Abstract
Actual evapotranspiration (ETa) has been insufficiently investigated in Greece. This study aimed to estimate annual ETa by empirical methods (Turc, modified Turc, and Coutagne) for the Peloponnese, Greece, a Mediterranean testbed, between 2016–2019, four of the warmest years since the preindustrial era, and compare them to MODIS ET. Furthermore, measurements of annual pan evaporation (Epan) were performed for two Class A pan stations in the Peloponnese with different reliefs and conditions. The empirical methods and statistical formulae (RMSD, MB, and NMB) were developed as models in ArcMap. The outcomes of the Turc method resembled MODIS ET ranges for all years, followed by those of Coutagne. The estimates by the modified Turc method were almost identical to MODIS ET. Therefore, the modified Turc method can be used as an alternative to MODIS ET (and vice versa) for the Peloponnese for 2016–2019. Moreover, the Epan at Patras University station (semiurban, low elevation) exhibited an upward trend resembling the trends of the empirical methods over the study years, whereas the Epan at Ladonas station (higher elevation, lakeside) required investigation on a monthly time scale. Additionally, the gradual decrease of pan-water icing at Ladonas in December (from 20 d in 2016 to 0 d in 2019) could imply an undergoing decrease in snowpack storage retention across the mountains of the Peloponnese.
Highlights
Annual ETa was calculated via a model that used land surface temperature (LST) Terra day and night images and meteorological data as inputs to implement Turc’s equation (Equations (1) and (2)) [74], which had been previously used for Greece [45,46]
Turc modified is recommended for annual areal ETa estimation in the Peloponnese for 2016–2019 as a preferable alternative to Moderate Resolution Imaging Spectroradiometer (MODIS) ET
In a comparison of estimates at the annual scale, it was found that all empirical methods produced narrower ranges of values than MODIS, and the range of the Turc method was the closest to MODIS
Summary
Based on the established relationship between land surface temperature (LST), or “skin temperature”, and near-surface air temperature (Tair), LST can be used as a satisfactory proxy for Tair despite the different physical meaning and responses of the two parameters to atmospheric conditions. LST is a global remote sensing product, and as such, its accuracy relies on several limiting factors: cloudiness and occasionally heavy aerosol loadings, land cover and the stage of crop growth, solar radiation and seasonality, and topography and elevation [14,15,16,17,18]. Precipitation is the limiting factor governing the range of ETa values. This is especially true for the southern Mediterranean region, where it is anticipated that rainfall will increase during summertime in the near future [21,22]
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