Performance Assessment of the SEVIRI Evapotranspiration Operational Product: Results Over Diverse Mediterranean Ecosystems

Evapotranspiration (ET) is an important variable in weather systems and hydrometeorological modeling. In this paper, an extensive validation was carried out on the spinning enhanced visible and infrared imager (SEVIRI) ET operational product, evaluating its accuracy at selected European sites. Validation was performed through comparisons with in-situ eddy covariance measurements belonging to the CarboEurope IP network. Comparisons were performed for selected cloud-free days with a satisfactory energy balance ratio in 2011. A total of nine sites covering six land covers were used in validating the ET retrieval accuracy from the operational product. A series of statistical metrics was computed to evaluate the agreement, which also included explored the variability of site characteristics and influence of land cover on ET performances. Overall, a good agreement was reported between the satellite-derived ET estimates and the ground measurements (d-index = 0.755, root mean square deviation (RMSD) = 0.107 mm h^-1). A minor negative bias of -0.015 mm h^-1 suggested only slight underestimation of the in-situ data. In terms of land cover, the highest agreement in ET was reported for the olive orchards and open shrubland sites (d-index = 0.893/0.867, RMSD = 0.041/0.050 mm h^-1). A systematic ET underestimation by SEVIRI was found for all land cover types. Results of this study are largely in agreement to previous analogous validation studies of the product. Our findings support the potential value of the SEVIRI ET product for regional to mesoscale studies and practical applications. The latter is of particular importance for water limiting environments such as those found in the Mediterranean basin, as accurate information on ET rates can provide tremendous support in sustainable water resource management as well as policy and decision making.