Modeling agro-hydrological processes and analyzing water use in a super-large irrigation district (Hetao) of arid upper Yellow River basin

High water consumption in large irrigation districts has resulted in large river water diversion and serious water use conflicts in the Yellow River basin (YRB). The excessive water applied is also a cause of the dual problems of soil salinity and water logging in the upper YRB, which further negatively impacts crop yields. This study is aimed at modeling and analyzing the agro-ecohydrological processes and water use performance in large irrigation districts of the YRB. The Hetao Irrigation District (Hetao), a super-large irrigation district located in the upper YRB, was selected as a typical research area. A watershed hydrological model (SWAT-AG) with enhanced capacity for simulating regional agro-ecohydrological processes was adopted in this study. We simulated the agro-ecohydrological processes in Hetao and analyzed the regional characteristics of depth to groundwater table, soil moisture and salt content, evapotranspiration and crop yield. Water accounting was further carried out to interpret water cycle processes and evaluate water use performance in Hetao. Results indicated that Hetao was characterized by shallow depth to groundwater table, high soil moisture and high evapotranspiration. For farmland, there was a decreasing trend for both soil moisture and evapotranspiration from the upper to lower regions in Hetao, but this decreasing trend was not found for natural land. Further, results showed soil salt content has strong spatial variations with land use type, crops and shallow groundwater environments. Correspondingly, crop yields presented a decreasing trend from the upper to lower regions of Hetao, with large spatial variabilities closely related to the spatial distribution of soil water and salt conditions across Hetao. It was worth noting that the regional water use efficiency was relatively low in Hetao, especially with large proportions of non-beneficial water consumption to total water consumption. Overall, this study provided a thorough understanding of agro-ecohydrological processes and their regional characteristics, and the current situation of irrigation water use issues in the whole Hetao district, and further provided valuable insights in improving water use and management in large irrigation districts of the upper YRB.