Calibration of the Hargreaves equation for the calculation of the reference crop evapotranspiration (ETo) in Salto, Uruguay

At the global level, agriculture is the main consumer of water with more than 70% of the use, using it with an efficiency of around 40 %. The decrease in the water available for agriculture requires that the efficiency of use be increased. One way to increase this efficiency is to accurately quantify the water needs of crops for proper irrigation management. Water needs can be estimated from the reference crop evapotranspiration value (ETo). Among the existing methods for calculating ETo, the FAO 56 Penman - Monteith equation (PM-FAO56) is the one recommended by the Food and Agriculture Organization of the United Nations (FAO). However, this equation requires a large amount of information that is often not available to the agricultural producer. There are other methods, such as the one proposed by Hargreaves, that require data that are more readily available. To contribute to water management, it is important to have equations that require little information to obtain accurate estimates of ETo. The general objective of this work is to calibrate the Hargreaves equation for the town of Salto, Uruguay. The methodology consisted of comparing the PM-FAO56 and Hargreaves-Samani methods, and calibrating the Hargreaves - Samani equation for a meteorological station by means of the Kt coefficient of the equation and the exponent, using the ETo obtained from PM as a reference value. -FAO56. A good correlation was found between the PM-FAO56 and Hargreaves methods. It is concluded that the Hargreaves model with the Kt coefficient modified to 0.15 and the exponent to 0.494 is an adequate methodology for the area of influence of the Salto - Uruguay meteorological station.