Simulating water saving interventions: Application in the lower Yellow River basin

Irrigated agriculture is put under simultaneous pressure to supply the needs of a fast growing population and to release water for other, higher valued uses. In response, solutions have to be devised to make a substantially more efficient and productive use of water in irrigation. This paper introduces OASIS(Options Analysis in Irrigation Systems), a new planning model for medium to large-scale irrigation systems. OASIS is mainly innovative in that it integrates recycling and captures all the main factors of the water balance, including non-process depletion from fallow lands and non-crop vegetation. It was developed as an attempt to provide a novel type of support to manage irrigation water within a broader context of basin water resources. OASIS was applied to simulate interventions in the Bojili Irrigation District(BID), a large-scale irrigation system located in the lower portion of the water-short Yellow River basin, in China. Simulations suggest that investments targeting higher conveyance and application efficiencies would not necessarily pay off as the system is already highly efficient in converting rainfall and irrigation supplies to crop evapotranspiration. Beyond the specific case study taken into account, the application performed clearly illustrates that there can be important trade-offs between high efficiencies and reuse. More generally, it emphasizes the crucial importance of supporting investment decisions by a more comprehensive picture of the water balance in irrigated areas. We believe that innovative tools such as OASIS can precisely prove useful for this purpose.