Insights from socio-hydrological modeling to design sustainable wastewater reuse strategies for agriculture at the watershed scale

Wastewater reuse in agriculture can be a viable option to solve future freshwater shortages but may need an additional treatment process (Stage-II) to become a safe option. As wastewater reuse interacts with many facets of coupled human and water systems, the introduction of Stage-II treatment systems in wastewater reuse in agriculture must be understood in terms of socio-hydrology. This paper builds on a place-based socio-hydrological model of a wastewater-reused watershed in South Korea and uses it to: (1) identify key parameters in human and water systems that have a significant impact on wastewater reuse in agriculture; (2) explore the impacts of changing agricultural environments by altering the key parameters; and (3) develop the possibility space of future changes from current decision-making. Key parameters concern the characteristics of urbanization, domestic water use, and greenhouse cultivation. Urbanization can reduce the demand for Stage-II irrigation within an urbanizing watershed by reducing irrigation areas and increasing water availability. Domestic water use has a large impact on the economics of indirect wastewater reuse. Greenhouse cultivation influences the demand for Stage-II irrigation, mainly by reducing water availability. Moreover, it could further affect the demand if the communities evolved to have a greater concern for the use of groundwater resources. The possibility space shows that wastewater reuse has a strong influence on groundwater and could relieve agricultural water deficits through the diversification of irrigation sources, and could be a more economical irrigation practice than groundwater irrigation under changing agricultural environments.