## 4 Results
### Assessment of PT-JPL-Thermal vs. MOD16 ET in the Donana Region  
From 2003 to 2012, the average evapotranspiration \(ET_{av}\) in the region including irrigated areas and natural ecosystems was estimated in 657 mm/year and 379 mm/year by the PT-JPL-thermal and MOD16, respectively. MOD16 reached 58% of the PT-JPL-thermal estimated \(ET_{av}\). The monthly average \(ET\) in the region, which is shown in Figure 5a, showed a low correlation (\(\rho\cong 0.48\)) and a large bias \(=-23.6\) mm between models for a number of pairs \(n_{p}=120\) months. At an annual time-scale for a \(n_{p}=10\) years, the agreement between models increased (\(\rho\cong 0.94\), \(p<0.001\)) and the bias remained large (see Figure 5b). In the Donana region, MOD16 showed a systematic negative bias with respect to the PT-JPL-thermal estimation for all the land cover classes. In addition, the timing of the peak intra-annual \(ET\) values did not coincide between models (Figure 6). The mixed-irrigation lands shown in Figure 6a,b presented maximum \(ET\) values in the summer (June to August) for the PT-JPL-thermal and spring (April to May) for MOD16. The rice fields presented maximum \(ET\) values from July to August for both the PT-JPL-thermal and MOD16 (Figure 6c). In the natural ecosystems, the PT-JPL-thermal showed maximum \(ET\) values in May for the wetland (Figure 6d), in June for the shrubland (Figure 6e), and in July for the coniferous forest (Figure 6f) while MOD16 detected maximum \(ET\) values in April for the three natural ecosystems. The spatial patterns of the normalized \(ET\) values (\(ET\)/\(ET_{av}\)) in Figure 7 showed high agreement between models in which both depict the areas with higher and lower \(ET\) rates accordingly except for the wetland. Both models identified the higher normalized \(ET\) values in the rice fields and coniferous forests, and identified \(ET\) values close to the region average \(ET_{av}\) in the mixed-irrigation areas and shrublands. However, a significant disagreement between both models was found in the \(ET\) for the wetland. It resulted well above and below the \(ET_{av}\) in the region in the estimations derived from the PT-JPL-thermal and MOD16, respectively. The scatterplots in Figure 8a,b show the relationship between the multi-year daily average \(ET\) estimations derived from the PT-JPL-thermal and MOD16 over the period from 2003 to 2012, which differentiate by irrigated areas and natural ecosystems. The correlation was found significant in the irrigated areas with \(\rho=0.74\) (\(p<0.001\)) and a bias \(=-0.73\) mm/day. In contrast, the correlation values were low in the natural ecosystems with \(\rho=0.17\) (\(p<0.01\)) and a bias \(=-0.90\) mm/day except for the shrubland, which showed a correlation value \(\rho=0.68\) (\(p<0.001\)) and a bias of \(-0.59\) mm/day. Figure 5: (**a**) Region-averaged \(ET_{av}\) (mm/day), (**b**) region-averaged \(ET_{av}\) (mm/year) derived from the PT-JPL-thermal and MOD16 in the study region (irrigated areas plus natural ecosystems) from 2003 to 2012. Figure 6: PT-JPL-thermal and MOD16 _ET_ seasonality over the period between 2003 to 2012. (**a–c**) in the irrigated areas (rice fields and mixed-irrigated lands) and (**d–f**) in the natural ecosystems (wetland, shrubland and coniferous forest). Figure 7: Normalized _ET_ values: _ET_/_ET_\({}_{av}\) where _ET_ is the multiyear average _ET_ per pixel and _ET_\({}_{av}\) is the average _ET_ within the region over the period between 2003 to 2012. (**a**) PT-JPL-thermal _ET_\({}_{av}\) = 1.81 mm/day and (**b**) MOD16 _ET_\({}_{av}\) = 1.03 mm/day. Figure 9a,b show the temporal correlation values between model estimations at seasonal (months) and inter-annual scales. Higher correlation values were found in the inter-annual \(ET\) dynamics compared to the seasonal correlations. The scatterplots in Figure 10 show the relationships between the PT-JPL-thermal and MOD16 \(ET\) estimations for all the land covers grouped for each month (\(n_{p}\) = 12,720 i.e., 1272 pixels in 10 years).