Modeling and assessing agro-hydrological processes and irrigation water saving in the middle Heihe River basin

Water use conflicts between agriculture and ecosystem have become a more severe and acute problem in the Heihe River basin (HRB). Excessive irrigation water use in the middle oasis of the HRB has caused gradual deterioration of water quality and eco-environment both in middle and lower HRB. The urgent issue is to make a quantitative analysis and an improvement of irrigation water use in middle oasis. In this paper, distributed agro-hydrological modeling was conducted to access the irrigation water use and potential water-saving in the major irrigation system of middle HRB (MOIS), using the GIS-based SWAP-EPIC model. The modeling work was based on the abundant data from field experiments, remote sensing, surveys and statistics, and previous eco-hydrological studies. The reliability of the distributed simulation was evaluated using the remote sensing data of actual evapotranspiration (ETa). Then, spatial distribution of irrigation water depth, ETa, deep percolation and crop yield and the related impact factors were systematically analyzed in MOIS. Results indicated that only 53% of total applied water was efficiently used through ETa, whereas deep percolation loss and canal conveyance loss accounted for 22% and 25% of the total applied water, respectively. The beneficial water use fraction was still low in MOIS, averaging only 0.70 on field scale and 0.52 on district scale. Water-saving analysis predicted that 15% of irrigation amount could be saved efficiently, with especial emphasis on the rational water allocation and distribution. In addition, our results related to agro-hydrological processes could provide very valuable information for improving the existing watershed hydrological modeling in the HRB.