**6. Conclusions**

Drought model outcomes cannot predict future conditions for a fact. Still, these results will aid researchers and stakeholders to have an idea concerning the order of magnitude of eventual future drought episodes. The associated uncertainty in climate model variables does not allow them to be used to define a single future path, even though the results can be valuable to design future system improvements and investments.

Overall, these results highlight that under the RCP8.5 scenario, cyclic drought episodes are expected to occur every twenty years with more than one year of drought state persistency. Further research can evaluate climate change impacts, updating models forecast every 5/10 years, to estimate a most reliable behavior forecasting. For the water supply side, renewable water resources are influenced by anthropogenic factors, precipitation, temperature, and other climate variables fluctuations, yet, we dismiss these variations in this study scope.

This study combined hydrological models and the latest greenhouse gas concentration scenarios to synthesize the proposed behavior of water sources in Barcelona. We showed that climate change is likely to affect local and regional water scarcity modestly. Moreover, this research forecasts a water-availability slightly downward trend from the middle of the 21st century. This proposed behavior does not mean that the annual water contributions are ever lower than the current ones. We identified an increase in drought cycle frequency, following a reduction in the average water availability, even in years of hydrological ascent.

By contrast, these reductions lead to a trend (i.e., the one conditioning the water supply system capacity) alleviated by a constant alternative source with the same magnitude and adding specific support when extreme events occur. With regard to the research methods, some limitations need to be acknowledged. After defining how the expected water availability decreases in the system, it is necessary to consider that these analyses do not consider the future growth of water demand or any new planned infrastructure. Likewise, this study does not consider variations in land-use future states. The reservoir watershed has undergone a revegetalization process since 1997, as assorted researches carried out in Catalonia indicates a farmland abandonment process and the resulting increase in forest mass [39]; as a result, we consider these land-use conditions will remain stable in the future.

Further research is expected to have a better understanding of the mechanisms underlying Barcelona reservoirs' management yielding an effective and sustainable water supply scheme, in conjunction with other hydrological involved processes. Adaptation measures studies, which take these variables into account, will need to be undertaken.

**Author Contributions:** E.F.-O.: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing—original draft preparation. E.M.-G.: Conceptualization, Validation, Resources, Writing—review and editing; Supervision, Project administration. R.M.: Investigation, Methodology, Visualization, Data curation, Resources. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the RESCCUE project, which is sponsored by the European Union's Horizon 2020 research and innovation program under grant agreement No. 700174, whose support is gratefully recognized.

**Acknowledgments:** The contents of this research are a part of the findings of the project RESCCUE, which has obtained funding from the EU H2020 (grant agreement n. 700174). Re-use of the knowledge enclosed in this paper for commercial and/or non-commercial purposes is allowed and free of charge, on the requirements of compliance by the re-user of the research, not distortion of the original meaning or information of this research and the non-liability of the project RESCCUE partners for any consequence stemming from the re-use. The project RESCCUE partners do not accept any liability for the errors, consequences, or omissions herein contained.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
