Determining the influence of irrigation efficiency improvement on water use and consumption by conceptually considering hydrological pathways

Improving irrigation efficiency is widely believed to be a promising opportunity for large water savings. However, more and more voices have been raised against this idea in recent years. This study investigated the impacts of irrigation efficiency improvement on water use and consumption by combining an agro-economic model with the conceptualization of hydrological pathways. The investigation was conducted under two different conditions, i.e., Case 1: unlimited water supply and restricted irrigatable land, and Case 2: limited water supply and unrestricted irrigatable land. At the scale of the WUU, we found that the water uses could be reduced significantly after improving irrigation efficiency, while the water consumptions would be of similar magnitudes for different irrigation techniques under the condition of Case 1. However, in the condition of Case 2, the water uses would be inelastic to the enhanced irrigation efficiency; and the water consumption would increase slightly if the fixed cost ratio is high. At the scale of the irrigation system, the reductions in water use, as a result of efficiency improvement, would be more and more insignificant in response to increasing water cost ratios and numbers of WUUs under the condition of Case 1. In contrast, the water uses would increase, although with small magnitudes, when the fixed cost ratios and the number of reuse cycles are relatively high under the condition of Case 2. This study demonstrated that alternative restrictions on water supply and irrigatable land could effectively constrain water use and consumption after modernizing the irrigation systems. The sensitivity of the major assumptions, and the uncertainties and limitations have been revealed and discussed, along with some implications for agricultural water managements. The findings can shed some light on the lively debate regarding the effectiveness of technological water saving measures.