Evapotranspiration Modeling Using Remote Sensing and Empirical Models in the Fogera Floodplain, Ethiopia

Abstract

Conventional methods and remote sensing were applied for the estimation of reference evapotranspiration and actual evapotranspiration over the Fogera floodplain. Reference evapotranspiration (ET0) by Modified Makkink (MM), Priestly-Taylor (PT) and Abtew (A) simple equations was compared to the Penman-Monteith (PM) estimations, in order to decide which method for ET0 is the most suitable alternative to PM in data scarce conditions. A comparison was also made to a satellite based energy balance approach that estimated actual evapotranspiration. For the remote sensing approach, images from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor were selected. For the study, data has been used from Bahir Dar meteorological station at a distance of 50 km from the floodplain and from Woreta weather station that is located in the floodplain. The comparison of results from the conventional methods indicated that the MM method performed best over the floodplain as compared to the PM approach while the PT and Abtew (A) simple equations only produced fair results. The latter two approaches required calibration of site specific coefficients that may have affected the estimation results. Accumulated actual evapotranspiration from the satellite based approach for the year 2008 was about 1,519 mm for rice, while the reference evapotranspiration by the PM approach was 1,498 mm. A comparison of these results with literature values of the crop coefficient of rice indicated that rice transpired at a potential rate.