Mean monthly and annual maps of evaporation over Canada have been prepared, and examples are presented. The maps represent time and space averages of evaporation from natural open water bodies having negligible heat storage. The analysis is based on 5-year class A evaporation pan data supplemented by 10-year climatologic data from 100 stations across Canada. The Christiansen formula is shown to be superior to other formulas tested for approximating pan data from other standard climatologic observations. The analysis takes account of the seasonal effects of freeze-up .and breakup on the availability of open water. A zonal classification of lake evaporation that emphasizes the large-scale climatic variations in this parameter acro• Canada is proposed.
For a 19-day period in July 1967, daily estimates of evapotranspiration were obtained from hourly calculations of the Bowen ratio above the forest canopy. The estimates ranged from 7.9 mm to 1.5 mm. The Bowen ratio was found to be very dependent on wind direction, sky condition, and basin aspect, which was a significant factor. Although the area is unhomogeneous, the results appear reasonable when compared with other estimates of evapotranspiration.
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