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Many attempts have been made to derive mathematical expressions relating evaporation and evapotranspiration, or consumptive use, to climatological data. IN the United States, the Blaney-Criddle formula is probably the best known for estimating consumptive use (2 and 3). Blaney (1) has also suggested that this formula is suitable for estimating evaporation as measured with a Weather Bureau pan. Other well known formulas are the Penman formulas (10), the Thornthwaite formula (15) and the Hargreaves formulas (8). Halkias, Beihmeyer and Hendrickson (6) suggest that water requirements of crops can be determined from atmometer data. Lowry and Johnson (() in an early paper showed that “valley consumptive use” could be estimated from temperature data with reasonable accuracy. Cummings and Richardson (5) and Richardson (13) have shown that evaporation is basically a function of insolation, and they have proposed formulas from which it can be estimated. Hamon (7) has recently suggested that potential evapotraspiration can be estimated from an empirical relationship involving sunshine hours and the saturated water vapor density at the daily mean temperature. Pruitt (12) has reported evapotranspiration data obtained with a large weighing lysimeter and has correlated these data with evaporation from pans and atomometers and with estimates by the Blaney-Criddle, Thornthwaite and PPenman formuals. Many other fomulas have been proposed. Criddle (4) and Halkias, et al, (6) have reviewed the literature and discussed the various formulas.