| Abstract | Hydrologists responsible for estimating runoff from melting snow have long been interested in estimating evaporation from snow cover. An exact estimation of evaporation appears impossible; even an order-of-magnitude is difficult. The current paper gives a literature review of evaporation experiments in other countries and gives a preliminary evaluation of some snow evaporation measurements in Ottawa during the 1956-57 season. Obtaining reliable evaporation measurements under field conditions is difficult. It involves measuring weight loss from open pans containing snow and is intended to apply to larger snow cover areas. Comparisons between calculated and measured values were quite acceptable. Evaporation coefficients were also compared with those calculated by others. Comparisons of measured evaporation rates show that all are within a general range of values. Order-of-magnitude snow evaporation from large snow covers can be predicted using present techniques, but the degree of accuracy is difficult to ascertain. Any formula used, however, is limited by the basic accuracy of the measured variables, wind speed and vapour pressures. For shallow snow covers with a long melt period predictions appear questionable. When the snow melt period is short, as during a Chinook, the evaporation from snow should be much less than the snow melt. |
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