A Simple Model for Determining Evaporation from High-Latitude Upland Sites

Wayne R. Rouse Dept. of Geography, McMaster University, Hamilton, Canada

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Robert B. Stewart Dept. of Geography, McMaster University, Hamilton, Canada

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Abstract

Energy-budget calculations and equilibrium, model estimates of evaporation from a lichen-dominated upland site in the Hudson Bay lowlands are presented. The energy-budget calculations reveal that the lichen surface is relatively resistant to evaporation with an average of only 54% of the daily net radiation being utilized in the evaporative process. Equilibrium model estimates of evaporation consistently over-estimate actual evaporation by 5 and 8% for hourly values and daily totals, respectively. A simple model, a function of the equilibrium model, is derived from a comparison of actual and equilibrium evaporation. The only inputs required for the model are net radiation, soil heat flow and screen temperatures. Tests of the model indicate that it will predict actual evaporation within 5% and that it can probably be applied to any high-latitude surface which exhibits a relatively large diffusive resistance to evaporation.

Abstract

Energy-budget calculations and equilibrium, model estimates of evaporation from a lichen-dominated upland site in the Hudson Bay lowlands are presented. The energy-budget calculations reveal that the lichen surface is relatively resistant to evaporation with an average of only 54% of the daily net radiation being utilized in the evaporative process. Equilibrium model estimates of evaporation consistently over-estimate actual evaporation by 5 and 8% for hourly values and daily totals, respectively. A simple model, a function of the equilibrium model, is derived from a comparison of actual and equilibrium evaporation. The only inputs required for the model are net radiation, soil heat flow and screen temperatures. Tests of the model indicate that it will predict actual evaporation within 5% and that it can probably be applied to any high-latitude surface which exhibits a relatively large diffusive resistance to evaporation.

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