Monitoring the hourly actual evapotranspiration through the energy balance and a weighing lysimeter

By having sufficient knowledge about evapotranspiration in space and time, it is possible to manage and plan the water management of a basin. Evapotranspiration can be obtained indirectly at a local scale through information recorded in agrometeorological stations, or regionally with the use of satellite data. In order to have reliable models, it is very important to validate the information generated with direct measures of evapotranspiration.Therefore, direct measurements of evapotranspiration in clay secano-soils covered by grasses and the use of the data generated for the validation of indirect measurements are presented in this study. To achieve this, hourly data from an energy balance station and direct measurements of a weighing lysimeter were used to study the water loss during two experimental campaigns carried out in Tandil (Argentina), in the months February-March and September 2017. The comparison of the methods was made for different moisture conditions of the soil. The energy balance model estimates approximate values of actual evapotranspiration for maximum values of soil moisture (0.01-0.15 mm hour-1), showing greater differences (0.1-0.35 mm hour-1) when the soil moisture tends to minimum values. However, it was demonstrated that a simple one-level model to determine the latter variable is applicable for areas with reference coverage, allowing simplifications in aerodynamic and crop resistance measurements (Allen et al. 1998). This contribution provides necessary information for the validation of satellite models applied to plains areas, where evapotranspiration is a term of great importance.