Abstract: 【Objective】The efficient utilization of agricultural water resources is a key measure to guarantee national food and water security. Crop water use efficiency evaluation is one of the main research fields of agricultural water management. Water footprint provides a new index for agricultural water use evaluation, and the quantitative evaluation on the influencing factors of crop water footprint will be helpful to the implementation of water footprint control and improvement of the agricultural water use efficiency. 【Method】Based on the concept of water footprint, the water footprint of spring wheat in Hetao irrigation district was quantified by using an improved calculation method and the temporal variation was analyzed. Sensitivity and contribution rate analysis were used to quantify the relationship between crop water footprint and its influencing factors. 【Result】The results show that water footprint of wheat declined significantly during the study period. It decreased from 4.71 m³·kg^-1 in 1981 to 1.52 m³·kg^-1 in 2010. The variation of water footprint of wheat displayed an obvious stage characteristic. It can be divided into three stages: fluctuate declining stage (1981-1987), rapid declining stage (1988-1995) and slow declining stage (1996-2010). And this variation characteristic was consistent with the variation of agricultural production and irrigation level in Hetao irrigation district. The blue water footprint accounted for the larger proportion (more than 90%), while for the share of green water footprint it was relatively small. Therefore, the production of wheat in the Hetao irrigation district mainly depended on blue water (irrigation water). Sensitivity analysis shows that the difference of sensitivity between the influencing factors was significant. The variations of water footprint of spring wheat was ±30%, ±24%, ±2%, ±63% and ±4% when sunshine hours, relative humidity, precipitation, irrigation water use coefficient and fertilizer rate per unit area varied at ±20%. Irrigation water use coefficient is the most sensitivity factor of wheat water footprint, following by sunshine hours, relative humidity, fertilizer usage and precipitation. Contribution analysis results show that the decline of relative humidity and the increase of precipitation led to the increase of wheat water footprint. On the contrary, the decrease of sunshine hours combined with the increase of fertilizer usage and irrigation water use efficiency led to the decrease of wheat water footprint. The contribution rates of fertilizer and irrigation water use coefficient were -36.89% and -39.42%, respectively, while the contribution rate of the total climatic factors was 2.80%. The increase of utilization coefficient of irrigation water had the largest contribution rate to the decrease of wheat water footprint during the study period, followed by fertilizer usage. The relative humidity, sunshine hours and precipitation had similar contribution rate to the variation of wheat water footprint. 【Conclusion】 The main kinds of influencing factors of crop water footprint are climate, agricultural production inputs and water use efficiency. As for Hetao irrigation district, the improvement of agricultural production and water use efficiency are the major driving forces that cause the variation of wheat water footprint in Hetao irrigation district, while the climate factors have little effect on wheat water footprint. The results of this study could provide reference for the water footprint control.

Key words: water footprint, sensitivity analysis, contribution rate analysis, Hetao irrigation district, spring wheat