An experience in estimating evapotranspiration using lysimeter in Hapugala, Sri Lanka

Efficient planning of water resources requires accurate evaluation of all components in the water budget. Evapotranspiration is an essential component of the water budget and the correct estimation of evapotranspiration is vital for improved water resources management. This study discusses about estimation of evapotranspiration using a simple technology which is economically viable for developing countries. In this study, daily reference evapotranspiration (ETo) was estimated based on the measurements from a non-weighable drainage type lysimeter. ETo estimations by Blaney Criddle, Radiation and Penman methods were compared with ETo estimations by the lysimeter measurements. It is revealed that the lysimeter estimations were overestimating the ETo during the months of February, March and April in year 2008 by 24%, 12% and 11% respectively compared to ETo estimations by the Penman method. Reasons for the above overestimations were discussed and recommendations for reliable ETo estimations by lysimeters were presented in relation to lysimeter design, installation, operation and maintenance.