Abstract
Accurate estimation of evapotranspiration (ET) is vital for water resource management. The FAO-56 Penman–Monteith (FAO-56 PM) is a standard method, but it requires numerous weather data. This challenges water resource managers to estimate ET in areas where there are no adequate meteorological data. Hence, simplified approaches that are less data intensive are the right alternatives. Here, ET was estimated using different approaches and their performances were evaluated in different ecosystems of Ethiopia. Surface Energy Balance Systems (SEBS) model was also used for spatio-temporal mapping of ET in the Fogera floodplain, Lake Tana Basin. The spatial average of actual ET (ETa) from remote-sensing (RS) data over the floodplain was less than the Penman–Monteith (PM) reference ET (ETo) in drier periods and larger in wet seasons. A sensitivity analysis of PM input variables at the Bahir Dar station showed that the incoming solar radiation and air temperature are most sensitive, and wind speed was found to be the least sensitive. The comparison of simple Enku (E) temperature method, Abtew (A) equation, modified Makkink (MM) method, and Priestley–Taylor (PT) method with the PM ETo in the different ecosystems of Ethiopia showed the MM method performed best in all the stations except Dire Dawa stations with coefficient of determination (R 2) of 0.94, Nash–Sutcliffe efficiency (NSE) of 0.88, root mean square error (RMSE) of 0.26 mm, and absolute mean error (AME) of 0.21 mm at Addis Ababa and Awassa stations. The performance of MM and PT methods in the dry and hot climate was poor. The E method performed consistently well in all the stations considered. While ET estimation from remotely sensed inputs has generally been improved, selection of the method of estimation is very important and should always be tested with observational data.
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Acknowledgments
This work was partly funded by an ITC fellowship grant, and partly by Bahir Dar University. We would like to thank the Ethiopan Metereological Agency for the data used in our study.
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Enku, T., van der Tol, C., Melesse, A., Moges, S., Gieske, A. (2014). Multi-model Approach for Spatial Evapotranspiration Mapping: Comparison of Models Performance for Different Ecosystems. In: Melesse, A., Abtew, W., Setegn, S. (eds) Nile River Basin. Springer, Cham. https://doi.org/10.1007/978-3-319-02720-3_16
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