**6. Summary and Conclusions**

This study determined the systematic behavior of an arid region's irrigation system within socio-hydrologic dynamics. A system dynamics model was developed for the lower Rio Grande region to determine the impacts of increased irrigation efficiency upon local hydrology and economics under different climate scenarios through 2099. The model simulated the variables' dynamics with three climate projections and surface inflow that corresponded to the three climate projections as inputs. Regional IE policy was tested as a model scenario. Results showed that regional IE policy could yield water for redistribution as increasing unit water supply in the field; however, it may also have unintended consequences such as decreased hydrologic connectivity, groundwater depletion, and negative economic impacts. Regional IE policy fails to reverse the declining trends of groundwater and regulate agricultural water demand. Specifically, irrigation return flow and abundance are increased in the majority of simulations. These benefits come at the cost of decreased connectivity and overall economic losses in all scenarios.

In these scenarios, losses to agricultural economies are observed, particularly in the short-term. This suggests that subsidies, technologies, or managemen<sup>t</sup> strategies that increase agricultural profits or decrease costs of IE infrastructure, particularly through the year 2050, are necessary for this IE policy to be economically viable. Water use in drought years and replenishment of groundwater in abundant years as well as economic incentives to offset the costs of infrastructure improvements will be necessary for the IE policy to result in sustainable agriculture and water resources.

Research on managemen<sup>t</sup> strategies for increasing water sustainability is a prerequisite for future development. System dynamics modeling provides insights into interdependent water systems and how they may enable social and economic development. Further efforts may increase understanding of water managemen<sup>t</sup> strategies, uncertainties of policy outcomes, and potential synergies. Successful implementation of this policy would include adaptive water managemen<sup>t</sup> that limits water use in drought years and replenishes groundwater in abundant years. Economic policies or incentives to mitigate investment costs, particularly through 2050, are a necessary addition for this IE policy to be viable.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/hydrology8020061/s1.

**Author Contributions:** Conceptualization, Y.B. and S.P.L.; methodology, Y.B., S.P.L. and A.G.F.; software, Y.B. and S.P.L.; validation, S.P.L.; formal analysis, Y.B.; resources, A.G.F.; writing and original draft preparation, Y.B.; writing review and editing, Y.B., S.P.L. and A.G.F.; visualization, Y.B; supervision, A.G.F.; project administration, A.G.F.; funding acquisition, A.G.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was provided by the U.S. Bureau of Reclamation/New Mexico State University Cooperative Agreement R16AC00002 and the New Mexico Agricultural Experiment Station, New Mexico State University.

**Acknowledgments:** We thank Ian Hewitt for his constructive revisions. The authors wish to acknowledge the anonymous reviewers for their insightful comments and helpful suggestions which improved the earlier version of the manuscript.

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