CLIMATOLOGY IN ARID ZONE RESEARCH 83 
arid research. For instance, with this concept it is possible to de- 
termine the water needs of an area and to evaluate the utility 
of the water supply to meet those needs. Through its use in the 
classification of climates, it becomes basic to any inventory of the 
arid regions of the world. It 1s possible to use it to work out a com- 
plete and accurate irrigation schedule that will permit the maxi- 
mum returns with the water available. Thus, it becomes more 
abundantly clear as studies of the concept of potential evapo- 
transpiration progress that it is a tool of increasing usefulness in 
the solution of problems not only in humid regions but also in the 
potentially important arid and semi-arid regions of the world. 
REFERENCES 
1. Bigelow, Frank H. 1907. Studies on the phenomena of the evapora- 
tion of water over lakes and reservoirs. Monthly Weather Rev. 35, 
311-16. 
2. Horton, R. E. 1944. Evaporation—Maps of the United States. 
Am. Geophys. Union, Trans. of 1943. Pp. 743-753- 
3. Langbein, W. B. 1951. Research on evaporation from lakes and 
reservoirs. U.G.G.I. Assoc. Intern. a’Hydrologie Scientific. Assemblée 
Générale de Bruxelles. Vol. 3, pp. 409-19. 
4. Mather, J. R. 1950. Manual of Evapotranspiration. Mzcrometeor- 
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Report No. 10, The Johns Hopkins Univ. Lab. of Climatology, 
Centerton, N. J. 
5. Mather, J. R. (Editor). 1954. The measurement of potential evapo- 
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Johns Hopkins Univ. Lab. of Climatology, Centerton, N. J. 
6. Mean monthly and annual evaporation from free water surfaces. 
U. S. Weather Bureau, Tech. Paver No. 13, July 1950. 
7. Meyer, A. F. 1942. Evaporation from Lakes and Reservoirs. Minn. 
Research Committee. Minneapolis. 
8. Reichelderfer, F. W. 1952. Physical basis of water supply for the 
United States. In H, The Physical Basis of Water Supply and Its 
Principal Uses. Pp. 11-24. Interior and Insular Affairs Committee, 
U. S. Congress. 
g. Thornthwaite, C. W. 1941. Atlas of Climatic Types in the United 
Sines Wee 40), UW, S.dDeon oF Zhi, SiGSo, Mose. I-02. INO, 21. 
10. Thornthwaite, C. W. 1946. The moisture factor in climate. Trans. 
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