Consumptive Use Derived from Evaporation Pan Data

by George H. Hargreaves,

Serial Information: Journal of the Irrigation and Drainage Division, 1968, Vol. 94, Issue 1, Pg. 97-106

Document Type: Journal Paper


Evapotranspiration measurements or computations provide basic information for the computation of irrigation requirements. Unfortunately, in underdeveloped or developing countries both evapotranspiration and weather data are usually of limited availability and for some proposed project areas nonexistent. Formulas and methods are required by engineers working on design and development of irrigation. These must permit the evaluation of needs and requirements for irrigation with an absolute minimum of data. Formulas are given for computing evaporation from climatic data. Ratios of evapotranspiration to Class A pan evaporation are given for a large number of crops. Crops are grouped together or assigned general classifications whenever possible. Consumptive use coefficients converting evaporation to evapotranspiration are given by 10% increments of the crop growing season or vegetative cycle. A method of computing utilizable rainfall is presented and a formula is given for converting evapotranspiration to irrigation requirements. Irrigation requirements may be computed with several levels of data availability provided temperature and rainfall measurements are at the disposal of the engineer constituting a minimum of data required.

Subject Headings: Evapotranspiration | Irrigation | Hydrologic data | Weather forecasting | Crops | Temperature measurement | Evaporation | Computing in civil engineering

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