**5. Conclusions**

This study attempted to investigate long-term water budget trends in the basin using only TerraClimate estimates, with which the annual averaged water storage in the major land distributions is assessed. The long-term water budget assessment has proven the hydrological constraints in the MB region under the current climate. These constraints found spatial variations due to an unequal distribution of precipitation over the basin.

From the Budyko curve analysis, we found that AET in the basin is mainly controlled by evaporative demand. This increase in demand makes the basin more arid, and with dwindling freshwater influx, causes the region to be water limited. The long-term climate statistics showed that its spatially averaged annual precipitation is ≈538 mm yr−1, while water consumption through AET is ≈415 mm yr−<sup>1</sup> and runoff is 123 mm yr−1, which indicates that the major contribution of AET in the basin is in response to the climate. It is noteworthy to mention that the temporal trend of AET is getting closer to precipitation in the North African base of the Atlas Mountains, where the water budget is ≈ 0 mm yr−1, including the Nile delta region, which shows pressure on external water resources. In contrast, the gap between AET and P is wider for Turkey, the Balkans, and the EU, with pronounced runoff patterns. The strong climate variability found in the recent decades for Turkey, the Balkans, and Southern Europe clearly indicates them as more vulnerable to climate effects and affected by irregular patterns.

As a whole, the basin is in a water deficit state due to the strong effect of evaporative demand and the limited water supply to the basin. Since these budget inferences are only based on TerraClimate estimates, which has gained confidence in recent studies, storage biases have not been verified with other global climate products and model-based estimations. The purpose of this study was to show the nature of water balance by already peer-reviewed and published data (TerraClimate) from a first-order perspective. With this, the study opens the opportunity to add more inputs from different model sources for hydrological sub-components, to contribute to the storage calculation over the basin.

Our results suppress the need for continuing serious actions on basin water storage at a large scale, and alarms about escalating climate fluctuations in the MB, especially in Southern Europe, Turkey, and the Balkans. Middle Eastern and North African ecosystems are fragile to water stress where remote sensing-based dynamic water budgeting is preferred for its irrigated, rain-fed, and pastoral land use systems.

**Author Contributions:** Conceptualization, Z.U. and A.G.; methodology, Z.U. and A.G.; data curation, Z.U.; writing—Z.U.; writing—review and editing, Z.U. and B.L.; supervision, M.M. and A.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is funded by (1) the CGIAR Initiative on Climate Resilience, ClimBeR and (2) Regional Water Harvesting Potential Mapping Project under SIDA and FAO.

**Data Availability Statement:** Source code is available on GitHub (https://github.com/zaib19/ Water-Balance-in-the-Mediterranean-Basin-between-1990-and-2020).

**Acknowledgments:** We acknowledge the doctoral scholarship to Z.U. from the Department of Innovation in Biology, Agri-food and Forest systems (DIBAF), University of Tuscia, Viterbo, Italy. We are also grateful to the International Center for Agricultural Research in the Dry Areas (ICARDA) for hosting the traineeship to Z.U. Thanks to the National Center for Atmospheric Research at the University of California for sharing the TerraClimate product publicly.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Appendix A**

**Table A1.** Class-wise 30-year averaged budget.


#### **References**


**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

MDPI St. Alban-Anlage 66 4052 Basel Switzerland www.mdpi.com

MDPI Books Editorial Office E-mail: books@mdpi.com www.mdpi.com/books

Disclaimer/Publisher's Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Academic Open Access Publishing

mdpi.com ISBN 978-3-0365-9349-4