Spatial variability and attribution analysis of water footprint of wheat in China

Abstract: Water use efficiency assessment is one of the core research items in water-saving agriculture. The water footprint (WF) of crop production is a comprehensive indicator reflecting water consumption types, quantities and water use efficiency during crop growth period. Based on the theory of water footprint, this study quantified and evaluated the regional differences of water footprint of wheat at the regional scale in Mainland China. Meanwhile, in order to find the dominant factors causing the regional differences of water footprint of wheat, correlation and path coefficient analysis were used to identify the relationship between water footprint of wheat and its impact factors. The results showed that there were obvious regional differences of water footprint of wheat in Mainland China. The water footprint of wheat was relatively low in the eastern part of Northeast China, most of Huang-huai-hai region, parts of the Lower-Middle Reaches of the Yangtze River and Sichuan province, which was less than 1 m3/kg; while the high values of water footprint of wheat were mainly distributed in Northwest China, the northwest of Inner Mongolia, the south of Lower-Middle Reaches of the Yangtze River and the south of Southwest China, which were more than 1.8 m3/kg. From the perspective of water type, the blue water footprint accounted for 49.02%, while the green water footprint accounted for 50.98% among the total WF of wheat. The green water proportion in wheat water footprint increased gradually from northern regions to southern regions. For instance, the proportion of green water footprint was 18.62% in Beijing, while it was more than 80% in most of southern regions. The regional distinction of green proportion in water footprint was in accordance with the precipitation on distribution. The region with abundant precipitation usually has a high proportion of green water in crop water footprint. There were 9 related factors selected for the attribution analysis: average temperature, relative humidity, growing season precipitation, solar radiation, wind speed, fertilizer consumption, pesticides consumption, agricultural machinery and irrigation share. The statistical analysis revealed that the regional variability of wheat water footprint, besides the crop varieties, was mainly caused by the regional disparities of agricultural production level, such as agricultural inputs and irrigation condition. On the other hands, the solar radiation and precipitation were the major climatic influencing factors causing the regional difference of water footprint of wheat. The indirect path coefficient of water footprint of wheat and its impact factors showed that solar radiation had indirect effects on water footprint through temperature, and precipitation mainly through relative humidity. Meanwhile, the fertilizer consumption, pesticides consumption, agricultural machinery power, irrigation had indirect effect on water footprint of wheat through each other influencing factors. The total influence coefficient analysis showed that the chemical fertilizer consumption, pesticides consumption, agricultural machinery and irrigation were the dominant factors that had an effect on water footprint of wheat. The results can provide information for plan-making of agricultural water management schedule.