AN EMPIRICAL RELATIONSHIP BETWEEN TEMPERATURE, VAPOR-PRESSURE DEFICIT AND WIND-SPEED AND EVAPORATION DURING A WINTER CHINOOK

Evaporation rates determined by energy balance and bulk transfer equations and confirmed with soil moisture sampling was regressed against average daytime temperature, vapour pressure deficit and wind speed over several chinook events between 1986 and 1988. The equation E = 0.45 exp (0.35 TBAR + 0.025 uBAR - 0.133 [e* - e]) yielded reasonable estimates of evaporation with surface soil moisture between saturation and near wilting point. E is evaporation in mm d-1, T, u and e* and e are temperature (degrees-C), wind speed (ms-1), saturation vapour pressure and vapour pressure (mb) respectively. The overbar denotes daytime average.