Determination of Evaporative Fluxes Using a Bench-Scale Atmosphere Simulator

Abstract

An accurate determination of evaporative fluxes is critical for efficient water management in semi-arid climates such as in the Canadian Prairies. The main achievements of this research are the design and operation of a bench-scale atmosphere simulator, performance evaluation using selected weather scenarios pertaining to regional atmospheric conditions, validation using established empirical correlations, and estimation of evaporation rates and the amount for a typical local water body. Results indicate that the measured data achieved the target values for the various parameters and the data were found to be stable during the 3-h test duration. The vapour flux was found to have large variation during summer (0.120 g∙s−1∙m−2 during the day and 0.047 g∙s−1∙m−2 at night), low variation during spring (0.116 g∙s−1∙m−2 during the day and 0.062 g∙s−1∙m−2 at night), and negligible change during fall (0.100 g∙s−1∙m−2 during the day and 0.076 g∙s−1∙m−2 at night). The measured vapour flux was generally within one standard deviation of the equality line when compared with that predicted by both the mass-transfer equations and the combination equations. The average evaporation ranged from 4 mm∙d−1 to 8 mm∙d−1 during the day and decreased to 1 mm∙d−1 to 3 mm∙d−1 at night. The 24-h evaporation was found to be 8 ± 1 mm∙d−1 from late April through late October. Likewise, the cumulative annual evaporation was found to be 1781 mm, of which 82% occurs during the day and 18% at night.