Water footprint assessment of crop production in Shaanxi, China

The water footprint, introduced by professor A.Y. Hoekstra, is an indicator of freshwater use that looks not only at direct water use of a consumer or producer, but also at the indirect water use. Therefore, it gives a great insight into how and where water is used in the supply chain and helps to form a proper basis for decision making. The water footprint consists of three components. The green water footprint refers to the consumption of green water resources, such as rainwater use. The blue water footprint refers to the consumption of blue water resources, such as surface- and groundwater. The grey water footprint refers to pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants during the process. The concept can be applied to a wide range of commodities, such as industrial products, agricultural crops and so on. Also, it can be applied at different scales, such as business scale, provincial scale or even globally. China has the largest population of the world, over 1.3 billion people, and is still growing. Next to this projected population growth, the economy of China is developing quickly. These factors combined will lead to a rising demand for food, that China’s domestic supply will not be able to meet in the future. China’s agriculture has been playing an important role in guaranteeing the food safety of the country. Agricultural production has to increase due to this growing demand for food in the future. This will lead to more water use, and since water is already scarce, to even more water scarcity. In some provinces there is more water scarcity than in others. Water scarcity also differs within provinces. Here a water footprint assessment related to agricultural crop production is carried out for the year of 2008 for a key agricultural province in China; the Shaanxi province. As a starting point the methodology of water footprints and water footprint definitions are followed as set out in Hoekstra et al. (2011). The assessment focuses on the crops related to agricultural production in the study area and the accounted crops represent 80% of cultivated land use and 77% of production of agricultural crops in the Shaanxi province. The model that has been used is the CROPWAT model and its definitions are based on Allen et al. (2008). The crop water requirement option is used, this means that adequate soil water is maintained by rainfall and/or irrigation so it does not limit plant growth or crop yield. The water footprint of consumption within Shaanxi in the year of 2008 was 18764 Mm3 yr-1 (40% green; 42% blue; 18% grey). The ten districts of the province showed a great variety concerning the water footprints, which can be ascribed to the difference in production values per district. The two major crops are Wheat (6352 Mm3 yr-1) and Maize (6337 Mm3 yr-1). Together they accounted for 68% of the total water footprint in the province. Compared to other studies the water footprints per unit mass of crop were slightly higher. Besides, we see a major shift from green to blue water use, due to the fact that the year 2008 was a relatively dry year. Cotton (7285 m3 ton-1) and Soybean (3785 m3 ton-1) have the largest water footprint per unit mass of crop. In comparison, Wheat (1347 m3 ton-1) and Maize (1157 m3 ton-1) have a low water footprint per unit mass of crop but have the most influence on the total water footprint related to crop production. The annual blue water scarcity was above 100% in the districts of Xi’an, Tongchuan, Weinan, Xianyang, Yan’an and Yulin in the middle and North Shaanxi. This could be part of the difference in climate between North and South Shaanxi, since the northern part is more arid and the southern part more humid. Also, the districts with the higher water footprints related to crop production are located in the North and in the middle of the province. This will lead to exhaustion of the water resources of these districts, such as surface and groundwater. Severe water pollution is only occurring in the Tongchuan district. Here the water pollution level is too high concerning the volume of freshwater that is required to assimilate the load of pollutants.