## 6 Conclusions  
We compared two RS evapotranspiration models in natural ecosystems and irrigated lands within the UNESCO protected Donana Mediterranean region from 2003 to 2012. The intensification of human activity in the surroundings protected areas jeopardizes the effectiveness of these areas for preventing the degradation of natural ecosystems. RS-based evapotranspiration models provide a valuable tool for assessing human pressures and the risk of natural ecosystems collapse. We validated the \(ET\) estimates obtained from the modified PT-JPL model (PT-JPL-thermal) that introduces land surface temperature (\(LST\)) with a thermal inertia approach as a proxy to the soil moisture status against the on-site calibrated hydrological model WATEN and compared inter and intra-annual \(ET\) patterns with the globally available product MOD16 \(ET\). The PT-JPL-thermal was found to reasonably reproduce the \(ET\) dynamics under our Mediterranean conditions (\(\rho\) = 0.78, \(\rho_{\text{1-month lag}}\) = 0.94) in contrast to MOD16 \(ET\) estimates, which pointed to poor model performance in the region. We found that MOD16 would allow us (i) to easily identify land uses with the lowest and largest water use and (ii) to assess inter-annual variability of \(ET\) in water-limited regions. However, the large negative bias (58% underestimation) found on MOD16 \(ET\) estimations in the evaluated land uses (irrigated areas plus natural ecosystems: wetland, shrubland, coniferous forest) would not allow MOD16 to approach the \(ET\) quantification under water-limited conditions. The PT-JPL-thermal reasonably approached \(ET\) rates in the region, revealing well-differentiated and coherent spatio-temporal patterns among the evaluated land uses. This study has proven that the use of the thermal inertia concept as a proxy indicator to soil moisture status, together with the re-formulation of the outgoing longwave radiation, is capable of reproducing \(ET\) at a regional level in semiarid environments. This requires only air temperature and incoming solar radiation from climatic databases apart from standard satellites and products freely available for \(ET\) estimations. In addition, this study highlights the potentiality to estimate \(ET\) of a simpler model less vulnerable to the uncertainties of multiple types of forcing data in comparison to more theoretically accurate models that require complex parameters difficult to characterize globally. **Author Contributions:** Conceptualization, M.C.M., M.G. ; Methodology, M.G., M.C.M., A.P.-O., L.J. ; Software, M.C.M., M.G., J.B.F. ; Validation, M.C.M., M.G., A.P.-O., L.J. ; Formal Analysis, M.C.M., M.G., L.T., L.J. ; Investigation, M.C.M., M.G., L.T., L.R., A.P.-O. ; Resources, M.G., J.B.F., A.P.-O., L.J. ; Data Curation, M.C.M., L.T., M.G. ; Writing-Original Draft Preparation, M.C.M., A.P.-O. ; Writing-Review & Editing, J.B.F., M.G., N.F. ; Visualization, M.C.M., J.B.F., A.P.-O., M.G., L.R. ; Supervision, A.P.-O., L.J., M.G. ; Funding Acquisition, J.B.F., M.C.M., A.P.-O., L.J., M.G. **Funding:** This research was funded by the Spanish Centre for Hydrographic Studies (CEH-CEDEX), the European Cooperation on Science and Technology under the COST Action ES1106 AGRIWAT, and the FORWARD project under the ERA-NET Cofund WaterWorks2015 Call. JBF was funded in part by NASA SUSMAP, IDS, and WWAO programs. The APC was funded by JBF. **Acknowledgments:** MODIS data were obtained through NASA's Earth Observing System Data and Information System EOSDIS, ([[https://search.earthdata.nasa.gov/search](https://search.earthdata.nasa.gov/search)]([https://search.earthdata.nasa.gov/search](https://search.earthdata.nasa.gov/search))). Climatic data were gathered from the IFAPA agro-climatic stations net, co-financed by the European Regional Development Fund (ERDF). We would like to thank [PERSON] and the Department of Environmental Engineering at Denmark Technical University for their valuable cooperation. Two anonymous reviewers provided useful comments and insightful suggestions to this manuscript.