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State-of-the-art approach for potential evapotranspiration assessment

Authors:
• Ryan Hanley Ltd

Abstract

The aim of the Ph.D thesis is the foundation of a new temperature-based model since simplified PET estimation proves very useful in absence of a complete data set. In this respect, the Parametric model is presented based on a simplified formulation of the well-established Penman-Monteith expression, which only requires mean daily or monthly temperature data. The model was applied at both global and local regions and the outcomes of this new approach are very encouraging, as indicated by the substantially high validation scores of the proposed approach across all examined data sets. In general, the parametric model outperforms well-established methods of the everyday practice. A second analysis which was examined as part of this thesis is related to which spatial techniques is the optimal in order to transform the point scale estimate in regional. A thorough analysis of different geostatistical model was carried out (Kriging, IDW, NN, BSS) and it can be concluded that the IDW even is the most simplify geostatistical model, it can be produce consistent spatial PET results. Another part of the thesis was the development of an R function for testing the trend significance of time series. The function calculates the trend significance using a modified Mann- Kendall test, which takes into account the well-known physical behavior of the Hurst-Kolmogorov dynamics. The function is tested in 10 stations in Greece, with approximately 50 years of PET data with the use of a recent parametric model. Finally, a number of hydrological, agronomist and climatologist applications are presented for lighting the robustness of the new Parametric approach in multidiscipline areas.
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... In addition, the SPEI better characterizes medium-to long-term droughts, i.e., those occurring in 3-to 6-month periods, than the SPI (Fung et al., 2020;Li et al., 2020). Furthermore, the SPEI is more suitable for use in areas where there is a long-term increase in air temperature and it better illustrates hydrological drought compared to the SPI or Palmer Drought Severity Index -PDSI , 2019Ionita and Nagavciuc, 2021). ...
... Of the many models proposed for estimating ETo, Penman-Monteith's FAO-56 method has been shown to have the highest accuracy (Maeda et al., 2011;Fan and Thomas, 2013;Mattar et al., 2016). Although its main drawback is the extensive data required for input (air temperature, sunshine, relative humidity, wind), Penman-Monteith's FAO-56 method is highly flexible and provides accurate ETo results, even with insufficient data for some climatic elements (Sentelhas et al., 2010;Tegos et al., 2017;Tegos, 2019;Prȃvȃlie et al., 2019Prȃvȃlie et al., , 2020. It works well in different climate types and is widely recommended for calculating evapotranspiration (WMO, 2006;Łabędzki et al., 2011Maeda et al., 2011;Xystrakis and Matzarakis, 2011;Fan and Thomas, 2013;Beguería et al., 2014;Djaman et al., 2018;Yassen et al., 2020). ...
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... The application of the Penman-Monteith method is not possible where detailed meteorological data is not available. In such a case, Lang [74] compares three radiationbased methods (Makkink, Abtew, and Priestley-Taylor) and five temperature-based methods (Hargreaves-Samani, Thornthwaite, Hamon, Linacre, and Blaney-Criddle) with the Penman-Monteith method on a yearly and seasonal scale. The key finding was that radiation-based methods for PET estimation performed better than temperature-based methods among the selected methods in the study area. ...
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