Assessment of water stress in Shaanxi Province based on crop water footprint

Water footprint, proposed by professor Hoekstra, is a new indicator of water consumption, which includes both direct and indirect water use. Water footprint of crop production is the volume of water consumed in producing per kilogram of crop. It not only reflects water use efficiency, but also the real water occupation in the process of agricultural production. This paper calculated both green and blue water footprints of crop production. For crop production, green water footprint reflects how much green water is consumed by producing per kilogram of crop, and blue water footprint is water consumed from sources such as surface water or groundwater. Quantification of crop water footprint will contribute to our knowledge of determining water utilization conditions in agricultural production and provide theoretical basis for improving water use efficiency by optimizing cropping patterns in relation to local water resources endowment. Using Shaanxi Province as the study area, this paper calculated water footprint of crop production (WFP) using a modified method that took into account water evaporation loss during transmission and distribution processes of water in crop fields. The paper then used the (blue) water stress indexes β_t (β_b) to determine the relationship between water resources and total/blue water footprints. Finally, the temporal and spatial distributions of WFP,β_t and β_b in Shaanxi Province were analyzed. The results showed large differences in WFP among crops and crop production areas, with a general declining trend in WFP. Water footprint of integrated crop production (IWFP) in Shaanxi Province dropped from 1.132 m³·kg^-1 to 0.931 m³·kg^-1 from 2000 to 2012. While Xi'an City had the lowest average IWFP (0.849 m³·kg^-1), Yulin City had the highest one (1.730 m³·kg^-1). The average annual total crop water footprint (WF) of Shaanxi Province was 127.39×10⁸ m³, with green water footprint (GWF) proportion of 50.22%. With similar spatial distribution characteristics of water footprint of crop production, crop water footprint varied significantly from 3.47×108 m3 in Tongchuan City to 24.19×108 m3 in Weinan City. The multi-year averages of β_t and β_b in Shaanxi Province were 0.255 and 0.187, respectively. Also β_t and β_b values for Weinan City and Xianyang City were 0.610 and 1.200, respectively. Weinan City and Xianyang City had the most severe water scarcity in Shaanxi Province. Apart from the southern area of Shaanxi Province, water unsustainable development challenges were noted in each of the districts in Shaanxi Province.