Penman's reference evapotranspiration estimates with simple low cost instruments for farmers

Abstract

The estimates of Penman's reference evapotranspiration (ETo) obtained from observations of wet and dry bulb thermometers, sunshine recorder and anemometer were compared to Penman's estimates obtained from values of class A pan and Piche evaporimeters and maximum and minimum air thermometers. In the later, global solar radiation was obtained from a simple linear regression between global solar radiation measured with a piranometer and class A pan evaporation, with a R² = 0,66. The R² between the two estimates was 0,93. ETo estimates from class A evaporation were less correlated with Penman's estimates using the traditional instruments with a R² = 0,73. The proposed methodology requires much cheaper instruments than the traditionally ones used for this purpose and are very simple to be managed by famers.