Potential of treated wastewater reuse for irrigation under semi-arid conditions and various climate scenarios

Water resources in arid and semi-arid regions are increasingly stressed by population growth and climate change, leading to growing challenges for agricultural production. This study investigates the potential of reusing treated wastewater (TWW) as a supplementary irrigation source under current and future climate scenarios. A comprehensive framework integrating economic and environmental dimensions is developed and applied to the Ablah region in the Beqaa Valley, Lebanon, where an operational wastewater treatment plant and irrigation network exists. Crop water requirements were estimated for major crops under baseline and projected climate conditions. Two scenarios other than the current were considered: a moderate scenario with reduced precipitation and increased reference evapotranspiration, and an extreme scenario with more pronounced climatic changes. Results indicate a substantial increase in irrigation water deficits under future conditions. An improved agricultural water management scenario incorporating higher shares of TWW was developed and assessed. The findings show that increasing TWW reuse can significantly reduce groundwater (GW) abstraction, support supplemental irrigation for cereals, and improve the economic feasibility of selected irrigation practices. An economic analysis demonstrated that TWW is more cost-effective ($0.18/m³) than GW ($0.48/m³). Furthermore, supplementary irrigation using TWW is economically viable for crops such as wheat and grapes, whereas GW-based irrigation is not feasible for wheat. The study introduces a novel integrated assessment framework combining water balance modeling with economic evaluation, providing a practical decision-support tool for sustainable irrigation planning and facilitating the adoption of TWW reuse in water-scarce regions.