1. Consumptive use of water for agriculture," by Robert L. Lowry, Jr., and Arthur F. Johnson;Proc. Amer. Soc. Civ. Engr.,1941
2. An approach toward a rational classification of climate," by C. W. Thornthwaite;The Geological Review.,1948
3. "Determining water requirements in irrigated areas from climatological and irrigation data " by Harry F. Blaney and Wayne D. Criddle U.S.D.A. S.C.S.-TP-96 Washington D. C. 1950.
4. "Irrigation Requirements insect on Climatic Data " by George H. Hargreaves . Paper 1105 IR-3 Journal of the Irrigation and Drainage Division Proc. Am. Soc. of Civil Engineers November 1956.
5. Natural evaporation from open water, bare soil and grass