitation events in this environment meant that both energy-limited and moisture-limited regimes occurred in quick succession. The range of minimum surface resistances is similar to those used in current land-atmosphere climate models, but they tend to be considerably greater during drying events. Four different physically based evaporation models were compared with hourly or daily Bowen ratio-energy budget measurements. Best results were obtained by using an aerodynamic approach. If high-quality sensible heat measurements are available, then the evaporation rate could be readily estimated by treating it as a residual in the energy budget equation. The Priestley-Taylor method is potentially valuable, but the objective specification of surface moisture availability is difficult in alpine tundra. An alternative approach using equilibrium evaporation plus a surrogate measure of surface water (daily precipitation) clearly stratified daily actual evaporation into wet and dry regimes, and may have some predictive value. evaporation, alpine, energy budget |
