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Parametric Modelling of Potential Evapotranspiration: A Global Survey

Department of Water Resources and Environmental Engineering, National Technical University of Athens, Heroon Polytechneiou 5, GR-157 80 Zographou, Greece
Arup Group Limited, 50 Ringsend Rd, Grand Canal Dock, D04 T6X0 Dublin 4, Ireland
Department of Agricultural Technology, Technological Educational Institute of Western Greece, 27200 Amaliada, Greece
Author to whom correspondence should be addressed.
Water 2017, 9(10), 795;
Received: 23 July 2017 / Revised: 2 October 2017 / Accepted: 13 October 2017 / Published: 16 October 2017
PDF [10739 KB, uploaded 20 October 2017]


We present and validate a global parametric model of potential evapotranspiration (PET) with two parameters that are estimated through calibration, using as explanatory variables temperature and extraterrestrial radiation. The model is tested over the globe, taking advantage of the Food and Agriculture Organization (FAO CLIMWAT) database that provides monthly averaged values of meteorological inputs at 4300 locations worldwide. A preliminary analysis of these data allows for explaining the major drivers of PET over the globe and across seasons. The model calibration against the given Penman-Monteith values was carried out through an automatic optimization procedure. For the evaluation of the model, we present global maps of optimized model parameters and associated performance metrics, and also contrast its performance against the well-known Hargreaves-Samani method. Also, we use interpolated values of the optimized parameters to validate the predictive capacity of our model against monthly meteorological time series, at several stations worldwide. The results are very encouraging, since even with the use of abstract climatic information for model calibration and the use of interpolated parameters as local predictors, the model generally ensures reliable PET estimations. Exceptions are mainly attributed to irregular interactions between temperature and extraterrestrial radiation, as well as because the associated processes are influenced by additional drivers, e.g., relative humidity and wind speed. However, the analysis of the residuals shows that the model is consistent in terms of parameters estimation and model validation. The parameter maps allow for the direct use of the model wherever in the world, providing PET estimates in case of missing data, that can be further improved even with a short term acquisition of meteorological data. View Full-Text
Keywords: potential evapotranspiration; Penman-Monteith method; parametric model; CLIMWAT 2.0 database; spatial interpolation; calibration; validation potential evapotranspiration; Penman-Monteith method; parametric model; CLIMWAT 2.0 database; spatial interpolation; calibration; validation

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Tegos, A.; Malamos, N.; Efstratiadis, A.; Tsoukalas, I.; Karanasios, A.; Koutsoyiannis, D. Parametric Modelling of Potential Evapotranspiration: A Global Survey. Water 2017, 9, 795.

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